T 0 ar M 19 1 TRINITY-SAN JACINTO ESTUARY: A Study of the Influence of Freshwater Inflows The preparation of this report was financed in part through funds made available by Senate Bill 137 of the 64th Texas Legislature. Texas Department of Water Resources LP-113 April 1981 TEXAS DEPARTMENT OF WATER RESOURCES Harvey Davis, Executive Director TEXAS WATER DEVELOPMENT BOARD Louis A. Beecherl Jr., Chairman George W. McCleskey Glen E. Roney John H. Garrett, Vice Chairman W. O. Bankston Lonnie A. uBo" Pilgrim TEXAS WATER COMMISSION Felix McDonald, Chairman Dorsey B. Hardeman, Commissioner Joe R. Carroll, Commissioner Authorization for use or reproduction of any original material contained in this publication, i.e., not obtained from other sources, is freely granted. The Department would appreciate acknowledgement. Published and distributed by the Texas Department of Water Resources Post Office 80x 13087 Austin, Texas 78711 ii . '. PREFACE The . Texas Water Plan of 1968 tentatively allocated specific annual amounts of water to supplement freshwater inflow to Texas' bays and estuaries. These amounts were recognized at the time as no lIOre than preliminary estimates of inflow needs based upon historical inflows to each estuary. Furtherrrore, the optimal seasonal and spatial distribution of the inflows could not be determined at the time because of insufficient knowledge of the estuarine ecosystems. Established public policy stated in the Texas Water Code (Section 1.003 as amended, Acts 1975) provides for the conservation and development of the State's natural resources, including "the maintenance of a proper ecological envirorunent of the bays and estuaries of Texas and the health of related living marine resources." Both Senate Concurrent Resolution 101 (63rd Legis lature, 1973) and Senate Resolution 267 (64th Legislature, 1975) declare that "a sufficient inflow of freshwater is necessary to protect and maintain the ecological health of Texas estuaries and related living marine resources." In 1975, the 64th Texas Legislature enacted Senate Bill 137, a mandate for "comprehensive studies of the effects of freshwater inflow upon the bays and estuaries of Texas ••• " Reports published as a part of the effort were to address the relationship of freshwater inflow to the health of living estuarine resources (e.g., fish, shrimp, etc.) and to present methods of providing and maintaining a suitable ecological environment. The technical analyses were to rnaracterize the relationships mich have maintained the estuarine environments historically and mich have provided for the production of living resources at observed historic levels. This report is one in a series of reports on Texas bays and estuaries designed to fulfill the mandate of Senate Bill 137. Six major estuaries on the Texas coast are part of the series, including (1) the Nueces estuary, (2) the Mission-Aransas estuary, (3) the Guadalupe estuary, (4) the Lavaca-Tres Palacios estuary, (5) the Trinity-San Jacinto estuary, and (6) the Sabine Neches estuary. Reports in the S.B. 137 series are designed to explain in a comprehens i ve , yet understandable manner, the results of these planning efforts. iii TABLE OF <::'rnTENI'S Chapter ~ Preface.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. iii Aclo1owledgeIIlents.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .... xxvii 1. SllI11Illary .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 1- 1 A. Coocepts and Methoos............................................................................. 1- 1 B. Description of the Estuary am the Surrounding Area........ I- 1 C.. Hydrol<>g'y.............. •0" .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 1- 2 D. Circulation and Salinity••••••.•••••••••• ; .••••• ;.......... I- 2' E. Nutrient Processes................................................................................. 1- 4 F. PrDnary and Secondary Bay Production •••••••••••••••••.•••.• : 1- 4 G. Fisl1.eries 1- 5· H. Estlinated Freshwater Inflow Needs.......................... I- 6 1. Evaluation of Estuarine Alternatives I- 6 2. Estuarine Circulation and Salinity Patterns I- 9 II. Concepts and Methods' for Determining the Influence of Freshwater Inflows Upon Estuarine Ecosystems••••••••••••••••••. A. Scope of Study••••••••••••••••••••••••••••••••••.•••..••••• B. Estuarine Envirorunent................•...................... 1. Introduction 2. Physical and Chemical Characteristics a. Topography and Setting b. Hydrology c. Water Quality 3. Biological Characteristics a. Food Chain b. Life Cycles c. Habitat 4. SUlllnary C. Evaluation of Individual Estuarine Systems••••••.••••.••••. 1. Introduction 2. Mathematical Modeling 3. Key Indicators of Estuarine Conditions a. Physical and Chemical Indicators (1) Freshwater Inflow (2) Critical Period (3) Circulation (4) Salinity (5 ) Nutrients b. Biological Indicators (1) Aquatic Ecosystem Model (2) Statistical Models (3) Finfish Metabolic Stress Analysis 4. Analyzing the Estuarine Ccmplex a. Synthesis of Competing Estuarine Responses b. Determination of Freshwater Inflow Needs (1) Estuarine Inflow Model v II- 1 II-1 II- 1 II- 1 II- 1 II- 1 II- 2 II- 2 II- 4 II- 4 II- 7 II- 9 II- 9 II-10 II-10 II-11 II-11, II-13 II-13 II-13 II-14 II-14 II-15 II-15 II-18 II-19 II-19 II-20 II-20 II-20 II-20 'TI'IBLE OF CDNTENTS (COnt I d. ) Chapter (2) Mcxlel Interactions c. Techniques for Meeting Freshwater Inflow Needs ( 1) Freshwater Inflow Management (a) Water Rights Allocation (bl Operation of Upstream Reservoirs , in, Contributing Basins (2) Elimination of Water Pollutants (3) Land Management 5. Surrmary II-21 II-21 II-22 II-22 II-22 II-23 II-23 II-24 III. Description of the Estuary and the Surrounding Area.•••••••.••.••• III- 1 A. Physical Characteristics " 111- 1 1• Intrcxluction III- 1 2. Influence of the Contributory Basins III- 1 3. -Geological Resources III- 4 a. Sedimentation and Erosion III- 4 b. Mineral and Energy Resources III-10 c. Groundwater Resources III-10 4. Natural Resources III-12 5. Data Collection Program 1II-15 B. Economic Characteristics•••••••••••••••••..•••...••••••••••. !!!-17 1. Socioeconomic Assessment of Adjacent Counties 111-17 a. Population III-17 b. Income III-24 c. Employment III-24 d. Industry 1II-24 e. Surrmary 1II-28 2. Economic Importance of Sport and Comnercial Fishing III-28 a. Intrcxluction, 111-28 b. Sport Fishing Data Base 1II-28 c. Sport Fishing Visitation Estimation Procedures 111-29 d. Sport Fishing Visitation Estimates III-31 e. Sport Fishing Visitation Patterns III-31 f. Sport Fishing Direct Expenditures 111-33 g. Sport Fishing Economic Impact Analysis III-33 h. Economic Impact. of Comnercial Fishing III-38 1. Surrmary of Economic Importance of Sport and Gammercial Fishing 111-38 IV. HydrolC>g'y .. A. Introouction .. B.. Freshwater Inflows " .. 1. Gaged Inflows from the Trinity Basin 2. Gaged Inflows from the San Jacinto Basin 3. Gaged Inflows from the San Jacinto-Br:-azos Coastal Basin 4. Ungaged Runoff Contributions 5. Ungaged Return Flows vi IV- 1 IV- 1 IV- 1 IV- 1 IV- 4 IV- 4 IV- 4 IV-11 Chapter C. D. E. TABLE OF CONTENTS (Cont I d. ) 6. Diversions 7. Combined Inflow 8. Precipitation on the Estuary 9. Total Fresh.water Inflow 10. Bay Evaporation Losses 11 • Freshwater Inflow Balance 12. variations in Inflow Ccmponents through Drought and Flood Cycles Quality of Gaged Inflows '" .. Quality of Es~uarine Waters •..••••...•••••••••••••.••..•.•. 1. Nutrient Concentrations in the Trinity-San Jacinto Estuary 2. . Heavy Metals 3. Pesticides and Herbicides SLInITlary.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ." .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. e. .. .. ~ IV-11 IV-11 IV-11 IV-13 IV-13 IV-13 IV-13 IV-13 IV-16 IV-16 IV-24 IV-24 IV-27 V.. ·Circulatioo an.d :;;alinity v- 1 A. Introouction '":.. .. .. .. v- 1 B. Description of the Estuarine Mathematical Models........... v- 1 1. Description of /ok)deling Process v- 1 2. Mathematical /ok)del Developnent V- 2 a. Hydrodynamic /ok)del V- 4 b. Conservative Mass Transport Model V- 6 c. Marsh ·Inundation /ok)del V- 7 ( 1) HYDELT V- 7 ( 2 ) M'IDELT v- 7 (3) calibration and validation of the Marsh Inundation Model V- 9 (a) Trinity River Delta V- 9 (b) Low Flow Simulations V-11 (c) Flood Simulations V-15 (d) Intensive Study Simulation V-42 C. Application of Mathematical Models, Trinity-San Jacinto Estuary ". .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. V-52 1• Hydrodynamic and Mass Transport Models V-52 2. Marsh Inundation Model V-54 3. Freshwater InflOW/Salinity Regression Analysis V-68 D. Stmrnary eo....................................................................................... V-73 Nutrient ProCesses ~ -:-... VI. Vl- 1 A. Introouction - - o.' •• ·VI- 1 B. Nutrient wading '................•......... VI- 2 C. Marsh Vegetative Production ' VI-13 D. Marsh Nutrient Cycling ; 0 ••• • '. • • • • • •• VI-16 E. Wetlands Processes VI-19 F. SllIIITlary_••••••• •_•••••••••-. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• VI- 21 VII. Primary and Secondary Bay Production•••••••••••••••••••••••••••••VII- 1 A. Introducti0t::l _ VII- 1 B. Pl1ytoplankton VII- 3 1. Data COllection VII- 3 2. Results of Analyses VII- 6 vii Chapter C. D. E. TABLE OF CXNI'ENI'S (Coot I d. ) Zooplanktorl ......•..........•... '.............•............. 1. Data Collection 2. Results of Analyses Benthos••••••••••••.•• •'•••.•••••••••••••• ~ •••••••••••.•••••• 1• Data Collection 2. Results of Analyses Stmmary.•.....••.•••.•••••..........••••••...•••••• '.. ~ .•••• .~ VII-14 VII-14 VII-17 VII-20 VII-20 VII-25 VII-28 VIII·. Fisheries 'VIII- 1 A. Introouction ; VIII- 1 B. Data and Statistical Methods•...•••••••.••..••.••••••.•....VIII- 2 C. Fisheries Analysis Results ••••••••••••••••••••••••• ~ •••••••VIII-12 1. Shellfish VIII-12 2. All Penaeid Shrimp VIII-17 3. White Shrimp VIII-20 4. Brown and Pink Shrimp VIII-20 5. Blue Crab . VIII-26 6. Bay Oyster VIII-26 7. Finfish VIII-32 8. Spotted Seatrout VIII-32 9. Red Drum VIII-32 10. Black Drum VIII-40 11. Fisheries Ccmponent Surmnary VIII-40 D. Freshwater Inflow Effects•..•••••••••••••..•••••••••.••••••VIII-40 1. Introduction - VIII-40 2. Shrimp VIII-44 3. Blue Crab VIII-45 4. Bay Oyster VIII-45 5. Finfish VIII-46 6. Spotted Seatrout· VIII-47 7. Red Drun VIII-47 8. Black Drum VIII-48 E. Harvest Response to Long and Short Term Inflow•••••••••••••VIII-48 F. Stmmary..•....••.....•........... ~ .•...................... . VIII-51 IX. Estimated Freshwater Inflow Needs................................ IX- 1 A. IntrOOuction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IX- 1 B. Methodology for Estimating Selected Impacts of Freshwater Inflow Upon Estuarine Productivity••••••••• C. Application of the Methodology to Compute Estimates of Freshwater Inflow Levels Needed to Meet Seiected Objectives••••••••••••••••••••••• 1.· Salinity Bounds for Fish and Shellfish Species 2. Monthly Salinity Conditions 3. Marsh Inundation Needs 4. Estuarine Linear Prograrmning Model Description a. Specification of Objectives b. Computation Constraints for the Model viii IX- IX- 1 IX- 3 IX- 7 IX- 7 IX- 9 IX-12 IX-12 Chapter D. 'UIBLE OF OJNTENTS (Cont I d. ) 5. Alternative Estuarine Objectives a. Alternative I: Subsistence b. Alternative II: Maintenance of Fisheries Harvests c. Alternative III: Shrimp Harvest Enhancement 6. A[:plication of· Tidal Hydrodynamic and Salinity Transport Models a. Simulation of Mean Monthly Circulation Patterns ( 1) . Simulated March, June, August and.October Circulation Patterns (2) Simulated January, February, April, May July, September, ~ovember and December' Circulation Patterns . b. Simulated Mean Monthly Salinity Patterns (1 ) Simulated April, May" Jl,lI1e, July and OCtober Salinity Patterns (2) Simulated November through March, August and September Salinity Patterns 7. Interpretation of the Physical Significance of the Estimated Freshwater Inflow Needs St.JITIIlary•••• "': •••••••••••••••••••••••••••••••• •"•••••• ; . ~ IX..,12 IX-13 IX-17 IX-20' IX-27 IX-30 IX-30 IX-43 IX-43 IX-44 IX-44 IX-57 IX-57 BibliC>g'ra~y •••••••••••••••••••••••••••••••••••••• •".............. x- 1 Apt>eIld i x. • • • • • • • • • . . • • • • • • • • • • . . • • • • . . • • • • . . • • • • . • • • • • • . . • • • • • • • • List of People Receiving the Draft Report •..•••••.••••••....••• A- 1 ix LIST OF FIGURES Figure Number Description Page Number I-10 I- 8 I, II, III · ~ ~ . 1-1 Predicted Anriual COIIIIIercial Fisheries HarVest and' Estimated Inflow Needs under 'rtlree Alternatives for the Trinity-San Jacinto Estuary•••• ; .•• c. ; : •••••••••• 1-2· Estimated Monthly Freshwater Inflow Needs for the Trinity-San Jacinto Estuary under Alternatives Locations of Texas Estuaries•.•.•.......••..••••••••••••• II- 3 component Schematic Diagram of a' Generalized Texas Estuarine Eoosystm ~ ~ ' ~ .. II- 5 Species composition of Estuarine Environments••••••••••.• Simplified .Trophic Relationships in a Texas Estuai:y•. ; ••• ! ' . II- 6 II- 8 Flow Diagram of Model Development ••.•..•.•.• ; •.• ;;~.;:•.• II-12 \ .Typical Variation of Freshwater Inflow Versus Salinity in a Texas Estuary .. .~., II-16 Zonat ion of a SaltMarsh in a Texas Estuary. ~ ; •• ; •• : ••• ; : II-17 Trinity-San Jacinto Estuary .. III- 2 Basins contributing to the Trinity-San Jacinto Estuary ,. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. III- 3 Geole>gic Map..................... .... .... .. .. .. .. .. .. .... .. .. .. .. .. .. .. .. .... .. .. .. .. .... .. .... .. .. .. 111- 7 Shoreline Physical Processes, Trinity-San Jacinto Estuary............................................................................................... 111- 9 Oil and Gas Fields, Trinity-San Jacinto Estuary.......••. III-11 Land Surface Subsidence in the Houston Area, 1943-1973... III-13 Land Use/Land Cover, Trinity-San Jacinto Estuary......... III-14 Natural Resources, Trinity-San Jacinto Estuary........... III-16 Data Collection Sites in the Trinity-San Jacinto Estuary. ... . . . . . . . . . . . • . . . . . . . . . . • . . . . . . . . . . . . . . . • . . . . . . III-18 x Figure Number· 3-10 4-1 4-3 4-4 4-5 4-6 4-7 4-8 4-9 4-10 5-1 LIST OF FIGURES (Cont' d. ) Description Locations of Gaging Stations, Trinity-San Jacinto Estuary•.••••.•••.••••• •'••.•••••' 0. ~ •••.. COmbined Monthly Inflow to the Trinity-San Jacinto ,Estuary,' 1941:-1976••.•••.•••••••••••••••••'••.••·•••.••• Ungaged Areas Contributing to Trinity-San Jacinto Estuary•..••.••••.•••..••••••.•.••..••••..• •,••..••,•...• Monthly Distribution of Oombined Inflow, Trinity- . San Jacinto Estuary, 1941-1976 ..•••.••••..••••..•••..•• Monthly Distribution of 'Ibtal Freshwater Inflow,: . Trinity-San Jacin~o Estuary, 1941-1976 ; •.••••.• Range of Values for Water Quality Parameters, Gaged . Inflow to Trinity-San Jacinto Estuary, October 1976- Sept~r 1977 ..-....••..."..•...•.....•. ~ •..... ~ . Data-Collection Sites in Trinity-San Jacinto ~s~uarY••.•• Distribution of'Ibtal Nitrogen' (as N)' Concentrations Occurring in. the Trinity-San Jacinto Estuary, . 1968--l977•.•......•......•.•...... ." ~ ..••.•• Distribution of 'Ibtal 'Phosphorus (as P) ConcEmtrations Occurring in the Trinity-San Jacinto Estuary, 1975-·1977•••••••••••••••••••••••••••••••••'•• ~ •.••••••••• Distribution of Organic Carbon Concentrations Occurring in the Trinity-San Jacinto Estuary, 1975-1977 •• ~••••••• . Distribution of 'Ibtal Kjeldahl Nitrogen Concentr~tions Occurring in the Trinity-San Jacinto Estuary, ." ·1975~1977 •••••••••••••••••••••••.•.•••••••••• ~.:. ~'.'. '••••• Relationship Between Tidal Hydrodynamic and SalInity .. ..; pa:ge' Number III-19 IV- 5 IV-.6 "., IV-12 IV-14 IV-17 rv-18 IV-20 IV-21 IV-22 IV-23 ~els.•.......... .. _._ .....••................ . -..... -e. • • v~. 3 5-2 5-3 5-4 Conceptual Illustration of Discretization of a Bay.•••••. Definition of variables in Cross section••...•••••••••••. Definition of Finite-Difference Segmentation for HydrooYn.arnic MOOel •••••••••••••••••• '••••• ~ ••••••••• xi V-5 V- 8 .. V- 8 LIST OF 'FIGURES (Cont 'd.) Figure Number 5-5 5-6 5-7 5-8 Description Page Number Deltaic Systems Boundaries of the Trinity Delta.......... V-10 Driving Tide Re=rd at Section 2, Morgan I s Point Gage, April 14-21, 1976................................ V-12 Comparisoo of Observed and Simulated water Stage at Section 92, Trinity River at Liberty Gage, April 14-21, 1976................................ V-13 Comparison of Observed and Simulated Tidal Eleva tions at Section 34, Old and Lost River Gage, April 14-21,· 1976............................................ v-14 5-9 Driving Tide Re=rd at Section 8, Point Barrow Gage, November 16-23, 1976............................. V-16 j, , 5-10 Conparison of Observed and Simulated Tidal Eleva- tions at Section 24, Old River Cutoff Channel, Novernl:::>e:r 16-23, 1976...................................................... V-17 5-11 Comparison of Observed and Simulated Tidal Eleva tions at Section 48, Anahuac Channel Gage, November 16-23, 1976 . V-18 5-12 Conparison of Observed and Simulated Tidal Elev~ tions, at Section 165, Sulphur Barge Channel Gage, Novetnl:>er 16-23, 1976 ••••••••••••••••••••••••·••••••••••• V-19 5-13 Driving Tide Re=rd at section 2, Morgan's Point Gage, June 1-16, 1976 " V-21 5-14 Comparison of Observed and Simulated water Stage at Section 92, Trinity River at Liberty Gage, June 1-16, 1976...................................................... V~23 ,5-15 Conparison of Observed and Simulated Tidal Elevations at Section 34, Old and Lost River Gage, June 1-16, 1976 e._ .. a._............... V-24 5-16 Trinity Delta System Showing Inundation Areas, June 1, 1976.......................................................... V-25 5-17 Trinity Delta System Showing Inundation Areas, June 5, 1976........................................................................ V-26 5-18 Trinity Delta System Showing Inundation Areas, June 9, 1976 "....... V-27 xii Figure Number 5-19 5-20 5-21 5-22 5-23 LIST OF FIGURES (Cont I d. ) Description Trinity Delta System Showing Inundation Areas, June 13, 1976•....•...•..•.•......•..............•..... Trinity Delta System Showing Inundation Areas, June 17, 1976 •• ;~.·••••••••••••••••••••••••. : •••••••••••• Tidal Elevation Record at Section 8, R:>int Barrow Gage, December 12-27, 1976 ......•....••....••..•••..... Comparison of Observed and Simulated Tidal Elevations at Section 24, Old River Cutoff Channel Gage, " Decernl:>er 12-27, 1976 . Comparison of Observed and Simulated Tidal Elevations at Section 48, Anahuac Channel Gage, December 12-27, 1976 ••••• ; ••••.•••••••••• ~ •••••••••••·•••••• ~ •• ~ ••• ·•• •••• Page-' Number V-28 V-29 V-32 V-33 5-24 ' Ccmparison of Observed and Simulated Tidal Elevations at Section 162, Lake Charlotte Gage, December 12-27, 1976••••••••••••••••••••••••••••••••••••••••••• ~ .'. • • • • • V-'35 5-25 5-26 5-27 5-28 5-29 5-30 5-31 5-32 Ccmparison of Observed and Simulated Tidal Elevations at Section 165, Sulphur Barge Channel Gage, December 12-27, 1976 •••••••••'•••••••••••••••••••• Trinity Delta System Showing Inundation Areas, December -12, 1976 . Trinity Delta System Showing Inundation Areas, December 16, 1976 ...•......•..•......•......-•.. .~'•...... Trinity Delta System Showing Inundation Areas, December 20, 1976•••••••••••••••••••• ·~ '~ ••••••• Trinity Delta System Showing Inundation Areas, Decent>e:r 24; 1976••••••••••••••••••••••••••• ~ •••• ~ ••••• Trinity Delta System Showing'Inundation Areas, December 28, 1976 .•..••.....••.....••........ ~ . Driving Tide Record at Section 2, Morgan's Point Gage, November 25-December 3, 1976••••••••••••.•• ; ••••• Comparison of Observed and Simulated Tidal Elevations Section 24, Old River Cutoff Channel' Gage, Nbvember 25-December 3, 1976••••••••••••• ~ ••••••• xiii .': - ~ V-36 v-37 V-38 V-40 V-4'1 V-43 v-44 , LIST OF FIGURES (Cont' d. ) Des=iption Figure Number Page Number 5-33 5-34 eat1parison of Observed and Simulated Tideil Elevations at Section 48, Anahuac Channel Gage, NOvember 25-oeoember 3, 1976••.••••..•.••••••••••..•••• Comparison of Observed and Simulated Tidal Elevations at Section 165, Sulfur Barge Channel, November 25- De~r 3, 1976 ~' . V-45 V-46 5-35 Comparison of Observed and Simulated Flows, Trinity-San Jacinto Estuary, November 30- 'Deqernl::>er 3, 1976 io '.. .. •.• .. .. .. .. .. .. .. .. .. .. V-48 5-36 Schematic Computational Grid, Trinity-San Jacinto Estuary' ".. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. V-53 5-37 Comparison of Observed and Simulated Tidal Eleva tions, Trinity-San Jacinto Estuary, July 21-23, 1976 - _ ' .. V-55 5-:38 cemparison of Observed and Simulated Flows, Trinity- San Jacinto Estuary, July 21-23, 1976••••••••••••••••• 5-39 cemparison of Observed (Surface and Bottan) and . Simulated Salinities, Trinity-San Jacinto Estuary, V-56 July 19-24, 1976...................................... V-58 5-40 5-41 5-42 5-43 5-44 5-45 5-46 Comparison of Observed, and Simulated Salinities, Galveston Bay, TDWR Station No. 2421.0300••••••••••••• CompariSon of Observed and Simulated Salinities, Galveston Bay, TDWR Station No. 2421.0200 ••••••••••••• Comparison of Observed and Simulated Salinities, Galveston Bay, TDWR Station No. 2421.0400 ••••••••••••• Comparison of Observed and Simulated Salinities, Galveston Bay, TDWR Station No. 2421.0100 ••••••••••••• Comparison of Observed and Simulated Salinities, Galveston Bay, TDWR Station No. 2422.0100••••••••••••• Comparison of Observed and Simulated Salinities, ~lveston Bay, TDWR Station No. 2422.0200••••••••••••• Simulated Trinity Delta Marsh Inundation,. High _. arld .IJOW Tides..' " ' .. xiv V-59 V-60 v-61 v-62 v-63 v-64 v-66 LIST OF FIGURES (Coot 'd.) . ,. \;; . V-74 V-71 ' Figure Number 5-47 5-:48 6-1 6-2 6-3 6-4 7-1 7-2 7-3 Description Page Nuniber Average M:lnthly Salinity versus Average M:lnthly . Gaged Inflow, Trinity Bay, 1925-1976•••••••• " ••• ;., •• Average M:lnthly Salinity versus Average M:lnthly Gaged Inflow, Galveston Bay, 1941-1976•••••••••••••••• Mean M:>nthly Organic Nitrogen Concentrations in Streams Contributing to the Trinity-San Jacinto' Estuary I 1970-1977 .....••....•.•..•..•......._••.. ~ . . . . VI- 4 Mean M:>nthly Inorganic Nitrogen Concentrations in Streams Contributing to the Trinity-San Jacinto Estuary, 1970-1977 ••• ·•••••• ~ •••••••.••••••••••••• :;•••• VI- S" Mean M:>nthly 'Il::>tal Phosphorus Concentrations in .. 'Streams Contributing .tothe Trinity-San Jac~nto Estuary, 1970-1977 •...•••••.•••••••.•••••••..••••••.•• VI~ 7 Mean M:>nthly 'Il::>tal Organic' Carbon Concentrations i,n Streams Contributing to the Trinity-San Jacinto ., Estuary, 1970-1977 · VI- 8 , Estuarine Food-Web Relationships Between Imp:>rtant' EooICJ9- ical Groups ~ '. . . . . . • . • .• VII- 2 Trinity-San Jacinto Estuary Hydrologic and Biologic SaJllple Sites VII- 4 Mean M:>nthly Phytoplankton Densities in Trinity c' Bay, September 1975-August 1976•••••••••••••••• ; •••••• VII- 5 " . . 7-4 . Seasonal Succession of Trinity Bay Phytoplankton. Groups. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• VII- 7 7-5 7-6 7-7 Daily Discharge of Trinity River at Romayor, July 1975-August 1976••••••••••••••••••• ~ ••••••••••••• VII-ll Prop:>rtion of ChloroP1yta (green algae) to 'Il::>tal. Algae••..•••••••..••••..•.•••••••••••••.•.•·••• '••••.••• VII-12 Prop:>rtion of BacillarioP1yta (diatcrns) to 'Il::>tal " Algae.•..••••.•••.•••'•••...•••••..•.•••••...•••.••••.. VII-13 xv LIST OF FIGURES (Coot 'd.) Figure Number 7-8 7-9 7-10 '"; 7-11 7..,12 7-13 7-14 Description Page Number Mean Monthly Zooplankton Densities in Trinity Bay, September 1975-August 1976••••••••••••••••••••••••••••• VII-15 Combined Proportion of Acartia tonsa, Barnacle Nauplii, and 'Copepodites to Total ZOOplankton Populations in Trinity Bay, September 1975- , August 1976••••_••••• '••••••••.•••••••••••••••••••• ~ ••.•••• VIi-16 Mean Monthly ZOOplankton Densities versus River Inflow in Trinity Bay, September 1975-August 1976•••••• VII-19 Mean Monthly Benthos Densities in Trinity Bay, September 1975-August 1976••••••••••••••••••••••••••••• VII-21 Relative Abundance of Major Benthic Groups in Trinity Bay, September 1975-August 1976•••••••••••••••• VII-22 Percentage Representation of Benthos Standing Crops in Trinity Bay, September 1975-August 1976••••••••••••• VII-27 Mean Monthly Benthos Densities and Mean Monthly Bottom Salinities in Trinity Bay, September 1975- August 1976 ...................................••·•....•• VII-29 8-4 8-1 Inshore canmercial Shellfish Harvest as a Function of Each Seasonal Inflow from Combined River and Coastal Drainage Basins, where all other Seasonal Inflow in the Multiple Regression Equation are held Constant at their Mean Values•••••••••,••••••••••••••••• VIII-14 8-2 Offshore Oommercial Penaeid Shrimp Harvest as a Function of Fishing Effort and Each Seasonal Inflow, fran can- bined River and Coastal Drainage Basins, \'t1ere all other Seasonal Inflow in the Multiple Regression Equation are held Constant at their Mean Values•••••••• VIII-19 8-3 Offshore Ccmnercial White Shrimp Harvest as a Function of Fishing Effort and Each Seasonal Inflow fran Can bined River and Coastal Drainage Basins, where all other Seasonal Inflows in the Multiple Regression Equation are held Constant at their Mean Values•••••••• VIII-22 offshore ,Oommercial Brown & Pink Shrimp Harvest as a Function of Fishing Effort and Each Seasonal Inflow fran Combined River and Coastal Drainage Basins, where all other Seasonal Inflows in the MUltiple Regression Equation are held Constant at their Mean Values ...........••.....•••...........••.•...•.... VIII-25 xvi Figure Number LIST OF FIGURES (Coot' d • ) Description Page Number 8-5 8-6 8'-8 Inshore COmmercial Blue Crab Harvest as a Function of Each Seasonal Inflow from Combined River, and COastal Drainage Basins, mere all other Seasonal Inflows in the Multiple Regression Equation are, held Constant at their Mean Values _ . Ccmnercial Oyster Harvest as a Function of Each Seasonal Inflow from the San Jacinto River, where all other Seasonal Inflows in' the Natural Log Multiple Regression Equation are held Constant at' their Mean Yalu~s ..............•. e._ •••••• '• ••• •• 0 ••••• Inshore COmmercial Finfish Harvest as a' Function of Each Seasonal Inflow fran the San Jacinto River, where all other Seasonal Inflows in the Natural Log MUltiple Regression Equation are held COnstant at their Mean Values . Inshore Camnercial Spotted Seatrout Harvest as a Function of each Seasonal Inflow at Trinity Delta, where all other Seasonal Inflows in the Multiple Regression Equation are held COnstant at their Mean Values••..••••••.•••••.....••••.....•••••••.•..••• . :' . ,-:; ....- VIII-28 VIII":31 VIII,.,34 VIII-37 8-9 Inshore COmmercial Red Drum Harvest as a Function o~ Each Seasonal Inflow at Trinity Delta, where all other Seasonal Inflows in th~ Multiple Regression Equation are held COnstant at,their Mean Values ........•........... '•...........••... ."•...'. . . . . .. VIII-41 9-1 9-2 9-3 9-4 Diagram' of Methodology for Estimating Estuarine Fresh water Inflows'Needed to Meet Specified Objectives.••••• Average ~nthly Salinities in Upper Galveston Bay under Alternative I " - " . " ' Average ~nthly Salinities in Trinity Bay Under Alternative I . Ccmparison between Mean Historical Freshwater Inflow and Inflow Needs under Alternative I , for the Trinity-San Jacinto Estuaty fran the San Jacinto River Basin•.....•....•• ~ •.••..•....••..••• xvii IX- 2 IX-16 IX-16 IX-18 Figure Number 9-5 LIST OF FIGURES (Cont' d. ) Description comparison between Mean Historical Freshwater Inflow and Inflow Needs under Alternative I' for the Trinity-San Jacinto' Estuary fran the Trinity River Basin....•.•...•.•••.......•....•.•••..•.• Page' Number IX-18 9-6 9-7 9-8 9-9 Estimated Freshwater Inflow Needs for the Trinity San Jacinto ~stuary under Alternative 1. •• ~ IX-19 Comparison between Trinity-San Jacinto Historical Fisheries Harvests and Predicted Harvests under Alternative I IX-19 Average Monthly Salinities in Upper Galveston 'Bay under Alternative II 0 IX-21 . Average Monthly Salinities in Trinity Bay under Alternative II IX-21 9-10 COI1tparison between Mean Historical Freshwater Inflow and Inflow Needs under Alternative II for. the Trinity-San Jacinto Estuary fran the San J.acinto River Basin....................................................................................... IX.-22 9-11 Compari1>OO between Mean Historical Freshwater InflOw and Inflow Needs under Alternative II for the or:inity-S~ Jacinto Estuary fran the Trinity . R1ver Bas1n - _ IX-22 9-12 Estimated Freshwater Inflow Needs for the Trinity-San Jacinto Estuary under Alternative II...•. : ....... , ....... rx-23 9-13 COI1tparison between Trinity-San Jacinto Historical Fisheries Harvests and Predicted HarVests under Alternative II IX-23 ,. , 9-14 Average Monthly Salinities in upper Galveston Bay under Alternative III.............................................................. IX-26 9-15 Average Monthly Salinities in Trinity Bay under Alternative III ~ ., .........•••••...•.......•... ; •. IX-26 9-16 Comparison between Mean Historical Freshwater Inflow and Inflow Needs under Alternative III for the Trinity-San Jacinto Estuary fran the San Jacinto River Basin under Alternative III •..••••••••.••••.••••• IX-28 xviii LIST OF FIGURES (Cont' d. ) Figure Number 9-17 Description Page .. Number comparison between Mean Historical Freshwater Inflow and Inflow Needs for the Trinity-San Jacinto Estuary from the Trinity River Basin under Alternative III ' IX-28 9-18 Estimated Freshwater Inflow Needs for the Trinity-San Jacinto Estuary under Alternative III ••••••• ~ •••••••••• IX-29 9-19 Comparison between Trinity-San Jacinto Historical Fisheries· Harvests and Predicted Harvests under Alternative III ' rx-29 9-20 Simulated Net Steady-State Flows in the Trinity-San .Jacinto Estuary under January Freshwater Inflow Needs, Alternative I IX-31 9-21 Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under February Freshwater Inflow Needs, Alternative I ~ IX-32 9-22 Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under March Freshwater Inflow Needs, Alternative I .........................•................. IX-33 , 9-23 Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under April Freshwater Inflow· Needs, Alternative r ~ .' IX-34 9-24 Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary Under May Freshwater Inflow Needs Alternative I ....•..•••••.•.•..•.•••••.•••••••••••••••. IX-35 9-25 Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under June Freshwater Inflow Needs, Alternative I •.......•••••••••••.........• ~ ..........•. IX-36 9-26 Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under July Freshwater Inflow . Needs, Alternative I ~ IX-37 9-27 Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under August Freshwater Inflow Needs, Alternative I rx-38 xix LIST OF FIGURES (COnt' d. ) Figure Number 9-28 Description Page Number ·Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary Under September Freshwater Inflow Needs, Alternative I................................... IX-39 9-29 Simulated Net Steady-State Flows in the Trinity-San . Jacinto Estuary under October Freshwater Inflow Needs, Alternative I................................... IX-40 9-30 Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under November Freshwater Inflow Needs, Alternative I ... e,_ •••••••••••••••••••••• "........ IX-41 9-31 Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary under December Freshwater Inflow Needs, Alternative I................................... IX-42 9-32 Simulated Salinities in the Trinity-San Jacinto Estuary under January Freshwater Inflow Needs, Alternative I (ppt).................................... IX-45 9~33 Simulated Salinities in the Trinity-San Jacinto Estuary under February Freshwater Inflow Needs, Alternative I (wt).................................... IX-46 . . 9-34 Simulated Salinities in the Trinity-San Jacinto Estuary under Mard'l Freshwater Inflow Needs, Alternative I (~t) :........................... IX-47 9-35 Simulated Salinities in the Trinity-San Jacinto Estuary under April Freshwater Inflow Needs, Alternative I (ppt).................................... IX-48 9-36 Simulated' Salinities in the Trinity-San Jacinto Estuary under May Freshwater Inflow Needs, Alternative I (ppt) •....•.•••.••...•.........••...•...• . IX-49 9-37 Simulated Salinities in the Trinity-San Jacinto Estuary under June Freshwater Inflow Needs, Alternative I (:PI,)t).................................... IX-50 9-38 Simulated S~inities in the Trinity-San Jacinto Estuary under July Freshwater Inflow Needs, Alternative I (ppt).................................... IX-51 xx LIST OJ FIGURES (COnt'd.) -:. .-. " Figure Number Description Page Number 9-39 Simulated Salinities in the Trinity-San Jacinto , Estuary under August Freshwater Inflow Needs, Alternat,ive I (Wt) ..............•.................... · .IX-52 9-40 Simulated Salinities in the Trinity-San Jacinto Estuary under Septanber Freshwater Inflow Needs; Alternative I (Wt) ' ' . IX-53 9-41 Simulated Salinities in the Trinity-San Jacinto Estuary under october Freshwater Inflow Needs, Alternative I (Wt) . IX-54 , 9-43 Simulated Salinities in the Trinity-San JacintO Estuary under November Freshwater Inflow Needs, Alternative I (ppt) ••••••••••••••••••••• ~ ••••••••••••• Simulated Salinities in the Trinity-San Jacinto Estuary under December Freshwater Inflow Needs, Alternative I (ppt) ~ •••••••••'••••••••••••••••••• ,', " ;' , " , xxi IX-55', " -,; IX-56 LIST (F 'mBLES Table Number 3-1 . Description, " . Reservoirs of COntributing Basins, Trinity-San Page Number 3-2 3-3 3-4 3-5 3-7 3-8 3-9 ., . Jacinto Estuary•••••••••••••••.•.•..••••••••••••••••••• 111- 5 U. S. Geological Sunrey (USGS) or COrps of Engineers (COE) Gages, Trinity--San Jacinto Estuary•••.•••...•••••••••••••••• ;, •• -~ 111-20 Population Estimates and Projections, Area Surrounding Trinity--SanJacinto Estuary, 197~~030•••••••••••••••••••••••~•••••••••••• ~-• •'•••"•••• 111-25 Employment by Industrial Section, Area Surrounding Trinity--San Jacinto Estuary, 1970•••••••••••••••••••••• III-26 . , Earnings by Industrial Sector, Area Surrounding Trinity-San Jacinto Estuary, 1970 •••••••••••••••••••••• III-27 Estimated Seasonal 9port Fishing'Visitation to the Trinity--San Jacinto Estuary, 1976-1977•••••••••• III-32 ,. . Estimated Seasonal Sport Fishing Visitation Patterns at the Trinity--San Jacinto Estuary, 1976-1977 ..••......••...•......•....••....•.••.•...•... 111-34 Estimated Average Cost per Sport Fishing Party by Type and Origin, Trinity--San Jacinto Estuary, 1976-1977 .........•..,......••.......•.............'••.•. 111-34 Estimated Sport Fishing Expenditures by Season and Fishing Party Type, Trinity-San Jacinto Estuary, 1976-1977 •••.•••••••••••••••••• .- •••••••••••.•• 111-35 3-10 Estimated Sport Fishing Variable Expenditures by Sector, Trinity--San Jacinto Estuary, 1976-1977•••••• III-37 3-11 Direct and Total Economic Impact from Sport Fishing Expenditures, Trinity--San Jacinto Estuary, 1976-1977 ................••......•.••.•.....•.•••...•.. 111-37 3-12 Direct and Total Econcrnic Impact of Crnunercial Fishing in the Trinity-San Jacinto Estuary••••••••••••• III-39 xxii Table NUmber 4-1 4-2 .4-3 4-4 4-5 5-1 5-2 5-3 5-4 5-5 5-6 LIST OF TABLES (Cont 'd.) Description Page· Nuinber Monthly Freshwater Inflow, Trinity-San Jacinto Es~uary, 1941-1976 •••••••••••••••••••••• ~ •••••••••••••• IV- 2 Annual. Freshwater Inflow, Trinity-San Jacinto Estuary, 1941~1976••••••••••••••••••••••••••••••••••••• ~ 3 . , . Runoff fran Ungaged Areas, Trinity-San Jacin~o,. Estuary .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. IV- 7 Monthly Inflows to the Trinity-San Jacinto Estuary for COrresponding Exceedance Frequencies••••••• rv-15 Ranges of Metals in Sediment Crn1pared to USEPA (1974) Dredge Criteria , 0-...................... IV-25 iiaiiy Flow Records for the Trinity River, June 1-,16, 1976 '.,..................... V 22 Daily 'Flow Records for the Trinity River, De~r 12-27, 1976 _ "e.".. .. .. .. .. .. V-31 ,Trinity Delta Inundation Study•••••••••••••••••••~........ V-67 Description of Data for Regression Analysis, Trinity-San Jacinto Estuary ~.... .. .. .. .. .. .. .. .. .. .. V-69 Results of Salinity Regression Analysis, TrInIty Bay ;. ,................. V-72 Results of Salinity Regression Analysis, Galv~ston Bay..........•....•.,......................... V-75 .',6-1 6-2 6-3 Range of Expected Inorganic Nitrogen Loading into .Trinity-San Jacinto Estuary, based on Mean Monthly Gaged Discharges••.••.•••••...•••••••••••• Range·.of Expected Organic Nitrogen Loading into Trinity-San Jacinto Estuary, based on Mean Monthly Gaged Discharges ....••••••...•••••.••••••• Range of Expected Total Phosphorus Loading into Trinity-San Jacinto Estuary, based on Mean Monthly Gaged Discharges•••••.....•••••••••••••..• -'-', xxiii VI- 9 VI-10 VI-11 LIST OF TABLES (Cont 'd.) Table NlUllber Description Page NlllIIber' 6-4 Range of Expected Total Organic Carbon Loading to the 'Trinity-San Jacinto Estuary Based on . Mean Monthly Gaged Discharges••••••••••• ; •••••••••••••. VI-12 6-5 'Scientific and Common Names of Important Plant· Species OCcurring in the Trinity River Delta••'........ VI:"15 6-6 Summary cif Nutrient . • • I • , Excl1ange Rates ~ .. 6-7 6-8 7-1 7-2 7-3 7-4 SUIlITIary of Nutrient Exchange Rates for Plant Types fran the LOwer Trinity River Delta Marshes Corrected for Wall Effects •••••••••• ; . Exchange Rates of Carbon, Nitrogen, and Phos phorus in the Linear Marsh from the Trinity River I:>elta _,_ .. ~ - .' Abundance of Phytoplankton Groups by Station in Trinity BaY, September 1975-August 1976.,••••• ~ ••••• Average Monthly Density of Major Phytoplanktoo . Species in Trinity Bay, September 1975- " -August 1976 • •" ;, ~ " Range of Mean Monthly .Zooplankton Densities: .,; ••• '••••••• NlUllber of Months iD W1ite Each Organisms Con- stituted 30 Percent .or More ,of the Total . - ' VI-18 VI-20 VII- 8 VII- 9 VII-'18 Standing Crop VII-26 8-1 8-2 8-3 8-4 8-5 Commercial Fisheries, Harvests' in the· Trinity-San Jacinto Estuary, 1962-1976 ~ ••••••• Offshore Commercial Penaeld' Shrimp Harvests in .Area No. 18, 1959-1976..•..•••.... ·......•. ,.."•• :••...... Seasonal Freshwater Inflow Volumes from Trinity Delta Contributed to Trinity-San Jacinto Estuary, 1959-1976 0; .. Seasonal Freshwater Inflow Volumes from San Jacinto River Contributed to Trinity-San Jacinto Estuary, 1959-1976•••••••••••••'•••••••.;'••••••• Seasonal volumes of Combined Freshwater Inflow Contributed to Trinity-San J ancinto Estuary, 1959-1976 . xxiv '-, VIII-4 VIII-5 VIII-7 VIII-8 VIII-9 LIST OF TABLES (Cont'd.) Table Number 8-6 8-7 Description Page Number Time series Aligrnnents of Dependent/Independent Data Variates for Fisheries Regression Analysis••••••• VIII-11 Equations of Statistical Significance Relating the .ShellfiSh Fisheries canponent to Freshwater Inflow Categories .••.•......•....•..•••••••••••.••.••. VIII-13 8-8 Equations of Statistical Significance Relating All Penaeid Shrimp FiSheries canponent to Freshwater Inflow Categories•••••••••••• ; ••••••••••••• VIII-18 8-9 Equations of Statistical Significance Relating the White Shrimp Fisheries canponent to Fresh- Water Inflow Categories -~ VIII-21 8-10 Equations of Statistical Significance Relating the Brown and pink Shrimp FiSheries Conponent to Freshwater Inflow Categories••••••••••••••••••••••• VIII-23 8-11 Equations of Statistical Significance Relating the Blue Crab Fisheries canponent to Freshwater Inflow Categories ; ' VIII-27 8-12 Equations of Statistical Significance Relating the Bay Oyster FiSheries Conponent to FreShwater Inflow Categories.•..••...••••...•••••••••••••.••...•. VIII-29 8-13 Equations of Statistical Significance Relating the FinfiSh Fisheries canponent to Freshwater Inflow Categorie~., VIII-33 8-14 Equations of Statistical Significance Relating the Spotted Seatrout Fisheries Conponent to Freshwater Inflow categories•••••• ~ ••••••••••••••••••• VIII-35 8-15 Equations of Statistical Significance Relating the the Red Drum Fisheries canponet to Freshwater Inflow Categories.•.........•..•.....••••...•...••..•. VIII-38 8-16 FIositive (+) and Negative (-) Correlation of FiSheries canponents to Seasonal FreShwater Inflow Categories••••.•••••••••••••••...•••..•...•..•• VIII-42 8-17 Comparison of Short-Term and Long-Term Seasonal Inflow Volumes Including Inflow Exceedance Freqllencies••.•••••••••.•••.•.•••...•••••••••..•••.••• VIII-49 xxv Table Number 8-18 LIST OF TABLES (Coot' d. ) Description Page Number Estimated Average Harvest Responses fran Fisl?eries Ccmponent Equations Using Short Tenn Mean Inflow, IDng-Tenn Mean Inflow and IDng-Tenn 50 Percent, Exceedance Frequ~ncy Inflow II II ~ II ~ .. II II .,~"""" II" VII I':"SO 9-1 9-2' 9-3 9-4 9-5 9-6 9-7 9-8 Salinity Limits, Preferences, and Optima for Selected Texas Estuarine-Dependent Species••••••• Salinity Characteristics of Upper Galveston Bay and Upper Trinity Bay.•.••..••••....••.•.•••••.•. Peak Discharges ~or 'Discrete Flood Events Greater than 20,000 ft3/sec in the Trinity River Delta, 1924~1977••••••••••••••••••••••••••••••• Frequency of Annual and Seasonal Flood Events, Greater than 20,000 ft3/sec in the Trinity River Delta, 1924-1977 •• ·•••••••••••••••••••••• ~ •••••• Criteria and System Restrictions for the Selected Estuarine Objectives ,. II" ~ II to II .. Freshwater Inflow Needs of the Trinity-San Jacinto Estuary Under Alternative 1. ••.•.•••••. ,.••••• Freshwater Inflow Needs of the TrinitY-Sari, Jacint~ Estuary under ,Alternative II....••••••.•••••• Freshwater Inflow Needs of the Trinity-San Jacinto Estuary under AlternativeIII ••••••••••••••••• " xxvi IX- 4 IX- 6 IX-10 IX-11 IX-14 IX-15 IX-24 IX-25 ACKNCMLEDGEMENTS Project Supervision - Administrative Staff Executive Directors Office Planning and Developnent Division Engineering and Envirorunental and Systems section Economics, Water Requirements and Uses Section - Seth C. Burnitt, Executive Assistant - Herbert W. Grubb, Director - William A. White, Assistant Director - Quentin W. Martin, Chief - Gerald Higgins, Chief Report Preparation Editing: Typing: Proofing: Charles Chandler Leal Byrd Jan Knox Zelphia Severn Jean Hobbs Leal Byrd Jan Knox Charles Chandler Drafting: canputer Graphics: other Technical Assistance: Nancy Kelly Leroy Killough Roger Wolff Nick carter Wiley Haydon Norman Merryman Chapter VI Chapter V - Circulation and Salinity Gordon Thorn Midlael Sullivan George Chang Norman "Merryman Chapter Authors: Chapter I - SLm'IlOary Numerous contributors Chapter II - COncepts and Methods Quentin Martin Gary Pmiell Chapter III - Description of the Estuary and the Surrounding Area Leal Byrd Jan Knox Butch Bloodworth Chapter VII Roy Morey - Nutrient Processes Al Goldstein Sandra Belaire Gary Powell - Primary and Secondary Bay Production Sandra Belaire Chapter IV - Hydrology Gary Laneman Charles Chandler . Stuart Madsen xxvii Chapter.VIII - Fisheries Gary Powell Chapter IX -" Estimated Freshwater Inflow Needs Quentin Martin Gary Powell Gordon Thorn OJAPI'ER I SUMMARY COncepts and Methods The ~ision of sufficient freshwater inflow to Texas bays and estuaries is a vital factor in maintaining estuarine productivity, and a factor con tributing to the near-shore fisheries productivity of the Gulf of Mexico. This report analyzes the interrelationships between freshwater inflows and estuarine productivity, and establishes the seasonal and lIOnthly freshwater inflow needs, for a range of alternative management policies, for the Trinity San Jacinto estuary of Texas. Simplifying assumptions must be made in order to estimate freshwater inflow requirements necessary to maintain Texas estuarine ecosystems. Abasic premise developed in this report is that freshwater inflow and estuarine productivity can be examined through analysis of certain "key indicators." The key J:i1ysical and chemical indicators include freshwater inflows, circula tion and salinity patterns, and nutrients. Biological irrlicators of estuarine productivity include selected commercially, important species. Useful species are generally chosen on the basis of their wide distribution throughout each estuarine system, a sensitivity to change in the system, and an appropriate life cycle to facilitate association of the organism with estuarine pro ductivity. Description of the Estuary and the Surrounding Area The Trinity-San Jacinto estuary consists of Trinity Bay, Galveston Bay, East Bay, west Bay' and several smaller bays. Areas contributing inflow to the estuary include the entire Trinity and San Jacinto 'River Basins and the Trinity-San Jacinto COastal, Basin, plus parts of the Neches-Trinity and San Jacinto-Brazos COastal Basins. The major marsh areas of the Trinity-San Jacinto, estuary are associated with the Trinity River delta. Active delta plains are covered with salt, brackish, and 'freshwater marshes. Most of the shorelines associated with the Trinity-San Jacinto estuary are balanced between shoreline erosion and sedi ment deposition. Land use in the area is dominated by urban and industrial uses. The City of Houston and the petro-chemical industrial a::rnplex are predominant fea tures. Inland areas and marshes contiguous to the Trinity-San Jacinto estuary system provide terrestrial and aquatic habitat for many species of wildlife including the endangered American alligator, the Whooping crane, the Atlantic ridley turtle, the brown pelican, and the Houston toad. Wildlife resources of the area enhance the opportunities for sightseeing, nature studies, and esthe tic benefits accruing to the naturalists. In addition, more than 149 thousand 1-1 acres of marshland are available to outdoor sportsmen for hunting cpportuni ties. These marsh areas support populations of migratory game birds for the hunting esthusiasts. The Trinity-San Jacinto estuary has historically been the overall leading fisheries resource base in Texas. The annual CCJllIIlercial bay harvest of finfish and shellfish in this estuary has averaged 8.9 million pounds (4.1 million kg; 96.1 percent shellfish) during the 1962 through 1976 interval. However, a large portion of each estuary's production of fish and shellfish is caught in the Gulf by oorrrnercial and sport fishermen. When these harvests are considered,' the total contribution of the estuary to the Texas coastal fisheries (all species) is estimated at 46.7 million pounds (21.2 million kg; 87.4 percent shellfish) annually for a recent five year period (1972-1976). Penaeid shrimp species dominate the shellfish harvests. Total economic impact of the estuary's o:mnercial fish and ,shellfish harvests on the State are estimated at $185.9 million per year, using an input-output analysis and 1976 dollar values. Similarly, the estuary's total sport and recreational fishing impact on Texas is estimated at $13.4 million annually. Hydrology Sources of freshwater inflow to the Trinity-San Jacinto estuary include gaged inflows from the contributing rivers and streams; ungaged runoff; return flows from municipal, industrial and agricultural s:>urces; and precipitation on the estuary. To acquire accurate inflow measurements, gaged stream flows require adjustment to reflect any withdrawals or return flows downstream from gage locations. Ungaged runoff is estimated by cx:rnputerized mathematical models using field data for calibration and verification. Rainfall is esti mated as a distance-weighted average of the daily precipitation recorded at weather stations surrounding the estuary. Freshwater inflows in terms of annual and monthly average values over the '1941 to 1976 period varied widely from the mean as 'a result of recurrent drought and flood conditions. On the average, total freshwater inflow to, the estuary is computed at 11.34 million acre-feet (14 billion m3) annually.' In general, the water quality of gaged inflows to the estuary from the Trinity River is good. No parameters were found in violation of existing Texas stream standards. Inflows from Buffalo Bayou and other 'urban drainage ways, however; contain significant nutrient loadings. Studies of past water quality in and around the estuary have noted the occurrence of heavy metals in sedirrent samples. IDeally, bottom sedirrent samples from the Trinity-San Jacinto estuary have exceeded the U. S. Environmental Protection Agency criteria for metals in sedirrent (prior to dredging) for arsenic, Cadmium, copper, lead and zinc. Circulation and Salinity The movements of water in the shallow estuaries and E!TIbayments along the Texas Gulf COast are governed by a mllleer of factors, including freshwater 1-2 inflows, prevailing' winds, and tidal currents. An irlequate understanding of mixing and J;hysical exchange in these estuarine waters is fundamental to the assessment of the J;hysical, chemical, and biological processes governing these illp)rtant aquatic systems. To fully evaluate the tidal hydrodynamic and salinity transport char- acteristics of estuarine systems using field data, the Texas Department of Water Resources developed digital mathematical nodels representing the' illp)rtant mixing and J;hysical exchange processes of the estuaries" These models are designed to simulate the tidal circulation patterns and salinity distributions in shallow, irregular, non-stratified estuaries. The basic. concept utilized to represent each estuary is the segmentation of .the J;hysical system into a grid of discrete elements. The models utilize numerical analy sis techniques to simulate the tellp)ral and spatial behavior of circulation and salinity patterns in an estuary. To properly evaluate the transport of water and nutrients through a deltaic marsh, it is necessary to describe and 'a:rnpute estimates of the con plex tidal and freshwater inflow interactions. A mathematical model based upon the IXtysical laws of conservation of mass and nomentum has been developed to simulate the passage of water and nutrients through the Trinity deltaic system. The computations are based upon use of a finite difference approxima tion to the equations which describe the governing IXtysicai relationships. The marsh inundation model is applied to the Trinity River delta. The delta system is represented as a series of interconnected shallow channels which are subject to varying levels of inundation, depending upon the tidal and riverine flow rates. The representation of the Trinity River delta includes the non-tidally influenced flood plain of the Trinity River fran the stream gages near Lost Lake and Lake Charlotte to the Wallisville levee. The model coefficients for calibration of the hydrodynamic nodel reflect ing each delta's hydraulic characteristics, were determined by simulating the flow conditions and water inundation depths in each delta, a:rnparing them with actual observed conditions, and adjusting the coefficients until irlequate agreement between observed and simulated conditions was.achieved. The numerical tidal'hydrodynamic and salinity mass transport models were applied to the Trinity-San Jacinto estuary, with the nodel representation of the system including Galveston Bay, Trinity Bay, East Bay, West Bay, and numerous smaller bays, San Luis Pass and Bolivar Roads. The hydrodynamic and mass transport models were calibrated and verified for the estuary. The extent of marsh inundation due to tidal and river floods in the Trinity River delta was. investigated utilizing the verified inundation model for this system. The flooded surface area of the Trinity delta was determined under both high and low tidal amplitudes, for four typical floods \\hich occurred on the Trinity River after the filling of Lake Livingston. Statistical analyses were undertaken to quantify the relationship between freshwater inflows from the Trinity and San Jacinto Rivers and salinities fran Trinity and Galveston Bays. Utilizing gaged daily river flows and observed salinities, a' set of lIOnthly predictive salinity equations was derived utilizing regression analyses for the indicated areas of the estuary. These 1-3 equations predicted the mean IOOllthly salinity as a function of the nean nonth ly freshwater inflow rate. Nutrient ~sses The deltaic marshes are important sources of 'nutrients for the.estuarine system. Periodic inundation events are natural and necessary in order for the deltaic marshes of the Trinity-San Jacinto estuary to deliver their fOtential nutrient materials (e.g., plant detritus) to the open waters of the bays. This will occur as a floodwave of freshwater moving across the'delta sweeping decayed macrophytic and . dried algal material out of the system. A sudden inundation event CNer the delta' marshes, following a period of dry emersion, results' in.a short period of high nutrient release from the established vege tation and sediments. During periods of high river discharge and/or extremely high tides that inmediately follow prolonged dry periods, the oontribution of carbon, IiJosphorus, and nitrogen from the deltaic marshes to the estuarine system can be .expected to increase dramatically. Aerial photographic studies of the Trinity River delta have prCNided insight into on-'going wetland processes. Dredging and diking have oombined to reduce·the extent of marsh flooding of the Trinity delta" The natural Trinity River deltaic wetland has been significantly modified by recent oonstruction projects. Extensive CNer-grazing and drainage imPrCNenient of marsh areas adjacent to the estuary is resulting in the displacement of some native marsh vegetation; The direct loss of wetlands due to these activities will probably have an adverse impact on the food-chain productivity of the Trinity-San Jacinto estuary. Primary and Secondary Bay Production The coornunity composition, distribution, abundance, and seasonality of the phytoplankton, ,zooplankton, and benthic invertebrates of the Trinity-San Jacinto estuary were employed as "indicators" of primary and secondary pro ductivity.· The estuarine coornunities identified are typical in that they were comfOsed of a mixture of freshwater, mar ine , and endemic - species ( i.e. , species restricted to the estuarine zone). Seven phytoplankton divisions represented by 132 taxa were oollected from Trinity Bay. A clear distinction in OOJmlunity cx:rnfOsition was· discovered between locations having significantly different salinity oonditions. A total of 70 zooplankton species representing nine phyla were identi fied. Correlation analysis revealed no·sign{ficant relationships between z0o plankton stand ing crops and freshwater inflows. However, these factors did exhibit a regulating influence on species cx:rnfOsition, seasonal occurrence, and distribution of zooplankton in Trinity Bay .as evidenced. by comparing stations. Six phyla represented by 72 benthic species were collected from Trinity Bay. . Although not statistically correlated with inflows or salinity, the benthic community appears to be similarly influenced by these factors. 1-4 The ~ytoplankton, zooplankton, and benthic fX)pulations in any l:ody of water respond to a oombination of IX1ysical and d:Jemical seasonal controlling factors. Thus, it is difficult to single out the influence of anyone of these factors on the entire CXlI1IIlunity. In Texas estuaries, there is always a collection of species which are capable of maintaining high standing crops, regardless of the salinity, as long as it is relatively stable CNer the species lifecycle, and provided that other ~ysiological requirements for that particular species group are met. If freshwater inflow is decreased, either partially or totally, the OOrrmunity composition .will generally shift toward the nore marine forms. Fisheries Virtually all of the Gulf fisheries species are estuarine-dependent. Commercial inshore harvests (1962-1976) fran bays of the Trinity-San Jacinto estuary rank first in shellfish and fourth in finfish of eight major Texas estuarine areas. In addition, the sport or recreational finfish harvest has been estimated at six times larger than the cxmnercial finfish harvest in the estuary. For the 1972 through 1976 interval, the average annual sport and comnercial harvest of fish and shellfish dependent UfX)n the estuary is esti mated at 46.7 million fX)unds (21.2 million kg; 87.4 percent shellfish). Although a large fX)rtion of each Texas estuary's fisheries production is harvested 'offshore in oollective association with fisheries production fran other regional estuaries, inshore bay harvests are useful as relative indica tors of the year to year variations in an estuary's surplus production. These variations are affected by the seasonal quantities and sources of freshwater inflow to an' estuary through eoological interact ions involving sal inity, nutrients, food (prey) production, and habitat availability. The effects of freshwater inflow 00 the Trinit~San Jacinto estuary are also reflected in the offshore harvests of the penaeid shrimp fishery. Therefore, the fisheries species can be viewed as integrators of their environment's oonditions and their harvests used as relative eoological indicators, insofar as they reflect the general productivity and 'health" of an estuarine eoosystem. A time series analysis of the cornnercial bay fisheries landings (1962 through 1976) and the oonrnercial offshore penaeid shrimp harvests (Gulf Area No. 18, 1959 through 1976) was undertaken to estimate the commercial harvests as functions of the seasonal freshwater inflows to the estuary. Regression equations derived in the analysis provide numerical estimates of the effects of variable seasonal inflows, oontributed fran the major freshwater rources, on the production of seafood organisms dependent 00 the estuarine eoosystem. The analysis also SUpfX)rts existing scientific information on the seasonal importance of freshwater inflow to the estuary. All significant inshore and offshore harvest responses to winter (Janua~March) inflow are estimated to be negative for increased inflow in this season. with exception of the in shore brown and pink shrimp component's fX)sitive response to Trinity delta in flow, all other significant inshore harvest responses are estimated to relate negatively to increased sumner (Jul~August) inflow. Offshore all shrimp and brown and pink shrimp fisheries components also relate positively to increased summer inflow, but negatively to increased spring (April-June) inflow. How ever, offshore white shrimp and inshore red drum, oyster and blue crab har vests relate positively to increased spring season inflow. Significant har vest responses to increased autumn (September-Qctober) inflow are fX)sitive, 1-5 except for the negative responses of the oyster and brONn and pink shrimp fisheries components. Increased late fall (November-December) inflow relates positively to several cfisheries ronponents (e.g., finfish, spotted seatrout, and red drum), but again is negatively related to oyster harvest. Where the estimated seasonal inflow needs of the fisheries oomponentsare similar, the components reinforce each other1 hONever, where corrponents are cCJTPE!titive by exhibiting opposite seasonal inflON needs, a nanagement deci sion nust be made to balance the divergent needs or to give preference to the C needs of a particular fisheries ronponent. A choice rould be made on the basis of which species' production is more ecologically characteristic and/or eronanically important to the estuary. Whatever the decision, a freshwater inflON management regime can only provide an opportunity for the estuary to be viable and productive because there are no guarantees for estuarine product ivity based on inflON alone, since many other biotic and abiotic factors are capable of influencing this production. HONever, most of these other factors are largely beyond human rontrol, whereas man's acivities can restrict fresh water inflONs to the detriment of fish and wildlife resources. Estimated Freshwater InflON Needs A methodology is presented which rornbines the analysis of theromponent physical, chemical and biological elements of the Trinity-San Jacinto estuary into a sequence of steps which results in estimates of the freshwater inflON needs for the estuary based upon specified salinity, marsh inundation and canmercial fishery harvest objectives. Monthly mean salinity I:x:>unds are established at locations in the estuary near the inflON points of the San Jacinto and Trinity River Basins. The upper and lONer limits on monthly salinity provide a salinity cranqe within which viable metal:x:>lic and reproductive activity can be maintained and normal historical salinity ronditions are observed. Marsh inundation needs, for the flushing of nutrients from riverine marshes into the open bays, are romputed and specified for the Trinity River delta. The San Jacinto River delta is limited in arealCextent and far smaller than the Trinity delta. As a result, no inflON requirements for inundation of the San Jacinto River delta are specified from the San Jacinto River Basin. The Trinity River delta is frequently sutmerged by floods from the Trinity River. Based upon historical ronditions and gaged streamflON records, fresh water inflON needs for marsh inundation are estimated and specified at 750 thousand acre-feet (924 million m3) in each of the months April, May and October. c 'Ihese volumes rorrespond to flood events with peak flON rates of 29,500 ft3/sec (836 m3/sec). Evaluation of Estuarine Alternatives Estimates of the freshwater inflON needs for the Trinity-San Jacinto estuary are computed by representing the interactions among freshwater inflONs, estuarine salinity, and fisheries harvests within an Estuarine Linear Programming Model. The model romputes the monthly freshwater inflows from the San Jacinto and Trinity River Basins which best achieve a specified oIr jective. 1-6 1he rronthly freshwater inflow needs for the Trinity-San Jacinto estuary were estimated for each of the three following alternatives: Alternative I (Subsistence): minimization of the annual a:.mbined fresh water inflow ~ile meeting salinity viability limits and marsh inun dation needs; Alternative II (Maintenance of Fisheries Harvest): minimization of annual OOIiibined freShwater inflow \J1i1e providing predicted annual conmercial bay harvests of red drum, spotted seatrout, shrimp, blue crab, and bay oysters at levels no less than their 1962 through 1976 mean values, satisfying marsh inundation needs, and meeting salinity viability limits; and Alternative III (Shrimp Harvest Enhancement): maximization of the pre- , dicted offshore commercial harvest of shrimp (in Gulf Area No. 18). while meeting salinity viability limits, satisfying marsh inundation needs, and utilizing an annual freshwater inflow from each of the Trinity and San Jacinto River Basins at a level no greater than their individual average annual historical (1941-1976) inflows. Under Alternative I (Subsistence), the Trinity-San Jacinto system, Yktich has functioned as both a mrrmercial shellfish and finfish producing system in the past, could continue to be an important fisheries producing estuary with substantially less freshwater inflow. Freshwater inflows totaling 6.85 million acre-feet (8,446 million m3; 67 percent estimated from gaged areas) annually are predicted to satisfy the basic salinity gradient and marsh inun dation needs, with resulting predicted increases in the a:.mbined commercial finfish and shellfish harvests of 16' percent, above average values for the period 1962 through 1976 (Figure 1-1). Under Alternative II (Maintenance of Fisheries Harvests), the predict,ed annual commercial bay harvests of red drum, spotted seatrout, shrimp, blue crab and bay oysters are required to be at least as great as historical (1962-1976) average levels. 1he marsh inundation needs and salinity bounds must also be satisfied. To satisfy these criteria, an annual freshwater inflow of 7.19 million acre-feet (8,865 million m3 ; 68 percent from gaged areas) is needed (Figure 1-1). 1he predicted a:.mbined finfish and shellfish annual commercial harvest (offshore shrimp included) for this Alternative is approximately 16' percent higher than the historical average. Under Alternative III (Shrimp Harvest Enhancement), the Trinity-San Jacinto estuary's annual freshwater inflow needs are estimated at 7.02 million acre-feet (8,656 mill ion m3 ; 68 percent from gaged areas), distributed in a' seasonally unique manner, to achieve the objective of maximizing the annual predicted commercial harvest of shrimp in the offshore area (Gulf Area No. 18) adjacent to the estuary (Figure 1-1). Annual inflows from the San Jacinto River Basin are limited by the average annual 1941 through. 1976 historic inflow from the basin, thus indicating that some . 15I- 0 :r: In '"L: '".<: In LL 0 10 () I- '"E E 0 (J 0 :J C c 5 -« ................ 6 ................ 4 ... 2 c o "0 '" '"Z ~ o :;: c I '" -o ~ .<: In '"l-LL o :J C C -« "0 '" -o E In W AVGH-Averoge Htstorlcol Annual Horve.! (1962-1976) AVGI-Average Historical Annual Inflow (1941-1976) ALTERNATIVE I SUBSISTANCE ALTERNATIVE II MAINTENANCE OF FISHERIES HARVEST ALTERNATIVE HI SHRIMP HARVEST ENHANCEMENT ~ PREDICTED HARVEST D ESTIMATED INFLOW NEEDS Figure 1-1. Predicted Annual Commercial Fisheries Harvest and Estimated Inflow Needs Under Three Alternatives for the Trinity-San Jacinto Estuary 1-8 '!he IIOnthly distribution of the inflow needs for each of the Alternatives and the average historical IIOnthly freshwater inflows for the period 1941 through 1976 are given in Figure 1-2. Estuarine Circulation and Salinity Patterns The munerical tidal hydrodynamic and salinity mass transport IIOdels were applied to the Trinity-San Jacinto estuary to determine the effects of the estimated freshwater inflow needs for Alternative I1I upon the average monthly net flow circulation. and salinity characteristics of the estuarine system. The IIOnthly simulations utilized typical tidal and meteorological conditions observed historically for each month simulated. The net circulation patterns simulated by the tidal hydrodynamic IIOdel indicate that the dominant simulated current in Galveston Bay is a net water movement along the Houston Ship Channel. '!his dominant current influences circulation in the other areas of Galveston Bay. The simulated net water movements in Trinity, East, and West Bays were generally dominated by internal circular currents. The simulated monthly circulation patterns indicated that the currents in the Trinity-San Jacinto estuary are wind dominated. The simulated salinities in the Trinity-San Jacinto estuary for the estimated m:mthly freshwater inflow needs under Alternative I vary CNer a wide range. Salinities throughout the estuary are lowest in the month of May, with average simulated salinities of less than 20 parts per thousand (ppt) CNer the entire estuary except near San Luis and Bolivar Passes. '!he highest levels of simulated salinities occur during the month of August, ~en salinities in Galveston Bay near Bolivar Pass exceed 30 ppt. The simulated salinities for Trinity Bay are generally less than 15 ppt throughout the year. The major portion of Galveston Bay has simulated salinities of between 15 and 20 ppt; however, during the high freshwater inflow months of April and May, the salinities in the bay are between 10 and 15 ppt. Since the middle portion of Galveston Bay has simulated salinities in all months below a target maximum allowable roncentration of 20 ppt, the fresh water inflow needs established by the Estuarine Linear Programming Model would be adequate to sustain the salinity gradients specified, within the objec tives, throughout the estuary. The estimated monthly freshwater inflow needs derived in this report are the best statistical estimates of the monthly inflows satisfying specified objectives for rorrrnercial fisheries harvest levels, marsh inundation and salinity regimes. '!hese objectives rover a range of potential management policies. A high level of variability of freshwater inflow occurs annually in Texas estuaries. Fluctuations in inflows are expected to rontinue for any average level of inflow into the estuary ~ich may be specified. Some provision should be made, however,· in any estuarine management program to prevent an increase (over historical levels) in the frequency of low inflows detrimental to the estuarine-dependent organisms. 17- The-aIternative having the lowest inflow level and thus the alternative - that would ilrrpinge most heavily upon salinities. I-9 I1600 i ; _ ),VG ; 1200~·· _ . __ ~V_G _ __/>NIL _ : I":.. _-"yo. __ I , ! .1. ..... _ ./>NIL _ 1 i 'I' I J I , [ [ [ [ I, I , I .[ r,V"'-jTTj~I [ [ . ~ __AYIL_; . I I I I I I I I . .• Of' •..••...•.• - •.•..••.... r,V"'-jTTj~, I I I I, I!__ ~v..G _ ~/~ ...;- ~v:::,__ ! ! ! !. ,AViL - ~ AVfL _ ~ --- ~--- 400 __AYG. __ 800 ....... -.. "U Q) Q) Z ~ o ;;: c > .s: + c o ::IE ~ l LL I () < o o S! ......, H, ~ o O lIA!!! !·!X!!! !.lOd/' 1't<\4/4 !·pa/! !·t(Y'IO !.lOf/' !'!XW/I "pal! l'lAIII !'b/\d/! !'K'N/J "iii I i I ; ii, j AVG - Average Historical Monthly Combined Inflow tan feb mar apr may [un lui aug sep oct nov dec Month ~ ALTERNATIVE I SUBSISTANCE 0 ALTERNATIVE 11 MAINTENANCE OF FiSHERIES HARVEST D ALTERNATIVE III: SHRIMP HARVEST ENHANCEMENT Figure 1-2. Estimated Monthly Freshwater Inflow Needs for the Trinity-San Jacinto Estuary Under Alternatives I, II, III CHAPTF.R II CCNCEPTS AND MEI'HODS FUR DErr'ERMINING 'IHEINFUJENCE OF FRESHWATER INF'ICMS UPCN ESTUARINE EXXEysrEMS Scope of Study Senate Bill 137 (64th Texas Leqislature) mandates a collq:>rehensive study of environmental variables, especially freshwater inflow, which affect Texas estuarine ecosystems. This report presents the results of the studies of the Trinity-San Jacinto estuary. In succeeding chapters, biotic and abiotic factors are conceptually related, enabling the use of numerical analysis for the identification of maintenance needs. Many estuarine maintenance needs are directly related to freshwater inflow and associated quality constituents. In sane cases, these needs may be exceeded in illq:>ortance by the basic avail ability of substrate and/or habitat in the ecosystem. Fundamental to these diset.issions is the concept of seasonal dynamics; that is, the environmental needs of an estuarine ecosystem are rot static annual needs. In fact, dynamic equilibrium about the productive range is roth realistic· and desirable for an estuarine environment. Extended periods'c of inflow conditions which oonsistently fall below maintenance levels can, h0w ever, lead to a degraded estuarine environment, loss of irrportant "nursery" functions for estuarine--dependent fish and shellfish resources, and a reduc tion in the potential for assimilation of organic and nutritive wastes. Dur ing past droughts, Texas estuaries severely' declined in their production of eoonomically illq:>ortant fishery resources and began to take on characteristics of marine lagoons, including the presence of starfish and sea urchin JXlpula tions (199). Chapter II and succeeding chapters will address a broad range. of estuarine ooncepts; errphasis is placed primarily on those ooncepts germane to the discussion of freshwater inflow needs of the Trinity-San Jacinto estuary. Estuarine Environment Introduction The bays and estuaries along the Texas Gulf Coast represent an irrportant eoonanic asset to the State. The results of current studies carried out under the Senate Bill 137 mandate will provide decision makers with irrportant information needed in order to establish plans and programs for each of the State's major estuarine systems. Physical and Chemical Characteristics Topography and Setting. A Texas estuary may be defined as the ooastal region of the state from the tidally affected reaches. of .terrestial inflow sources to the Gulf of Mexioo. Shallow bays, tidal marshes, bayous, creeks and other bodies of water behind barrier islands are included under this definition. Estuarine systems contain sub-systems (e.g., individuals bays), lesser but II-1 ,recognizable units with characteristic chemical, physical and biological regimes. Primary, secondary, and tertiary bays, although interrelated, all require study for proper understanding and management of the canplete system. The primary bay of an estuary is directly connected to the Gulf of Mexico. This area of the estuary is generally saline (seawater) to brackish, depending upon the proximity to areas of exchange between the bay and Gulf waters. secondary bays empty into the primary bay of an estuary and are thus rerroved from direct flow exchange with the Gulf. In secondary bays, the salinities are usually lower than the primary bay. In terms of energy input to the estuarine systems, the IlOst productive and dynamic of estuarine hab itats are the tertiary bays. Tertiary bays are generally shallow, brackish to freshwater areas ~ere sunlight can effectively penetrate the water column to support ];hytoplankton, benthic algae, and other sutmerged vegetation. Substantial chemical energy is produced in these areas through ];botosynthetic processes. These nutritive biostimulants are distributed throughout the estuarine system by inflow, tides, and circulation. Texas has about 373 miles (600 kilometers) of c.pen~cean or Gulf shore line and 1,419 miles (2,290 kilometers) of bay shoreline, along ~ich are located seven major estuarine systems and three snaller estuaries (Figure 2-1). Eleven major river basins, ten with headwaters originating within the boundaries of the state, have estuaries of major or secondary importance. These estuarine systems have a total c.pen-water surface area of IlOre than 1.5 million acres (607,000 hectares) with IlOre than 1.1 million acres (445,000 hectares) of adjacent marshlands and tidal flats (480). Physical charac teristics of the Trinity-San Jacinto estuary are described in Chapter III. Hydro~. A primary factor distinguishing an estuary from a strictly marine environment is the input of freshwater from various s::>Urces. Sources of freshwater inflow to Texas estuaries include: ( 1) gaged inflow (as measured at the IlOSt downstream flow gage of each river system), (2) ungaged runoff, and (3) direct precipitation on the estuary's surface. The measurement of each of these sources of freshwater inflow is neces sary to develop analytical relationships between freshwater inflow and result ing changes in the estuarine environment. Gaged inflow is the simplest of the three sources to quantify; however, gaged records do require adjustment to reflect any diversions or return~flows downstream of gage locations. Canputation of ungaged inflow requires utilization of a variety of analy tical techniques, including cOmputerized mathematical watershed IlOdels, soil moisture data, and rimoff coefficients developed from field surveys. Direct precipitation on an estuary is assumed to bea distance.,-weighted average of the daily precipitation recorded at weather stations in the coastal regions adjacent to each bay. IV. The hydrology of the Trinity-San Jacinto estuary is described in Chapter Water Quality. The factors ~ich affect the water quality of aquatic ec0 systems and their importance to the various biological canponents include nutrients, such as nitrogen and ];hos];horus; the basic cellular building block, II-2 Locolion mop estuary Laguna Madre estuary Figure 2-1. Bose f'om Officiol $101" High...oy Mop of Tuos, 1971 Locations of Texas Estuaries II-3 carbon; trace elements necessary for biological growth; the presence of sufficient concentrations of dissolved oxygen for respiration of aerobic organisms; and the occurrence of toxic chemicals that may inhibit growth and productivity. (Figure 2-2). The presence of fOllutants can have significant impacts UfOn estuarine water quality. Economic and business developnent activities may result in changes to the Plysical and chemical quality of the runoff. Waste loads which enter the aquatic ecosystem can be of several types, including predominantly municipal and industrial effluent and agriCUltural return flow. The presence of toxic chemicals can have a detrimental impact UfOn the quality of estuarine waters and the indigenous aquatic ecosystem. Water quality considerations are discussed in Chapter IV and Chapter VI. Biological Characteristics An estuarine ecosystem comprises a myriad of life forms, living inter dependently, yet all dependent on the "health" of the aquatic environment. Among the general groupings of life forms that occur in the estuary, the most prominent are bacteria, phytoplankton (algae), vascular plants (macrophytes), zooplankton, benthic infauna, shel~fish and finfish. Salinity, temperature, and fOtentially catastrophic events (e.g., hurri canes) are factors that largely control and influence species composition in these ecosystems. While the number of species generally remains low, numbers of organisms within a single species may be high, fluctuating with the seasons and with hydrologic cycles (212, 77,207). The fluctuating conditions provide for a continuing shift in dominant organisms, thereby preventing a specific species from maintaining a persistent dominance. Natural stresses encountered in an estuarine ecosystem are due, in part, to the fact that these areas represent a transition zone between freshwater and marine environments. Biological stlarval organisms may migrate into the estuary because of food and physiological requirements for lowered salinity (139, 534), and/or for protection against predators and parasites (144, 197). Juvenile forms use the shallow "nursery" areas during early growth (92), migrating back to the Gulf of Mexico in their zrlult or sub adult life stage. For high marsh productivity to occur, the timing of freshwater inflow, inundation (irrigation) of marshes, and nutrient stimulation (fertilization) of estuarine plants must coincide with the subtropical climatic regime of the GUlf region. Nature's seasons provide environmental cues, such as increases or decreases in salinity and temperature, that enable estuarine-dependent species to reproduce and grow successfully in the coastal environments. These species have zrlapted their life cycles to the natural schedule of sea sonal events in the ecosystem and also to reduce cx:mpetition and predation. Coincidence of seasonal events, such as spring rains, inundation of marshes and increased nutrient cycling is made more cx:mplex by both antecedent events and ambient conditions. For example, winter inundation and nutrient stimula tion of marshes may not be as beneficial to the estuarine system as similar) events in the spring because low winter temperatures do not sUp]X)rt high biological activity. Consequently, the growth and survival of many econ omically imp:>rtant seafood species will be limited if antecedent events and ambient conditions are unfavorable and far fran the seasonal optimum. Further, the entire ecosystem can lose productivity through disruption of energy flow and become altered by slight, but chronic stresses (547). Virtually all (97.5%) of the Gulf fisheries species are considered estuarine-dependent (93); however, the seasonal aspects of their life cycles are quite different. Some species, such as the redfish, spawn in the fall and the young are partiCUlarly dependent on migration to and utilization of the II-7 FROM RIVER NUTRIENT· ORGANIC INPUT PHYTOPLANKTON (floating algae) ~?arflC'JIa,e Qrgen\C II/\atter Large Adult Game Fish (Redfish, Seatrout, Flounder) ~I::::::::::::: ORGANIC:;?E: DETRITUS~I~~' n: ;;n,::: BENTHIC ALGAE AND VASCULAR PLANTS': I Diopatra I f I Chironomid I , t Amphipods I Polychaetes Larvae H H I CD Figure 2-4. Simplified Trophic Relationships in a Texas Estuary [After WRE (540)] "nursery" habitats during this season. Others, such as the penaeid shrimp, spawn primarily in the· spring and early sumner, and their young IlOve inshore to shallow, low salinity estuarine areas for growth and developnent at this time. Not all estuarine-dependent species are migratory between the marine and estuarine environments 1 however, there are few true year-round residents (e.g., bay oysters) capable of ng several factors; including freshwater inflow, tidal exchange and evaporation. Freshwater inflow also transports sediments and nutrients into the estuarine system. During flood stage, many square miles of marsh habitat are inundated and inorganic nutrients deposited in the marsh. 'lllese nutrients are converted to an organic state by primary production and bacteriological action and then drawn into the overylying water column. The subsidence of the floodwaters and the subsequent dewatering of the marshes results in the movement of organic nutrients from the marsh into the nearby tertiary and secondary bays. However, large volumes of freshwater inflow can also be detrimental, depressing biological productivity and flushing even the primary bay of an estuarine system. Flood events may resuspend and transport sediments, increasing turbidity and causing a rapid decrease in the standing crop of P1ytoplankton, zooplankton, benthos and fisheries PJPulations. The period of time necessary for recovery of the estuarine system after such an event is governed by variables such as season of the year, temperature, food availability and subsequent freshwater inflows. (2) Critical Period.· An understanding of the concept of "critical period" is necessary in order to understand the importance of freshwater in flow to Texas estuarine systems (117, 175). There are basically two types of critical periods that must be considered--long term and seasonal. The first, or IIDre general type, is that resulting fran extended years of drought with extreme low freshwater inflow, creating stressful or lethal conditions in the estuary. A second type of critical period occurs on a seasonal basis, whereby lowered freshwater inflow affects the growth and maturation of delta marsh habitats, the utilization of "nursery" areas by juvenile fish and shellfish, and the transport of sediment and nutritive substrate materials (especially detritus) to the estuary. Long-term critical periods of multi-year droughts affect entire estuarine systemS, while short-term critical periods relate to habitat-specific or species-specific seasonal needs. Where seasonal needs conflict between estuarine-dependent species and limited freshwater is available for distribu- II-13 tion to an estuary, a management decision may need to be made to give preference to selected species. .This decision could be made on the basis of historical dominance of the system by one or IIDre species, that is, whether the estuarine system has historically been a finfish or a shellfish producing area. The physical characteristics of each estuarine system are a reflection of . long-term adaptations to differing salinity, nutrient, and sedimentary balances. Among such distinctive characteristics are bay size, number and size of contributing marshes, extent of submerqed seagrass comnunities, species diversity, and species dominance. The timing of freshwater inflows can be extremely .important, since adequate inflow during critical periods can be of greater benefit to ecological maintenance than abundant ,inflow during noncritical periods. ' (3) Circulation. The IIDvement of waters within an estuary largely determines the distribution of biotic and abiotic·constituents in the system. To study the IIDvement of estuarine waters under varying conditions, tidal hydrodynamic mathematical models have been developed and applied to individual Texas estuaries ( 173) • Each model computes velocities, and water surface elevations at node points of a computational grid superimposed on an estuary. Estuarine characteristics along any given vertical 'line (the water column) are assumed to be horrogeneous. The tidal hydrodynamic model takes into account bottom friction, sub merged reefs, flow over low-lying barrier islands, freshwater inflow (runoff), any other inflows, ocean tides, wind, rainfall, and evaporation. 'n1e model may be used to study changes in erosion and sedimentation ratterns produced by shoreline development and to evaluate the dispersion characteristics of waste outfalls. 'n1e primary output from the tidal hydrodynamic model is a time history of water elevations and velocity ratterns throughout the estuary. Output data are stored o~ magnetic tape for later use. The tidal hydrodynamics model is described in detail {n Chapter V. (4) Salinity. A knowledge of the distribution of salinities over time at points throughout an estuary is vital to the understanding of environmental conditions within the system. To better assess the variations in salinity, a salinity transport mathematical model has been developed (173, 174) to' simulate the salinity changes in response to dispersion, molecular diffusion and tidal hydrodynamics. This model is a companion model to the hydrodynamic model described previously. The mass transport model is used to analyze the salinity distributions in shallow, non-stratified, irregular estuaries for various conditions of tidal amplitude and freshwater inflOw. The model is dynamic and takes into account location, magnitude, and quality of freshwater inflows; changing tidal condi tions; evaportion and rainfall; and advective transport and dispersion within the. estuary. The primary output of the model is the tidal-averaged salinity change in the estuary due to variations in the above mentioned independent variables. This model, in conjunction with the tidal hydrodynamic model, can also be used to assess the effects of development proiects such as dredging and filling on circulation and salinity ratterns in an estuary. n-14 In this study, relationships between inflow and sal inity ~re established using the statistical technique of regression analysis. Regression analysis is a method of estimating the functional relationship anong variables. The relative accuracy of such a predictive model, cnnrnonly measured in terms of the correlation coefficient, is dependent upon the correlation of salinities to inflow volumes. The statistical relationship between salinity and inflow can generally be represented as an reciprocal function (Figure 2-6). This functional form plots as a straight line on log-log graph paper. The statistical regression models differ from the salinity transport model in that the transport model analyzes the entire estuary to a resolution of one nautical mile square, while each statistical model represents the salinity at only a single p:>int in the estuary. These models canpliment each other, however, since a statistical model is considered ITDre accurate near a river's mouth and the salinity transport model provides better predicted salinities at p:>ints in the open bay. The salinity transport model and the statistical regression. models are described in Chapter V. (5) Nutrients. The productivity of an estuarine system depends upon the quantity of necessary nutrients such as carbon, nitrogen and {i1osphorus. Thus, the transportation and utilization of these nutrients in the system is of major importance. The most significant sources of nutrients for Gulf estuaries are the tidal marshes and river deltas (40, 163). . A hypothetical cross-section of a typical salt water marsh is illustrated in Figure 2-7. Note the typical low channel banks which may be inundated by high tides and high river flows. Inorganic materii;l1s and organic detritus trar1sported and deposited in salt marshes by river floods are assimilated in the marshes through biological action and converted to organic tissue. This conversion is a=mplished by the primary producers (phytoplankton and macrophytes) of the marsh ecosystem. The primary producers and organic materials produced in the marsh are then transported to the bay system by the inundation and subsequent dewatering process. This process is controlled by the tidal and river flood stages. To properly evaluate the transport processes through a deltaic river marsh it is necessary to estimate the canplex tidal and freshwater inflow interactions. A mathematical model (set of equations) based upon the appro priate {i1ysical laws was developed for determining flows, water depths, and nutrient transport in the Trinity River delta (61, 64). This model applies in cases of both lo_flow and flood conditions. The results of freshwater inflows upon the marsh inundation and dewatering processes are estimated through the application of this marsh inundation model (see Chapter V). Biological Indicators. Terms like "biological indicators", "ecological indi cators" , "environmental indicators" , and others found in the scientific literature often refer to the use of selected "key" species. Usually such key species are chosen on the basis of their wide distribution throughout the system of interest (e.g., an estuary), a sensitivity to change in the system (or to a single variable, like freshwater inflow), and an appropriate life cycle to permit observation of changes in organism densities and productivity in association with observations of environmental change. II-15 + 1 I 1 1 I 1 tl CJlI <1 111 I 1 I 1 1 1 I _-1- _ I I 1 I I I 1 I I I -6Q ....0'------1 --.1 _ o Freshwater Inflow (0) Figure 2-6. Typical Variation of Freshwater Inflow Versus Salinity in a Texas Estuary II-16 +----... ~ MEDIUM SPAATINA LEVEE MARSH ~ SALICORNIA DISTICH LIS MARSH H H I ~ -.J ~ JUNCUS MARSH ~ SHORT SPARTINA MARSH MUD/ALGAE - TALL SPARTINA EDGE MARSH PHYTOPLANKTON AND SUBMERGED VEGETATION --- - ---- ~!~ TIDE PRODUCTION UNITS MARSH ZONATION Figure 2-7. Zonation of a Salt Marsh in a Texas Estuary (275) Dr. Eugene Odum has remarked that "ecologists constantly employ· such organisms as indicators in exploring new situations or evaluating large areas" (187). Odum also notes that large species often serve as better indicators than snall species because a larger and IlDre stable biomass or standing crop can be supported with a given energy flow. The turnover of snall organisms may be so great that the particular species present at anyone rroment may not be very useful as a biological indicator. In the 1975 American Fisheries Society Water Quality Statement, Dr. H. E. Johnson stated that "fisheries provide a useful indicator of the quality and productivity of natural waters. Continuous high yield of fish and shellfish is an indicator of environmental conditions that are favorable for the entire biological CXlI1I1lUnity. In a number of recent environmental crises, fish and shellfish have served as either the link between pollution and human problems or an early warning of an impending contamination problem." If every estuarine floral and faunal species could be IlDnitored and integrated into a research program, the maximum data base would be achieved: however, there are always time and financial limitations that make this irrpos sible. It is believed that the use of indicator or key species that emphasize the fishery species is reasonable and justified, especially when one considers the type of ecosystem and the availability of time and IlDney which limit the number of environmental variables that may be investigated in depth. Use of several diverse species avoids problems IlDst commonly associated with a single chosen indicator, wherein data may be dependent upon that particular species' sensitivity. The "key" species approach is used in these studies of the Texas bays and estuaries. ( 1) Aquatic Ecosystem Model. Attempts to understand the complex inter actions within Texas estuarine ecosystems have lead to the developnent of a sophisticated estuarine ecologic model (ESTECO: 540, 275). The model was formulated to provide a systematic means of predicting the response of estuarine biotic and abiotic constituents to environmental changes. Ecoloqi cal modeling techniques involve the use of mathematical relationships, based on scientific evidence, to predict changes in estuarine constituents. While the principal focus of the ESTECO model is to simulate those quan tities that are considered to be the IlDst sensitive indicators of the primary productivity of an estuarine environment (Le., salinity, dissolved oxyqen, nutrients, and algae), the higher trophic levels are also taken into account. The trophic categories included in the model are [ilytoplankton, zcoplankton, benthos, and nekton (fish). Since the life cycles of algae and the higher forms of biota that depend on them, as well as the life cycles of bacteria and other decomposers, are intimately related to water quality, a complex set of physical, chemical and biological relationships have been included in the ESTECO model which link the various abiotic oonsti tuents to several forms of estuarine biota. While the estuarine ecologic model provides a valuable conceptual tool for understanding estuarine ecosystems, the validity of the current version of ESTECO in predicting long-term estuarine constituents has not yet been proven. As presently structured, the .estuarine ecologic model is capable of producing useful results over short time periods, but lacks the refinement necessary to accurately represent the long-term phenomena which occur in the estuarine rr-18 system. Also, the oomprehensive data to accurately calibrate the estuarine ecologic nDdel for simulation periods in excess of one year are not yet available. Further refinement of the nDdel is anticipated as these data become available. At present, the nest serious deficiency of the estuarine ecological nDdel is its inability to accurately describe and predict the standing bianass of carmercially important finfish and shellfish which spend p.:>rtions of their life cycles in the estuary. Thus, for plrposes of this study, statistical analysis techniques are used to predict the productivity of the higher 'trophic levels under various freshwater inflow conditions. The statistical nDdels are described below. (2) Statistical Models. An investigation of the effects of freshwater inflow on an estuary necessitates the use of existing information on' the system's hydrology and biology. In nest cases, numerical analysis of this information allows the denonstration of statistical relationships between freshwater inflow and dependent environmental variables such as fishery pro duction. The use of linear regression analysis allows the developnent of a variety of descriptive and predictive relationships between seasonal fresh water inflows and carmercial harvest of finfish and shellfish. The specific regression equations for estimating harvest of sp.:>tted seatrout, red drum, black drum, white shrimp, brown and pink shrimp, blue crab, and bay oyster as a function of the reported quantities of seasonal freshwater inflow are o::m puted using data fran each estuarine system (Chapter VIII). These regression equations can be used to compute estimates of the estuarine productivity, in terms of harvested fisheries bianass, as a function of seasonal freshwater inflow. However, there are variations in the historical harvest data which are not explained by variations in seasonal freshwater inflow. These varia tions may be due to other factors such as temperature, predation and disease. The described relationships 'are useful in defining the p.:>ssible impacts and interactions between freshwater inflows and the bianass pt.oduction in various trophic levels. Many of the o::mplicated relationships arong trOphic levels within an cquatic ecosystem are not yet o::mpletelyunderstood and data about them are not available, so the mathematical representations required to describe such Fhenanena have not been adequately def ined. Therefore, regres sion techniques are applied in these studies as a useful tool in understanding these interactions. (3) Finfish Metabolic Stress Analysis. The health of organisms in an estuarine ecosystem is dependent upon a number of factors. Wohlschlag (320, 321) and Wakeman (538) have reported on the stress of salinity manges upon the metabolic activities of several Texas estuarine fish species. For exam ple, Wakeman measured the maximum sustained swinrning speeds of four' estuarine fish species (I.e., sp.:>tted seatrout, sheepshead, and black and red drum) at 28 degrees celsius O'ler a range of salinities (10-40 parts per thousand, FPt) normally encountered in the estuary to determine their cptima. All of these species are of' CXJllIllercial and recreational imp.:>rtance; therefore, results of these metabolic research studies are valuable in the planning and management of the Texas estuarine systems and their production of renewable fish re sources. Salinity ranges and salinity cptima have also been determined ',for II-19 several other estuarine-dependent fish and shellfish species (including shrimp, crabs, and oysters), and are presented in Chapter IX. Analyzing the Estuarine canplex ~theSiS of =tin* Estuarine Resbinses. The developnent of environmental eling tec J.ques as increased e capability of the planners to make intelligent and o:::>mprehensive evaluations of specified developnent alterna tives and their impact on 'GUatic ecosystems. Due to the tremendous a:rnplex i ty of 'GUatic ecosystems and their importance in water resources planning, sophisticated mathematical techniques are being continually developed and used for assessment of alternative projects and programs. Any desired management objective for the biological resources of. an estuary must include a value judgment concerning a:rnpeting interests. Where seasonal salinity needs are o:::>mpetitive arrong estuarine-dependent species (e.g., one species prefers low salinities in the spring and another prefers high salinities in the same season) a management decision may be required to specify a preference to one or !lOre species' needs. Such a decision could be made on the basis of which organism has been !lOre characteristic of the estuary of interest. Additionally, needs for freshwater in the contributing river basins must be balanced with the freshwater needs of the estuary. Techniques for the synthesis of inflow alternatives are in Chapter IX. further discussed I I Determination of Freshwater Inflow Needs. ( 1) Estuarine Inflow Model. In order to establish an estimate of the freshwater inflow needs for an estuary, . mathematical techniques are applied to integrate the large number of relation ships and constraints, such that all of the information can be used in con sideration of competing factors. The relationships and constraints in this formulation consist of: 1) statistical regression equations relating annual fisheries harvest to seasonal inflows, 2) upper and lower bounds for the inflows used in the regression equa tions for harvest, 3) statistical regression equations relating seasonal salinities to seasonal freshwater inflows, 4) upper and lower bounds on the seasonal inflows used in a:rnputing the salinity regression relationships, and 5) environmental bounds on a !lOnthly basis for the salinities required to maintain the viability of various 'GUatic organisms. Constraints (2) and (4) are required &> that the inflows selected to rreet a. specified objective fall within the ranges for which the regression equa tions are valid. Thus, in this analysis errors are avoided by rot extrapolat ing beyond the range of the data used in developing the regression relation ships. The constraints listed above are incorporated into a special linear programning (LP) llOdel, to determine the !lOnthly freshwater inflows needed to meet specified marsh inundation, salinity, and fisheries objectives. The rr-20 optimization procedure used to assess alternative objectives is formulated in a oomputer code based upon the simplex algorithm (42) for the s:>lution of linear programs. A linear program may be used to reach an q;>timLUn s:>lution to a problem where a desired linear objective is maximized (or minimized) subject to satisfying a set of linear constraints. The output fran the LP model provides rot only the seasonal freshwater inflows needed to maximize the desired objective function, \\hich in this case is stated in terms of marsh inundation, salinity, and fisheries harvested, tot also the predicted harvest levels and salinities reSUlting fran the I1Ddel's freshwater inflow regime. The harvests that are predicted under such a regime of freshwater inflows can be canpared with the average historical harvests to estimate changes in productivity. Use of the estuarine inflow I1Ddel is described in Chapter IX, (2) Model Interactions. The estuarine linear {X"ogranrning I1Ddel incor porates salinity viability limits and o:mnercial fisheries harvest factors considered in determining interrelationships between freshwater inflows and estuarine key indicators, inclUding the marsh and river delta inundation requirements. The schedule of flows for marsh inundation and for maintaining salinity and productivity levels are combined into one constraint in the I1Ddel by taking the largest of the minimLUn required values for the two plrposes. Thus, if the flow in March reqUired for inundation is greater than the flow needed for salinity gradient control and fisheries harvest (production), then the March inflow need only be equal to the inundation requirement. A seasonal schedule of inflows needed by the estuary to meet the specified objectives is thus derived. A process for synthesis of estimated freshwater inflow needs for the Trinity-San Jacinto estuary is discussed in Chapter IX. Techniques for Meeting Freshwater Inflow Needs. The freshwater inflows needed to maintain an estuary's ecology can be provided from both unregulated and re gulated s:>urces. The natural inflows from uncontrolled drainage areas and direct precipitation will possibly continue in the future at historical levels, since man's influence will be limited, except in those areas \\here major water diversions or storage projects will be located. Inflows from the major contributing river basins, however, will probably be subject to signifi cant alteration due to man I s activities. A a:mpilation and evaluation of existing permits, claims and certified filings 00 record at the 'IDWR indicate that should diversions closely approach or equal rates and volLUnes presently authorized under existing permits and claims presently recognized and UFheld by the Texas Water Ccmnission, such diversions could equal or exceed the total annual runoff within several major river systems during- s:>me years, par ticularly during drought periods. Total annual water use (diversions) do not yet approach authorized diversion levels in nest river basins, as evidenced by both mandatory and voluntary a::.mprehensive water use reporting information systems a:lministered by the 'ImR. With a::.mpletion of major new surface-water developnent and delivery systems, such as the major conveyance systems to convey water fran the lower Trinity River to the Houston-Galveston area, however,. freshwater inflows to some bay systems may be progressively - n-21 reduced and/or points of re-entry (in the form of return flows) may be sig nificantly altered. (1) Freshwater Inflow Management. The freshwater runoff fran the regu lated watersheds of the upstream river basins may be managed in several ways to insure the passage of necessary flows to the estuaries. These include the granting of water rights for surface-water diversion and storage consistent with the freshwater inflow needs of the estuary. Water 'Rights Allocation. Adjudication of surface-water rights in Texas is an extremely important factor in addressing the issue of allocation and possibly ultimately the appropriation of .State water specifically for estuarine maintenance. In 1967, the Texas Legislature enacted the Water Rights Adjudication Act, Section 11.301 et seq. of the Texas Water Code. The declared purpose of the Act was to require a recordation with the Texas Water Ccmnission of claims of water rights which were unrecorded, to limit the exercise of those claims to actual use, and provide for the adjudication and adminis tration of water rights. Pursuant to the Act, all persons wishing to be recogniZed who were claiming water other than under permits or certified filings were required to file a claim with the oamrnission by september 1, 1969. Such a claim is to be recognized only if valid under existing law and only to the extent of the maximum actual application of water for beneficial use without waste during any calendar year frem 1963 to 1967, inclusive. Riparian users were allowed to file an additional claim on or before July 1, 1971 to establish a right based on use fran 1969 to 1970, inclusive. The adjUdication process is a:mplex and, in many river basins, extremely lengthy. The procedures were designed to assure each claimant, as well as each person affected by a final determination of adjudication, all of the due process and constitutional protection to which each is entitled. Statewide adjudication is currently approximately. 72 percent unt of supplemental water inflow for estuaries on an annual basis, it was, (and is still) clearly reoognized that the cm:>unt .specified is rot nere than a preliminary estimate. FurtheIllOre, the optimum seasonal and spatial distribution of these supplemental inflows oould not be determined at that time because of insufficient knowledge of the estuarine eoosystems. Attention must be given to the possibiiities of providing storage capa city in existing and future reservoir projects specifically for alloca tion to estuarine inflows, with releases timed to provide the nest bene fit to the estuary. Developnent of institutional arrangements \\hereby repayment criteria for such allocated storage are determined and asso ciated oosts repaid will be needed. E\::>tential transbasin diversions to convey "surplus" freshwater fran "water-rich" hydrologic systems to water-deficient estuaries will. also have to be studied and costs will have to be computed. Additionally, structural rreasures and dlanneLnodi fications which might enhance marsh inundation PDOQesses using less freshwater will have to be evaluated. These are all a part of planning to meet the future water needs of Texas. (2) Elimination of Water Pollutants. The presence of toxic pollutants in freshwater inflows can have a detrimental effect upon productivity of an estuarine eoosystem by suppressing biological activity. Historically, pollu tants have been discharged into rivers and streams and have oontaminated the coastal estuaries. Imposition of wastewater discharge and streamflow water quality standards by State and Federal governmental agencies has had and will continue to have a significant impact upon pollutants entering estuarine waters. Presence of toxic pollutants in the Texas estuaries will continue for the foreseeable future in some areas as oompounds deposited in sediments become resuspended in the wateroollunn by dredging activities and \\hen severe storms cause abnormally strong currents. This report does not include a ccrn-. prehensive assessment of water pollution problems in the Trinity-San Jacinto estuary, but other ongoing studies by the Department of Water Resources do address such problems. (3) Land Management. The uses of watershed areas are of particular importance to the contnbution of nutrient materials from the land areas sur rounding Texas estuaries. In coastal areas, significant contributions of nutrients are provided to the estuary by direct runoff. Re!roval of marsh grasses in coastal areas through overgrazing by livestock and through drainage improvement practices can result in substantial reductions in the volume of II-23 nutrients contributed to an estuary. '!his report OOes not consider land management techniques in detail, although land management is an alternative technique in any coastal zone management plan. Surnnary '!he ~1s10n of sufficient freshwater inflow to Texas bays and estuaries is a vital factor in maintaining estuarine prodilctivity and a factor con tributing to the near-shore fisheries productivity of the Gulf of Mexico. '!he methodology for establishing freshwater inflow needs described in this report relies heavily on the use of mathematical and statistical models of the important natural factors governing the estuaries. Mathematical models relating estuarine flow circulation, salinity transport, and deltaic marsh inundation processes were developed' based upon FOysical relationships and field data collected from the system, and utilized to assess effects of freshwater inflows. Simplifying assumptions mus:t be made in order to estimate freshwater inflow requirements necessary to sustain Texas estuarine ecosystems. A basic premise described in this report is that freshwater inflow and estuarine productivity can be examined through analysis of certain "key indicators." The key FOysical and d1emical indicators include freshwater inflows, circula tion and salinity patterns, and nutrients. Biological indicators of estuarine productivity indude selected COIlI1IE!rcially important species. Indicator species are generally d10sen on the basis of their wide distribution through out each estuarine system, a sensitivity to d1ange· in the system,' and an appropriate life cyde. to facilitate association of the organism with the estuarine factors, particularly seasonal freshwater inflows. An estuarine inflow model is used in these studies to estimate the IlOnth ly freshwater inflows necessary to meet three specified fish harvest (pro- . duction) objectives subject to the maintenance of salinity limits for selected organisms. Where seasonal needs c:nmpete between estuarin~ependent species, a d10ice must be made to give preference to one or IlOre species' needs. Additionally, society's economic, social, and other environmental needs for freshwater in the contributing river basins must be balanced with the fresh water needs of the estuary. n-24 OlAPl'ER III DESCRIPI'ION OF' 'IHE ES'IUARY AND 'IHE SURroUNDIN:; AREA Physical Characteristics Introduction The Trinity-San Jacinto estuary oovers about 600 square miles (1,600 square kilometers) and includes East Bay, Galveston Bay, Trinity Bay, west Bay and several smaller bays (Figure 3-1). Water depth at mean low water varies from less than six feet (1.8 m) in west Bay to Oller 10 feet (3.1 m) in Galves ton Bay. Depths in the dredged dlannels range up to 40 feet (12 m). The' study area lies in the Upper Coast climatolCXjical division of Texas in the warm temperate' zone. Its climatic type is classified as subtropical (humid with warm sumners). The climate is also predominantly marine tecause of the proximity of the Gulf of Mexioo. Polar Canadian air masses frequent the basin in winter causing brief periods of' 0001, foggy and rainy weather ( 373) • Rainfall is fairly evenly distributed throughout the year. Excessive rainfall can occur in a short time period when slow--rroving thunderstorms or tropical disturbances pass Oller the area in late sumner. Influence of Contributory Basins Drainage areas oontributing inflow to the Trinity-San Jacinto estuary include the Trinity and San Jacinto River Basins, the Trinity-San Jacinto Coastal Basin, and parts of the Neches-Trinity and San Jacinto-Brazos Coastal Basins (Figure 3-2). The Trinity River Basin, largest of the oontributory basins, has a total drainage area of 17,969 square miles (46,540 km2). Fran its headwaters in southeastern Archer County, the west Fork Trinity River flows in a oouth easterly direction to its oonfluence with the Clear FOrk Trinity River near downtown Fort WJrth. From here, the west Fork Trinity oontinues in a general ly easterly direction until its merger with the Elm Fork Trinity River in the eastern part of the City of Dallas. At this ]:Oint, the Trinity River begins and flows in a southeasterly direction to Trinity Bay. Major tributaries of the west FOrk include Clear Fork Creek, Village Creek, and Mountain Creek. Major tributaries of the Elm Fork Trinity River include Spring Creek, Clear Creek, and Denton Creek. Major tributaries of the Trinity River telow the confluence of West Fork and Elm Fork include Mlite Rock Creek, East Fort Trinity River, Cedar'Creek and Richland Creek. Average annual runoff in the upper Trinity River Basin ranges from about 150 acre-feet per square mile (714 .3 m3/ha) in the headwaters of the west Fork to 400 acre-feet per square mile (1,905 m3/ha)· in the headwaters of the East Fork. Average annual runoff in the middle of the basin is about 300 III-l . AN JACINTO RIVER 95°00' I.H/6 San Luis Pass TRINITY RIVER TRINITY BAY LAKE ANAHUAC Figure 3-1. Trinity-San Jacinto Estuary . III-2 INDEX MAP o 30 60 Kilometers o 30 60 Miles 7 TRINITY ;0'''''00\ TIR~lNJrry ~ \ SAN JACI'lTO \ SArM JACi~TO \ S"N J"CIIlTO- BRAZOS Figure 3-2. Basins Contributing to the Trinity-San Jacinto Estuary III-3 acre-feet per square mile (1,222.9 m3/ha) and increases to CNer 550 acre feet per square mile (2,619.4 m3/ha) near the routh. However, during the drought year of 1956 average annual runoff for the entire basin was less than 60 acre-feet per square mile (285.8 m3/ha). . The San Jacinto River basin has a to~in~~ jea of 3,976 square miles (10,298 kJn2). The two major branches ofe-S acinto River include the west Fork and East Fork with drainage areas of 1,750 and 1,050 square .miles (4,532 km2 and 2,720 kJn2), respectively. . Average annual runoff is about 350 acre-feet per square mile (1 ,667 m~/ha) within the city limits of Houston, Texas. The lowest runoff rate also occurred in 1956 with a basin average of about 70 acre-feet per square mile (333 m3/ha). Contributing areas of the Neches-Trinity Coastal Basin are bounded on the east by the drainage area of Oyster Bayou. Total drainage area contributing to the estuary system is 430 square miles (2,048 m3/ha). Total drainage area of the Trinity-San Jacinto Coastal Basin is 247 square miles (640 kJn2). The major stream in this area is Cedar Bayou. Total drainage area rontributing runoff in the San Jacinto-Brazos Coastal Basin to the estuary is 961 square miles (2,489 kJn2). This basin is bounded on the west by the drainage area of Chocolate Bayou. Major streams within this coastal area include Clear Creek, Dickinson Bayou, Moses Bayou, Highland Bayou, Hells Bayou and Mustang Bayou. Most of the roastal basins are less than 25 feet (7.5 m) above rrean sea level. The drainage is poorly defined and is affected by irrigation and drainage canals. Runoff generally exceeds 900 acre-feet per SIuare mile (4,286 m3/ha). There are a total of 35 major reservoirs existing or under construction within the contributing area of the Trinity-San Jacinto estuary (Table 3-1). Geologic Resources Sedimentation and Erosion. The Trinity-San Jacinto estuary's main rource of sedunent is the Trmity River. Headwaters of the Trinity River carry sediment ranging from 0.70 acre-feet/square mile (3.33 m3/ha) to 1.06 acre feet/ square mile (5.05 m3/ha) annually as it flows through the North Central Prairie, Western Cross Timbers, Grand Prairie, and Eastern Cross Timbers phy siographic provinces (262, 273). Within the Blackland Prairie the annual sediment production rate is 0.77 to 0.85 acre-feet/square mile (3.7 to 4.1 m3/ha). As the Trinity River flows southward into the East Texas Timber lands the annual sediment production rate decreases to 0.16 acre-feet/ SIuare mile (0.76 m3/ha). The East Fork of the San Jacinto River contributes an average of 0.037 acre-feet/square mile (0.18 m3/ha) of sediment annually. Most, if not all, of this sediment is trapped by Lake Houston thus keeping it from entering Galveston Bay (274). As the Trinity River enters Trinity Bay flow velocities decrease and the sediment transport capability is reduced; thus, sediment is deposited near the headwaters, forming a bay-head delta. The delta ..nich formed at the ITOuth of 1II-4 Table 3-1. Reservoirs of Contributing Basins, Trinity-San Jacinto Estuary ----------------- ----------------------------------------------- : : : : : : Reservoir : Type of : Year Dam : Surface : Conservation : Conservatioo : Floo:'i Control : Total Storage Name : Use(s) a/ : Completed : Area b/ : IDol Elevation: RJol Storagec/: Storage : thousand ac-ft : -: : Acres-: ft (msl) : thousard ac-ft: thousaOO ac-ft ------- ------- - --~------- - --- _:_------- ----_._-~-- -------- --- -:.------- -- ---- -_._:_-------- ---- -:_-_.------ -- - --.-_:- -- ---. ------- - ---- Trinity River Basin BridgefOrt W.S.,R 1932 13,000 836.0 38'6,420 386,420 Alron G. carter W.S.,R 1956 1,540 920.0 20,050 20,050 Eagle M::>untain W.S.,R 1932 9,200 649.1 190,460 190,460 Vbrth W.S.,R 1914 3,560 594.3 38,130 38,130 Weatherford W.S.,R 1957 1,210 896.0 19,470 19,470 Benbrook W.S.,R,F.C. 1950 3,770 694.0 88,250 76,550 164,800 Arlington W.S.,R 1957 2,275 550.0 45.710 45,710 Lakeview d/,f/ W.S.,R - 7,470 522.0 176,900 127,100 304,000 M::>untain creek W.S.,R 1936 2,710 457.0 22,840 22,840 Kiowa R 1970 560 700.0 7,000 7,000 Lewisville W.S.,F.C.,R 1955 23,280 515.0 464,500 525,200 989,700 Grapevine W.S.,F.C.,R 1952 7,380 535.0 188,550 246,950 435,500 North e/ W.S.,R 1957 800 510.0 17 ,000 17,000 White Rock W.S.,R 1911 1,119 458.0 10,740 10,740 Lavon W.S.,F .C.,R 1953 21,400 492.0 456,500 291,700 748,200 Ray Hubbard W.S.,R 1969 22,745 435.5 490,000 490,000 Trinidad e/ W.S.,R 1925 740 284.5 7,450 7,450 H Terrell - W.S.,R 1955. 830 504.0 8,712 8,712 H Forrest H Grove e/,d/ W.S.,R - 1,502 359.0 20,038 20,038J, Cedar Creek- W.S.,R 1966 33,750 322.0 679,200 679,200 Waxahachie W.S.,R 1956 690 531.5 13,500 13,500 Bardwell W.S.,F.C.,R 1966 3,570 421.0 54,900 85,100 140,000 Halbert W.S.,R 1921 650 ,368.0 7,420 7,420 Navarro Mills W.S.,F.C.,R 1963 5,070 424.5 63,300 148,900 212,200 Fairfield e/ W.S.,R 1969 2,350 310.0 50,600 50,600 Houstoo County W.S.,R 1966 1,282 260.0 19,500 19,500 Livingston W.S.,R 1969 82,600 131.0 1,750,000 1,750,000 Wallisville d/ W.S.,R - 19,700 4.0 58,000 58,000 Anahuac ~ - Ir. 1914 5,300 5.0 35,300 35,300 San Jacinto River Basin Lewis Creek e/ W.S.,R 1969 1,010 267.0 16,400 16,400 Conroe - W.S.,R 1973 20,985 201.0 430,260 430,260 Houston W.S.,R 1954 12,240 43.8 146,700 146,700 Sheldon W.S.,R 1943 1,700 50.5 5,420 5,420 Barker F.C. 1945 - -- - 207,000 207,000 Mdicks F.C. 1948 - -- -- 204,500 204,500 a,r-lV:8.-~lVa£ei -SuppTyTmay -filcTude-municTpar~- -manuracfLirfrig;-frrfg<3"£""[oo; -s£eciii" -e1"ecfiic-'to~i -aoo!oi -riifrifiij" -usesf' - R. - Recreation F.C. - Flood. control Ir. - Irrigation only h/ At conservation pool elevation c/ Includes sediment storage d/ Under construction e/ Off channel reservoirs depending upon diversions from a:'Jjacent streams arrl/or reservoir releases for finn supply!! Land purchase initiated only the Trinity River is of a type ~ich develops'tmder oonditions of high sedi ment inflow into a relatively quiescent body of water (Le., Trinity Bay). The major marsh areas in the Trinity-San Jacinto estuary are associated with deltas. Delta plains' are oovered with fresh, brackish, and saline marshes. In order for marshes to propagate there must be a balance between sediment deposition and compactional subsidence. If there is excessive ver tical accretion, marsh vegetation is replaced by mainland grasses, shrubs, and trees. Where subsidence is more rapid than deposition, the plants drown and erosion by waves and currents deepen the marsh to form lakes or enlarged bay areas. At present, marsh surface-water level relationships of the Trinity delta are stable. Sedimentation rates and subsidence apparently are near equilibrium. Other important oources of estuarine sediments include: ( 1) Direct runoff or drainage from oontiguous land and marsh areas to the estuary; (2) Wind blown sediments, important in areas near sand dtmes and non urbanized areas; and (3) Normal ecological and biological processes producing organic sedi ment from the marine life and cquatic vegetation, often making up a large percentage of total estuarine sediments. The mainland shore is characterized by near vertical bluffs cut into Pleistocene sand, silt, and mud (Figure 3-3). Erosion of these bluffs fur nishes sediment to the a:1jacent lakes, marshes, and bays. The type of sedi ment deposited depends on ~ether the a:1jacent bluff is canposed of' pre daninantly sand or mud. Energy levels (erosional capacity) in the Trinity-San Jacinto estuary are dominated by wind action since the range of astronanical tides is only bout 0.5 foot (0.15 m); Winds blowing across the bay generate tides of two or three feet (0.6 or 1 m) and cause a change in water level at the shoreline (302). These changes in water levels produced by the wind are called wind tides. Shoreline and vegetation changes within the Tririity-SanJacinto estuarine system and in other areas of the Texas Gulf Coast are the result of natural processes (305, 302). Shorelines are in a state of erosion, accretion, or are stabilized either naturally or artificially. Erosion produces a net loss in land; accretion produces a net gain in land; and equilibrium oonditions pro duce no net change in land area. Most of the shoreline areas associated with the Trinity~San Jacinto estuary are balanced between erosion and deposition (Figure 3-,4). The nature of beaches is an indicator of the extent of shoreline stability. Sediments of the mainland beaches are a mixture of sand, shell, and rock fragments, with shell and rock fragments the most common oonstituents. This is an indication that little sand is currently being supplied to these beaches by rivers. Processes that are responsible for the present shoreline oonfiguration and that are oontinually modifying shorelines in the Trinity-San Jacinto estuary include astronomical and wind tides, longshore currents, normal wind and waves, hurricanes, river flooding, and slumping along cliffed shorelines. Astronanical tides are low, ranging from about 0.5 foot (0.15 m) in the bays to a maximum of about two feet (O.6 m) along the Gulf shoreline. Wind is a major factor in influencing ooastal processes. It can raise or lower water III-6 9 • ~ 'A!l', o San Jocinlo- Bra zos Brozos-Colorodo Figure 3-3. Geologic Map Lovoco-Guodalu e / J) ./ /". // > ./ > a:: ..;: a: UJ ~ Contact ~ Goliad Sand i~~ Looarro Cloy j{ Oa v,ll, :mdSlone Cotahoulo Tuff B W'lIi$ Sand EXPLANATION I:~b"} Beaumont Cloy ~ lissie Formation IP /0 J -1...--- _ ...1·-........__ I-;~~q i Alluv,um, beach SO'ld, ond J lerrace deposlls f Geology (Idtlpted hom Oeoloqlc Mop 01 T4IIIlCI [Oonoo. Stephenson and Go,dllllr,I937) O-;"....;5~;;;;;;.!:'O;;"..~I'5 Miles o 5 10 15 Kilometers Per~elltage frequency of surface wind dligejl'on, 19<11·1945Jnd 1953-1956 ViCloriU.' C.NlJ·SIJftFM" 5"""'0'''''',0'''.' .hm,,,,,,,,....,,, ,..,,,•. ''' ....10.' "" 10.'~ ,,".co) Figure 3-6. Land Surface Subsidence in the Houston Area, 1943-1973 (302) III-13 60frenlonds Weiland. 0 Rangeland 0 Cropland. dry I~ONE I -1'1- a 5 10 15 MIt..e a 5 10 15 Kllom.,o.. $ I WeIero EXPLANATION Urban Cropland ,Irrigated Forett Land I~ Figure 3-7. Land Use/Land Cover, Trinity-San Jacinto Estuary (269) H H '( --~ In the inrnediate vicinity of the Trinity-San Jacinto estuary, the u. S. Department of the Interior manages the Anahuac National Wildlife Refuge. In addition, the State of Texas has a fish hatchery, three State parks and the Sheldon Wildlife Management area. Archeological sites within the area inch cate utilization of the region from the Archaic to Historic stages (370). Important historic sites (Figure 3-8) include the Presidio San Augustin de Ahumada and the Mission Nuestra senora de la Luz. Founded in late 1756 or early 1757, both the mission and presidio \unds (:4.1 million kg; 96.1 percent shellfish) during the 1962 through 1976 interval. However, a large p:>rtion of each estuary's production of fish and shellfis~ is caught in the Gulf by OOIlUllercial and sport fishermen. When these harvests ;are considered, the total contribution of the estuary to the Texas coastal fish eries (all species) is estimated at 46.7 million p:>unds (21.2 million kg; 87.4 percent shellfish) annually for a recent five year period (1972-1976). Penaeid shrimp species dominate the shellfish harvests. Data Collection Program The Texas Department of Water Resources realized during its planning activities that, with the exception of data from the earlier Galveston Bay Study, limited data were available on the estuaries of Texas. Several limited research programs were underway; however, these were largely independent of III-15 • • • o • • '/. • SAN JACINTO BATTLEGROUND • •• • • 0 • • • • • •() • • TRINrrV • " RIVER •• • ANAHUAC NATIONAL WILDLIFE REFUGE DOUBLE ~ BAYOU • ROLLOVER PASS TRINITY' BAY EAST BAY • • ., . • • • • • • 0 • • • .* HOUSTON· • SHIP C.HANtJEL ~ • • • • • MOSES. BAYOU I .: I~~'--- ;L --::: :II~::ETERSo ~ ,DICKINSON.~ BAYOU • • CHOCOLATE BA\OU • I I GALVESTON BAY I I I I I I I I I I J I I I I f " RH"';,~~ ~~" _r \ I~BAY ~~~. ~l~--, , . 0 \ . * 0. 0 . . . \00~AR\~ GALVESTON ISLAND ROADS \ SAN LUIS PASS STATE PARK H H H I ~ '" Figure 3-8. Natural Resources, Trinity-San Jacinto Estuary (378) one another. The data rollected mder any me program were oot a:rnprehensive, and since sampling and measurement of environmental aJ1d ecological parameters under different prograffi'S were rot· accomplished simultaneously, the resulting data rould rot be reliably rorrelated. In SJIlle estuaries, virtually 00 data had been collected. A program was therefore initiated by the Department, in cooperation with other agencies, to collect the data .ronsidered essential for analyses of the physical and water quality dlaracteristics and ecosystems of Texas' bays and estuaries. To begin this program, the Department ronsulted with the u. S. Geological Survey and initiated a reconnaissance-level investigation program in September ·1967. Specifically, the initial objectives of the program were to define: ( 1) the occurrence, rource and distribution of nutrients; (2) cur rent patterns, directions, and rates of water ROVement; (3) physical, organic and inorganic water dlaracteristics; and (4) the OCcurrence, quantity, and dispersion patterns of water (fresh and Gulf) entering the estuarine system. To avoid duplication of w:)rk and to promote coordination, discussions were held with other State, Federal and local agencies having interests in Texas estuarine systems and their management. Principally, through this cooperative program with the U. S. Geological Survey, the Department has continued to collect data in all estuarine systems of the Texas Coast (Figures 3-9 and 3-10, Table 3-2). Calibration of the estuarine nodels (discussed in Chapter V) required a considerable anount of data. Data requirements included information on the quantity of flow through the tidal passes during rome specified period of reasonably ronstant hydrologic, meteorologic, and tidal conditions. In addi tion, a time history of tidal amplitudes and salinities at various locations throughout the bay· was necessary. .Canprehensive field data oollection was undertaken on the Trinity and San Jacinto estuary on July 20-23, 1976. Tidal amplitudes were measured simultaneously at numerous locations throughout the estuaries (Figure 3-9). Tidal flow measurements were made at several dif ferent bay cross-sections. In addition, conductivity data were collected at many of the sampling stations shown in Figures 3-9 and 3-10. Studies of past and present freshwater inflows to Texas' estuaries have used all available sources of information on the physical, dlemical, and biological dlaracter istics of these estuarine systems in an effort to define the relationship between freshwater and nutrient inflows and estuarine environments. Economic Characteristics Socioeconanic Assessment of Adjacent Counties The econanic significance of the natural and man-made resources asso ciated with the Trinity-San Jacinto estuary is reflected in the direct and indirect linkages of the bay-supported resources to the econanies of Brazoria, Chambers, Galveston and Harris Counties. Trends in p:>pulation, earnings by industry sector, and personal income levels are presented for the four counties. EO;>ulation. The p:>pulation of the four county study o approximately 2.3 percent annually between 1970 Harris Counties grew the fastest, at average annual III-17 area experienced a growth and 1975. Brazoria and rates of 2.5 percent and ~ LAKE ANAHUAC o~o::::~:::::~IO MILESE 16 l(ILO~f.TERS ~/ JACINTO HIllE/? _~IOve(leof 95"00'~>_,_r1)'--' I f,ri.: 6 " TEXAS Locotion Mop -440r -110 ~ EXPLANATION Dota - cOllection line numb Data-coli . tr.~tlon sit. numb.r Figure 3-9. Data-Collectio .n SItes in th T· . .e nmty-S .an Jaclnt Eo stuary III-18 o 5 10 MilesO"~'5'~"IOC-"5'Kilometers III~19 EXPLANATION I USGS stream flow with water quality ... USGS streamflow •USGS Me gage or COE tide gage D USGS tide gage or COE tide gage,dlscontlnued •Portlol record USGS streamflow With water quality Figure 3-10. Locations of Gaging Stations, Trinity-San Jacinto Estuary Table 3-2. U. S. Geological Survey (USGS) or Corps of Engineers (COE) Gages, Trinity-San Jacinto Estuary Station Nt.nnber Station Description Pericxr--:-- of Operating Record Entity Type of Record --'------- " . " ----------"---_._------_:._------- 42540 66500 67500 68000 68520 69000 69720 70000 70500 71000 73700 74150 74250 74500 Stream Gages East Bayou nr. Stowell, TK. Trinity River at Romayor Cedar Bayou nr. Crosby, Tx. West Fork San Jacinto River nr. Conroe Spring Creek at Spring Cypress Creek nr. Westfield Lake Houston nr. Sheldon East Fork San Jacinto River nr. Cleveland Caney Creek nr. Splendora Peak Creek at Splendora Piney Creek nr. Piney Point Cole Creek at Deihl Road, Houston Brickhouse Gulley at Costa Rica Street, Houston Whiteoak Bayou at Houston 1967-72 1924- 1971- 1961- 1939- 1944- 1954- 1939- 1943- 1943- 1963- 1964- 1964- 1936- USGS USGS USGS USGS USGS USGS USGS USGS USGS USGS USGS USGS USGS USGS Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording --------------------------------------------------------------------- (continued ) 1II-20 Table, 3-2. U. S.GeologicalSurvey (USGS) or Corps of' Engineers (COE) Gages, Trinity-San Jacinto Estuary (cont 'd.) Station : , Number' Station Description : PeriOd of' Record : Operating Entity Type of Record ----'------- 75000 75500 75730 75770 76000 76500 76700 77000 78000 67900 69200 74550 75100 75650 Brays Bayou at Houston 'Sims Bayou at Houston Vince Bayou at Pasadena Hunting Bayou at Hwy. 610 Greens Bayou nr. Houston Halls Bayou at Houston Greens Bayou at Ley Road Clear Creek nr. Pearland Chocolate Bayou nr. Alvin Partial Record Stream Gages Lake Creek nr. Conroe Cypress Creek nr. Humble Little White Oak Bayou at Houston Brays Bayou at Scott Street 'Berty Bayou at Forest Oaks Street " 1936- 1952- 1971- 1964- 1952- 1952- 1962, 1964, 197J- 1963- 1959- 1968- 1970- 1971- 1971- 1964- USGS USGS USGS USGS USGS USGS USGS USGS USGS USGS USGS USGS USGS USGS Continuous Recording Continuous Recording Continuous, Recording 'Continuous Recording Continuous Recording Continuous Recording Continous, Recording Continuous Recording Continuous Recording Limited Data Limited Data Limited Data Limited Data Limited Data (continued) 1II-21 Table 3-2•. U. S. Geological' Survey (USGS) or Corps of Engineers (COE) Gages, Trinity-San Jacinto Estuary (cont'd.) Type of Record Operating Entity ------=Pe~r~iOd-------'------- : of Record Station DescriptionStation Number :.-_----=-_._--- 4 Tide Gages Railroad Causeway to Mainland 1962- mE Continuous Recording 5 Galveston Harbor, Ft. Point 1968- mE Continuous .Recording 6 Galveston Bay Entr. Channel, 1962- So. mE Continuous Recording 7 North Texas City Dyke 1962- mE Continuous Recording 8 Hanna Reef, Moody Pass 1962- mE Continuous , Recording 9 Marsh Point, Sun Oil Channel 1962- mE Continuous Recording 10 Seabrook, Texas Parks & 1970- Wildlife COE Continuous Recording 11 Trinity Bay, Point Barrow 1962- mE Continuous Recording 12A Morgan Point, Barbours Cut 1962-65 mE Continuous Recording 13 Texaco Oil Dock, Galenda Park 1962- mE Continous Recording 14B Chocolate Bayou, uost Lake, 1975- AMOCO Dock mE Continuous Recording 15 Highway Bridge, San uouis Lake 1968- mE Continuous Recording 42545 Galveston Bay nr. Marsh Point 1975-76 USGS Continuous Recording 67000 Trinity River nr. Liberty 1922- USGS Continuous Recording ._---------------------------------------- (continued) 1II-22 Table 3-2. U. S. Geological Survey (USGS) or Corps of Engineers (COE) Gages, Trinity-San JaCinto Estuary (cont'd.) -----=---- Station Number . . Station Description Period of Record Operating Entity Type of Record 67110 67113 67117 67210 67230 67725 67260 67301 67310 697205 74700 74800 77650 77700 Big Caney Creek nr. Mont 1976-77 Belvieu 'Sulfur Barge Carial nr. Wallis- 1976-77 ville Lake Charlott nr. Wallisville 1976- Old River nr. Mont Belvieu 1977- Old River Lake nr. Wallisville 1976- Lost River nr. Wallisville 1976- Old River Cutoff Channel nr. 1976- Wallisville Anahuac Channel at Anahuac 1976- Galveston Bay nr. Crystal Beach 1975-76 San JaCinto nr. Sheldon 1970- Buffalo Bayou at 69th Street, 1961- Houston Keegans Bayou at Roark Rd., 1964- Houston Moses Lake - Galveston Bay nr. 1967- Texas City Highland Bayou at Hitchcock 1963- 1II-23 USGS USGS USGS USGS USGS USGS USGS USGS USGS USGS . USGS USGS USGS USGS Continuous Recording Continuous Recording .Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording Continuous Recording 2.4 percent, respectively; while Chambers and Galveston Counties increased at more rrodest rates of 1.0 percent and 1.4 percent annually. During the same period, the State of Texas was gaining population at an annual growth rate of 1.7 percent. In 1975, the population of the four oounty area was 2,279,400. Harris County acoounted for 86.1 percent followed by Galveston County with almost eight percent. Population forecasts for the period 1970 to 2030 indicate that the population of the study area can be expected to increase 214 percent by the year 2030. Harris County is projected to remain the nest populated oounty in the area, and also the second fastest growing, with an annual rate of. growth (2.0 percent) exceeded only by Brazoria County (2.1 percent) . Estimates of future population for the four oounty area are presented in Table 3-3. Inccrne. Real personal inccrne for the four oounty study region ccmprised approximately 21 percent or $7.52 billion of the state's estimated personal inccrne in 1970. Harris County accounted for nere than 87 Percent of the regional estimate, followed by Galveston (7.8 percent) , Brazoria (4.6 percent), and Chambers (.6 percent). Employment. In 1970, an estimated 820,862 persons were anployed in the study area, and almost 87 percent of these (711,749) worked in Harris County. Chambers County had the lowest anployment, only 0.5 percent of the regional total. Seventy-six percent of the region's anployed labor force is distributed anong eight major industrial sectors (Table 3-4). More IoOrkers are involved in wholesale and retail trade than any other sector -- over 182 thousand or 22.2 percent of· the total. Manufacutring is also a major anployer in the area, accounting for 168 thousand IoOrkers, Oller 20 percent of the labor force. Industry. The "basic" industries in the area, Le., those I>hich produce tangible output largely for export, are manufacuturing, agriculture-forestry fisheries, and mining (Table 3-5). These sectors account for Oller 24 percent of all anployment in the study area. In oodition to the basic sectors are the service sectors: wholesale and retail trade, professional services, oonstruc tion, civilian government, and amusement and recreation. These sectors anploy over 52 percent of the region's IoOrkers. The service sectors provide goods and services to the basic industries as well as to the general public and are, in varying degrees, dependent upon them. The most important basic sector of the regional econcrny, in terms of total earnings, as well as anploYment, is manufacturing (Table 3-5). Most of the manUfacturing activity is ooncentrated in the production of machinery products, chemicals and petroleum refining and related products. III-24 Table 3-3. Ft>pulation Estimates and Projections, Area Surrounding Trinity-San Jacinto Estuary, 1970-2030 (272) -: : : : : 1970-2000 : 1970-2030 County 1970 1975 : 1980 : 1990 : 2000 : 2010 : 2020 : 2030 : Annual % : Annual % O1anqe : Olange Brazoria 108,312 122,800 140,300 176,900 218,400 262,500 314,500 375,000 2.4 2.1 Annual %Change 2.5 2.7 2.3 2.1 1.9 1.8 1.8 Chambers 12,187 12,800 13,600 14,900 16,500 18,600 21,500 25,700 1.0 1.3 Annual %Change 1.0 1.2 .92 1.0 1.2 1.5 1.8 Galveston 169,812 1B2,000 197,200 226,000 257,600 291,600 333,500 384,BOO 1.4 1.4 Armual %Change 1.4 1.6 1.4 1.3 1.3 1.4 1.4 Harris 1,741,912 1,961,BOO 2,243,400 2,763,500 3,357,100 4,005,300 4,746,200 5,601,300 2.2 2.0 Annual %Change 2.4 2.7 2.1 2.0 1.8 1.7 1.7 Area Total 2,032,223 2,279,400 2,594,500 3,181,300 3,849,600 4,578,000 5,415,700 6,386,800 2.2 1.9 Annual %Change 2.3 2.6 2.1 1.9 1.7 1.7 1.7 H H State Total 11,198,655 12,193,200 13,393,100 15,593,700 18,270,700 21,540,600 25,548,400 30,464,900 1.6 1.7H I Annual %Change 1.7 1.9 1.5 1.6 1.7 1.7 1.8 N lJ1 Table 3-4. Employment by Industrial Sector, Area Surrounding Trinity-San Jacinto Estuary, 1970 (266) --- - -- - - 1970-- - -- - --- --- _._- - -Percent: : : of Total Employment : .. : : : : of Study sector. . Brazoria: Chambers : Galveston : Harris : 1btal : Area Wholesale and Retail Trade ·6,707 974 12,225 162,540 182,446 22.2 Manufacturing 11,765 521 13,156 143,039 168,481 20.5 Professional Services 5,483 604 13 ,087 115,339 134,513 16.4 Construction 5,303 507 6,390 63,348 75,548 9.2 Agriculture, FOrestry, and .... Fisheries 1,475 587 1,033 5,666 8,761 1.1 .... .... I Mining 975 342 629 20,246 22,192 2.7IV '" Civilian Government 468 166 3,213 24,617 29,469 3.6 Amusement and Recreation 180 4 464 5,729 6,377 •78 All Other 6,455 586 14,814 171,225 193,080 23.5 1btal 39,811 4,291 65,011 .711,749 820,862 100.0 ------------------------------ _.- ----------_.- --------- Table 3-5. Earnings by Industrial Sector,· Area Surrounding Trinity-San Jacinto Estuary, 1970 (265) - - _.._- 197(J ----- Percent of Total Earnings : : : : : Area : in Study Sector : Brazoria: Chambers : Galveston : Harris : Total : Area (Thousands of 1967 Dollars) Wholesale and Retail Trade 35,926 5,425 67,132 1,169,536 1,278,019 19.9 Manufacturing 98,738 4,116 103,565 1,288,845 1,495,264 23.2 Professional serviCes 19,516 2,235 47,754 551,470 620,975 9.6 Construction 34,944 3,474 43,166 560,727 642,310 10.0 H Agriculture, Forestry, andH H Fisheries 6,342 2,624 4,554 32,725 46,246 .72I '"-J Mining 10,219 3,727 6,758 285,038 305,741 4.7 Civilian Government 26,456 3,111 59,359 595,922 684,847 10.6 Amusement and Recreation 709 17 1,873 30,300 32,899 .51 All Other 32,9~6 2,937 81,74?- 1,213,186 1,330,801 20.7 County Totals 265,785 27,666 415,902. 5,727,749 6,437,102 100.0 -- - ~- 'Ibe mineral wealth of the area is also an important factor in its econ omy. In 1976, the four counties produced CNer $1.5 billion "-Orth of oil, gas, stone, clay, sand and gravel, cement, magnesium ,and lime. 'Ibese mineral products supply raw materials for the petroleum refining and petrochemical industries and other manufacturers, as well as inputs for the construction sector of the economy. The area surrounding the Trinity-San Jacinto estuary produces a signifi cant portion of the coastal region's agricultural output, with 1977 annual receipts from crops and livestock of $108.2 million. All four counties were rice and soybean producers; other major regional crops were grain sorghum, cotton and corn. Crop production accounted for 72 percent of regional farm income, and the remaining 28 percent originated from livestock and poultry enterprises. In crldition, the bay-supported commercial fishing industry prer of fishermen per party, the average nllllt>er of oours fished per party, and the proportion of boat fishermen actually fishing in the study area.' Each of these average oomputations was stratified according to calendar quarter and fishing strata (boats or wade-bank). The roving count sample survey consisted of I::oat trailer counts at each of the designated boat ramps within the study area (estuary system). An adjustment of the boat trailer count was made to correct for those I::oats which were not fishing in the estuary System. Sample data fran the I::oat party personal interview survey were used to estimate .the proportion of I::oat parties that were fishing in the study area. . The estimated number of fishing parties at the' Trinity-San Jacinto estuary for the study period is stated as follows: T = Z + W where: T = Estimated total annual fishing parties, Z = Estimated number of I::oat· fishing parties, and W= Estimated number of wade-bank fishing parties. Each of the components of the total fishing· party estimating. equation is defined and explained below: 4 Z = 1: k=1 where: zk, (k = 1, 2, 3, and 4 j and pertains to the calendar quarters of the year beginning with September 1, 1976. Z = Estimated number of I::oat parties fishing in the Trinity-San Jacinto estuary for the period September 1, 1976 through August 31, 1977. III-29 Zk = Estimated number of boat parties fishing in the Trinity-San Jacin to estuary during the kth calendar quarter of the study period. 4 W= z; Wkl (k = 1, 2, 3, and 4) as explained above. k=1 where: W = Estimated munber of wade-bank parties fishing in the Trinity-San Jacinto estuary for the period September 1, 1976 through August 31, 1977. . WI{ ':' Estimated number of wade-bank parties fishing in the Trinity-San Jacinto estuary during the kth calendar quarter of the study period. The equation and definitions presented above give the results of the sample estimates of the types of fishing in the estuary. The typical quarter ly sample analysis and individual canputing methods are stated and defined below for the general case, for weekends. Since roITing count and interview data were not collected on weekdays in this study period, weekday analyses were based on the weekday/weekend visitation distribution as observed in the motor vehicle license plate survey. The results for weekdays and weekend days were Slll11lled to obtain estimates for the entire quarter. For boat fishing: x, , . I\ . Hk Dk f r Nll'kJ Z i=1 J'=1k = -=---"'---'-_-'-_-:::c:- where: Zk = Estimated number of boat fishing parties on weekend days in quarter k, Bk = Estimated proportion of trailers for which there were boat parties fishing in the study area in quarter k, on weekend days, Hk = Number of hours' SUbject to being surveyed per weekend day in quarter k (14 hours per day in fall, 12 hours per day in winter, 14 hours per day in· spring, and 15 hours per day in sunrner), r = Number of sample boat sites within the study area, ~ = Weekend days in quarter k, . "= Number of trailers counted per hour on weekend days at· site i on day j, in quarter k, Nik = Number of times site i was surveyed on weekend days during quarter k, and III-3D 11k = Average number of oours fished per boat party on weekend days in quarter k. No data were oollected for wade-bank and pier fishing in this study period: therefore, the estimate of wade-bank and pier parties was based on the relation of wade-bank to boat fishing and pier to boat fishing as d:Jserved in a 1975 study of Galveston Bay (295). These typical terms for each fishing type were sumned as described above to d:Jtain the total annual sport fishing visitation estimate in parties. The number of perSOtlsper party, oost per party per trip and oounty of origin of each party were also conputed. Sport Fishiria Visitation Estimates. Results fran the visitation estimation equations in icate that 305.8 thOusand fishing parties visited the estuary during the period September 1, 1976 through August 31, 19770 (Table 3-6). Sea sonal visitation as a percentage of annual visitation ranged fran a high of more than 37 percent for the sunmer quarter to a low of approximately 13 per cent during the winter quarter. The distribution of fishing parties by strata indicates that wade-bank fishing acoounted for 46.8 percent of annual visita tion followed by boat fishing with 45.1 percent (Table 3-6). Sport Fishing Visitation Patterns. Although the personal interview informa tion included the rounty of residence of the interviewee, the mmDer of inter views (558 in all) was too small to estimate a general visitation pattern to the estuary system. Thus, an intensive survey was undertaken in the stmrner of 1977 to d:Jserve, in oonjunction with the roving oount, the nvtor vehicle license plate numbers of fishing parties. Fran the license plate m.mt:>ers, the vehicle's registration oounty, presumably the fishing party's oounty of residence, oould be detennined. In this way, the effective sample size was increased. ' The results of the survey show that over 86 percent of fishermen at the Trinity-San Jacinto 'estuary came from the following five oounties -- Harris (61.6 percent of the sunrner 1977 visitation), Galveston (12.8 percent), Brazoria (5.6 percent), Jefferson (4.6 percent), and Fort Bend (1.7 percent). A nvre general visitation pattern distinction of "local" and "nonlocal" was also made. "Local," for the purposes of this study, includes oounties within approximately 60 miles of the estuary area. For the Trinity-San Jacinto, estuary, these rounties are Brazoria, Chambers, Harris, Galveston, Liberty, Waller, Fort Bend, and Montgomery. "Non-local" canprises all' other Texas counties and out-of-state visitors. Since it is expected that the proportions of local and nonlocal bay sport fishennen vary from season to season, an attempt was made to estimate this, pattern for seasons other than the Stmrner period. The only infonnation avail able on visitation patterns for all seasons was the sample of persOha! inter view data which, in oodition to the small number of observations, was felt to be biased toward local parties. Thus, the stmrner license survey visitation pattern was canpared to the stmrner interview pattern, for the purpose of ~uting an oojustment factor. This was applied to the remaining quarters of 1II-31 Table 3-6. Estimated Seasonal Sport Fishing Visitation to the Trinity-San Jacinto Estuary, 1976-1977 a/ Fall 36.8 (2.50) Winter 13.5 (2.14) Spring 35.9 (2.38) Summer 51.7 H (2.69) H H I Total All 137.9w '" seasons (2.51) Season EI Boat Werle-Bank : Pier thousands oCPart ies 27.2 4.7 (2.06) (1.94) 22.5 3.6 (1.83) ( 1.88) 40.5 6.5, (2.05 ) (2.13) 53.0 9.9 (1.95) (2.66) 143.2 24.7 (1.98) (2.27) Total - All Strata 68.7 (2.29 ) 39.6 ( 1.94) 82.9 (2.20) 114.6 (2.35 ) 305.8 (2.24) a;.;r-Tfie-figures in parenthesis indicate the average J1llI1tler of fishermen per party -fertlie - 'respective fishing type and quarter. . b/ Fall = September, October, and November - Winter = December, January, and February Spring = March, April, and May . Summer = June, July, and August interview· data to renove the bias toward local data and provide a IlOre ac curate reflection of year-round visitation patterns (Table 3-7). Sport Fishing Direct Expenditures. During the interview, a question was asked of the party head for total expected o:>st of the trip for the entire group, including food, lodging, and gasoline. The personal interview survey sample of fishing party expenditure data was grouped by origin (local or nonlocal). The average cost per party for the various fishing types and origins (Table 3-8) was applied to the a:'\justed visitation distribution estimates (Table 3-7) and visitation estimation by type (Table 3-6) to ootain an estimate of total sport fishing expenditures (Table 3-9). More than 39 percent of the estimated total expenditures ($4.13 million) were made during the sunrner and nine percent were made during the winter quarter (Table 3-9). Sport Fishing Eo:>nanic Impact Analysis. Sport fishing expenditures exert an effect upon the eo:>nanies of the local regions \>tlere fishing occurs and tJFOn the entire State because of .transport ion expenses, sport fishing equiprrent sales, and service sector supply and demand linkages directly and indirectly associated with fishing expenses. The direct, or initial, business effects are the actual expenditures for goods and services purchased by sport fishing parties. For this analysis, variable expenditures fur transportation, fuod, lodging, and other materials and services purchased were classified by eo:>n omic sector. Specifically, the expenditures that vary with size of party, duration of trip, and distance traveled; Le., variable expenditures, were classified into: recreation (including marinas, mat rental fees, and mat fuel); fisheries (bait); eating and drinking establishments; lodging services; and travel (gasoline and auto service stations). Equiprrent expenditures fur boat insurance, mats, motors, trailers, and fishing tackle are rot available. Thus, this analysis is an understatement of the total business associated with sport fishing in the Trinity-San Jacinto estuary. Indirect impacts are the dollar values of goods and services that are used to supply the sectors \>tlich have made direct sales to fishing parties. Each directly affected sector has supplying sectors fran \>tlich it purchases materials and services. The total arrount of these successive rounds of pur chases is known as the indirect effect. The total business effects of pur chilSes of supplies and services by fishing parties upon the regional and state economies include the direct and indirect incomes resulting fran the direct fishing business. Each eo:>nanic sector pays wages, salaries and other forms of income to errq:>loyees, owners and stockholders \>tlo in turn spend a p:>rtion of these incomes on goods and services. In this study, the rrethod used to cal culate this total impact is input-output analysis, using the Texas Input Output Model:J 276) and regional input-output tables derived fran the State model (282).1 The expenditure data o:>llected by personal interviews of a sample of fishing parties at the Trinity-San Jacinto estuary (Table 3-9) indicated only the magnitude of variable expenditures by sport fishermen. . To estimate the sectorial distribution of all expenditures, the interview data were supple mented with data fran estimated retail sales in 1975 by marine sport fishing y Il'Iput-output relationships were estimated for Calhoun, Victoria, Jackson, Refugio, and Wharton Counties. III-33 Table 3-7. Estimated Seasonal Sport Fishing Visitation Patterns at the Trinity-San Jacinto Estuary, 1976-1977 Visitation Fall Winter : Spring Surrrner 'lbtal-Annual thousands of parties IDcal 57.4 39.6 76.6 98.2 271.8 Nonlocal 11.3 6.3 16.4 34.0 ._- 'lbtal Visitation 68.7 39.6 82.9 114.6 305.8 ------ ----- Table 3-8. Estimated Average Cost per Sport Fishing Party by Type and Origin, Trinity-San Jacinto Estuary, 1976-1977 : Average Cost Weighted per Party Boat Wade-Bank Pier Average 1976 dollars IDcal 15.75 7~53 7.37 11.20 Nonlocal 34.27 31.86 19.35 31.98 1II-34 Table 3-9.. Estimated Sport Fishing Expenditures by season and Fishing Party Type, Trinity-San Jacinto Estuary, 1976-1977 : Season 2/: Boat Wade-Bank Pier Total Percent thousands of 1976 dollars Fall 691.2 313.1 43.7 1,048.0 25.4 Winter 212.1 169.5 27.0 408.6 9.9 Spring 616.2 379.8 53.4 1,049.4 25.4 Surrmer 951.8 583.7 89.7 1,625.2 39.3 Total 2,471.3 1,446.1 213.8 4,131.2 100.00 P Fall = SepteIiiber, october and Noveinber Winter = December, January and February Spring = March, April and May Surrmer = June, JUly and August f III-35 related industries in the west Gulf: of Mexico region (Mississippi delta to Mexican border) (517). Tb account for different origins and types of fishing parties, 'variable expenditures were analyzed for each of the four types of fishing' parties: local boat parties; local wade-bank parties; nonlocal wade bank parties; and nonlocal boat parties. Variable expenditures, except for travel, were classified as having been made within the local region, since that is the site at ~ich the service is produced. For the'travel sector, it was assumed that one-half of the expenditures occurred within the local area and one-half occurred elsewhere in the state en route to the study area. ' The results of 'the survey show that variable sport fishing expenditures in the local area of the Trinity-San Jacinto estuary were CNer $4.0 million. In addition, there was an estimated $125 thousand spent outside the region, within Texas (Table 3-10). M:>st of the expenditure impact, over 96 percent, accrues to the region. However, ~en the total impacts are calculated, the regional gross impact of over $9.16 million accounts for only 68 percent of the gross dollar value statewide (Table 3-11). This spreading of impact re sults from business and industry market linkages among regional establishments and suppliers throughout the State. A significant portion (over 36 percent) of the direct expenditures by sport fishermen in the region results in increased personal incomes for regional households directly affected by the sport fishing industry. Fran these data it is estimated that regional househOlds received an increased annual income of over $2.73 million fran the Sport fishing business in the area (Table 3-11). Statewide, the income impact amounted to over $3.82 million, annually. The input-output analysis estimated a total of 255 full time job equiv alents directly related to sport fishing in the Trinity-San Jacinto estuary region in 1976 through 1977. Statewide, an additional eleven full time job equivalents were estimated to be directly related to the expenditures for sport fishing. The total employment impact to the state econany was 450 full time job equivalents (Table 3-11). Revenues to state and local governments (including,schools) are positive ly impacted by the increased business activity and gross dollar flows fran sport fishing business. The total, statewide state tax revenues amounted to $139 thousand, with $91.3 thousand collected in the lOcal reg ion. Most of the state revenues were received fran the rest of the State and not fran the sur rounding estuarine region. However, the total tax revenue impacts for local jurisdictions were concentrated within the region ~ere an estimated $155.6 thousand resulted fran direct, indirect and induced sport fishing expenditures (Table 3-11). In addition, local governments outside the Trinity-San Jacinto estuary region collected an estimated $41 thousand in taxes on travel expendi tures by fishing parties in 1976 through 1977. The data show that sport fishing in the Trinity-San Jacinto estuary region has a larger econanic impact within the region than areas outside the region, $4.22 million canpared to $9.13 million, respectively. However, data necessary to analyze the effects of sport fishing equipment business were not available. Thus, the annual statewide gross output impact of over $13.38 million represents a contribution to the State's economy fran only the variable expenditures by sport fishermen in the estuary region and does not include the effects of purchases of sport fishing equipment. III-36 Table 3-10. Estimated Sport Fishing Variable Expenditures by sector, Trinity San Jacinto, Estuary, 1976-1977 Bait Travel Food lDdging Recreation a/ Total thousands of 1976 dollars Total 947.2 909.9 1,014.6 308.6 950.9 4,131.2 b/ a:r--Marinas;li5at£uel, ana bOat rental. ---------------- h/ Adjusted for travel expenditures outside the study area of $125.1 - Expenditures in the region = $4,006.1 thousand • . Table 3-11. Direct and TotaUV Econanic Impact .fran Sport Fishing Expenditures, Trinity-San JaCinto Estuary, 1976-1977 b/ ~._----- Direct E! Regional State Regional Total State d/ ------------------ -='--- . . ---_._-------_._-~---_.---- _._._--- OUtput (thousands) Employment (Man-Years) Income (thousands) State Tax Revenues ( thousands) Local Tax Revenues ( thousands) $4,006.1 255 1,477.1 $4,131.2 266 1,539.5 35.7 53.5 $9,162.7 368 2,732.6 91.3 155.6 $13,385.8 450 3;829.4 139.0 217 .4 Total - direct, indirect, and induced Values in 1976 dollars Direct impacts for the region and state differ due to the travel expendi ture adjustment Statewide expenditures include the regional impacts Data not available III-37 Econanic Impact of canmercial Fishing. The analysis of the a:nunercial fishing industry in the Trinity-San Jacinto estuary was ocmewhat limited by the avail ability of estuary-specific data. Estimates made of the estuary's total contribution to Texas commercial fisheries harvests were based on the inshore offshore catch distribution. However, the specific markets into which the fisheries catches were marketed are not known. Thus, for this portion of the analysis it was assumed that the markets were in' Texas and 'that the statewide average prices were appropriate and applicable. ' The average annual conrnercial fishing contribution of the estuary was estimated at 827,700 pounds (375,440 kg) of finfish and 40,792,500 pounds (18.5 million kg) of shellfish for the period 1972 through 1976. Using 1976 average dockside finfish and shellqsh prices ($.357 per lb. and $1.456 per lb., respectively), the direct commercial value of fish and shellfish attrib uted to the estuary was estimated at $59.69 milhon (1976 dollars) (469). Shrimp, blue crab, and oysters constituted approximately ,97 percent of this value. The Texas economy-wide total business resulting fran conrnercial fish catch attributed to the Trinity-San Jacinto estuary was estimated using the 1972 Texas Input-output fobdel fisheries sectOr multipliers. 'lbtal value of' the catch was $59.69 million, direct' employment in the fisheries sector was 2,174, and direct salaries to fisheries employees was $19.94 million (Table 3-12). Gross Texas business resulting from fishing, processing, and marketing the catch attributed to the estuary was estimated at $185.93 million. In direct supporting and marketing activities provided an a:lditional 2,173 full time job equivalents regionally and an .a:lditional 2,446 full time job 'equiv alents statewide. Gross personal income in Texas attributed to the estuarine fishing and supporting sectors was estimated at $51.13 million, state taxes at $1 .69 mill ion, and taxes paid to local units of cpvernments throughout Texas" as a result of this fishery business, at $2.35 million (Table 3-12). Summary of Econanic Impact of the Sport and Commercial Fisheries. Analyses have been performed to canpute estimates of the quantities of sport and CXIIl mercial fishing and the economic impact of these fisheries upon the local and state economies. Sport fishing expenditures exert an effect upon the econdnies of the local regions where fishing occurs and upon the entire State because of trans portation expenses, sport fishing equipment sales, and service sector supply and demand linkages directly and indirectly associated with fishing expenses. Direct business effects include expenditures for cpods and services purchased by sport fishermen (transportation, food, lodging, equipment). Indirect impacts are the dollar value pf cpods and services that are used to supply the sectors which make these direct sales to fishing parties. Other indirect impacts include wages, salaries and other forms of inCXIlle to employees, owners and stockholders. The method of input-output analysis, using both the Texas Input-output Model and regional tables derived from the state model, was used to calculate the total impact. The results showed that variable sport fishing expenditures in the local area were greater than $4.0 million. In a:ldition, there was an estimated $125 thousand spent outside the region, within Texas. III-38 Table 3-12. Direct and Total a/ Economic Impact of Ccmnercial Fishing in the Trinity-San Jacinto Estuary ---:--------:-----""'lbtar----- Fishing Sector Output 59,689.4 ( 1000' s 1976 $) Employment 2,174 (Man-Years) Income 19,942.2 (1000' s 1976 $) State Tax Revenues 226.8 (1000's 1976 $) Local Tax Revenues 268.6 (1000's 1976 $) Regional State . . -------- -_._._-- 126,839.9 185,932.4 3,815 4,619 42,237.6 51,131.8 1,199.8 1,689.2 2,047.3 2,345.8 a; Total = rtion of the Neches-Trinity Coastal Basin, Trinity-San Jacinto Coastal Basin, and the San Jacinto-Brazos Coastal Basin, contribute to the estuary. The previous chapter of this retort (Chapter III, "Influence of Contributory Basins") describes up stream reservoirs in the Irajor basins. The present chapter deals with aspects of the quality and quantity of freshwater inflow fran a historical perspec tive. Freshwater Inflows Freshwater inflow contributions to the Trinity-San Jacinto estuary con sists of (1) gaged inflow fran the Trinity and San Jacinto River Basins and San Jacinto-Brazos Coastal Basin; (2) ungaged runoff; (3) return flows fran municipal, industrial and agricultural sources in ungaged areas; and (4 ) direct precipitation on the estuary. The following paragraphs will consider each of these individually. In crldition to freshwater inflow, evaporation from the bay surface is considered to arrive at a freshwater inflow balance. Gaged ~J?.flows from the ':I]:"inity Basin The Trinity River Basin has a total gaged drainage area of 17,186 square miles (44,755 kJn2). This inflow enters the estuary through the Trinity delta at the northern edge of Trinity Bay. Gaged contributions of the Trinity River Basin to the estuary have averaged 5,381,000 acre-feet/year (6,608 million m3/yr) over the period 1941 through 1976 (Table 4-1). Gaged yield from the Trinity Basin (1941-1976) has averaged 313 acre-feet per square mile (1,490 m3jha). Gaged Trinity Basin inflows have accounted for 55 percent of the combined inflowl/ and 47 percent of the total freshwater inflowY to the Trinity-San Jacinto estuary CNer the 1941 through 1976 period (Table 4-2). TT--Cciiib"Tned -inflow = (gaged inflow) + (ungaged inflow) + (return flows from - ungaged areas) - (diversions below last gage)Y Total freshwater inflow = (combined inflow) + (direct precipitation on, the estuary) • N-1 Table 4-1. M:::mthly Freshwa'ter Inflow, Trinity-San Jacinto Estuary, 1941-1976 ~ .GAGED .GAGEO .GAGED .lOBi... • • • TRINITy.. • TOTAL • BAY .FRESHiliATER. MO~TH .TRINIT.s.JlC •• SJ~8QZ.GAGfO .UNGAGEO.RETUDN. RIvER .COM8INED.PRECIPITATION.FRESHWAT£R.E~APORATION. INFLOW FLOh. FLOw. FLu~. FLO~.INFLO~. FlOWS.DIVERSIONS. INFLOW. ON BAY • INFLOw • LOSSES • BALANCE ------------------------------------------------------------------~---------------------------------------------------------- tiPusarrls of acre-feet AV~RAGE OVER ALL VI: AR::, JAi'OiJA.RY 523 187 8 719 212 17 I 948 113 1062 65 997 fEbRUARY 480 115 8 6 b4 242 5 1 912 lC14 1017 63 953 !'~Ak CH 579 I I R 6 704 172 15 5 887 86 974 77 896 AP.[( Il 624 163 7 8 IS 245 29 2S lOb 5 126 1192 90 1101 ~t. Y IJ59 198 12 1209 294 32 36 1559 138 1698 118 1579 JUNE 652 Ib5 1 3 831 249 34 42 1073 136 1209 146 1062 Jul Y 256 74 9 340 183 69 42 550 152 703 160 542 AUGUST 103 42 e 1 :. 3 173 54 32 349 168 517 115 342 SEPTEMp£R 145 86 1 1 243 223 50 21 496 157 653 154 499 OCTOBER 230 106 7 344 193 23 4 555 122 678 144 534 fliOVEMBER 316 135 7 409 150 12 2 619 124 743 105 631 DECEMBER 409 122 B 53° 196 20 2 754 135 889 18 810 ~ tv TOT ALS 'S376 1591 104 7080 2532 3bO M:mHLY 448 1 33 9 S 9r1 211 30AVERAGE 213 18 9767 814 1561 130 11335 945 1375 115 9952 829 ~ FDun1ing errors ma.y result in snall differences between Tables 4-1 ani 4-2 Table 4-2, Annual Freshwater Inflow, Trinity-San Jacinto Estuary, 1941-1976 ~ Y ----------------------------------------------------------------------------------------------------------------------------- .GAGED .GAGED .GAGED .TOTAL . TRINITY . . TOTAL . BAY .FRESH .. ATER. YEAR • TRI~IJ.S.JAC •• SJ-8RZ.GAGr.D .UNGAGED.RlTUPN. RIVER .COHBINEO.ppECIPITATION.FRESHWATER.E\iAPORA~ION• INflOW F" l C~, • FLOW. FLO .... FLOW.!NFLO". . FLOWS.DIVERSIONS. INFLOW . ON BAY . INFLOW . LOSSES • BALAI'tCE ------------------------~-----------------~-----------------~----~----------------------------------------------------------- 1 q", 1 1 033& 3982 159 14477 l.l899 122 12C 19378 2348 21726 1121 20605 1942 9206 1722 77 110 GS 2574 136 145 13570 1117 15287 1268 1&+019 1943 3853 1231.1 f5 5152 2651 102 192 7163 1756 9519 1267 8252 19114 8142 2331 1<1 10634 3860 151 191 14&+ 54 18 18 16272 1261 15005 1945 12275 3151 1 38 15564 l.i438 154 134 19972 2137 22109 1261 20842 19146 9865 4416 20£., 14487 6238 IbO 183 20702 2891 2359'3 123B 22355 1947 5286 1505 81 6877 1561 102 162 8 Li 1 3 1230 9643 1266 8377 1948 3799 544 70 4413 1109 171 240 5453 996 64tt9 1266 5183 19"19 5303 2608 218 8129 4807 192 259 12869 21B1 15056 1239 13817 1950 6962 2012 90 9064 1874 187 220 10905 1270 12175 ItHt+ 10761 1951 15Q3 228 44 177S 713 206 277 2"'17 1184 3601 1385 2216 1952 2302 773 82 31 57 2019 205 249 5132 14'14 6576 1386 5190 1953 3975 1366 123 5464- 2179 203 230 7616 1585 9201 11./-74 7727 1954 1272 ' 386 34 1692 3SO 276 279 2045 BOO 28'45 1592 1253 1955 1782 409 47 2238 1768 320 214 4112 1578 5690 1532 4158 1956 918 121 1 5 1054 599 326 106 1873 1040 2913 1592 1321 1957 11885 1740 133 13758 3772 319 143 17706 1663 193b9 1443 119146 1958 5926 1006 67 7001 2312 351 ,163 9481 1519 11000 11414 9586 l Q 59 4733 1979 198 6910 3993 348 191 11060 1755 12815 1652 11163 1 1960 5413 2950 128 8491 2767 373 215 11416 1523 12939 1534 114051 9 61 6250 3157 188 9595 4070 3bB 235 13818 1869 15687 1503 111184 w 1962 3603 587 65 4255 939 419 271 5342 1177 6519 1532 1f981 1963 1522 438 42 2002 677 445 266 2858 865 3723 1208 2515 1964 2199 681 sa 2938 1395 448 219 4562 1204 5766 1238 .. 528 1965 4673 63n 53 5356 1038 469 238 6625 1119 771111 1533 6211 1966 6113 1562 143 7878 3655 514 204 11843 1935 13178 1031 12747 1967 2Jb6 224 4 1 2331 801 S33 265 3400 1103 1f503 1295 3208 1968 7906 2302 163 10371 3295 551 2" .13973 1636 15609 1270 14339 1969 71123 1350 106 8879 2187 562 252 11376 1578 129511 1321 11627 1970 3030 962 105 4097 2957 575 266 7363 1735 9098 135B 17QO 1971 2258 359 67 2684 1109 6J5 259 4149 1293 5442 1574 3868 1972 2487 1373 128 3988 2507 625 220 6900 1399 8299 141f5 6851l 1913 11 039 4021 245 15305 5802 559 211 21455 2241 23696 1406 22290 1914 7581 2552 16u 10293 2882 632 251 13556 1597 15153 1502 13b51 1975 7222 1627 9b 8945 2229 610 221 11563 1873 13436 14 18 12018 1976 3538 1215 111 4864 1306 695 205 6660 1387 8047 1485. 6562 -------------------------------------------------------------------------------------------------------------- TOTAL 193708 57503 3907 2~511f! 'J1338 13154 7830 351780 56472 40,8252 497142 358510 .l!vERAGE 5391 1597 11"19 7087 2537 365 217 9772 1569 11340 1382 9959 ~'I(OlAN 5009 13&9 lro 6891 2270 349 220 8947 1578 10321 1396 8981 PERCENT 47.5 + 14.1 + 1.D = 62.5 + 22.4 + 3.3- - 2.~ = 86.2 + 13.9 = 100.0 , 12.2 PERCENT 55.1 + 16.4 + 1 • <: = 72.6 + 26.0 + 3.8 2 • 3 = 100,.0 , 16.1 a/ Units are thousarrls of acre-feet W Roun::1ing errors nay result in small differences l::etween Tables 4-1 ani 4-2 , Gaged Inflows from the San Jacinto Basin The total gaged drainage area of the San Jacinto River Basin is 3,520 square miles (9,167 km2), of l>t1ich 1,741 square miles (4,534, km2 ) were gaged above Lake Houston prior to 1953. An crlditional 2,828 square miles (7,365 km2) of drainage area have been gaged since 1953. The magnitude of San Jacinto River Basin flow passing into the estuary is dependent on the spills from Lake Houston. To determine the p:>rtion of the San Jacinto River flow that enters the estuary through Lake Houston, the mag nitude of spills was developed by means of a reservoir cperation study from 1954 through 1976 (Figure 4-1). Over the period 1941 through 1976, average annual gaged inflow to the estuary from the San Jacinto River Basin was 1,597,000 acre-feet (1,970 million m3) (Table 4-2). Gaged yield from the San Jacinto River Basin (1941-1976) has averaged 454 acre-feet per square mile (2,162 m3jha). Gaged San Jacinto River Basin inflows accounted for 16 percent of the combined inflow and 14 percent of the total freshwater inflow over the 1941 through 1976 period. Gaged ~nflows from the San Jacinto-Brazos Coastal Basin The total gaged drainage area of the San Jacinto-Brazos Coastal Basin is ' 126.1 square miles (328 km2). The Clear Creek gage at Pearland (USGS Gage #08077000) and Chocolate Bayou gage near Alvin (USGS Gage #08078000) were utilized for determining gaged freshwater inflow. Over the period 1941 through 1976, average annual inflow to the estuary fran the San Jacinto-Brazos Coastal Basin was 109,000 acre-feet (130 million m3 ) (Table 4-2). Gaged yield from the San Jacinto-Brazos Coastal Basin (1941-1976) has averaged 865 acre-feet per square mile (4,119 m3jha). Gaged basin inflows accounted for 1 .2 percent of the combined inflow and 1.0 percent of the total freshwater inflow over the 1941 through 1976 period. Ungaged Runoff Contributions Ungaged drainage areas contributory to the Trinity-San Jacinto estuary include some 2,640 square miles (6,875 km2).1/ in the San Jacinto Brazos Coastal Basin, the Trinity-San Jacinto Coastal Basin, Neches-Trinity Coastal Basin, the Trinity River Basin, and the San Jacinto River Basin. To facilitate the study of inflow contributions, the ungaged drainage area imnediately contributing to the Trinity-San Jacinto estuary and above Lake Houston was divided into 45 subbasins (Figure 4-2). Using a Thiessen network (387) the weighted daily precipitation was determined for each subbasin (Table 4-3). A water yield model l>t1ich uses daily precipitation, Soil Conser vation Service average curve numbers, and soil depletion index (Beta) to pre dict runoff from small watersheds was calibrated with the 16 gaged subbasins located within the contributing drainage area (374). Statistical correlations between annual and m::mthly gaged total inflow and simulated runoff were used to determine the "goodness of fit" of the calibration procedure. The cali brated model was then applied to the ungaged subbasin to calculate the ungaged runoff (Table 4-3). 17-wIth-the installation of one coastal gage in 1972, the ungaged drainage - area decreased to 2,575 square miles (6,706 km2 ). IV-4 II11I1 I ~ NG UV ~Iy ljJ '\w I,J vo ~004445~~480~~~U~~~~~~w~ue~~~~68~70nnn~nnn YEAR 500 5000 4500 4000 ,-.. l- LL I (..J 3500« 0 0 S! ~ 3000 ~ 0 .... C - 2500 H 'f >-- U1 .<::. -c 20000 :::E "U Ql C - 1500 .n E 0 (..J 1000 Figure 4-1. Combined Monthly Inflow to the Trinity-San Jacinto Estuary, 1941-1976 EXPLANATION O....""""""""5'O:- ~2,O Mil., USGS. GAGING STATIONS .08069000 Streamflow Inlo Lake Houston .06076000 Streamflow Inla Ungaged Areos *oaoeo7zo Reservoir Contents Gage .(.~ Ungoged Area Boundary of Area Contributing to Lake Houston San Jacinto River Basin Boundary 11020 Subbasin Number (See Tobie 4-3) Figure 4-2. Ungaged Areas Contributing to Trinity-San Jacinto Estuary IV-6 Table 4-3. Runoff f«:tll Ungaged i\reas, Trinity-San Jacinto Estuary ---- --------_.- -------,-- .-- --- ---: ------- -werr for a particular hydrologic soil-cover canplex (374) !=i/ Soil rroisture depletion coeffici~nt (374) rv-7 (continued) ------------- _.~------ -~-~-- --,---_. ----~-- ---------:.------_. --~----~- --------=-------------_.---_:..------------=-----------~----- _.- --=-------- 11070 Chocolate Bayou tidal 11080 Chocolate Bayou a1:ove tidal 24220 Trinity Bay including MJuth of Trinity River 24230 East Bay 2424-0 West Bay 24250 Clear Lake 24260 Tabbs Black Duck Scott Burnett and San Jacinto Bays 20.0 0204 LOO 755 82/73.4 52.7 0204 LOO 757 82/73.4 170.0 0235 LOO 1208 88/63.7 .. 260,0 0235 LOO 1208 88/63.7 4-0.0 0204 LOO 672 80/80.0 80.0 4307 .91 694 80/84.2 0204- .09 48.0 4307 LOO 706 80/89.4 24310 Moses Lake drains Texas City 24320 OlOlXllate Bay 24360 Barbours Cut - Bayport Channel 10061 Brefficient (374) IV-9 Table 4-3. Runoff from Ungaged Areas, Trinity-San Jacinto Estuary(cont'd) Subbasin Description -- --- -- _.- --_:_-- -- --- -- -_:_- --_._------_.__:_- --_._-------_. --_._--- ~ ----_._--_:....._- --------~- ---~ ._--_:_--_._- 10100 Caney 98.0 Creek 10101 CanBy 105.0 Creek near SplendoriJ. 10110 Peach 41.0 Creek 10111 Peach 117.0 Creek near Splendora 10120 Honea 445.0 -, Co~ Reservoir 10091 Cypress Creek near W3stfield 285.0 2206 .324 4323 .021 4327 .053 4704 .172 9076 .124 9448 .306 6280 1.00 3298 .053 1956 .860 6280 .087 6280 1.00 6280 .460 1956 .504 8265 .036 0244 .015 0635 .107 1956 .158 3298 .028 4382 .393 6024 .299 413 451 440 71.4/102.2 72/121.5 74.2/91.9 73/115.5 72.8/97.S 73/115.7 .69 .71 .63 08069000 08070500 08071000 1945-76 1944-76 1944-76 a/ National weather Service '6/ P€rcentage of area of influence expressed as a factor (3S7) 'iil An assigned par<:llneter Eor a particular hydrologic soil-cover canplel( (374)N Soil rroisture depletion o::.efficient (374) rv-l0 During the period 1941 through 1976, ungaged runoff averaged 2,537,000 acre-feet/year (3.13 billion m3/yr) and runoff yield averaged 961 acre-feet/mi2 (4,576 m3jha)J1. Ungaged inflow accounted for 26 percent of the combined inflow and 22 percent of the total freshwater inflow to the Trinity-San Jacinto estuary CNer the 1941 through 1976 period (Table 4-2). ' Ungaged Return FloWS Return flows from municipalities and industries within the ungaged sub basins were estimated from data provided by the Texas Department of Water Resources (TDWR) self-reporting system. Irrigation return flows in ungaged areas were calculated using agency data collected in rice irrigation return flow studies (376, 379). Average return flows CNer the 1941 through 1976 period were approximately 365, 000 acre-feet per year (450.6 million ffi3/yr) • Estimated ungaged return flow accounted for four percent of the combined inflow and three percent of the total freshwater inflow to the Trinity-San Jacinto ,estuary CNer the 1941 through 1976 period (Table 4-2). Diversions Reported diversions for municipal, industrial and irrigation use within the ungaged subbasins were provided by the Texas Department of Water Resources (TDWR) reported water usage system. Average diversions CNer the 1941 through 1976 period were approximtely 217 ,000 acre-feet per year (267.9 million m3). Estimated diversions accounted for 3.8 percent of the combined inflow and 3.3 percent of the total freshwater inflow to the Trinity-San Jacinto estuary (Table 4-2) over the 1941 through 1976 period. Combined Inflow A category called combined inflow was obtained by aggregating gaged Trinity River Basin and San Jacinto River Basin inflow, gaged San Jacinto Brazos Coastal Basin contributions, ungaged runoff, and estimated ungaged return flows. Over the period 1941 through 1976 combined inflows averaged 9,772,000 acre-feet per year (12.05 billion m3/yr) (Table 4-2). Combined inflow accounted for 86 percent of the total freshwater inflow to the Trinity San Jacinto estuary,CNer the 1941 through 1976 period. Average ITPnthly dis tributions of combined inflow are shown in Figure 4-3. Precipitation on ,the Estuary Direct precipitation on the 353,730 acre (143,153 ha) surface area of Trinity-Sari Jacinto estuary was calculated using Thiessen-weighted precipita tion techniques (387). Over the 1941 through 1976 period, annual mean pre cipitation arrounted to 1,569,000 acre-feet per year (1.93 billion m3/yr). Direct precipitation accounted for 14 percent of the total freshwater inflow to the Trinity-San Jacinto estuary CNer the period 1941 through 1976 (Table 4-2) • .!/Ungageddrainage area held constant at 2,640 sq. mi. (6,875 kJn2). IV-ll 4500,------------------------------------, Ave = AVERAGE MONTHLY INFLOW D 10 pet. PROBABILITY OF EXCEEDANCE 4000 ........... rzJ 50 pet. PROBAB I L ITY OF EXCEEOANCE ~ 90 pc t. PROBAB ILI TY OF EXCEEOANCE 3500 . I Combined Inflow = (gaged inflow) + (ungaged inflow) + (return flows from ungaged areasl (diversions below last gage). 3000 ,....... L- o Q) >- '-.. ~ Q) Q) -I Q) L- 2500 ............................•........................................................................................ NG_, . - ... 1._ , , , , , , .AVs;.. I '500 "Q) c ..0 E o u 1000 500 'MG' -, AVG_ AVG. ,-'N_G. ..Avs;... .~ ~ 'Ir'i-';i-'-rll ran. feb mar apr may jun lui Month aug sep oct nov dec Figure 4·3. Monthly Distribution of Combined Inflow,' Trinity·San Jacinto Estuary, 1941·1976 IV-12 1 1 1 I I I I , I I i I, Total Freshwater Inflow Total freshwater inflow includes gaged Trinity River Basin and San Jacinto River Basin inflows, gaged San Jacinto-Brazos Coastal Basin contribu tions, ungaged runoff, return flows from ungaged areas and direct precipita tion on the estuary. For the 1941 though 1976 period, average annual fresh water inflow arrounted to 11,340,000 acre-feet (14.00 billion m3). Average monthly distributions of total freshwater inflow are shown in Figure 4-4. Bay Evaporation Losses Gross surface evaporation rates for the estuary \- " -- 3000 __ . QJ '".... I '"- o ,:t o 2500 . '-' ~G_, If,VG ........... -.... ~ o ;;:: c '- 2000 QJ .... o ~ .s::. III QJ '- ..... 1500 o .... o I- 1O00 500 o _A'LG- o J I . - . - - - - - - - . . .. . .. I .. _ '.. ~ .. _. .. . . o o I o 0 o I o _AV_G- I I ~SJ_ o J :.:/N..G·J lAVG fan feb mar apr may fun [u I Month aug sep oct nov dec Figure 4-4. Monthly Distribution of Total Freshwater Inflow', Trinity-San Jacinto Estuary, 1941-1976 IV-14 'low. Table 4-4. Monthly Inflows. to the Trinity-San Jacinto Estuary for Corresponding Exceedance Frequencies !y, !Y ._--_._------~-~---------_._----_._-------------------._~-----_._--------~--- -~~~-----------_ .. _.----- Month Gag-ed Trinity :Gag-ed San Jacinto :Gaged san Jacinto-- : 1btal Ungaged Basin Inflow Basin Inflow :BraZOs Basin Inflow: Inflow Ungaged Inflow' Conbined Inflow Precipitation on Bay Total Freshwater Inflow Bay Evap:::lration Losses _______t==~~~===~O% -==~O%;Io.J --)~dI_}_Q:~_t=~i====~~C~=~O% -=t_~o.!-- -~O-%-=~l1% ~--JQ!==S=O% _S:6%;--l=Cff=~5.Q.'!...--=~% ±=D!~~~%.- __~o-L=-f~f~~ --5~~~~~qf= -;--fO~~=- -50~~='- -90%=t January 1,402 289 58 586 80 10 22 4 o ! ,978 389 73 679 106 15 2,438 573 130 221 96 40 2,592 710 194 84 64 49 February 1, 130 3"19 March 1,403 353 87 88 595 87 338 61 11 10 23 15 5 3 o 1,597 442 118 944 114 12 - 2,197 638 176 o 1,704 441 112 531 65 6 2,126 575 152 216 204 86 30 2,325 745 229 64 17 2,237 661 192 85 98 62 77 44 59 April 1,359 406 122 440 85 17 16 4 ,1,793 529 157 757 106 14 2,331 696 210 259' 98 37 2,530 811 265 122 88 63 May 2,563 632 155 556 99 17 28 8 2 3,047 798 205 852 127 12 3,816 998 254 301 97 31 4,008 1,130 312 142 119 97 J=e 1,635 401 95 417 50 6 34 8 2,075 513 123 797 86 7 2,689 641 148· 319 93 26 2,795 779 214 178 145 117 July 596 150 37 193 31 5 22 7 2 800 214 56 510 71 8 1,212 361 109 311 121 45 1,463 511 178 201 159 124 1 August 218 69 22 93 21 5 18 5 320 110 38 492 ,49 3 772 224 65 322 133 52 1,102 362 118 207 173 146 ~ V1 September 334 86 22 194 37 8 25 7 .• 2 556 146 39 774 89 7 1,124 139 90 376 113 29 1,426 453 143 189 152 122 October 550 111 November 718 152 December 1,093 234 23 215 28 33 306·36 48 . "374 58 4 4 8 16 20 23 2 2 5 o 809 160 32 605 36 0 1,290 256 52 o 1,009 213 47 467 51 0 1,370 321 76 o 1,489 309 61 551 111 10 1,923 482 116 306 80 15 1,569 351 79 246 98 39, 1,537 454 138, 256 115 50 2,082 629 183 177 132 103 142 104 77 114 82 58 a:,r-Unlts-arethousands-of-acre':feet-y. Exceedance frequencies indicate the prob_ability that the cor"resp::mding rronthly inflow will be exceeded during the givenrronth near Alvin). The range of water quality parameters that ~re experienced in the 1977 water year are tabulated in Figure 4-5. During the period, four to 12 samples ~re available for IlDst parameters. Student's t-tests were performed on the data to determine if any statis tical difference (two-tailed test) was evident arrong the sample means for the three gaging stations. It was found that for many parameters, differences between the mean values were not statistically significant. However, sample means from Buffalo Bayou at Houston ~re significantly higher (statistically) than the other two stations, for total ammonia nitrogen, total nitrate nitrogen, total organic nitrogen, total phosphorus, and biochemical oxygen demand, reflecting its urban runoff contribution. Sample means from the Trinity River at Romayor were significantly lower (statistically)' than the other two stations for silica, sodium, fluorIde, total organic carbon and biochemical oxygen demand; and higher for disso!ved oxygen. The sample mean from Chocolate Bayou near Alvin was significantly higher (statistically) than the other two stations for magnesium. ------ In general, the water quality of Trinity River flows draining to the Trinity-San Jacinto estuary is very good. Inflows from Buffalo Bayou and other urban drainage ways reflect significant nutrient loadings. Inflows from Chocolate Bayou indicate slight contamination from unknown oources. Lack of sampling data en the quality of inflows from the San Jacinto River below Lake Houston make comparisons difficult, but quality is believed to be g::xxJ. No parameters ~re found in violation of Texas stream standards. Qual~_of ~stuarine ~aters Nutrient Concentrati~~in the Trinity-San ~~~into Estuary Historical concentrations of carbon, nitrogen, and phosphorus in Texas estuarine systems are largely unknown. Until 1968, water quality parameters in the open bays had not been IlDnitored on a regular long-term basis. A regular program of water quality data collection in Texas estuaries was ini tiated by the cooperative efforts of the U. S. Geological Survey and the Texas Department of Water Resources. Manpower and IlDnetary constraints now limit the number of sites and frequency of sampling. While insufficient data precludes a determination of seasonal nutrient concentrations in the estuary, the data available from 1975 through 1977 can be used to determine general concentrations of carbon, nitrogen and phosphorus (CNP) in the Trinity-San Jacinto estuary. The estuary was divided into five major segments for the analysis: (1) Upper Galveston Bay (which includes those sampling stations north of sampling line 350); (2) Lower Galveston Bay (which includes those sampling stations at and south of sampling line 350); (3) Trinity Bay; (4) west Bay; and (5) East Bay (Figure 4-6). Only those sample sites located away from major population or industrial centers in open bay waters were considered, since nutrient con centrations near these locales might bias resultant concentrations in open waters. Freshwater discharges from the Trinity River and contributions from the deltaic marshes of the Trinity delta have been a major oource of nutrients for rv-16 .0 5 o 5 .3 00 00 4. 1s.8 I- "- f-. .... .- .- 5·j4 17 36 43 3l- - '- -- - :- - - - ;12 2 24 2 i~ - - ...... -- - -- .- -I 370 2' ...,... 32 47 f -- ---'- c;.; .... .. - -- .- 0 - - - - 18 , .9 8.3 :~ _. -- '- -- .- _. -- I--. -- 7.8 9 - - - *Silica, Si02 mgtl *Calcium, Ca+2 mgtl *Magnesium, Mg+2 mgtl *Sodium, Na+ 1 mgtl Bicarbonate, HC03- 1 mgtl "Sulfate, S04-2 mgtl *Fluoride, F- t mgtl *Manganese, Mn+2 IJgtl * Iron, Fe+2 Fe+3 J,lgtl "Dissolves'Solids mgtl (sum of constituents) Total Ammonia mgtl N Nitrogen Total Nitrate mgtl N Nitrogen Total Nitrite ,mgtl N Nitrogen Total Organic mgtl N Nitrogen Total Phosphorus mgtl p Total Organic mgtl C Carbon e:ochemical Oxygen mgtl 0 Demand (BDD,I *Dissolved Oxygen mgTI 0 Total Nonfiltrable mgtl 0 Residue *Chloride, CI-1 mgtl pH • Range of values reported at USGS Station 08066500, Trinity River at Romayor. Range of values reported at USGS Station 08074000, Buffalo Bayou at Houston. Range of values reported at USGS Station 08078000, Chocolate Bayou near Alvin. Mean of reported values. Dissolved fraction only. Figure 4-5. Range of Values for Water Quality Parameters. Gaged Inflow to Trinity-San Jacinto Estuary. October 1976-September 1977 rv-17 JAONTO RIVFif Study areo TEXAS Locotion Mop -44or _110 -.L- ANAHUAC EXPLANATION DatJ-coll€ction linu numbcr Dutn-collection site number for Nitrogen, Phosphorus, Tot"1 o,~,nic Car bun, "nd Tul'll Kield~hl Nitrogell • Pesticide Data only ... H"~vy MeL"i Da'" ()nly @ sampling '1"tio" with recordea heavY metals and pesticide dota Figure 4-6. Data-Collection Sites in Trinity-San Jacinto Estuary IV-18 the Trinity-San Jacinto estuary. The Trinity River accounts for 78 percent of . the gaged freshwater inflow to the estuary. The watercourses that drain the City of Houston empty into the Houston Ship Channel, and subsequently contri bute inflow to Upper Galveston Bay. This inflow constitutes only 6.9 percent of the gaged flow to the estuary; yet CNP concentrations are high enough that total nutrient loadings from this source outweigh those from the Trinity River inflows. From this discovery it ~lUld be expected that Upper Galveston Bay and Trinity Bay \\Duld experience higher nutrient concentrations than other portions of the estuary, a result that is generally borne out by the water ·quality data (as discussed below). The CNP data for each of the five distinct PJrtions· of the estuary were tabulated, averaged, and subjected to standard statistical methods for c0m parison of the means (student's t-test) to determine \\hich of the p::>rtions of the estuary, if any, consistently exhibited CNP concentrations significantly different from others. Frequency histograms of grouped nitrogen, {ilosphorus, organic carbon and total Kjeldahl nitrogen data were also plotted in Figures . 4-7 through 4-10. Anrnonia nitrogen, nitrite nitrogen and nitrate nitrogen were sumned for each sample to arrive at total available nitrogen concentrations. Arrm:mia riitrogen and total organic nitrogen were sumned for each sample to arrive at total Kjeldahl nitrogen concentrations. Total organic carbon ranged from 3.3 rng/l to 17 rng/I. Student's t-test analyses revealed that the concentrations of organic carbon in Upper Galveston Bay were significantly higher (95 percent confidence level) than those in Lower Galveston and West Bays. There was no significant difference between the concentrations found in Upper Galveston Bay and Trinity Bay segments. In addition, student's t-test analyses revealed that the concentrations of organic carbon in Trinity Bay were significantly higher (95 percent confidence level) than those concentrations in Lower Galveston Bay and West Bay. Total Kjeldahl nitrogen ranged from 0.11 rng/l to 1.61 rng/I. Student's t-test analyses revealed that the concentrations of total Kjeldahl nitrogen in Upper Galveston Bay were significantly higher (95 percent confidence level) than those concentrations of total Kjeldahl nitrogen in Trinity Bay, Lower Galveston Bay, and West Bay. In addition, the total Kjeldahl nitrogen concen trations in Trinity Bay were also significantly higher (95 percent confidence level) than those concentrations in Lower Galveston and west Bays. The con centrations in East Bay were significantly higher (95percent confidence level) than those concentrations found in Trinity Bay. Total phosphorus concentrations ranged from 0.08 rng/l to 0.55 rng/I. Student's t-test analyses revealed that the concentrations in the Upper Galveston Bay segment were significantly higher (95 percent confidence level) than those concentrations of {ilosphorus in all other remaining bay segments. Likewise, the concentrations in Trinity Bay were also significantly higher (95 percent confidence level) than Lower Galveston Bay, East Bay and West Bay. Total nitrogen concentrations ranged from 0.03 mg/l to 0.67 mg/I. Student's t-test analyses revealed that the concentrations of nitrogen in the Upper Galveston Bay segment were significantly higher (95- percent confidence level) than those concentrations in all other segments but East Bay. Also, rv-19 I El I 66-.7016-.20 .21- .2526-.3031-3536-40 41-45 46-.5001- 05 06- .1011- .1500-0.1 40T EXPLANATION _____ Upper Galveston Bay 35 + ~ I22ZI ____ Trinity Bay "I I ~ ____ Lower Galveston Bay~ 25 ISSS] ____ West Bayc:J ____ East Bay' u u o 20 ~ 0 :;; D E 15 ::J z 10 1 5 N 0 Concentration Range Groups (mg/I) Total Nitrogen Figure 4-7. Distribution of Total Nitrogen (as N) Concentrations Occurring in the Trinity-San Jacinto Estuary, 1968-1977 EXPLANATION ~ Lower Galveston Bay _____Upper Galveston Bay ISSS3 West Bay 51-5546-50.41- A5 E2ZJ Trinity Bay c::::::J East Bay .36- AO26-3031- .3521- .2516-20.11- .1506-1001- 050.0-01 30 ~ 25 '"uc :" '; 20 u u 0 a 15~ '".D E ::J Z 10 5 ~ N ~ Concentration Range Groups (mg/l) Total Phosphorus Figure 4-8. Distribution of Total Phosphorus (as Pl Concentrations Occurring in the Trinity-San Jacinto Estuary, 1975-1977 35 30 ~ '"uc 25~ ~ OJ U U 0 20 ~ 0 6; .0 15E OJ 1 z '" 10 '" 5 EXPLANATION _____ Upper Galveston Bay ~ ____ Trinity Bay ~ ____ Lower Galveston Bay ISSSI ____ West Bay c::::::::J ___ :..- East Bay ~ • bn f3n •§n I"l 00- 20 21- 40 41-60 61-80 8.1-10.0 10.1-12.0 12.1-14.0 Concentration Range Groups Img/II Total Organic Carbon 14.1-160 161-180 Figure 4-9. Distribution of Organic Carbon Concentrations Occurring in the Trinity-San Jacinto Estuary, 1975-1977 35 30 '" "<.>~ 25 ~ "<.><.> o 20 -0 ~ ".Q 15E "z 10 H 5 'f tv W EXPLANATION _____ Upper Galveston Bay 122ZI Trinity Bay ~ _ _ _ _ Lower Galveston Bay ~ WestBay c=:J East Bay 00-.20 .21 - .40 41 -60 .61- .80 81 - 1.0 1.01- 12 1.21- 14 141-1.6 1.61-1.8 Concentratian Range Groups (mg/O Total Kjeldahl Nitrogen Figure 4-10. Distribution of Total Kjeldahl Nitrogen Concentrations Occurring in the Trinity·San Jacinto Estuary, 1975-1977 the roncentrations of nitrogen in Trinity Bay were significantly higher (95 percent ronfidence level) than those roncentrations in the Lower Galveston and and West Bays. Heavy Metals The scope of this section is rot intended to be a a:rnprehensive analysis of the sources from which heavy metals originate in the area. The purpose is to summarize the available data on the heavy rretals and give the range of values that have been found in sampling efforts. Samples of the bottom sediments in the Trinity-San Jacinto estuary were collected by the Texas Department of Water Resources at 16 data rollection sites shown in, Figure 4-6 for the period of record 1974' through 1978. The heavy metals detected included arsenic (As), cadmium (Cd), ropper (Cu), lead (Pb), manganese (Mn), nickel (Ni), zinc (Zn), and mercury (Hg). Statistical analyses were rot possible due to the limited number of samples for the test period from 1974 to 1978. The range of values for heavy metals detected in Galveston Bay, Trinity Bay, Clear Lake, west Bay, East Bay, Texas City Ship Channel, Tabbs Bay, Bayport Channel, Christmas Bay and Choco late Bay are listed in Table 4-5. Accumulation of metals in I::ottom deposits may rot be detectable in over lying water samples, yet still exert an influence from time to time. Wind and tide induced water I1Ovements, ·ship traffic and dredging activities are oome physical processes that can cause mixing of materials from the sediment into the water. Chemical changes resulting from seasonal temperature fluctuations, oxygenation, and respiration, can influence 'the rate of I10vement and distribu tion of dissolved substances between water and sediment. Microorganisms liv~ ing on the I::ottom (benthos) also play an important role in the circulation of metals by taking them up from the sediment, rometimes ronverting them to rrore toxic forms. Heavy metals in sediment and water may pose a threat to fish and shellfish as these organisms generally roncentrate certain toxic metals in their bodies when feeding in polluted areas. Reduction of productivity in the area may be the result of toxic effects of heavy rretals upon organisms, and may have an ultimate effect on man if he is exposed to heavy metals through edible fish and shellfish. Sediment samples from SJme areas of the Trinity-San Jacinto estuary exceed the u. S. Environmental Protection Agency criteria for metals in the sediments (prior to dredging).' The following ron stituents have been found in violation of these standards in at least one sample: arsenic, cadmium, ropper, lead, and zinc (Table 4-5). Pesticides and Herbicides 'Samples of the Ix:>ttom sediments in the Trinity-San Jacinto estuary were collected at five data rollection sites shown in Figure 4-6 for the period from 1974 to 1978 through the Texas Department of Water Resources sampling program. The data were analyZed for pesticides and herbicides roncentrations. The parameters detected were heptachlor and heptachlor expoxide but at levels below or equal to detection limit of 0.1 )Jg!kg. Statistical analyses were not possible due to the limited number of samples available. rv-24 Table 4-5. Ranges of Metals in Sediment Compared to USEPA (1974) Dredge Cri teria ~ Station --_ .. Location!:'! : Galveston Bay : Trinity Bay : Clear Lake : East Bav : Dredge & USGS : : : : : : : : : : Criteria Station: 2421.04 : 2421. 05 : 2421.06 : 2422.01 : 2422.04 : 2425.012 : 2425.02 : 2425.014 : 2423.01 Number: Parameter "'\.. : Uni ts are nq/kg Arsenic 2.12-14.0* 4.5-43.0* 2.57-7.10* 5.7-10.0* 0.55-3.0 4.2-43* 3.4-14* 4.7-12.0* 3.43-9.0* 5 Cadmium 0.52-<2.0 0.5-<2.0 0.83-1. 9 0.01-<2.0 <0.6-1.7 0.5-<2.0 0.5-<3.0* 0.9_<2.0 0.510-1.3 2 Copper 4.0-14.0 6.0-18.0 7.02-15.2 1.0-8.0 1.0-10.4 31.0-64.0* 33.0-196* 26-44 2.05-7.0 50 Lead 3.4-24.6 11.2-61.1* 17.1-32.8 7.3-25.4 2.75-13.8 21.6-39.8 15.0-67.6* 24.0-64.6* 4.0-22.4 50 Manganese 183.9-327 151.0-330.0 308.3-502.3 288.8-876 64.9-1121.9 178-355 225-799 168.2-340 126.6-184.5 Mercury , <0.10 <0.10-0.20 '<0.10 0.10 <0 •. 10 0.05-<0.10 <0.10-0.20 0.07-0.20 <0.10 Nickel 5.0-10.7 7.0-28.0 12.5-20.7 7.3-23.0 2.4-19.0 13.2-25 13.1-33 12.1-29.0 5.3-16.5 50 H Zinc 25. 1~53.0 25.7-106.0* 41.7-68.0 19.~-61.4 9.4-36;2 51.3-82.0* 40.3-12540* 50-77* 28.0-56.4 75 'f IV a/ Includes data from reference (277)lJ1 b/ See Figure 4-6 for station locations -. Denotes at least one sample in violation of EPA's dredge ,spoil criteria Dredge Criteria Table 4-5. Ranges of Metals in Sediment Canpared to USEPA (1974) Dredge Criteria ~ (cant'd.) .---Statlon----,-----TexasC[ty-----,-----------:-------- -- -------,-----------,------ Location IY :.__~hip Chann.~l ._~Tab!J.~~: Bayport Channe~ : Chocolate ~.'- C1J.r:istrna~: West Bay & USGS: : :: : : : Station : 2437.01 : 2437.03 : 2426.01: 2438.01 : 2432.01: 2434.02 ...:::.-..::c24::.:2",4".",0.:..1-" _Number: --------------------------------------------------- -- - Parameter" : ___________ .•.• __ .4_'. •• ,..__ . .• .. _. __ .. _ ____________l!n_i:.t:.~_a.~IT9/kg . ._. _ 11.6-22.4 50 Arsenic 3.6-11.0* 7.1-11.0* 3.5-9.6* 2.36-5.0* 4.58-9.0* Cadmium 0.01-2.4* 1.0-2.4* <1.0-3.5* <1.0-1.03 0.9-1.5 Copper 0.01-21.8 14.8-60.5* 9.6-17.3 6.5-13.8 5.5-11.0 Lead 0.05-50.0* 38.7-60.1* 26.6-57.8* 6.0-30.8 15.3-47.3 Manganese 354.8-1043.6 256.0-397.0 227.4-434.7 185.1-352.0 500-983.6 Mercury <0.10 <0.10 0.40 <0.10 <0.10 Nickel 21.0-27.8 19.3-26.6 17.5-25.3 10.9-23.6 14.5-37.0 Zinc 29.8-80.1* 56.2-84.0* 61.2-104.9* 23.2-64.6 34.5-90.2* 6.0* <1.0 7.0 10.0 363 <0.10 35.0 3.36-4.1 0.59-1.87 5.9-14.0 10.8-50.5* 196.0-345.8 0.20 17.8-70.2 5 2 50 50 75· -aT-includes-data-fran-reference(277)------------------------ --- --- -----..------------.----------- b/ See Figure 4-6 for station locations ~ *". Denotes at least one sample in violation of EPA' 5 dredge S[X>il criteria I IV '" Sl.IImt1ary Sources of freshwater inflow to the Trinity-San Jacinto estuary include gaged inflows from the contributing rivers and streams; ungaged runoff; return flows from municipal, industrial and agricultural S::lUrces; and precipitaiton on the estuary. Measurement of sources of freshwater inflow adds to the understanding of inflow timing and volumes and their influence on bay pro ductivity. To acquire accurate inflow measurements, gaged stream flows require adjustment to reflect any withdrawals or return flows downstream from gage locations. Ungaged runoff is estimated by canputerized mathematical models using field data for calibration and verification. Rainfall is esti mated as a distance-weighted average of the daily precipitation recorded at weather stations surrounding the estuary. Freshwater inflows in terms of annual and monthly average values over the 1941 to 1976 period varied widely from the mean as a result of recurrent drought and flood conditions. On the average, total freshwater inflow to the estuary is estimated at 11.34 million acre-feet per year (14 billion m3). In general, the water quality of gaged inflows to the estuary from the Trinity River is good. Inflows from Buffalo Bayou and other urban drainage ways reflect significant nutrient loadings. No parameters were found· in violation of existing Texas stream standards. Studies of past water quality in and around the estuary have noted the occurrence of heavy metals in sedi ment samples. Locally, bottom sediment samples from the Trinity-San Jacinto estuary have exceeded the U. S. Environmental Protection Agency criteria for metals in sediment (prior to dredging) for arsenic, cadmium, copper, lead and zinc. Basic hydrologic data described in this Chapter (Chapter IV) is used as input to modeling studies discussed in Chapters V, VIII, and IX. IV-27 QlAPI'ER V CIRCULATICN lIND SALINITY Introduction The estuaries and embayments along the Texas Gulf Coast are characterized by large surface areas, shallow depths and irregular boundaries. These estuarine systems receive variable influxes of freshwater ,and return flows which enter through various outfall installations, navigation channels, natural stream courses, and as runoff from contiguous land areas. After entering the estuary, these discharges are subject to convective nDvements and, to the mixing and dispersive action of tides, currents, waves and winds. The seaward flushing of the major Gulf Coast estuaries occurs through narrow con stricted inlets or passes and in a few cases, through dredged navigable chan nel entrances. While the tidal amplitude at the nDuths of these estuaries is normally low, the interchange of Gulf waters with bay waters and the inter change of waters arrong various segments have a significant influence on the circulation and transport patterns within the estuarine system. Of the many factors that influence the quality of estuarine waters, mix ing and physical exchange are arrong" the JIDst important. These same factors '\ also affect the overall ecology of the waters, and the net result is reflected in the benefits expressed in terms of the economic value derivable from the waters. Thus, the descriptions of the tidal hydrodynamics and the transport characteristics of an estuarine system are fundamental to the development of any comprehensive multivariable concept applicable to the management of estuarine water resources. Physical, chemical, biological and economic analy ses can be considered only partially complete until interfaced with the hydro dynamic and transport characteristics of a given estuarine system. The following sections of Chapter V will a::ldress the development and application of the hydrodynamic, mass transport, and marsh inundation JIDdels used to evaluate the circulation and salinity patterns of the Trinity-San Jacinto estuary. ' Description of_the Estuarine Mathematical Models Description of Modeli~ocess A shallow estuary or embayment can be represented by several types of models. These include physical JIDdels, electrical analogs and mathematical models, each of which has its own a::lvantages and limitations. The a::laptation of any of these JIDdels to specific problems depends upon the accuracy with which the, model can simulate the prototype behavior to be studied. Furthermore, the selected JIDdel must permit various alternatives to be studied within an efficient and economical framework. A mathematical model is a functional representation of the physical behavior of a system or process presented in a form available for oolution by V-l any acceptable method. The mathematical statement of a process consists of an input, a transfer function and an output. The output fran a given system or component of a system is taken to be related to the input or oome function of the input by the transfer function. Because of the nonlinearities of tidal equations, direct solutions in closed form seldom can be obtained for real circumstances unless many simpli fying assumptions are made to linearize the system. When toundary conditions required by the real system behavior become excessive or complicated, it is usually convenient to resort to a numerical method in \>hich the system is discretized ro that the boundary conditions for each element can be applied or defined. Thus it becomes p:>ssible to evaluate the complex behavior of a total system by considering the interaction among individual elements satisfying cOlll1lOn boundary conditions in succession. The precision of the results obtained depends; however, on the time interval and element size selected and the rate of mange of the p,.enomena being studied. The greater the number of finite time intervals used over the total period of investigation, the greater the precision of the expected· results. Numercial methods are well adapted to discretized systems \>here the transfer functions may be taken to be time independent wer Short time inter vals. The developnent of high-speed digital computers· with large meITOry capacities makes it p:>ssible to rolve the tidal equations directly- by finite difference or finite element techniques within a framework that is toth effi cient and economical. The rolutions thus obtained may be refined to meet the demands of accuracy at the burden of additional cost by reducing. the size of finite elements and decreasing the time interval. In addition to the con straints imp:>sed on the rolution method by budget restrictions or by desired accuracy, there is an optimum size of element and time interval imp:>sed by mathematical considerations \>hich allow a solution to be obtained \>hich is mathematically stable, convergent, and compatible. Mathematical Model Developnen~ A mathematical model to simulate the tidal and circulation patterns in the Trinity-San Jacinto estuary was developed by Tracor, Inc. for the Texas Water Quality Board's Galveston Bay Project (390-420). This model was modi fied by personnel of the Engineering and Environmental Systems Section for use as a long~range water resources planning tool. A conservative transp:>rt model designed to simulate salinity distributions in the Trinity-San Jacinto estuary was adapted from a similar model developed by Masch (173) for the Lavaca-Tres Palacios estuary. These models are designed to simulate the tidal· and circu lation patterns and salinity distributions in a Shallow, irregular, non stratified estuary. The two models are sequential (Figure 5-1) in that the tidal hydrodYnamic model Computes temp:>ral histories of tidal amplitudes and flows. These are then used as input to the conservative mass transp:>rt model to Compute vertically averaged salinities (or ·concentration of any other con servative material) under the influence of various source salinities, evap:>ra tion, and rainfall. Both of these models have "stand alone" capabilities, although it must be recogniZed that the mass transp:>rt model ordinarily cannot be operated unless the tidally generated convective inputs are avail able. v-2 DATA INPUT GEOMETRY, BATHYMETRY, INPUT TIDES, DEPTHS, HYD INFLOWS, DIVERSIONS, RETURN FLOWS, WIND, ~ TIDAL RAINFALL, EVAPORATION, HYDRODYNAMIC ROUl,>HNESS, CORIOLIS MODEL ACCELERATION / BASIC OUTPUT ITIDAL AMPLITUDESCOMPONENT TIDAL VELOCITIES r + +- 1 NET AVERAGE AVERAGE CIRCULATION VELOCITIES DEPTHS VELOCITIES PLOTS DISPERSION COEFFICIENTS DATA INPUT SAL SOURCE CONCENTRATIONS SOURCE LOCATIONS SALINITY GULF SALINITIES MODEL EVAPORATION RATES RAINFALL RATES ~ / M'''OU''"' /SPATIAL SALINITY VARIATIONSTEMPORAL SALINITY VARIATIONS Figure 5-1. Relationship Between Tidal Hydrodynamic and Salinity Models· (173) V-3 Hydrodynamic Mode1'. ' Under the assumption that the bays are vertically ~ll­ mixed, and the tidally generated convection in either of the two area-wise coordinate directions can'be presented with vertically integrated velocities, the mathematical maracterization of the tidal hydrodynamics in a' bay system requires the simultaneous solution of the two-dimensional dynamic equations of motion and the unsteady continuity equation. In suitlna\:y,th,e equations of motion neglect the Bernoulli terms but include wind stresses and' the Coriolis acceleration, and can be written as: e [ 1] fq '\; + K V~ sin e [ 2] The equation of continuity for unsteady flow can be expressed as a~ a~ + ah __~ +, ay at r - e where [3] x,y = horizontal Cartesian coordinates t= tiine ~,~ = vertically integrated x and y components of flow per unit width, respectively (x and y 'taken in the plane of the surface area) g = acceleration due to gravity' h = water surface elevation with respect to mean sea level (msl) as datum d = total water depth (h-z) z = bottom elevation with respect to msl q = (qx2+ qy 2)!:l ,= magnitude of flow per unit width f'=dimensionless ,bed resistance coefficient from the Manning Equation Vw _= wind speed at a specified elevation above the water surface'~ angle 'between the wind, velocity vector and the x-axis K = dimensionless wind stress coefficient 'Q = Coriolis parameter = 2wsin¢ w = angular velocity of the earth = 0.73 x 10-4 radlsec ¢ = latitude = 29.5° for the Trinity-San Jacinto estuary r = rainfall intensity e = evaporation rate. The numerical solution utilized in the hydrodynamic .model of the Trinity-San Jacinto estuary involves an explicit computational scheme >.here equations [1], [2], and [3] are solved over a rectangular grid of square cells used to represent in a discretized fashion thej,Xlysiography and various boundary conditions found in this bay system (Figure 5-2)., This explicit formulation of the hydrodynamic model requires for stability a computational time step, lit, < lsi(29dmax)!:l , >.here II s is the cell, size and dmax the maximum water depth encountered in the computational matrix. The numeri cal solutions of the basic eqUations and the programming teChniques have been described previously (173). V-4 TIDAL GENERATED ,-VEl.OCITIES :: ~ ' --c::: GULF OF MEXICO· " (BAY BOTTO'" / ---~~=::::~= TIDAl.~'I- ~ " ..~ •.,. C"'~P'''III,"",,,,,,..t 0_,,,'°' of • "" \m' / TYPICAl. CO",PfJfArlO NAL~ CELl. 1 Ul The following data comprise the basic set for applying the tidal hydrodynamic model. Time varying data should be supplied at hourly intervals. Physical Data topographic description of the estuary bottom, tidal passes, etc. location of inflows (rivers, wastewater discharges, etc.) Hydrologic - Hydraulic Data tidal condition at the estuary llDUth (or opening to the ocean) location and magnitude of all inflows and withdrawals from the estuary estimate of bottom friction wind speed and direction (optional) rainfall history (optional) site evaporation or coefficients relating surface evaporation to wind speed. Conservative Mass Transport Model. The transport process as applied to sal1nity can be described througn-the convective-dispersion equation I'.hich is derivable from the principle of mass conservation. For the case of a two- dimensional, vertically-mixed bay system, this equation can be written as: a(cd) a(~c) d(hen inundated, the flood plain serves principally as vollDlle storage and carries relatively little longitudinal momentum. Neglecting Coriolis acceleration and surface wind-stress, the governing equations are the conservation of longitudinal nornentum and con tinuity for one-dimensional tidal flows: and aQ + a (Q) at 'ax A + gA aH + _gn 2 Q tl = 0 ax 2.22 AR '/3 [ 1] aH +..! aQ _ Qf = 0 at B ax As [ 2] In equations [1] and [2], Q is the flow in the oonveyance channel; A is the cross-sectional area of the conveyance channel; H is the water level; R is the hydraulic radius; n is Manning's roughness parameter; B is the lateral width; As is the surface area including lateral storage; z is the height of channel bottom above an 'arbitrary datum; Qf is the lateral discharge into the chan nel; g ,is the acceleration of gravity; x is the distance in the longitudinal direction; and t is time. Solution of Equations [1] and [2] utilize the "leapfrog" method of finite differences \>hereby water depths, inundated surface areas, and lateral channel discharges are determined at the center of each segment" \>hile longitudinal flow quantities and velocities are determined at segment boundaries (Figures 5-3 and 5-4). This solution technique has been proven to be stable for hyper bolic systems, such as those described by Equations [1] and [2], so long as lit < (!:x/c); where lit is the solution time step, and ,c is the maximum phase velocity of a wave.JI • (2) MTDELT. The mass-transfer sul:rrodel, Ml'DELT, used in conjunction with the hydrOdynamic sul::m:xJel, simulates the influence of exchange rates on nutrient levels in the deltaic system. MTDELT can simulate organic nitrogen, ammonia, nitrite, nitrate, total phosphorus,' total 'carbon, and t~ species of algae. ,MTDELT uses the one-dimensional mass continuity equation: ..! --.2.. (AC ) A at + ..!2 (AUC)A ax 1 a = - ._- A ax ac +(AE ---) -- S L ax [3] V-CISapproximated as (gD)~ -- local water velocity. + U, \>here D is water depth and U is the V-7 1.-(:- Latera 1Storage Conveyance Channel Cross-sectional Area A Flow 0 Horizontal Datum B --I H Latera I Storage Figure 5-3. Definition of Variables in Cross Section (173) An,B n Zn_I/2,H n_I/ 2 , ----., Ofn -1/2, ASn_1/2 Zn ~ 1/2 Hn + 1/2· ·Of n + I/ 2 As n + 1/2 Figure 5-4.. Definition of Finite-Difference Segmentation for Hydrodynamic Model (173) V-8 In equation [3], C is the oonstituent ooncentration; EL is the longitudinal dispersion ooefficient, and S represents sediment transfer, biological re actions, plant intake, influent sources, and withdrawal sinks. (3) Calibration and Validation of the Marsh Inundation Model. The hydrodynamic subrodel, HYDELT, was calibrated .and valIdated for-theTrinity River Delta by Hauck (52, 62). Trin~River Delta. For the purpose of inundation analysis, the area of . the Trinity River delta of ooncern is that region shaded in Figure 5-5. (The segmentation schematic utilized for the Trinity delta is also shown on this same figure). This shaded area is oonsidered to be biologically the ITDst important area of the Trinity marsh systems, bounded on the south by the Wallisville levee and oontinuing northward to the beginning of the cypress swamp area. The eastern boundary is the Trinity River, and the area extends westward from the river to the beginning of the uplands. Included within this area are all major marsh regions subject. to inundation from river flow. This marsh area is highly productive and inundation to a minimum depth of 0.5 ft. (0.15 m) oontinually for two days should result in the flushing of nutrients into Trinity Bay. Another· large productive marsh region lies to the oouth of the Wallis ville levee. However, this region is omitted from the study area because it is not significantly influenced by Trinity River water elevations due to the presence of the levee, but rather tidal elevations, independent of river flow, determine water levels in this region. The periods chosen for simulation were selected based on tides and fresh water inflow and on the availability of data to verify the velocities and water depths predicted by the model. The availability of a:3equate verification data restricted the period of study to October 1975 through February 1977. The majority of verification data oonsists of water elevations (river stage or tide record) from oontinuous recording gages operated by the U.S. Geological Survey (USGS), U.S. COrps of Engineers (USCE) and TDWR. From October 1975 through September 1976, water eleva tion reoords were available from the gage at the oonfluence of the Old and Lost Rivers (section 34) and from the gage on the Trinity River at Liberty (section 92). Beginning October 1976 through February 1977 tide reoords were available from the gages on Anahuac Channel at Anahuac (section 48), on the Old River Cutoff Channel (section 24), on Lake Charlotte (section 165), on the SUlphur Barge Channel (section 162) and on the Lost River near Wallisville (section 200). Unfortunately, the tide records from the Lake Charlotte and Lost River gauges were often unuseable as verification data. The Lake Charlotte gage does not reoord water elevations below 1.1 ft. (0.3 m) and the Lost River gage was not operating reliably during a majority of the. period. Daily stage readings for the stream gage at Liberty were also available for this time period. In addition, for January 1977 tide data are available from the Old River gage near Mont Belview (same location as Old and Lost River gage, section 34) • In addition, from November 30 through December 2, 1976, an intensive hydrologic and biologic study was oonducted jointly by USGS, 'IDWR and Espey, Huston & Associates personnel. For various pxtions of this three-day period, instantaneous velocity and flow measurements were taken V-9 Study Area Boundary Deltaic Marsh Study Area Segments Used for Modeling Purposes '0 @ ® ..-rY f;l .... I 1.5If) 0: 1.0LLI f- 1 DATE 1976 Figure 5-11. Comparison of Observed and Simulated Tidal Elevations at Section 48, Anahuac Channel Gage, November 16-23, 1976 (52) MEASURED SIMULATED TIDE TIDE I November 23November 22November 21November 20 DATE 1976 November 19November 18November 17November 16 ~ 0.5 ~ a:~ MSL ,~ __~_~~--;::;;;';:-;;~~;:;;;;:;;;;-'~;:;;;:~:::;;;;;;;;;;;~-;;;;;;;;;;"'-J-;;;;;;;;;;;-;;;-"~~;:;;;;~'0,I,a: -0.5 ,l1J ,~ I~ -10' I-' 2.0 11. ~ z 150 iii > 1.0l1J -l l1J 'f ~ \J:J Figure 5-12. Comparison of Observed and Simulated Tidal Elevations, at Section 165, Sulphur Barge Channel Gage, November 16-23, 1976 (52) CXJde were apparently oot violated in the P'lysical system. As for the low-flow equilibrilDll cases, the first day of the simulation was anitted because of the required "start-up time". ,Because of the long duration of both of these floods, three to four weeks, only that p::>rtion of the flood which resulted in significant influences on the delta was simulated. The first of these floods was simulated as the period June 1 through June 16, 1976. 'Itlis simulation case represents a nearly ideal flood case ~an a meteorological viewpoint. Heavy rains of as much as five inches occur red over much of the Trinity watershed on May 31 and June 1, and 00 other significant rains occurred during the remainder of the simulation period. period. Errors due to rainfall on the lower watershed during the, flood ~r se are minimal. For the entire period winds were of m:x1erate speed rom the northeast on the first nine days and shifting to the ooutheast for the last seven days. 'Itle driving tide at /obrgan's Point during this time was initially diurnal, changing briefly to semidiurnaland then re turning to diurnal (Figure 5-13). Because special calculations were performed by the USGS, flows in the Trinity River at Ranayor plus esti mates of the additional inflow occurring between the Ranayor and Liberty gages were available. A maximlDll daily-average flow of 33,200 ft3jsec (940 m3jsec) was measured at the Ranayor gage on June 3. A listing of the daily flows used as input to the m:x1el are presented in Table 5-1. Withdrawal at section 86 for irrigation purp::>ses was calculated to be 1,000 ft3jsec (28 m3jsec). The comparison of simulated and measured water elevations for the Liberty gage and the Old and Lost River gage are shown in Figures 5-14 and 5-15. The flood passage as recorded at the Liberty gage is satisfactorily simulated. 'Itle simulated water elevation does show significant error over the last four days, June 13-16 ; however, for the remainder of the period, simulated elevations are within two feet (0.6 m)of recorded elevations. 'Itle simulated and measured water elevations at the Old and Lost River gage also compare favorably. The simulation does indicate rising water elevations before they were measured, particularly June 3-5. The peak water elevation and its duration are simulated quite accurately as is the gradual subsidence of the flood. The simulated flood levels in the delta at four day intervals on June 1, 5, 9, 13 and 17, 1976 are presented in Figures 5-16 through 5-20, re spectively. 'Itlis sequence of figures indicates the water level above bank elevation at hour 0000 CST for each day mentioned and depicts the rise and subsequent fall of water levels with the passage of the flood. On June 1 (Figure 5-16) m:x1erate levels of inundation are indicated because of the relatively high tides of this period. By June 5 (Figure 5-17) flood waters are causing increased water levels in the upper delta and along the Trinity River, and by June 9 (Figure 5-18) the maximlDll water levels are occurring throughout the delta area. 'Itle June 13 and 17 simulations (Figures 5-19 and 5-20) indicate water levels as the flood waters recede. The second flood was simulated for the period December 12-27, 1976. Due to heavy rainfall of approximately 5.0 inches (13 em) on the deltaic region during this period and because the streamflow gage at Ranayor was inoperative, it was difficult to estimate flow in the Trinity River. 'Itle gaged flow from the Goodrich gage was used as the headwater flow condi- V-20 2.0 L5 ~ !-= .... ~ 1.0 z 0 0.5 ~ ~ ~ MSL w June 1 June 2 June 3 June 4 June 5 June 6 June 7 June 8 W U Ii! a: :;) 1 C1l '" a: I ~ I \ A -,2.0 w ' '" ~ !i :> ... ..J '" a: 4. I I I , I IW ! I I Iti t I I3' MSLl I I Jun. 1 Jun.2 Jun.3 Jun.4 Jun. 5 Jun. 6 Jun. 7 Jun. 8 Jun.9 Jun. 10 Jun.11 Jun.12 Jun.13 Jun. 14 Jun. 15 Jun. 16 'f N W DATE 1976 - -- MEASURED TIDE SIMULATED TIDE Figure 5-14. Comparison of Observed and Simulated Water Stage at Section 92, Trinity River at Liberty Gage, June 1-16, 1976 (52) 2.5 2.0 1.5 -'3.0 June 8June 7June 6June 5June 4 - ~-- ............. 4- ........... _ .....~- --- ...... June 3 -, - June 2 - - - - - MEASURED TIDE SIMULATED TIDE June 1 -------- ... .F .... ---- 3.0 2.5 2.0 t 1.5 ~ z 1.0 0 ~~ 0.5 lJJ ..J lJJ MSL lJJ f ~ '" a:: "" ~ Ul a:: lJJ ~~ , I I I I I I I '1.0 . June 9 June 10 June 11 June 12 June 13 June 14 June 15 June 16 DATE 1976 Figure 5-15. ComparisonotObserve.d and Simulated Tidal Elevations at Section 34, Old and Lost River Gage, June 1-16, 1976 (52) , /" FLOODPLAIN WATER STAGE Do GJ 0.1-1.011 liE] 1.l~2.0ft • 2,1-3.~1I .3:6+11 LAKE ANAHUAC f Figure 5-16. Trinity Delta System Showing Inundation Areas, June 1, 1976 (52) V-25 / FLOODPLAIN WATER STAGE Do 00.1-1.011 EJ 1.1-2,011 _ 2,1-35H _ 3,6+11 LAKE ANAHUAC f ANAHUAC Figure 5-17. Trinity Delta System Showing Inundation Areas, June 5,1976 (52) V-26 f t ...-4--r-rtJ- ANAHUAC Do ANAHUAC LAKE o 0,1-1.0ft I2illl 1.1-2.011 • 2.1-3_~" _ 3.6+11 FLOODPLAIN WATER STAGE POND Figure 5-18. Trinity Delta System Showing Inundation Areas, June 9,1976 (52) V-27 FLOODPLAIN WATER STAGE Do D O.II.Oft ~ 1.1-2.0fl _ 2.1-3.~ft _ 3.6+11 LAKE ANAHUAC f I ANAHUAC Figure 5-19. Trinity Delta System Showing Inundation Areas, June 13, 1976 (52) V-28 f Do 80.1·1.0fl ~ I.I-Z.0ft _ Z.lrtion of the Ul It: W I « ~ 1.5 1.0 0.5 MSL -0.5 -1.0 -1.5 , V I I I , , I , '-2.0 December 20 December 21 December 22 December 23 December 24 December 25 December 26 December 27 1976 Figure 5-21. Tidal Elevation Record at Section 8, Point Barrow Gage, December 12·27, 1976 (52) - -- MEASURED SIMULATED TIDE nDE MSL 1.5 2.0 0.5 1.0 December 19December 18December 17December 16December 15 - ......... ~-- ........_/ December 14 . '"' ' /'-'\.[ ............./·" -~ ......"'" '"', 1/ .-....-.... / ....... - 2.0 ~ .,.: . .!:!. . I. 5 z 0 1.0 ~ ~ 0.5 L1J MSL L1J December 12 December 130 ~ II:: 'f ::;) (f) w w II:: I!:! c( :it -0.5 December 20 December 21 December 23 December 24 December 25 December 26 December 27 DATE 1976 Figure 5-22. Comparison of Observed and Simulated Tidal Elevations at Section 24, Old River Cutoff ~hannel Gage, December 12-27, 1976 (52) ---- MEASURED TIDE SIMULATED TIDE 2.0 . t 1.5 z 0 1.0~ :> III ...J 0.5 III IllMSL U December 12 December 13 December 14 December 15 December 1~ December 17 December 18 December 19~ 0: .:;) Ul 'f w 0:.. III r---... /\. r---.... , 2.0~ - ~ .. - . - - . - -- . - - 1.5 1.0 0.5 MSL December 20 December 21 December 22 December. 23'- December 24 . December 25 December 26 December 27 DATE 1976 Figure 5-23. Comparison of Observed and Simulated Tidal Elevations at Sectipn 48, Anahuac Channel Gage, December 12-27, 1976 (52) -- - MEASURED SIMULATED TIDE TIDE I-' IL 5.0 z 0 ii 4.0:> '"..J "'. 3.0 '"<.JIi': 2.0a: ::> II'" .-~-- -- -------- - ----- -- /'/' /-- ----- --------~ 'f w lJl a: 1.0 ~~ MSL' I I I I I I , I I I I I I I 1 , Dec. 12 Dec. 13 Dec. 14 Dec. 15 Dec. 16 Dec. 17 Dec. 18 Dec. 19 Dec.20 Dec. 21 Dec. 22 Dec. 23 Dec. 24 Dec. 25 ·Dec. 26 Dec. 27 DATE 1976 Figure 5-24. Comparison of Observed and Simulated Tidal Elevations at Section 162, Lake Charlotte Gage, December 12-27, 1976 (52) - -- - MEASURED TIDE SIMULATED TIDE ,.: "- z 0 ;:: ;; W ...J W W U ~ Q: OJ 1J) 'f Q: ~ W ~ aI 8.0 7.0 6.0 50 4.0 3.0 2.0 1.0 I-----~--­ -~J ~~/~ ~ / ~----~---------"\ "', ..... MSL' I I I I I I I I I I I I I I I I Dec. 12 Dec. 13 Dec. 14 Dec. 15 Dec. 16 Dec. 17 Dec. 18 Dec. 19 Dec. 20 Dec. 21 Dec. 22 Dec. 23 Dec. 24 Dec. 25 Dec. 26 Dec. 27 DATE 1976 Figure 5-25. Comparison of Observed and Simulated Tidal Elevations at Section 165, Sulphur Barge Channel Gage, December 12-27, 1976 (52) FLOODPLAIN WATER STAGE Do 00.1-1.011 8 1.1-20ft f• 2.1-3.!:i1t.3.6+" 0 , "m Fiuure 5-26. Trinity Delta System Showing Inundation Areas, December 12, 1976 (52) V-37 / POND FLOODPLAIN WATER STAGE Do [§J OJ-LOft ~ \.I-2.0f! • 2.'-3.'311 .3.6+11 LAKE ANAHUAC f Figure 5-27. Trinity Delta System Showing Inundation Areas, December 16, 1976 (52) v-38 FLOODPLAIN WATER STAGE Do o OJ-I.Oft §!] 1.l-2.0ft • 2.1-3.,ft _ ;3.6+ft LAKE ANAHUAC f Figure 5-28. Trinity Delta System Showing Inundation Areas, December 20. 1976 (52) \ V-39 FLOODPLAIN WATER STAGE Do o O,I-I.Oft ISE!J 1.1-2.0fl .2.I-3,'f1 .36+fl LAKE ANAHUAC f Figure 5-29. Trinity Delta System Showing Inundation Areas, December 24,1976 (52) V-40 f ~~!E::tANAHUAC ANAHUAC' Do LAK£ EJ O,I-LOft ~ 1.1-2.0ft .2.1-:Hifl .3.6+ft °iooiiii.......ooiiiiiiiii~....~..m FLOODPLAIN WATER STAGE POND COOLING Figure 5-30. Trinity Delta System Showing Inundation Areas, December 28, 1976 (52) V-41 passage of the flood crest. Maximum levels of inundation occur on approximately December 24 (Figure 5-29). A rapid receding of flood waters occurs as indicated on Figure 5-30 for December, 28. Because of a cembination of wind setdown on the bay water elevations on December 26 and 27 and the gradual receding of the flood stage, the delta flood levels lower quite rapidly. Intensive Study Simulation. An intensive diurnal biological and hydro dynamic study was oonducted by the USGS, 'IDWR and EH&A from November 30 through December 3, 1976. During this period two diurnal field programs were oonducted, one from approximately 1100 CST !'«:Jvember 30 to 1000 CST December 1 and the other from 1100 CST December 2 to 1000 CST December 3. In order to take advantage of the flow verification data obtained during this study, a simulation was oonducted for the period November 26 through December 3, 1976. Streamflow was nearly oonstant at approximately 2,400 ft3jsec (68 m3jsec) with diversions calculated to be 60 ft3jsec (1.7 m3jsec). The driving tide at Morgan's Point was diurnal during the entire period (Figure 5-31). The wind during this time was light except for November 28 and 29 when rroderately strong north winds per sisted. A large wind setdown is apparent in the driving tide on these same two days. The simulated and measured. tides for the gages on the Old River Cutoff Channel, Anahuac Channel and the Sulphur Barge Channel are presented in Figures 5-32 through 5-34, respectively. Due to the low tides, the Lake Charlotte gage was not recording during this period and the Lost River gage was not recording properly, so neither of these records are avail able. The measured and simulated tides at the Old River Cutoff Channel and at Anahuac Channel compare favorably. The tidal anplitude is repro duced accurately and the tide Fhasing is within a oouple of hours. As in a previous simulation, the 0.3 ft. (0.09 m) datum error between measured and simulated tides is evident at toth gages. Besides the datum error, the major simulation inaccuracy occurs during the low tides resulting from the wind setdown. Taking into account the 0.3 ft. (0.09 m) datum difference, the simulated tide is approximately one foot too low during setdown conditions. The simulated and measured tidal amplitude and Fhase also cx:rnpare favor ably at the Sulphur Barge Channel gage (Figure 5-34). As at the two previous gage locations, the low tide period is px>rly simulated. In addition, the simulated tide is approximately 0.3 ft. (0.09 m) higher than the measured tide for IIOSt of the period. This error was not apparent in the previous simulations and can not be easily explained. Water elevation in the Sulphur Barge Channel is controlled by a cx:rnbina tion of tides and river stage. Since the streamflow gage at lOnayor was inoperative at this time, input flows for the Trinity River were esti mated from the measured flow at the Goodrich and the Liberty gages on November 30 arid December 1 during the intensive inflow study. An aver estimate of river flow would result in a mean water elevation that is too high, which could be· an explanation of the 0.3 ft. (0.09 m) error. As noted previously, flow measurements from several sampling sites pro vide a source of additional verification data. In fact, flow measurement is a IIOre preferable form of verification data than water-level records, since the objective of the rrodeling work is the simulation of transport V-42 a: "".... -15.. . ~ t z o j::: ;! W ...J W w u it a: :::> (f) 2.0 1.5 1.0 0.5 -0.5 -1.0 -2.0 I , I , I , I I I , W -l w 0.5 w MSLu ~ a: -0.5:::> '" a: -1.0 ,. w I- ..--. u +2000 .. Ul \,;;-.. $+- Ell.... '-' 3: Ell 0 ..J +1000 Ell ... Ell Ell O+---.,--+---fr------,---r---..----H,...---,----, -1000 -30 NOV 400 1 DEC 2400 -2 DEC 2400 -3 DEC 2400· Figure 5-35. Comparison of Observed and Simulated Flows, Trinity-San Jacinto Estuary, November 30-December 3, 1976 (52) v-48 +2000 Lost RIver IH-10 - SIMULATEDnear Ell MEASUREDSec 192 FLOW INTO RIVER Ell + FLOW OUT OF RIVER +1500 ~ Ell +1000 +1000 Co tt on Bayou Sec 132 ---- ,..... tJ +500 tJ +500Ql Ell QlIII III ;;:-.... (IJl "-.. .... .... .... 0 .... a '-' '-' ~ ~0 0 ...J -500 ...J -500Lo... .... -1000 -1000 2400 , . 2-DEC 3 DEC -1500 ""'" ""'" Ell -2000 2400 2 DEC 3 DEC Cove Bayou Cr. 055 Bayou +1000 Sec 120 Ell +1000 Sec 125 ---- ,..... 0 +500 Ell Ell tJ +500Ql Ql III III ;;:-.... ;;:-.... .... .... .... 0 .... a '-' '-' ~ ~ 0 0 ...J -500 ...J -500 ""'"Lo... Lo... -1000 2400 -1000 2400 2 DEC 3 DEC 2 DEC 3 DEC Figure 5-35. Cant. V-49 1200240024002400· Lake Pass +200 S\C 158 -400 """ l200 EB 2 DEC 2400 3 DEC -600 ,....... +100 0 +60 Mac Lake '"Sec 165 trt~ III,....... ;:--... 0 - '" +40 @ EB EB .... 0III '-' EB;:--... EBEB ~ EBEB - EBEB.... +20 0 EB '-" EB -' ~ u... -tOO l200 1200 0 0 -'u... 1 00 -20 -200 2400 30 NOV 1 DEC 30 NOV 1 DEC +600 near Wa lit sv ill e Sec 169 -200 ,........., +-400 o' '"III;:--... -.::. +200 +1000 Old RIver near IH-10 Sec 33 +800 +600 ,....... - SIMULATED 0 +400 EB MEASURED '" FLOW INTO RIVERIII;:--... + FLOW OUT OF RIVER - .... +200 '-' ~ EB0 0 -' ._---, u... -200 30 NOV DEC 2 DEC 3 DEC Figure 5-35. Cont. V-50. Upper Long Is. Bayou +6000 Sec 2;; +4000 \ -4000 Figure 5-35. Cant. V-51 - SIMULATED Ell MEASURED FLOW INTO RIVER + FLOW OUT OF RIVER slight tidal phase errors can result in considerable error ~en comparing nearly instantaneous simulated and Jreasured flows, the rragnitudes and direction of flow compare favorably at rrost sampling sites. Large discrepancies do occasionally occur, especially at the Cutoff, but the model is capable of simUlating flow direction and rragnitude at rrost locations in, the delta in a satisfactory rranner. A major objective of this study was to apply a one-1:1imensional hydro dynamic model to the flow regime within the Trinity River Delta and test the efficiency of 'the model by simulating periods for which tidal eleva tion and flow verification data were available for the system. This objective has been realized to the extent that the test applications indicate the model is capable of replicating observed water surface elevations within acceptable limits to predict flow regimes necessary for inundation of the marsh areas. Amplitude and phase of the tidal record were replicated accurately at several tide gage locations in the system. A slight (0.3 ft. or 0.09 m) displacement of the observed and simulated tidal records was in constant evidence at the Anahuac Channel and the Old River Cutoff gages. A study of relative water levels in the system, independent of model results, strongly suggests the discrepancy is in the data and not an error in the model. Limitations of available flow data prevent an unqualified judgeJrent on the model's ability to predict absolute levels of flow throughout the system. However, the model did exhibit the ability to replicate proper flow direction and periodicity. The major discrepancy in the model simulations occurred during the periods of strong north winds, which results in wind setdown in bay and deltaic waters and periods of low flow such as the onset of flow reversal at slack tide. This could be due to the occurrence of bi-directional flow or simply because the flows are below the threshold of the model's capabilities since the model was designed to predict the occurrence and extent of rrarsh inundation during periods of high tides and/or moderately high streamflow conditions. Application of Mathematical Models, ~inity-San Jacinto Estuary Hydrodynamic and Mass Transport Models The =nputational grid neb«>rk used to describe the Trinity-San Jacinto estuary is illustrated in Figure 5-36. The grid is superimposed on a rrap showing the general outline of the estuary. Included in the grid network are the locations of islands (solid lines), subnerged reefs (dash lines), inflow points, and tidal excitation cells. The x-axis of the grid system is aligned aFProximately parallel to the coastline, and the y-axis extends far enough landward to cover the lower reaches of all freshwater sources to the bay. The cell size (one square nautical mile) is based on (1) the largest p;:>ssible dimension that would provide sufficient accuracy, (2) the density of available field data, and (3) computer storage requirements and o::rnputational time. Similar reasoning is used in selection of the o:::rnputational time step except that the maximum possible time step in the hydrodynamic model is constrained by the criterion for mathematical stability. In the indexing scheme shown in Figure 5-36, cells are numbers with the indices 1 < i < IMAX = 45 and 1 < j < JMAX = 32. With this arrangement, all model parameters such as water depths-; V-52 4540353025 X-DIRECTION p NAUTICAL MILES 201510 INFLOW POINTS NO FLOW BOUNDARIES SUBMERGED BOUNDARIES 5 .-- 30 25 I CLEARCREEK TRINITY TRINITY /1 ~IVER ,I 1 1 BAYGALVESTON BAY ~ 20 ;-., ..J z :;;:0 DICKINSONf= ..J U « BAYOU UJ u a: f- a OJ >- « 15 1z 'f MOSES_q 1-,U1 Iw CHOCOLATE BAYOU BAYOU I ---I lOYSTER1 EAST BAY BAYOU 1O[ L{;ut DA;UU OAIUU ~ • , - HALLS BAYOU -- c:: WEST BAY 5 III ~ ~I v--..,______.-~r, I BOLIVAR ROLLOVERPASS ROADS Figure 5-36. Schematic Computational Grid, Trinity-San Jacinto Estuary (173) flows in each ooordinate direction, I:ottom friction, and salinity can be identified with each cell in the grid. The basic data necessary for the development, verification and calibra tion of the mathematical m::x1els include Gulf tides, measured tide at discrete points throughout each estuary, gaged freshwater inflows, estimate of ungaged and return flows, wind magnitude, direction and duration, evaporation, and measurements of conservative constitutents (chlorides, specific conductance or total dissolved solids, IDS) throughout the estuary and at each inflow source. Such a oompilation of data for a specified period of time is referred to as a "data package". 'Illrough successive applications of the m::x1el to several independent data packages, the m::x1el is calibrated and verified. Data packages necessary for the calibration and verification of the estuary m::x1els are obtained through a oooperative program with the u.s. Geological Survey. Especially important is the oomprehensive data collection effort conducted in the estuary during July 1976. A representative sample of the results of the calibration of the Trinity San Jacinto Estuary m::x1els using data obtained during the July 1976 field study are presented in Figures 5-37 to '5-39 to demonstrate the ability of the models to simulate observed values of tidal amplitude, flow, and salinity throughout a tidal cycle at several locations in the estuary. To test the m::x1el' s abilities to simulate the salinity response of the estuary over an extended time period, an operation schedule was developed to calculate the variation in salinity distribution during 1974 through 1976. The two-year period was divided into 39 consecutive hydrologic se quencesl/. The minimum time period used as a hydrologic sequence was seven days. Seasonal averages were' used for the meteorological and tidal inputs. The results of the m::x1el operation showed reasonable agreement with observed data (Figures 5-40 to 5-45). l'erfect agreement could not be expected since the simulated results represented average salinity conditions for the time period covered by the hydrologic sequence ~ile the measured data were an instantaneous response of the estuary to the specific tidal, freshwater inflow, and meteorological conditions present at the time of the measurement. Marsh Inundation Model Studies were performed on the Trinity River delta in an effort to delin eate flow distribution patterns and establish areas that WJuld be subject to the previously defined inundation criterion of 0.5 feet (0.15 m) of depth per 48 consecutive hours. In the Trinity delta study, estimates were made of the percentage of the delta surface area subject to inundation through the interaction of varying freshwater inflows and selected tides. The Trinity delta stUdy area is the shaded area shown in Figure 5-5. This shaded area is considered to be bio logically the most important area of the Trinity marsh systems, I:ounded on the 17-A:nyorologic sequence is defined as a time period for ~ich the daily - inflow to the estuary can be reasonably represented by the mean daily inflow during that period, Le., the variation in daily flow about the mean daily flow is small ~en =npared to the magnitude of the mean daily flow. V-54 Galveston Boy at Seabr~o~~__ 3 2 o ]~.. ~-'-I~~'--,-,----,,----" m ~ ~ 40 ~ Time (hours) o In E c o :;: 2 o > '"...... '" 1U o .... ... :J VI o+--.'---~-.,~~~~-,----~-r,~---,----".c-.-------" o m 20 ~ 40 50 Time (hours) East Boy at Marsh Point 3 Ell Ell EllEllEllEll Ell Ell EllEll Ell Ell Ell.2 Ell Ell Ell EllEll EllEllEllEl)E!lEll EllEllEllEll ] I I , , I 0 10 20 . 30 40 ·50 Time (hour s) LEGENO Ell= OBSERVEO -=s 'IolULATED Figure 5-37. Comparison of Observed and Simulated Tidal Elevations, Trinity-San Jacinto Estuary, July 21-23, 1976 V-55 100 Total Flow, Galveston Ship Channel at Pelican Island ~o 0 e e -50 e -100 0 10 i 20 TIme 30 (hours) I 40 I 50 100 Total Flow, San Luis Pass ~ -50 o u.. ,....... () Q) III ~ ..... .... o o o ~ '-' ~o o -\;-------'--+- -100 o I 10 I 20 Time ----, 30 (hours) I 40 1 50 100 Total Flow, Houston Ship Channel at Baytown 50 o-f-~-----'----\---=- -50 504020 30 TIme (hours) 10 -100 -f----------,,--------.------.,------r-----., o LEGEND e=09SERVED -=SllotULATED Figure 5-38. Comparison of Observed and Simulated Flows, Trinity-San Jacinto Estuary, July 21-23,1976 V-56 800 Total Flow, Houston Ship Channel at Texas City DIke 666 e e e 46ei A u CI> In 200 ;;;---. . ... o o o ....... ~ o ~200 ""400 504026 30 Time (hours) 10 -600 +="-'-=='---ir-'===--=-=---y-'-=--=--=-=--==-'>rL-==='-T--===' o _ LECENO e= OBSERVEO -=S IIlULATEO 24&/ec 2!Kl/50 210/40 3tCl/40 !2O/M 340/.tO 3-40/10 545/20 345/40 3!Kl/40 M3/50 5M/70 370/20 570/50 375/"0 377/BC ~ ,'. ,I, 30 r-- "-E '"'-" <: 200 -0 L. -<: CD () <: 0 U to >- -<: - 0 (fl 0 TDWR-USGS LIne / SIt e 580/20 580/40 !MIt! 381/10 420/20 <430/20 440/30 4&0/50 410/50 470/10 !5OO/'lO 510/50 520/50 5JO/50 550/50 5tO/20 , - I - I I - I I I. - - I ! 30 r-- "-E '"'- <: 200 -0 L. -<: '"() <: 0 U 10 >- - <: - 0 (fl 0 TDWR-USGS LIne / SIt e o Surface _ Computed for July 21-23,1976 r::z:J Obse r ved J u IY 19,1976 Bo tt am I2J Observed July 24,1976 Bottom - Figure 5-39. Comparison of Observed (Surface and Bottom) and Simulated Salinities, Trinity-San Jacinto Estuary, July 19-24, 1976 V-58 i f'., ---1- Ii . LEGEND += TOWR SlllULATEO SALINITY f'.,= TOWR OBSERVED SALINITY iI "--·-~··-··~+I~- ,I 40.0 35.0 30.0 C' 25.0 "-0> ....... >- 20.0 :: c: - '1' 0 15.0Vl . '" I f'.,\J;) 0 ., f'., 10.0 5.0 ,DO 'j r M A M~J J A s',o'N"'D'rrTM'A M J'j-A'S~O~Nr[j-'J'r-~A'M-J-rArSTb'N'[j, 1974 1975 1976 Figure 5-40. Comparison of Observed and Simul'ated Salinities, '., Galveston Bay, TDWR Station No. 2421,0300 S'O'N'D'j'F 'M'A'M'j'j 'A'S'O'N'D'j 'F 'M'A'M'j'j 'A'S'O'N'D 1975 1976 LEGEND += TOWR SIMULATED SALINITY LI= TDWR OBSERVED SAL INI TY I i I ,,;, , i i '-" /i "i- t I! If /L1 \/\ -I I\~ ~I/\ LI If\I~ ~ 1 ~ \~ )\t/ ~ "*A LI I ¥ ~ LII ~ ! , , -- J_ ------ -- --- - --_ .._--- ._--- 0.0 'j 'F 'M ' A.M' j , j 'A 1974 40.0 35.0 30,0 r-. 25.0 '-0> ...... >- 20.0 := c - - 20.0 -c -0 15.0Vl 'f '" 10.0~ 5.0 0.0 'J 'F 'M ' A 'M· j , J A 1974 S'O'N'D'j 'F 'M'A'Mj'j 'A'S'O'N'D'j'F'M'A'M'jjAS'O'N'D' 1975 1976 Figure 5-42. Comparison of Observecj and Simulated Salinities, Galveston Bay, TDWR Station No. 2421.0400 .. - .. IIi! LEGEND +=TDWR SlllULATED SALINITY .c:. = TDWR OBSERVED SALI NITY D.! 1\ ·1, , 1-'-·-- (, I .c:. \ I -- I I i --~-._~ I.c:. ..J:,__'~ " ' I---'------------_.- ..__.._- · 40.0 35.0 30.0 ,-. 25,0, 0> ~ >- 20.0 ~ c - 0 U1 15,0 ']= '" '" 10,0 5,0 0.0 'J 'F 'M ' A' M' J ' J ' A 1974 S'O'N'D'J'F M A M J'JA'S'O'N'D'J 'F 'M'A'M'J'J 'A'S'O'N'D 1975 1976 Figure 5-43. Comparison of Observed and Simulated Salinities, Galveston Bay, TDWR Station No. 2421.0100 40.0 'I LEGEND +=.TDWR'SlllULATED SALINITY t>=,TDWR' OBSERVED SALINITY 35.0 -11------'- SON I i I -L I -~'T'----------"" h I t>~ S'ON'D"JF'M'AM A'M' J'J, ASO 1974 I -----', /\: :~--;if--_...:~\-.- --i \V' ,- ,/.' "' -I .._-_. 30.0 ,.-... 25.0 "'- '"....., >- 20.0 ~ c -' .;:' 0 V1 15.0 I·'a, w 100 5.0 0.0 Figure 5-44, Comparison of Observed and Simulated Salinities, Galveston Bay, TDWR Station No. 2422.0100 LEGEND +=TDWR SllAULATED SALINITYL'> = TDWR OBSERVED SALI NI TY --/ ~-------~- i I I ---.---.-----.-------- ~:~- -J-----~---------------- 00 . j F M A M - j -j -A -S~O-r;r_I5'J -F-~rA-M- j . j A'S 0' N 'D ' j F 'M - A '~.C J' j 'A'S' 0' N 'D ' 1974 1975 1976 t+----------,.;~--t, .. -----T-----------f-/~L'>--- ----~ ;- , i . " . A .V: / ,I \ / i:" \ i\ i' j -->----+ _ .-cIA . ! ! \. " . [-. i 5,0 I ! ----- -- r -----tt'.. -.i-t --\H-r --- ---t----- ~:// ~ A l~\ \(V i Figure 5-45. Comparison of Observed and Simulated Salinities, Galveston Bay, TDWR Station No. 2422.0200 south by the Wallisville levee ana ooritinuing' northward to the beginning of the cypress swamp area. 'ItJe eastern Ixmndary is the Trinity River, and the area extends westward from the river to the beginning of the uplands. Included within this area are all major marsh regions subject to inundation fran river fllM. This marsh area is highly 'productive and inundation should result in the flushing of nutrients into Trinity Bay. Hydrographic input into the mcdel was taken from an idealized hydroqraph that was oonstructed from parameters derived from five flood events which occurred on the Trinity River after Lake Livingston had filled. Details of this hydrograph can be found in the Trinity River delta inunnation study (52). six flood peaks, ranging in magnitude from 10,000 ft3jsec ,(283 m3jsec) to 35,000 ft3jsec (991 m3jsec) in increments of 5,000 ft3jsec (142 m3jsec), were selected to fulfill the freshwater infllM requirements of the model. In addition, two independent tide reoords from the Morgan's Point tine 'gage were selected which oorrespond to the low and high tide ronditions. F..ach of the six flood cases were simulated with toth a high and low driving tide in an effort to differentiate those areas which wouln be inundated as a result of high fllMs, and those areas which would be inundated as a result of the inter action of high freshwater inflows and high tidal amplitude. , Driven by low tide oonditions the mcdel shlMS that no inundation will occur within the study area ,during floods of less than 203000 ft 3jsec (566 m3~sec). . From flood peaks of 20,000 ft3jsec (566 ~ jsec) to 30,000 ft jsec (850 m3jsec) the percent of study area inundation will increase fran 5 to 22 j:lercent, and Trinity River floods with peak discharges in excess of 30,000 ft3jsec (850 m3jsec) will sharply increase the percentage 'of' study area inundated (Figure 5-46). A 35,000 ft3jsec (991 m3jsec) flood will inundate.79 percent of the marsh study area during low tide oonditions. High tide oonditions, on the other hand, will cause some inundation with in the stUdy area for all six of the flood peaks simulated (Figure 5-46). The model predicts that increases in flood peaks from 10,000 ft3jsec (283 m3jsec) to 20,000 ft3jsec (566 m3jsec) will mcderately increase the amount of the study area that will be inundated. Between floods peaks of 20,000 ft3jsec (566 m3jsec) and 25,000 ft3jsec (708 m3jsec), however, the area inundated increases dramatically from 44 to 91 percent, re~ectivelY. The two remaining flood peaks simulated, 30,000 ft3jsec (850 m jsec) and 35,000 ft3jsec (991 m3jsec) will completely inundate the study area. with.low tidal conditions at Morgan's point, the mcdel predictions indi cate that a flood peak in excess of 30,000 ft3jsec (850 m3jsec) will be required to achieve a high percentage of inundation of the study area. When tides are higher than normal" hlMever, the study area will be inundated by floods of lesser magnitude•. A flood peak of 25,000 ft3jsec (708 m3jsec) would appear to be the most iudicious use of water for inundation PJrposes when the Morgan's Point tide stage is above normal. As a result of these studies, curves were developed relating the per centage of marsh area inundated to a function of flow, for toth low and high tides. These re~ults are prese~ted in F~gure. 5-46 and Tahle 5-3 • . v-65 o 100 lce FLOOD VOLUME (ACRE-FEET x 1000) 30e 4GC 50C 60C 70G 300 900 1000 /, )<, / ' . x-------X / ;< , , , , , , , , , f' / ,'---f::' HIGH TIDE -{) --,,--------- LO,W_.T.!.QE ,h--' .-- 0-- , , , / , / / / , , / , , , , / , , , , , , , , i/' r x- - --X , / , , , , , I LOW TIDE , , , HIGH TIDE , , , , , 100 Cl w >- « Cl 30 Z ~ Z - I (/) a:: 60« :::;: 'f u.. 0'> a 0'> >- Z W 40 U a:: w c... 20 LEGEND '<= FLOOD PEAK " (.= FLOOD VOLUWE ,--(>' (.)< __ ol(- -,. 0' OlE )t~, r. I I f , ii' , o 10 20 30 40 50 60 FLOOD PEAK (ft'/ sec X 1000) 70 30 90 100 Figure 5-46. Simulated Trinity Delta Marsh Inundation, High and Low Tides Table 5-3. Trinity Delta Inundation Study --peai<-:..----,---Frciii---,----Plood---:--- Total --,------------rnl.iiidatronrr-------.- Discharge , _Duration : Volume : Discharge :_____ Percent : Acres.- WW : High : lDw : High 10,000 9 87,572 44,150 0 11 0 940 15,000 16 184,961 93,250 0 . 13 0 1,097 20,000 19 371,906 187,500 5 44 405 3,629 25,000 21 567,281 286,000 20 91 1,639 7,585 'f 30,000 21 758,689 382,500 22 100 1,864 8,328 '" ...., 35,000 21 976,874 492,500 79 100 6,589 8,328 '!I Inundation of 0.5 feet -for 48 consecutive hours Freshwater Inflow/Salinity Regression Analysis Changes in estuarine salinity patterns are a function of several variables, including the magnitude of freshwater inflow, tidal mixing, density currents, wind induced mixing, evaporation and salinity of source inflows •. In the absence of highly saline inflow and neglecting wind effects, the volumes of antecedent inflow and the tidal mixing are the nDst important factors af fecting salinity. Salinities immediately inside the Gulf passes vary markedly with flood and ebb tide; the iJ}fluence of tidal mixing attenuates with dis tance traveled inside the estuary fran the Gulf pass. The dominance of the effe~t of freshwater inflow on estuary salinity increases with an increase in proximity to freshwater inflow sources. The areal extent of the estuary influenced by freshwater inflow varies in propor tion to the magnitude of freshwater inflow except during conditions of extreme drought. Regression analyses of measured salinities versus freshwater inflow are carried out to verify and quantify suCh a relationship. The average daily salinities were assumed to be related to gaged stream flows by one of ·the following relationships: n ( L i=l -bQt .)-1 [ 1] or [2] [ 2] andQ in Equations [1] t-i The term i=l represents the antecedent inflow conditions, while Qt-k· represents the present inflow condition taking into consideration streamflow time lag between the gage and the estuary. The regression coefficients were determined using a step-wise multiple regression procedure (16). a 1 n a2 St = aO (Qt-k) (i;1 Qt-i) where St is the average salinity of· the t-th day; Qt-k or Qt-i is gaged streamflow k or i days antecedent to the t-th day; b is a IXlsitive number between zero and one;· n is an integer; and an, a1 and n La2 are regression coefficients. The regression equations developed for Trinity Bay used salinities obtained by the Texas Department of Water Resources (IDWR) at statewide monitoring net\<,Qrk station No. 2422.03 (Figure 4-6) and gaged streamflows recorded for the Trinity River near Romayor (Table 5-4). The daily average salinity is related to the daily gaged streamflow by . St = -1.62 + 2528.5 29 ( L i=l Q . )-0.5 t-1 [3] where St and respectively. variation (r2) nificant ( C1 = Qt-i are salinity and streamflow in ppt and ft3/sec, With a correlation coefficient (r) of 0.88 and an explained of 0.77 percent, the regression is tested to be highly sig .01) • V-68 Table' 5-4'. Description of Data for. Regression Analysis, Trinity~San Jacinto' Estuary ." . .... . . ---_._._------_.._-------------------_ ..._-------------- ----------------~ .. . . . .. . . . . --Bay Salinity Station's! Period' of Record: USGS Station Inflow Period of'Record: No. of: Observations for Regression : :. . : :.:: ------------------_.__._-------------_._------_.__...._--_.--------"<'"---------------:----------------,---- Galveston 'IDWR Monitoring Station. 1005.01 <:. I' a \D Trinity TDWR Monitoring Station 2422. 03: May 1969· to Sep•. 1977 May' 1969' to' Dec., 19'77' Trinity River near' Ri:mayor Derived San Jacinto Basin' inflow Jan'•. 1925' to Sep~. 1977 Jan; 1941' to, Dec., 1976 33 82' aj-Se'e-pigure,4-6'-for station -locat[ons'---------------------------- Monthly salinity-inflow relationships were derived using equation [3] to generate daily salinities for the period of streamflow reoord, 1925 through 1976. The oomputed daily salinity values were averaged I1Dnthly over the study period, and the averages were :related to the I1Dnthly ,average flows by the geometric equation [4J where Sm and Om are I1Dnthly average salinity and gaged flow in ppt and ft3/sec, respectively, Co and Cl are regression coefficients, and ( tse ) is a random component (66 ) • The frequency analyses for Trinity-San Jacinto estuary indicate that both I1Dnthly salinity data and I1Dnthly gaged streamflows are approximately log-normal distributed. Therefore, the random component has a normal distribution and can be expressed by tSe (66), ...nere t is a standard normal deviate with zero mean and unit variance, and Be is the standard error of estimate of In (Sm) on In (Om). Resulting oorrela tion coefficients of equation [4J for Trinity Bay (Table 5) for the twelve months (r) ranged from 0.82 to 0.92, which are highly Significant (a. = .01). The average oondition of [4] over a 12-l1Dnth period, i.e., the relation ship of the mean I1Dnthly averages, is fitted to the equation 'S - 656 8 Q -0.576 y- ~ • y i where ~ and Qy are mean I1Dnthly average salinity, and ft (sec, respectively.' The equation and the limits of Sv versus Qy are plotted in Figure 5-47. of equation 15] are listed in Table 5-5. [5) and gaged flow in ppt 95 percent confidence The other statistics The analysis for Galveston Bay, used the salinities obtained by the Texas Department of Water Resources (TOOR) at statewide I1Dnitoring network station No. 1005.01 (Morgan's Point) and the derived San Jacinto River Basin monthly inflow as described in Chapter IV, (Hydrology). The I1Dnthly inflows to daily flow by were uniformly divided into daily flows. Daily salinity is related to daily flow by s =t 29 0.61 + 3404.7 ( E i=O [ 6) The oorrelation is highly significant with a oorrelation coefficient (r) of 0.72. Using equation [6J to generate mean daily salinity for the period of streamflow record, 1941 through 1976, the relationships between canPlted monthly mean salinities and I1Dnthly mean streamflows were determined as shown in Table 5-6. The average oondition of the relationships can be fitted to the equation s = 217.4 Q -0;355 y y V-70 [7] 10'11====1 I~ I ~II~ x ~·X f~""x~~";" ~ x .... )( x x>X x ... ~ . x , xI x x *.""#.C,J, '.x '")( ':N.I J{_)( x X " "'. ll••", x "li xx ." , >:.-x -:><><"'1xXYXh-. ", Xh":':rF 'k x x x x '" w"~ 1'11x,X * x x x ,'" ...-r-~.'Si"'" _~r'll{ .Jx'li'ux "-hJ:T:rJr::~x r 10< l"J I *"x. x I x~ )qX~ I xl.?C>l.I'< "')(_x x x )( Ilx -~ x 'i~ x-J" "'?i: *~",'~ ~~~~"'"x LEGEND x=SlliULATEO DATA 1 ISOL 10=EQUAT ION OOTTED=UPPER L1l1IT. 9S pet. ConfIdence OASHED=LOWER L1l1IT. 9S ~ct. Conffdence t I I lit i I ........ -a. a. "'" >- :!: 10'c -0 'f (/) -J ........ ~ (/) "'" x x 'fxxx x xxl ~ I , .r .... xx xx x ... ,x x )( X)C '" '" xxx ...... x x x 'x o xx .... ~ x 10 . , , '" I 10' • 10' 104 10' (Q) Freshwater Inflow (ftl/sec) Figure 5-47. Average Monthly Salinity Versus Average Monthly Gaged Inflow, Trinity Bay. 1925-1976 Table 5-5. Results of Salinity Regression Analysis, Trinity Bay : : : Regression Equation : Correlation : Explaine:.'l : Stan:jard Error Station : Class : (S in j:pt and Q in ft3/sec) : Coefficient : Variation : of Estimate : F-test r : r' : 5e : : : IDiIR 29 -0.5 2422.03 Daily St = 1.62 + 2528.5 ( " Qt-i) 0.88 0.77 3.11 ** i=l -0.590 Jan. S = 775.1 Q , 350 ~ Q ~ 30,000 0.91 0.83 0.309 ** -0.622 Feb. S = 987.7 Q , 450 ~ Q ~ 37,700 0.87 0.76 0.343 ** -0.582 Mar. S = 663.5 Q , 530 ~ Q ~ 42,100 0.90 0.81 0.315 ** -0.627 Apr. S = 1037.9 Q , 420 ~ Q~ 65,700 0.84 0.71 0.398 ** 'f -0.589 ...., May S = 746.9 Q , 1,280 ~ Q ~ 62,000 0.82 0.68 0.410 ** IV -0.673 Jun. S = 1175.5 Q , 460 ~ Q ~ 45,100 0.87 0.76 0.422 ** -0.616 Jul. S = 677.2 Q , 230 ~ Q ~ 28,500 0.94 0.89 0.241 ** -0.587 Aug. S = 626.5 Q , 200 ~ Q ~ 10,100 0.94 0.88 0.197 ** -0.440 Sep. S = 290.3 Q , 210 ~ Q ~ 14,900 0.92 0.85 0.290 ** -0.393 Oct. S = 204.9 Q , 180 ~ Q ~ 14,900 0.82 0.67 0.343 ** -0.514 Nov. S = 483.6 Q , 270 ~ Q ~ 30,800 0.83 0.69 0.406 ** -0.555 Dec. S = 674.7 Q , 350 ~ Q ~ 43,200 0.88 0.77 0.353 ** -0.576 All S = 656.8 Q 0.89 0.80 0.382 ** ** Indicates a statistical significance level of a 0.01 (highly significcmf) where Sy and Ov are ~an monthly respectively. TIle equation and the versus Qy are plotted in Figure 5-48. are listed in Table 5-6. average salinity and gaged flow, 95 percent confidence limits of Sv The other statistics of equation [71 The above freshwater inflow-salinity relationships can be used to provide preliminary estimates of the response of the estuary to proposed freshwater inflow regimes. Such a technique allows a quick screening of the inflow regimes that have the least desirable impact on salinity patterns in the estuary. Only the most promising inflow regimes then remain to be analyzed in detail using the estuarine t~dal hydrodynamic and salinity transport models. In future studies,' the regression equations developed here may be useful in determining the impact of modified long-term freshwater inflow patterns on the estuary, including the imposition of alternative river basin development. and management plans on the hydrology of the contributing river basins. Surmnary The movements of water ip the shallow estqaries and anbayments along the Texas Gulf Coast are governed by a nunt>er of factors, including freshwater 'inflows, prevailing winds, !IDd tidal currents. An crlequate understanding of mixing and physical exchange in these estuar~l1e I'fClters is f4l1damel1ta:j. to the assessment of physical, chemical, and biologic!,!l processes governing these important aquatic systems. To fully evaluate the tiqal hydrodynamic and Sillinity traqsport char acteristics of estuarine systems using field .data, the Texas Department of water Resources developed digital mathematical models representing the important mixing and physical exchange processes of the estuaries, These models are designed to simulate the tidal circulation patterns and-salinity distributions in shallow, irregular, I1On-stratified estuaries. The basic con cept utilized to represent each estuary is the segmentation of the physical system into a grid of discrete elements. The modelS utilize numerical analy sis techniques to simulate the teniporal and· spatial behavior of circulation and salinity patterns in an estuary. To properly evaluate the transport of water and nutrients through a deltaic marsh, it is necessary to describe ~d canpute estimates of the can plex tidal and freshwater inflow interactions. A mathematical model based upon the physical laws of conservation of mass arid rromentUffi- has' been developed to simulate the passage of water and nutrients through· the Trinity deltaic system. The computations are based upon use. of a finite difference approxima tion to the equations which describe the governing physical relationships. i The marsh inundation model is applied to the Tinity River delta. The delta system is represented as a series of interconnected shallow dlannels which are subject to varying levels of inundation, depending upon the tidal and riverine flow rates. The representation of the Trinity River delta includes the non-tidally influenced flood plain of the Trinity River from the stream gages near Lost Lake and Lake Charlotte to the Wallisville levee. The San Jacinto River delta is much smaller in areal extent than the Trinity delta, and was not considered of sufficient significance to warrant extensive analysis of its inundation characteristics. V~73 ,\O'I:_-~- i ---l--r-TTfffEI=-~-,'~~--i~~---~-=-±t+f-+-,t~~~-T~-"'T l= =1=----[--+-1, +lTn'-_m!--,t~r-,~-- _c•• t~ - I-+ I I I I I I 1- : Ii; I I I rr I ! ···i- X , ' i I I ! I I I I J '-4 I' i i t i ': i L i: ! ; . ! t' : -r ' '--1-,1,: - I ;n" !,' -----1' I! ii, .' I -- ..+---- - •. -'f---1--+-+--Ij .3 i I :' ; i I i 'I' Ii' i i! -~+'-+---+--+-i---+ =I i : :: :' i ,T:Ii i "" 'L~ ~;~ J;: 1 t : : , : : tttn-:'i ;, Ii, , < ~'"xt-.I.'T:T " -- -r- 'I!'~ :,( I x < ~ ~ ~: I , : ! I I I ! ! I : I:<~: ( "it.<)( I 4{A ,I:! ! i I I, ~)( 1 )(bl';-~i)()( <,XX __ l"i,( l\OCfx J. -I-I( _: !! t ,- I 'I -~" ~_x, ~ I < II ~: 1,(' X - - _ ' lxx X ,X XX "-- ':- :to l: =01 (f) ...., r-.. ... (f) ......- Figure 5-48, Average Monthly Salinity Versus Average Monthly Gaged Inflow, Galveston Bay, 1941-1976 Table 5-6. Results of Salinity Regression Analysis, Galveston Bay , , , Regression Equation , Correlation : Explained , Standard Error Station , Class , (S in wt and Q in ft3/sec) , Coefficient : Variation , of Estimate , F-test r , r' , se , , , 'lU'IR 29 -0.5 1005.01 Daily St = 0.61 + 3403.7 ( ,Qt-i) 0.72. 0.52 5.76 ** i=O -0.413 Jan. S = 355.3 Q 300 -'- Q -'- 13,560 0.96 0.92 0.140 ** -0.323 Feb. S = 163.5 Q , 150 -'- Q -'- 13.700 0.84 0.71 0.265 ** -0.318 Mar~ 5 = 152.7 Q , 150 -'- Q -'- 9,630 0.73 0.54 0.296 ** -0.352 Apr. S = 221.8 Q , 500 ~ Q ~ 15,500 0.87 0.75 0.209 ** -0.364 ')= May S = 228.2 Q , 400 ~ Q ~ 15,100 0.88 0.78 0.208 ** ...., -0.313V1 Jun. S = 141.6 Q , 240 -'- Q -'- 16,970 0.82 0.68 0.264 ** -0.453 Jul. S = 454.9 Q , 440 -'- Q -'- 9,430 0.85 0.73 0.229 ** -0.359 Aug. S = 215.5 Q , 340 -'- Q -'- 11,840 0.82 0.67 0.188 ** -0.330 Sep. S = 195.0 Q , 420 -'- Q -'- 12,890 0.89 0.79 0.154 ** -0.337 Oct. S = 181.1 Q , 200 -'- Q -'- 21,060 . 0.90 0.81 0.205 ** -0.360 Nov. S = 240.8 Q , 250 -'- Q :'. 29',040 0.85 0.72 0.284 ** -0.417 Dec. S = 378.7 Q , 350 :'. Q ':'. 9,640 0.87 0.76 0.247 ** -0.355 All S = 217.4 Q 0.89 0.80 0.382 ** -**IndlcateSa--statisticalslgniflcanee leV"el-of-Ci-";-O'.-Ol{hIghlY signiftcant)-------- TI1e oorrect l1Ddel ooefficients for calibration of the hydrodynamic l1Ddel, reflecting the delta's hydraulic characteristic, were determined by simulating' the flow oonditions and water inudation depths in the delta, cunparing them with actual field data, and adjusting the ooefficients until adequate agreement between observed and simulated oonditions was achieved. The numerical tidal hydrodynamic and salinity mass transport l1Ddels were applied to the Trinity-San Jacinto estuary, with the l1Ddel representation of the system including Galveston Bay, Trinity Bay, East Bay, west Bay, and numerous smaller bays, San Luis Pass and Bolivar Roads. TI1e hydrodynamic and mass transport l1Ddels were calibrated and verified for the estuary. The extent of marsh inundation in the Trinity River delta was investigated utilizing the verified inundation l1Ddel for this system. TI1e surface area of the Trinity delta flooded was determined for four typical flood hydrographs, v.bich occurred ,on the Trinity River after the filling of Lake Livingston, under high and low tidal amplitudes. Statistical analyses were undertaken to quantify the relationship between freshwater inflows from the Trinity and San Jacinto Rivers and salinities from Trinity and Galveston Bays. Utilizing gaged daily river flows and observed salinities, a set of lIOnthly predictive salinity equations were derived utilizing regression analyses for the indicated areas of the estuary. TI1ese equations predicted the mean lIOnthly salinity as a function of the mean monthly freshwater inflow rate. V-76 OlAPTERVI NUI'RIENT PROCESSES Introduction Biological productivity is keyed to a variety of P1ysical and chemical processes. These include favorable conditions of temperature, salinity, and pH, as well as a sufficient energy s:>urce (e.g., sunlight. and tides) to drive the biological processes. In addition, readily available supplies of inorganic materials are essential, the IlDSt obvious being carbon, nitrogen, and P1osphorus (CNP). No less important, but required in gnaller arrounts are silicon, sodium, potassium, manganese, chlorine, and sulfate ions. Other essential elements are required in trace arrounts. In the majority of aquatic ecosystems, these elements are available in quantities necessary to support biological production. A deficiency of any one, however, may be sufficient to limit biological productivity. In IlDSt cases, nutrients required in the largest arrounts are quickly depleted from the surrounding medium. Their concentrations can consequently be considered arrong the IlDSt important factors relating to biological productivity. The ratios of the three IlDSt important elements -- carbon, nitrogen, and P1osphorus -- to lesser ones are such that a deficiency of anyone of the three will act as a limiting factor regulating the level of productivity in the system. CNP (carbon to nitrogen to P1osphorus) ratios vary from organism to organism. Carbon is normally required in the greatest quantity followed by nitrogen and P1osphorus. Generally, oceanic species have a reported value of 106:16:1 (142). Nitrogen to P1osphorus ratios for a variety of P1ytoplankton species are usually in the range of 10-12:1 (142). Nitrogen and P1osP1orus are considered to be the "critical" nutrients in aquatic ecosystems since carbon is rarely, if ever, limiting. due to the readily available supply of atIlDspheric CO2 and the ability of autotrophic organisms to use this form. The arrount of nitrogen required in an aquatic ecosystem is generally greater than P1osphorus; biological productivity is therefore IlOSt likely to be nitrogen-limited. This has been reported to be the case in a number of estuaries (530, 532, 159, 220, 225, 133), including those in Texas (368, 369) • Nutrients can be brought into the estuary in either particulate or dis solved forms. Both forms may be O)JTlpDsed of organic and inorganic components. Particulate nutrients may exist in the form of detritus from decaying vegeta tion, sewage and industrial waste effluents, or nutrients a:lsorbed onto silt, clay, and various mineral particles. In general, &>me form of mixing is necessary to keep particulate materials (especially the larger ones) in suspension. Mixing forces may be in the form of wind-driven circulation, as in the shallow bays of the Texas coast, or as induced currents from the rivers and streams that feed the estuaries. The three natural sources of nutrients to the estuaries are streams and rivers, rain, and seawater. Seawater is not usually considered as a nutrient VI-1 source; however, there may be a oonsiderable exchange of seawater with bay water, depending upon prevailing oonditions, and some nutrients may enter from this source. Rainfall probably does not act as a major nutrient source either, although soluble ammonia may be available in the atmosphere at times. On the Texas ooast, the major source of nutrients is freshwater inflow from the rivers and streams that empty into the estuary. Inflows suspend and transport nutrients of natural and man-made origin. The following sections describe the methodology used to determine the nutrient oontribution of the Trinity and San Jacinto Rivers to the Trinity-San Jacinto estuary, the importance of deltaic marshes to biological primary pro duction, and finally the role deltaic marshes play in trapping, storing, and converting inorganic nutrients to plant biomass and the subsequent transport of this biomass to the estuarine systems. Nutrient wading Attempts to determine the arrount of nutrient loading from a riverine source to an estuary have been oonducted by smith and Stewart (229). The basic methodology includes a determination of mean annual flow magnitudes and mean annual concentrations of the nutrient species; simple multiplication is used to arrive at a loading in pounds (or kilograms) per year. The U. S. Geological Survey (USGS), in cooperation with the Texas Department of Water Resources, has maintained daily stream discharge records of the major rivers and tributaries that empty into Texas bays and estuaries. Nutrient concentra tion and water quality data have been oollected systematically for these rivers only.since the late 1960's. Nutrient contributions to the Trinity-San Jacinto estuary are derived primarily from (1) river inflow; (2) local ungaged runoff; and (3) biogeo chemical cycling in deltaic and peripheral salt or brackish water marshes. In addition, nutrients may be contributed by point source discharges or return flows. The adjaCent Gulf of Mexico, by comparison, is nutrient-poor; result ing concentration gradients -are such that a net transport of nutrients out of the bay/estuary system toward the Gulf normally occurs. Numerous complicating factors such as the magnitude of. freshwater inflows, winds, currents, and biological activity all contribute to the complexity of processes that may be occurring at any time. The Trinity River oontributes freshwater and nutrients to the northeast arm of the estuary, Trinity Bay, near Wallisville, Texas. White Oak, Caney, Peach, Spring, and Cypress Creeks along with the east and west forks of the San Jacinto River empty into Lake Houston northeast of the City of Houston. Downstream, the San Jacinto River channel is the canrron wateroourse that carries freshwater and nutrient contributions from the basin to the estuary. Greens, Hunting, Halls, White Oak, Brays, and Sims Bayous drain areas in and around Houston and contribute discharge and nutrients to Buffalo Bayou, known as the Houston Ship Channel in its downstream reach. The mean annual total discharge measured at the closest non-tidally influenced gage for the major freshwater inflow sources to the Trinity-San .Jacinto estuary is about 6.93 million acre-feet (8,550 million. m3). The Trinity River oontributes an average annual inflow of 5.42 million acre-feet (78.2 percent of the total) to the estuary. Contributions' from the San VI-2 Jacinto River and its tributaries to Lake Houston are about 0.88 million acre-feet (12.6 percent). Since significant diversions are made from Lake Houston to supply the water needs of the City of Houston, the amount of freshwater oontributed to the estuary from this oource is much less, usually negligible. Mean annual oontributions from Buffalo Bayou upstream from the Houston Ship Channel and those streams oontributing to it are 0.47 million acre-feet (6.8 percent), including return flows fran the City of Houston. There are three additional sources of gaged freshwater inflow to the Trinity-San Jacinto estuary: (1) Cedar Bayou, 56 thousand acre-feet/year (0.8 percent); (2) Clear Creek, 26 thousand acre-feet/year (0.4 percent); and (3) Chocolate Bayou, 78 thousand acre-feet/year (1.1 percent). U. S. Geological Survey discharge and water quality data aver the period of reoord 1970 through 1977 were used to calculate the potential nutrient loading contributions from the Trinity River, the San Jacinto River tributaries, and the Buffalo Bayou tributaries. The results of analyses of nutrient loadings from each freshwater inflow oource should be interpreted as estimates based on limited data. The estimated loadings reflect the order of magnitude and range that might be expected during periods of similar climatic and streamflow oonditions. Studies were oonducted in the Trinity River delta to gain insight into nutrient oontributions from this brackish intertidal marsh to the Trinity estuary. The studies involved seasonal intensive field sampling efforts aver a one or tw::> day period and laboratory tests using vegetation/sediment oores taken from the delta. As is the case with riverine water quality, an analysis of the deltaic marsh oontribution is inadequate based upon data oollected aver one to tw::> years on a seasonal basis. More data are needed, particularly for extreme events such as floods, hurricanes, and droughts, in order. to refine these analyses. Water quality data oollected by the U. S. Geological Survey indicated mean monthly organic nitrogen ooncentrations in the Trinity River at Romayor, ranged from 0.39 mg/l to 0.79 mg/l. Mean monthly organic nitrogen concentra tions in Cedar Bayou, Trinity River, and the west Fork San Jacinto River were consistently within a similar concentration range (Figure 6-1). Mean monthly organic nitrogen concentrations in Buffalo Bayou and its tributaries through out the City of Houston generally ranged from 1.0 mg/l to slightly ITDre than 2.0 rng/l. Unusually high mean organic nitrogen values observed in Halls Bayou during October and August may not have been representative of the true mean. (The October mean is based on only tw::> data points. The August mean includes an unusually high organic nitrogen value of 16.0 mg/l recorded in 1977; exclUding this data point, the mean monthly concentration for August is calculated to be 1.02 mg/l, in line with those values observed for other nearby wateroourses in the City of Houston drainage.) No obvious seasonal patterns of organic nitrogen concentration variation are apparent fran the data. The majority of the mean monthly inorganic nitrogen concentrations in the Trinity River, the West Fork San Jacinto River, Cedar Bayou, and Chooolate Bayou were less than 1.0 mg/l. The one exception was a value of 1.47 mg/l for May in Chocolate Bayou (Figure 6-2). This appears to be the peak of a spring time rise in inorganic nitrogen concentrations for this watercourse. With the exception of Greens Bayou, mean monthly inorganic nitrogen concentrations in watercourses that empty into the Houston Ship Channel ranged between 2 mg/l to VI-3 LEGEND 0= TRINITY RIVER ... = CEDAR BAYOU += W.F. SAN JACINTO x = BUFFALO BAYOU ¢ = WHITEOAK BAYOU v = BRAYS BAYOU lii:I ~ SIMMS BAYOU * ="HUNTING BAYOU • = GREENS BAYOU III = HALLS BAYOU .D' = CHOCOLATE BAYOU NW DEC FEB APB AlAY mN JU' AUG SCPO '" '".. '".. q .. '" '"~M M ~ t; ~ ~ ~~ qM 0 t:: ""~'" '":<;N N t3 ~ 0 Uq q N N ~ t; ""~ ~~~ "" :3 :3 :;t==:::::;.===::::===-;===;==:::::,;:;:===::===:;===;====~==~~===l:;OCT NOV DEC JAN FEB liAR APR JLAY JUN JUL AIlG SEP MONTH Figure 6-1. Mean Monthly Organic Nitrogen Concentrations in Streams Contributing to the Trinity-San Jacinto Estuary. 1970-1977 VI-4 q 0> NW DEC TEB APR JUN LEGEND 0== TRINITY RIVER ~ == CEDAR BAYOU + == W.F. SAN JACINTO x == BUFFALO BAYOU 0- == WHITEOAK BAYOU v = BRAYS BAYOU ~ == SIMMS BAYOU x == HUNTING BAYOU • == GREENS BAYOU e == HALLS BAYOU 11 == CHOCOLATE BAYOU JUL q 0> q q ~<- <- -::: l> ~ ~ 0 ;j";<0 0 h "'<: ~q :iJ:;,;'" tl "; 0 uq ~ "k1 l> "'<: f;j ~::::..,~ "'<: q q N N 2l~~~~~~g2l OCT NOV DEC rEa MAR APR JUN JUL AUG SEP MONTH Figure 6-2. Mean Monthly Inorganic Nitrogen Concentrations in Streams Contributing to the Trinity-San Jacinto Estuary, 1970-1977 VI-5 slightly higher than 8 rng/I. Concentrations in Greens Bayou were generally 1.0 rng/l or less. With the exception of Chocolate Bayou, there are no apparent seasonal trends for inorganic nitrogen concentrations in these watercourses. Mean IlPnthly total phosphorus concentrations less than 1.0 rng/l occurred in the Trinity River, Cedar Bayou, the west FOrk San Jacinto River and ChoCo late Bayou (Figure 6-3). Mean IlPnthly total phosphorus concentrations in the other watercourses ranged fran 1.0 mg/l to 5.0 mg/l. Halls Bayou, however, is an exception as several concentration values exceeded 5.0 mg/I. Halls Bayou is also the only watercourse where a seasonal trend may be evident, with the highest concentrations occurring in the fall and the lowest occurring in winter. Mean IlPnthly total organic carbon (TOC) concentrations ranged fran 6.0 rng/l to 27 rng/l (Figure 6-4). Concentrations in the Trinity River and West Fork San Jacinto River were as a rule lower than those in the other water courses. The distinction is less obvious for TOC than it is for the nitrogen and phosphorus parameters. There are no apparent seasonal trends for TOC in any of these watercourses. The potential ranges for nutrient contributions fran each stream in fluent to the Trinity-San Jacinto estuary are presented in Tables 6-1 through 6-4. Nutrient contributions (in kilograms per day) were calculated using the maximum and minimum concentration observed for each of the twelve IlPnths mer the period of record (1970 through 1977) and the llEan IlPnthly discharges for each stream. Nutrient concentration data were not readily available for several of the tributary streams to the San Jacinto River above Lake Houston, nor were suitable data available for the reach of the San Jacinto River below Lake Houston. USGS water quality data have been recorded only for the west Fork San Jacinto River. Texas Department of Water Resources statewide water quality IlPnitoring net\>Qrk data were available for the East Fork San Jacinto River. Carbon, nitrogen and phosphorus (CNP) concentrations in the East Fork were within the concentration range of reported observations fran the west Fork in the U. S. Geological Survey records. The range of CNP values reported in the USGS data for the West Fork San Jacinto River were assUI1Ed to be representative of the concentrations expected in the East Fork San Jacinto River, Spring Creek, Cypress Creek, Caney Creek, and Peach Creek where dis charge measurements but not water quality data were available. The mean monthly discharges of these six tributaries to Lake Houston were sUITllled for each of the twelve IlPnths to arrive at a total IlPnthly inflow. The CNP ranges reported by the USGS for the West Fork San Jacinto River were applied to these monthly totals to determine potential nutrient loading into Lake Houston. These values are presented in Tables 6-1 through 6-4 under the heading: San Jacinto River/Lake Houston. At present the percentage of these values passed through Lake Houston to the estuary is unknown. The data are presented for canparison of the potential nutrient contribution of the San Jacinto River system with the other streams that contribute to the estuarine system. The Trinity River, which contributes 78 percent of the gaged freshwater inflow to the estuary, is also responsible for contribution of the bulk of the nutrient loading, thus dellPnstrating the importance of freshwater discharge in the transport of nutrients to the estuarine system. The watercourses that drain the City of Houston empty into the Houston Ship Channel, and subsequently contribute inflow to Upper Galveston Bay. This inflow constitutes only 6.9 percent of the gaged flow to the estuary, yet CNP concen- vr-6 LEGEND 0= TRINITY RIVER a = CEDAR BAYOU .. = W.F. SAN JACINTO + = BUFFALO BAYOU x = WHITEOAK BAYOU <> = BRAYS BAYOU ~ = SIMMS BAYOU • = HUNTING BAYOU ~ = GREENS BAYOU • = HALLS BAYOU e = CHOCOLATE BAYOU , NOV DEC FEB , >US APB MAY AUG SEP~ q 0> q q ~<- <- ~ ~ ~ ~ ~~ :a 0 h ~ [::q ;J :e;" tJ ~ 0 l.lq q .. .. ~ ~ ~ ~ q~~ '"~ ;J ;J MONTH Figuye'6-3. Mean Monthly Total Phosphorus Concentrations in Streams Contributing to the Trinity-San Jacinto Estuary, 1970-1977 VI-7 NOV DEC FEB liAR APB IiAY JUN JUC LEGEND o=TRINITY RIVER .. = CE:DAR BAFOU + = W.F. SAN JACINTO X = BUFFALO BAFOU ¢ = WHITEOAK BAYOU '\l = BRAYS BAFOU ~ = SIMMS BAYOU)( = HUNTING BAYOU • = GREENS BAYOU iII = HALLS BAFOU II = CHOCOLATE BAFOU AUG :3-l---_~---.:.,...~--~- ---_---_---_-~-_---~---~---_l_:3 OCT NOV DEC ," JlAR APR ,JUN ,JUL AllG S.EP MONTH Figure 6-4. Mean Monthly Total Organic Carbon Concentrations in Streams Contributing to the Trinity-San Jacinto Estuary, 1970-1977 VI-B Table 6-1- Range of Expected Inorganic Nitrogen Loading to Trinity-San Jacinto Estuary Based on Mean Monthly Gaged Discharges : : : : : : : : : : Jan. : Feb. : Mar. : Apr. : May : Jun. : Jul. : Aug. : Sep. : Oct. : Nov. : Dec. . . : :. . blograms per day Trinity high 11 ,454 21,939 1,687 16,113 27,210 10,819 1,501 972 1,389 2,510 5,418 17,230 River low 2,813 3,011 337 537 4,535 1,056 0 40 58 179 1,761 562 Cedar high 87 72 80 443 385 323 20 22 207 57 81 355 Bayou low 37 7 12 30 74 65' 6 5 28 40 23 23 San .Jacinto high 1,277 1,970 650 2,454 1,061 2,180 1,079 502 419 557 1,238 762 River/Lake low 681 229 217 94 367 67 131 0 183 144 232 166 Houston Buffalo high 2,058 2,362 3,425 5,336 2,766 2,741 1,580 1,789 1,004 2,697 5,573 5,479 Bayou low 799 528 565 192 1,241 365 479 309 330 470 605 448 White Oak high 1,243 1,159 607 975 1,902 2,322 886 420 1,061 804 1,789 877 Bayou low 200 500 341 325 293 179 148 291 128 106 153 68 ;:i Brays high 2,382 2,943 1,315 1,856 3,385 2,203 1,914 957 2,164 1,558 3,438 2,313I Bayou low 568 1,242 370 715 450 186 294 451 483 133 381 138 '" Sinms high 1,531 2,987 1,029 1,136 3,244 4,447 1,079 988 1,727 1,578 2,073 2,048 Bayou low 222 519 289 320 312 72 105 209 85 74 147 184 Hunting high 307 613 297 264 504 522 327 497 711 291 431 297 Bayou low 18 110 52 81 81 74 76 62 103 85 81 82 Greens high 687 504 228 389 ,590 578 326 191 617 403 353 662 Bayou low 181 106 33 84 120 23 39 65 97 147 187 73 Halls high 254 796 263 679 677 680 1,070 433 794 572 447 701 Bayou low 102 247 14 147 105 20 277 4 114 241 180 190 Chocolate high 75 62 77 495 637 383 55 79 100 79 15 78 Bayou low 17 5 1 27 92 90 14 5 20 7 8 13 Table 6-2. Range of Expected Organic Nitrogen Loading to Trinity-San Jacinto Estuary Based on Mean Monthly Gaged Discharges : : : : : : Jan. : Feb. : Mar. : Apr. : May : Jun. :' Jul. : Aug. : Sep. : Oct. : Nov. : Dec. : : : : kIlograms per day Trinity high 13,263 15,701 2,474 21,484 41,226 26,389 10 ,504 3,604 4,687 7,710 13 ,546 16,106 River low 5,426 2,366 450 5,908 24,323 5,278 6,860 2,592 4,456 717 8,367 0 Cedar high 240 159 64 396 412 945 112 171 349 127 253 283 Bayou low 58 29 26 84 70 ,176 29 14 87 70 44 82 San Jacinto high 3,234 3,528 1,570 4,058 6,531 3,052 992 ,800 1,256 1,078 2,747 3,116 River/Lake low 1,745 870 541 849 2,041 671 316 58 850 233 2,399 0 Houston Buffalo high 2,216 1,736 4,110 1,103 2,151 1,827 764 762 1,465 878 1,242 1,389 Bayou low 119 8 34 197 323 208 127 99 161 201 240 108 White Oak high 499 884 549 834 654 949 1,165 336 335 435' 831 305 Bayou low 48 189 38 58 70 58 36 44 56 38 44 20 ;S I Brays high 1,076 582 547 912 866 1,291 684 554 385 354 880 845~ 0 Bayou low 30 162 72 82 123 118 89 306 89 73 91 51 Simms high 1,229 623 701 609 504 533 831 659 296 279 844 447 Bayou low 34 60 38 61 98 220 47 0 47 49 38 32 Hunting high 113 150 62 126 228 121 69 191 65 119 55 147 Bayou low 9 5 7 17 23 24 8 14 16 17 6 9 Greens high 306 313 192 593 348 173 147 153 796 129 140 185 Bayou low 22 38 18 52 77 42 32 15 25 118 20 70 Halls high 384 141 57 205 266 331 229 110 212 268 227 115 Bayou low 11 17 8 27 18 18 0 10 21 103 15 30 Chocolate high 302 322 102 337 1,051 1,040 269 306 533 182 135 129 Bayou low 43 53 8 91 115 175 81 79 137 70 38 23 Table 6-3. Range of Expected Total Phosphorus Loading to Trinity-San Jacinto Estuary Based on Mean i-bnthly Gaged Discharges : : : : : : : : : : Jan. : Feb. : Mar. : Apr. : May : Jun. : Jul. : Aug. : Sep. : Oct. : Nov. : Dec. . . : :. . kllograms per day Trinity high 3,215 12,905 495 6,445 8,245 4,486 3,430 972 1,331 1,793 5,689 4,120 River low 1,407 860 225 2,417 4,535 2,639 1,286 324 810 717 1,626 936 Cedar high 60 25 34 171 158 68 23 182 111 40 71 72 Bayou low 34 17 16 15 12 55 6 6 39 13 37 33 San Jacinto high 553 550 839 849 857 2,046 600 451 432 629 658 829 River/Lake low 298 137 81 0 286 101 153 44 65 107 232 99 Houston Buffalo high 1,583 1,962 2,512 2,148 1,564 2,076 1,019 1,211 571 1,631 3,064 4,013 Bayou low 483 400 320 366 518 349 331 202 410 445 497 478 White Oak high 760 791 679 399 857 2,048 821 456 838 644 701 785 Bayou low 183 205 246 272 50 129 25 144 106 118 135 68 ;S I Brays high 1,285 1,488 887 1,417 2,466 1,519 1,139 1,166 1,393 843 1,499 2,395~ ~ Bayou low 173 679 321 528 333 106 180 268 199 218 212 169 Simms high 819 1,480 739 905 1,225 941 1,052 628 1,044 726 764 1,285 Bayou low 149 312 280 244 130 110 47 48 83 80 76 242 Hunting high 124 132 100 116 441 283 82 134 176 135 125 103 Bayou low 27 57 25 37 125 40 29 51 44 51 31 42 Greens high 573 522 225 390 600 535 383 280 343 412 280 516 Bayou low 57 137 27 139 70 26 44 64 85 176 66 93 Halls high 261 882 159 542 840 735 500 588 794 617 392 548 Bayou low 58 176 19 35 ·69 .28 235 59 79 350 147 76 Chocolate high 41 32 20 44 76 71 35 38 70 65 34 43 Bayou low 17 7 4 17 19 33 9 10 30 12 8 18 Table 6-4. Range of Expected Total Organic Carbon Loading to the Trinity-San Jacinto Estuary Based On Mean Monthly Gaged Dis- charges : : : : : : : Jan. : Feb. : Mar. : Apr. : May : Jun. : Jul. : Aug. : Sep. : Oct. : New. : Dec. : : : kilograms per day Trinity high 221,044 172,068 22,491 375,962 453,488 263,890 87,894 64,798 63,656 80,681 176,099 224,734 River low 118,500 86,034 17 ,093 53,709 272,093 163,611 50,378 31,994 28,935 46,616 59,603 86,148 Cedar high 6,029 1,301 2,842 5,444 8,232 3,259 1,024 1,529 4,361 3,026 2,994 4,373 Bayou low 1,232 1,055 510 1,089 1,873 1,857 829 282 1,396 3,026 230 2,315 San Jacinto high 36,599 41,234 32,487 61,343 53,062 36,895 10,030 13,098· 15,700 32,325 46,423 36,463 River/Lake low 26,811 10 ,079 27,073 15,100 22,858 17,776 4,143 2,620 6,803 16,522 20,116 13,259 Houston Buffalo high 26,906 26,411 13,700 15,097 25,416 14,950 7,644 6,277 153,836 13,171 18,218 13,120 Bayou low 9,496 9,810 6,279 4,065 8,602 5,897 3,720 3,676 9,303 5,519 7,287 5,865 ;:i White Oak high 7,367 5,121 2,313 5,439 4,057 5,821 3,119 1,321 6,517 4,175 10,907 7,414Bayou low 2,852 466 1,214 1,632 2,705 2,587 1,642 1,080 1,676 1,461 3,116 1,701 I ~ '" Brays high 5,380 6,468 2,641 5,522 11,329 5,317 6,608 1,643 6,225 5,983 5,865 4,508 Bayou low 1,734 1,455 1,339 1,921 4,665 2,620 2,506 726 3,172 1,686 1,043 2,141 Sirruns high 5,772 9,609 2,930 3,827 5,762 4,390 4,025 1,955 3,479 4,469 6,052 3,724 Bayou low 1,303 3,376 1,249 2,105 2,641 2,383 1,428 484 1,600 1,815 1,242 2,048 Hunting high 1,563 573 1,874 1,117 1,176 1,617 995 860 1,529 970 666 402 Bayou low 205 265 187 349 698 590 216 207 1,000 970 274 402 Greens high 3,695 4,140 1,666 3,758 3,097 2,602 2,029 1,975 2,470 1,764 3,312 2,249 Bayou low 981 1,409 625 289 1,819 882 518 440 1,386 306 612 741 Halls high 2,195 1,411 1,985 1,852 2,230 1,176 1,529 1,176 2,381 1,029 2,266 1,274 Bayou low 604 176 441 662 695 492 412 278 390 82 355 701 Chocolate high 6,039 5,527 2,830 5,478 7,963 4,398 2,602 2,166 4,665 2,793 3,161 4,290 Bayou low 1,466 691 512 1,117 3,822 2,837 2,255 790 2,266 1,653 969 1,565 trations are high enough that total nutrient loadings from this source out weigh those from the Trinity River inflows. Fran this discovery it oould be expected that Upper Galveston Bay and Trinity Bay WJuld experience higher nutrient ooncentrations than other fX)rtions of the estuary, a, result that is' generally borne out by the ,water quality data. Marsh Vegetative Production An estuarine marsh is a complex living systan I.>hich provides: (1) detrital materials (small decaying particles of plant tissue) that are a vital basic food source for the estuary, (2) "nursery" habitats for the young of eoonomically important estuarine--dependent fisheries species, (3) maintenance of water quality by filtering upland runoff and tidal waters, and (4) shore line stabilization and other buffer functions. Perhaps the IlOSt striking dlaracteristics of a marsh is the large arrount of photosynthesis (primary production) within the systan by the total plant community (Le., macrophytes, periphytes, and benthic algae); thus, estuarine marshesare recognized as arrong the WJrld's IlOSt productive areas (187,188). Marshes of the Atlantic and Gulf roasts are no exception since the inhabiting rooted vascular plants have adapted advantageously to the estuarine environment and are known to exhibit high biomass production (343, 537, 39, 211, 345, 338, 428, 10). As a result, the marshes are large-scale contributors to estuarine productivity, providing a' major source of particulate (i.e., detrital) substrate and nutrients to the microbial transformation processes at the base of the food-web I.>hich enrich the protein levels and food, value for oonsuming organisms (43, 44, 240, 190, 546, 164, 163, 40, 201, 46, 140, 234, 106, 105, 112). Recent research has dellOnstrated a oorrelation between the area of intertidal salt marsh vegetation and the corrrnercial harvests of penaeid shrimp (424). For Texas estuaries, the statistical relationship indiCates at least 30 fX)unds of shrimp harvested (heads""ff weight) per acre of intertidal marsh (33.6 kg/ha). Marsh areas may be of greater ecological value if sectioned into &nall tracts by the drainage dlannels of transecting bayous and creeks (78). The rationale for this suggestion is found in "edge-effect" benefits; that is, a higher edge length to marsh area ratio provides JlDre interface and a greater opportunity for exchange of nutrients and organisms across the boundary between open aquatic and marsh habitats. Deltaic marshes at the headwaters of an estuary generally exhibit a dendritic pattern of drainage dlannels and are especially important because they form a vital link between an inflowing river and its resulting estuary. Here, the direct effects of freshwater inflow! salinity fluctuations are primarily physiological, affecting both seed ger mination and plant growth, and are ultimately reflected in the oompetitive balance among plant species and the presence of vegetative "zones" in the marsh (332, 203, 198, 185, 103, 228). The Trinity-San Jacinto estuary receives its major input from the Trinity River and the marshes of the Trinity delta. Adams (60) has delineated nine vegetation wnes which represent the major distinguishable vegetative a:ro munities in the delta. The above ground net primary production of the rooted vascular plants (macrophytes) is estimated at 96.6 million dry weight fX)unds per year (43,824 metric tons!year) OI7er the 13,379 acre (5,414 ha) study area. VI-13 Annual net production (ANP) varies from a low of 1,918 dry ~ight ]XJunds per acre (215 g/m2 ) in sampled stands of arrowhead (Sag~ttari~'t!ami..n~) to a high of 26,623 dry ~ight pounds per acre (2,984 gfiii2) in sampled stands of the common reed Phragmites cOl1uuunis. The average ANP over the entire study area is estimated to be 7,222 dry ~ight pounds per acre (819.5 g/m2 ) with approximately 51 percent of the total ANP occurring in the lower delta marshes . south of Old River Lake and ~st of the Trinity River, 20 percent in the middle delta marshes south of IH-10 between Old River Lake. and the Trinity River, and 29 percent in the upper delta marshes north of IH-10. The predominant macrophytes in the Trinity delta include ~z::.t:.ina @t:.enf!., Aste..E. subulatus, .Echi!!.ochloa muric~t:?-, Al_te~C!n.thera Ebiloxeroides , ~~UIIl. _liv~ra : Spartlna : SClrpuS : Saglttaria Nutrient : lanceolatum macrostachya : ~crostachya : patens : arnericanus : lancifolia : (kg/ha/d) Salinity 1.0 2. 19 -68. 15. 38. Total Suspended -0.136 -0.096 -3.854 -7.587 -4.843 -2.274 Sclids ;y' Volatile Suspended -0.013 -0.003 -0.641 -1.465 -0.587 -0.754 Sclids Biochemical Oxygen 0.000 0.000 -0.008 -0.096 -0.017 -0.019 Demand (5 day) ;y' Total Organic Carbon -0.004 -0.002 0.283 -0.449 0.260 -0.100 Total Kjeldahl 0.000 0.000 0.007 0.024 0.006 0.012 ;::j Nitrogen ;y' I Total Kjeldahl 0.000 0.000 0.001 0.002 0.005 0.008~ 00 Nitrogen Particulate Total 0.000 0.000 0.007 0.007 0.002 0.004 Kjeldahl Nitrogen Organic Nitrogen 0.000 0.000 0.000 0.001 0.005 0.008 Ammonia-Nitrogen 0.000 0.000 0.016 0.026 0.017 0.018 Nitrite-Nitrogen 0.000 0.000 0.000 0.001 0.000 0.000 Nitrate-Nitrogen 0.000 0.000 0.075 0.126 0.078 0.080 Total Phosphorus;y' 0.000 0.000 0.018 0.036 0.025 0.020 Total Phosphorus 0.000 0.000 0.018 0.024 0.026 0.018 Particulate Total 0.000 0.000 0.033 0.061 0.033 0.048 Phosphorus Ortho Phosphorus 0.000 0.000 0.014 0.039 0.026 0.022 ;y' Results for unfiltered samples. uptake of nitrogen .and Fhosphorus species in the intertidal marsh zone I'biie there appears to be nO net uptake or release of these nutrients' fran the samples collected in the Mac Lake area. There is also evidence that attached algae, found in laboratory samples collected fran the lower delta, dJrninate the exchange process. The results fran the linear marsh JlOdel containing across-section of the lower delta vegetation and sediment are believed to be nore representative of actual CNP exchange rates than those calculated fran the' laboratory core reactor studies (Table 6-8). These results also canpare favorably with those' reported in the literature for other Texas coastal marshes. Hauck and Ward (62) determined that the ten square mile (2,590 hal marsh lyihg to the south of the Wallisville levee is primarily intertidal and large ly uninfluenced by Trinity River water elevations. Applying CNP exchange rates given in Table 6-8; this portion of the marsh might p:>tentially export as much as 11,000 kg/d of total organic carbon ('roC) under the proper canbina tion of seasonal conditions and tidal elevation (inundation). Likewise, proper conditions could result in the release of 250 kg/d total Fhosphorus, 114 kg/d inorganic nitrogen, and 205 kg/d organic nitrogen. Results fran the linear marsh JlOdel suggest that under certain cbnditions the lower. delta may act as a 'roC and nitrogen sink. The deltaic marshes are llnportant sources of nutrients fiJr the estuary. Periodic inundation events are necessary in order for the Trinity delta marshes to deliver their ..p:>tential nutrient stores to the <:.pen waters of the bay. 'Ibis will occur as the water noving across the delta sweeps decayed macrophytic and dried algal mat material out of the system. Following'a period of emersion, a sudden inundation event CNer the delta marshes will result in a short period of high nutrient release fran the established vegeta tion and sediments (311). 'Ibis Period may last fiJr one or two days and is .followed by a rapid decrease in release rates toward the seasonal equilibrium. During periods of high river discharge and/or extremely high tides that im mediately follow prolonged dry periods, the contribution of carbon, Fhos phorus, and nitrogen fran the deltaic rrarshes to the estuarine system can be expected to ihcrease dramatically. wetlands Processes The concept of the coastal zone as an area of general environmental con cern has come about only during the past decade or so. Landmark legislation along these lines includes the Coastal Zone Management .Act of· 1972 which errphasizes that ..... it is the national p:>licy to preserve, protect, develop, and where possible, to restore or enhance, the resources of the Nation's coastal zone for this and succeeding generations..... More recently, Executive Order 11990 of May 24, 1977, ordered federal agencies with resp:>nsibilities in, or pertaining to, the coastal zone to ..... take action to minimize the destruction, loss or degradation of wetlands, and to preserve and enhance the natural and beneficial values of wetlands ..... In pursuit of this goal, the Texas Department of Water ~sources has funded aerial photographic studies with the Texas A&M Rarote Sensing Center to provide baseline characterization of key coastal wetlands in Texas in order to Canparatively evaluate the various components of the marsh systems. The fol- VI-19 ~ Results from unfiltered samples. !?I Some or all data below detectable limits. VI-20 lowing description of the Trinity River delta is a by-product of seasoncil aerial J;t1otographic studies oonducted during the 1978-1979 growing season (258). '!he Trinity River delta is a relatively stable system whose outlet lies along the eastern side of an extensive deltaic wetland which fronts some 10 miles (16 kriI) along upper Trinity Bay. Signs of man's activities are readily apparent throughout the delta, extending fran Trinity Bay northward to Devers Canal. Left to its own devices, the lower river w::>uld quite probably. have slowly extended its delta bayward in the long term. However, the river outlet has been· channelized and aligned, with spoil banks lining the extreme tip. Construction. of Livingston Dam upstream, coupled with dredging and diking downstream, have CXlIIIbined to reduce flooding of the Trinity delta except under extreme flood conditions. The natural· deltaic wetland has been significantly nodified by three recent construction projects. '!he construction of Lake Anahuac, an irrigation storage reservoir just north of the town of Anahuac, provided water for rice farming and in turn encouraged conversion of large areas of wetlands southeast of the Trinity River delta to rice culture. COnstruction of the 2 miles x 3 miles (3 km x 5 km) cooling porid along the northwestern edge of Trinity Bay has resulted in a direct loss 6f productive wetland area. (The associated thermal power plant receives influent water fran the San Jacinto estuary some seven miles [11 km] to the southwest and discharges into Trinity Bay). Can- pletion of Wallisville Dam and impoundment of Wallisville Reservoir will also result in the loss of a sizeable area of viable wetlands. The direct, irre placeable loss of wetlands will ITOSt certainly impact the food chain pro ductivityof the Trinity-Jan Jacinto estuary. The long-range condition 'of the wetlands environment will be considerably affected by the kinds of decisions which are made over the next few years. The proper environment If,Quld, in the case of the deltaic marshes, be one in which there is a healthy seasonal cycle of ernergence-to-maturation-to-senes cence-to-detrital utilization. Acre for acre, the wetlands' are aJTK)ng the ITOSt productive areas on earth. Therefore, the direct and indirect impacts of water, power, and navigational developnent; oil and gas production; and expansion of agricultural and cattle-raising activities in the coastal zone should be of oonsuming interest. Summary The deltaic marshes are important sources of nutrients for the estuarine system. Periodic inundation events are natural and necessary in order for the marshes of the Trinity-San Jacinto estuary to deliver their potential nutrient stores to the open waters of the bays. This will occur as the slug of fresh water ITOving across the delta sweeps decayed macrophytic and dried algal mat material out of the system. A sudden inundation event over the delta marshes, following a period of ernersion, results in a short period of high nutrient release from the establishEid vegetation and sediments.. This period may last one or tlf,Q days and is followed by a period in which release rates decrease rapidly until they approach the seasonal equilibrium. During periods of high river discharge and/or' extremely high tides that llmnediately follow prolonged dry periods, the oontribution of carbon, J;t1osphorus, and' nitrogen fran the VI-21 deltaic marshes to the estuarine system can be expected to increase dramatically. Aerial photographic studies of the Trinity River delta have provided an insight into on""",:!oing wetland processes. Construction of Livingston Dam upstream, coupled with dredging and diking downstream, have cx:mbined to reduce flooding of the Trinity delta except under extreme flood conditions. The natural Trinity River deltaic wetland has been significantly modified by three recent construction projects: (1) Lake Anahuac, (2) a large thermal power plant cooling pond, and (3) Wallisville Dam and Reservoir (uncanpleted). The direct loss of wetlands due to these construction activities will llDst Cer tainly impact the food-chain productivity of the Trinity-San Jacinto estuary. The long-range condition of the wetlands environment will be considerably affected by the kinds of decisions which are made CNer the next few years with regard to water, power, and nav~gational developrrent; oil and gas production; and expansion of agricultural and cattle-raising activities in the coastal zone. VI-22 QIAPl'ER VII PRIMARY 1\ND SECCtIDARY BA.Y PRJDUcrIOO Introduction A large number of environmental factors interact to cpvern the OITerall biological productivity in a river fed, embayment-type system such as the Trinity-San Jacinto estuary. In order to describe the "health" of an estuarine ecosystem, the food-web and its trophic levels (e.g., primary and secondary bay production) must be nonitored for a long enough period to estab lish seasonality, distribution of production, and ccmnunity canposition. Ecological variables which were studied and are discussed herein include the abundance (counts per unit volume or area), distribution, and species canposi tion of the phytoplankton, z=plankton, and the benthic invertebrates. All biological ccmnunities are energy-nutrient transfer systems and can vary only within certain limits regardless of the species Present. In a much simplified sense, the basic food supply (primary production) is determined by a number of photosynthetic species directly transforming the sun's energy into biomass that is useful to other rrernbers of the biological ccmnunity not ca pable of photosynthesis. Thus, the concept of primary ahd secondary pro ductivity emerges. Fundamentally, primaI:y productivity represents the auto trophic fixation of carbon dioxide by photosynthesis in plants; secondary productivity represents the production of herbivorous animals \'ohich feed on the primary production canponent. . The integrity of biological systems then stems mainly from the nutritional interdependencies of the species canposing them. 'Itlese interdependencies form a functional trophic structure within the estuary (Figure 7-1). The phytoplankton (free-floating plant cells) form a portion of the base of this trophic structure as primary producers. Estuaries benefit fran a diversity of phytoplankton by experiencing virtually year-round. photosynthesis and production. Shifts in cornnunity canposition and replacement of many species throughout the seasonal regime provide ·an efficient ajaptation to seasonal· manges in biotic and abiotic factors. Secondary production evolves as the phytoplankton producers are consumed in turn by the z=plankton (tiny, suspended or free-floating animals) and filter-feeding fishes; planktonic detritus is also utilized by many benthic invertebrates. Characteristically, each estuary has identifiable· phytoplankton, z0o plankton, and benthic comnunities. Since these ·organisms respond to their total environment in a relatively short time-span, they can be employed as "indicators" of primary and secondary production, especially in the <:pen bay areas. Therefore, the main objectives of this analysis are to describe the ccmnunity composition, distribution, density, and seasonality of the following important ecological groups: phytoplankton, zooplankton, and benthic inverte brates. Data presented in this report for each of the lower food main categories ( i.e., phytoplankton, zooplankton, and benthos) were· obtained fran a study VII-l TERRESTRIAL INVERTEBRATE HERBIVOR S INVERTEBRATE PREDATORS MAN Figure 7-1. Estuarine Food-Web Relationships Between Important Ecological Groups (77) VII-2 performed by Espey,. Huston and Associates, Inc. ( 63) under' interagency contract with the Texas Department of Water Resources. The objective of the study was to determine species diversity and standing crops of the phytoplankton, zooplankton, and' soft-bottom benthic assemblages of Trinity Bay. Hydrographic, cnemical, and biological samples were collected I1Dnthly from Trinity Bay from September 1975 through August 1976 at six stations rang ing from the I1Duth of the river CNer the extent of the bay (Figure 7-2). In situ profiles of salinity, conductivity, temperature, and dissolved oxygen were obtained at each sampling site. Surface water samples were analyzed for nitrite nitrogen, nitrate nitrogen, anm:>nia, organic nitrogen, ortho-phos phate, total I*tosphorous, and total organic carbon. Phytoplankton Data Collection Seven divisions represented by 132 phytoplankton species were collected from the Trinity Bay system: Bacillariophyta - diatoms [54 taxa]; O1loro phyta - green algae [45 taxa]; Cyanophyta - blu~reen algae [14 taxa]; Pyrro phyta - dinoflagellates [9 taxa]; Euglenophyta - [7 taxa]; eryptophyta - [2 taxa]; and Chrysophyta - golden-brown algae [1 taxon]. It may be of interest to note that many of the species collected, especially the Chlorophyta, are considered to be freshwater forms and their presence is perhaps an indicator of the prevailing low salinity regime found in the Trinity Bay system. Surface and bottom I*tytoplankton. samples were collected at each station and these data were pooled in the following analysis. Phytoplankton concen trations in a single (pooled) sample ranged from 10,200 cells/l at site 5 . (November 1975) to 1,276,000 cells/l at site 1 (February 1976) (Figure 7-3). Mean I1Dnthly densities ranged from 33,200 cells/l in November 1975 to 488,800 cells/l in July 1976. A smaller peak was recorded in February 1976 (354,800 cells/I). The seasonal maxima in later winter and rnidsUlllller were dominated by. diatoms and blu~reen algae, respectively. Species diversity values exhibited a great deal of variability. For example, a diversity value of 2.0 was calculated for the February 1976 sample . at site 1; the following I1Dnth the diversity value increased to 3.8. An extremely large bloom of the diatom Skeletonerna costatum (723,400 cells/I) occurred in February at this site while no "blooming" IXlpulations were 0b served in March. Similarly, a July bloom of the blue-green algae Oscillatoria at station 5, (311,200 cells/I) produced a diversity value of 2.6; in August the value increased to 4.2. In general, major blooms (greater than 20,000 cells/I) caused low species diversities; high diversity values were usually found in the absence of blooming populations. Over the 12-rnonth study period the mean percentage representation of each phytoplankton division for all stations was as follows: Diatoms Green algae Blu~reen algae VII-3 41.6% 24.2% 23.0% ANAHUAC NATIONAL WILDLIFE REFUGE o LAKE ANAHUACTRINITY RIVER TRINITY BAY • • 42 \ \ \ , \ \ \ \ \\, HOUSTON \......-- 1 SHIP \ CHANNEL \, , , ,, \ , , \ \ \ \ AN JACINTO RIVER 95"00' I.Hf6 C/locolale Bey 'll~S'\ ,\"~~"Pass l3S"C'O' Figure 7-2. Trinity-San Jacinto Estuary Hydrologic and Biologic Sample Sites (56) VII-4 SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG 1400 1400 1260 1120 1280 1120 ---~ 840 840 ~ I '-l I1;3t.>~~ 700 7000 h ~ ..; '560~ h ~ ~ 420 420 140 o 0 SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG (SEPTEMBER 1975 - AUGUST 1976) LEGEND O~STATION 1 a~STKrION 2 + = STATION 3 x = STATION 4 V~STKrION ~ "~STKrION 6 Figure 7-3, Mean Monthly Phytoplankton Densities in Trinity Bay. September 1975-August 1976 VII-5 Dinoflagellates Euglenoids Others 5.9% 2.6% 2.7% The seasonal succession of Trinity Bay j:tlytoplankton groups, averaged over all stations, is shown in Figure 7-4. The diatom ccmponent was particularly large in February and April 1976 samples. As previously mentioned, a bloom of the diatom Skeletonema costatum was responsible for the February peak. The April peak was due largely to bloaning >X'pulations of Thalassionema nitzschoides and Navicula abunda. The blue-green algae comprised over 70 percent of the total standing crop in July 1976 due to large numbers of Oscillatoria. Populations of Prorocentrum caused the dinoflagellate representation to rise to 32 percent in January 1976 samples. No other major ccmpositional shifts were observed during the sampling period. The' percent abundance of the major P1ytoplankton groups was averaged over all sampling dates (Table 7-1). Stations 3, 4, and 5 under the direct in fluence of the Trinity River, had a relatively low representation of diatoms; the green and blue-green algae appeared to be the nest prevalent at these stations. The opposite was true for stations 1, 2 and 6. The average nenthly densities of the five nest prominent P1ytoplankton taxa are listed in Table 7-2. The blue-green algae Oscillatoria and the diatom Skeletonema costatum produced conspicuous bloans in July and February, respectively. The haloj:tlHous freshwater diatom Cyclotella meneghiniana was ubiquitous throughout the year but reached maximum densities in January 1976; another diatom Nitzschia closterium was nest prevalent in May-June samples. Ankistrodesmus~. a green algae, was also ubiquitous throughout the year. Results of Analyses Trinity Bay j:tlytoplankton densities observed during the Espey, Huston and Associates study were similar to values reported for other marine areas and estuaries of ~xas. Average standing crop for the 12-month study was 171,400 cells/I. Moseley et al. (19) state that P1ytoplankton densities of 730,000 cells/l occurred in Cox Bay, ..nile Espey, Huston and Associates (49) reported phytoplankton densities of 133,000 cells/l from Sabine Lake. Standing crops observed by Holland et al. (325) in the Nueces and Mission-Aransas estuaries ranged from 55,000 cells/l in Copano Bay to 790,000 cells/l in Nueces Bay. Some of the green and blue-green algae collected are representative of typical forms found in freshwater reservoirs of the southwestern United States. Diatoms and dinoflagellates found in Trinity Bay were a mixture of freshwater, brackish, and marine species that frequently occur in coastal. areas of the Gulf of Mexico. Although euglenoids are generally regarded as freshwater organisms, species such as Euglena and Eutreptia are frequently tolerant of salinity. Phytoplankton species vary markedly in their ability to withstand dlanges in salinity. Accurate halobion classification of nest species found in Trinity Bay is impossible due to insufficient culture experimentation on salinity optima and tolerances. Chu (22) noted that although cell division can continue in freshwater for nest estuarine species, most freshwater species cannot grow in salinities exceeding 2 ppt. Foerster (67) found, however, that VII-6 90 n. 0 D:: 80u Cl z 0 z 70 <[ l-(/) Z 0 I- 60 ><: z <[ -'n. 0 50I- >- I n. -' <[ I- 400 l- t.. 0 w 30 Cl <[ I- Z W u 20D:: W n. 10 DOTHERS ij~~Y;;;\;';i:] EUGL ENOIOS ~ DINOFLAGELLATES r»»1 BLUE-GREEN ALGAE:-:-:.:.:.:-:.;.:.: ~ GREEN ALGAE _DIATOMS Figure 7-4. Seasonal Succession of Trinity Bay Phytoplankton Groups VII--7 Table 7-1. Abundance of Phytoplankton Groups by Station in Trinity Bay, September 1975 - August 1976 ~~ la/ 2 3 4 5 6Group : . . :. (percent) Diatoms 61.5 53.3 25.8 21.9 43.8 49.3 Green algae 17 .2 18.2 27.0 35.5 21.4 21.9 Blu~reen 6.5 17.1 36.5 28.6 26.0 23.2 algae Dinoflagellates 7.0 7.2 4.1 4.3 4.7 2.2 Euglenoids 5.4 2.5 2.4 1.3 2.3 1.5 Others 2.4 1.7 4.2 3.4 1.8 1.9 Total Standing 100.0 100.0 100.0 100.0 100.0 100.0 Crop :~;;rRefer to Figure 7 2rorfocat1ons of Stations 1· through -~----- VII-8 Table 7-2. Average ~thly Density of Major Phytoplankton Species in Trinity Bay, September 1975 - August 1976 -----_._-- : : : Species :_:~:~:~:~:~:~:.:_:~:~:~ . . . . : : : : : : : :. . . . ---- --_.~-- --- - - - ---- - --_.~ -~ .._-- - - nurrber/ml Blue-green Algae Oscillatoria 0.1 0.8 0 0 0 0 0.1 0 0 1.6 309.8 0.5 Diatoms , Skeletonema- 0 0 0 35.3 6.9 207.8 3.6 2.1 0 0 0 0 costatum Cyclotella 1.6 1.6 1.5 10.8 61.1 2.6 0.5 1.4 2.5 15.5 2.7 4.6 ::1 meneghiniana H I ID Nitzschia 4.6 0 0- 0.2 0.1 3.6 1.3 4.5 26.8 57.6 1.5 2.0 closterium Green Algae Ankistrodesmus 25.8 54.8 1.5 1.5 0-.3 1.7 0.7 0.7 0.5 8.2 7.7 1.7 many freshwater species can resume growth after exposure to seawater if placed in a freshwater medium. Estuarine plankton were divided by Perkins (200) into three cx:mponents: "( 1) autochthonous populations, the permanent residents; (2) temporary auto chthonous populations, introduced from an outside area by water lIOvernents, are capable of limited proliferation only and are dependent upon reinforcement from the parent populations; and (3) allochthonous populations, recently introduced from freshwater or the <:pen sea, are unable to propagate. and have a limited survival potential." The Trinity bay system supports a phytoplankton population derived from the entire range described above. The Euglenophyta (e.g., Euglena and Trachelaronas) are representative of the permanent auto chthonous populations. Tenporary autochthonous species include diatoms (e.g., Skeletonema costatum)and dinoflagellates (e.g., Prorocentrum). The allodl thonous element is difficult to define but is probably represented by diatoms and green algae derived from roth marine and fresh environments. Freshwater inflows from river. sources may act to transport freshwater phytoplankton species into the estuarine system. Although river flows func tion to lower salinities and to transport nutrients, detritus, and dissolved organic materials into the bay, the rate of river flow through an estuary can also have contrasting effects. More nutrients and freshwater plankton may be imported to the system with increased flow rates, thus increasing standing crops and primary production. .At very high flow rates or flood conditions, however, the high turbidities, salinity changes, and flushing out of indigenous populations may depress phytoplankton abundance and productivity. Correlation analysis of combined river inflow (gaged and ungaged) versus mean phytoplankton standing crops from the Trinity Bay study, oowever, re vealed a lack of correlation (ex > 0.05). This was due, in part perhaps, to the atypical Trinity River inflows during this period. Normally, peak periods of inflow occur in late spring and early fall. However, in 1975 the fall maximum was absent and the spring 1976 peak was sustained well through July (Figure 7-5). A lIOre detailed analysis ,was performed in ~ich the lIOnthly conbined river inflows were compared to average lIOnthly phytoplankton densities at stations 3, 4, and 5 (lagged one lIOnth). The analysis revealed a very highly significant (ex = 0.01) correlation coefficient (r 2 = 0.778), implying that about 60.5 percent of the variations in phytoplankton standing crops at these stations were due to fluctuations in river inflows. Winsrorough and Ward (56) utilized data oollected from the Espey, Huston and Associates study and discovered a clear distinction in oanmunity composi tion between these stations (3, 4, and 5), dominated by the outflow of the Trinity River, and the lIOre saline stations 1, 2, and 6; The green algae were predominant at the former ~ile diatoms dominated collections at the latter (Figures 7-6 and 7-7). Results were compared with an earlier study of Galves ton Bay reported by Copeland 'and Fruh (32). The Galveston Bay study included phytoplankton collections in February, April, July, and October 1969 in Trinity Bay. The number of species identified by Copeland and Fruh were about half those encountered in the ESpey, Huston and Associates study. The pre dominance of the green algae was no!: noted at 'the rive~influenced stations.· VII-l0 8 ~ § 0 § 8 8 ~ ~ 8 8 0 2 8.. Q ~ 0 8 ·Sl~- en .. ., .. N N !!l :1 « - 5 c -, .-I -, . ::l; - ./ « ~ L ::l; UJ "- -' ) « u ~ f-en-' -,«u>=a: UJ 0> lL .., f- 0 z UJ C> .-'z ... :I: 0U < en « 3> -, J!! u ~ § § 0 ~ ~ 0 0 8 0 0§ 0 0 00 5l 0 0N .. '" .. N.. '" N Figure 7-5. Daily Discharge of Trinity River at Romayor, July 1975-August1976 .(56) VII-ll o z o N ..,. C!; M" ., Z -" t!>"0 j:: " "0 0« ., .., Z '" '"« ~ cl5CJ) ., ..J 0.. X W 0 • 8 oCD o... oon o '" o N 3"!"" lVlOl ~O lN3:>1l3d Figure 7-6. Proportion of Chlorophyta (Green Algae) to Total Algae (56) VII-12 plankton actually represent two separate categories: the holoplankton and the meroplankton. Holoplankton are true zcx>plankton that spend their entire life cycle as animal plankton (e.g., copepods, cladocerans, larvaceans, maetognaths, and ctenophores). Meroplankton, Inwever, represent only certain life stages of animal species that are otherwise oot considered planktonic (e.g., larval stages of barnacles, oysters, shrimp, crabs, and fish) • Many zcx>plankton species found in Trinity Bay are widely distributed along the coasts of the United States, while others may even have a world wide distribution. For example, Green (77) reports that Acartia tonsa may be found in the Central Baltic Sea areal Brachionus ql!adridentata is also known fran parts as distant as the Aral Sea of Russia. Other zcx>plankton studies conducted in estuaries and bays along the Texas coast have produced similar results to this study. As previously IlEntioned, barnacle nauplii and the calanoid copepod Acartia tonsa were the daninant zooplankton forms in Trinity Bay. This agrees with studies in Sabine Lake (421, 49), in Lavaca Bay (293), in San Antonio Bay (291), and in the Nueces and Mission-Aransas' estuaries (325). Maximum and minimum mean nonthly densi ties in Triility Bay were also similar to results fran the studies mentioned above (Table 7-3). Mean nonthly zcx>plankton standing crops fran the Trinity Bay study are canpared with canbined (gaged and ungaged) river inflow in Figure 7-10. Freshwater inflow can influence zcx>plankton in several ways. Estuarine zooplanktOn standing crop composition can be altered by importation of fresh water species. Inflows can also transport zcx>plankton food resources into the system in the form of I=hytoplankton and detritus. However, zcx>plankton comnunities may also be adversely affected by increased river inflows. Sudden shifts in salinity and flushing out of autochthonous populations can decrease zooplankton standing. crops. As reported by Perkins (200) the primary factor influencing the composition and abundance of estuarine zooplankton is develop ment rate versus flUshing time. Saltwater intrusions, on the other hand, act to (1) import marine zcx>plankton into the system1 (2) import marine I=hyto plankton as a food sourcel and (3) increase salinity. Correlation analyses revealed no significant statistical relationships between zcx>plankton populations and river inflows. However, freshwater inflow/salinity manges were important factors regulating the species canposition, seasonal occurrence, and distribution of zcx>plankton canIDimities during the Trinity Bay study. Diversities at stations 3, 4 and 5, closest to the river's nouth, were directly related to the rate of river flOWl that is, diversity manges were closely allied to the presence or absence of freshwater taxa. Stations 1, 2 and 6 were located in areas of considerable mixing of VII-17 Table 7-3. Range of Mean IUlthly ZOOplankton Densities (individuals;m3) System Minimum Maximum ----- Trinity Bay (63) 1,235 (Dec. 1975) 190,560 (Apr. 1976) Nueces Bay (325) 832 (Oct. 1973) 8,027,855 (Feb. 1974) Corpus O1risti Bay (325) 1,722 (Dec. 1972) 53,657,037 (Mar. 1973) Copano Bay (325) 1,296 (Sep. 1974) 53,536 (Feb. 1973) . Aransas Bay (325) 2,497 (Dec. 1972) 3,008,679 (Feb. 1974) Sabine Lake (49) 381 (Apr. 1975) 20,042 (Oct. 1974) Lavaca Bay (293) 1,980 (Oct. 1973) 27,846 (Feb. 1974) San Antonio Bay (291) 820 (Jun. 1973) 46,296 (Feb. 1973) VII-18 200,000 1 J500 EXPLANATION 1\ 1450 - Zooplankton ,ll T ISO,OOO ---...- River Inflow I I 800I I I I I \ I I I I14,000 I • 700 I \I \I \I I12,000 I \ 600 (f) ">- I \ 0c m0 I \ 6' '" ~ I \ ~::;; ;0 "- I \ I \0 "I m~ 10,000 I \ I 500 ~ I \ I \ 0;-c \ -0 I \ I 0~ I :Ec \ I0 I0- I \ I 00 \ I 00N I I 0S,oOO \ \ 400~ I I J>0 \ \ "LL I I CD '" I \ I \ , " 0 \ mu I I \ ~U) \I \ -f\ \ I 06,000 I \ 300 "I \ I \ \ '"/ \ I \ I / \ I \I \\ \/ " I \ I \/ I 1 \4,000 / • \ 200 / \/ \/ " / \ ~--J/2,000 100 Sep Oct Nov Dec Jon Feb Mar Apr May Jun Jul Aug Figure 7·10. Mean Monthly Zooplankton Densities Versus River Inflow in Trinity Bay. September 1975·August 1976 VII-19 water masses and zooplankton; conrnunities oonsisted mainly of brackish water species and species preferring more saline waters. The ecological niches for zooplankton are such that cptirnal oonditions· for growth and survival occur at different times of the year for different species. Optimal conditions for a given species result in high nurrbers of individuals for that species as long as· favorable conditions last. If condi tions are favorable for more than one species at the same time, the dominant or more COIlpetitive species will be found in the highest numbers followed by smaller increases in populations of the other species involved. Because the species in an area can vary in density and species predcxninance as well as fluctuate seasonally during the year, reliable conclusions on the plankton populations of an area can only be drawn on the basis of long-term investiga tions with regular catches. Benthos --- Data Collection A total of 4,608 organisms representing 72 species in six phyla were identified fran benthic samples oollected during the 12-rnonth Espey, Huston and Associates study (63). Triplicate samples were collected at each station with a 6 x 6-inch Ekman dredge. Results discussed herein are reported as individuals/m2• The rnost prominent Iilyla were the Annelida \>hich accounted for 49 percent of the species identified, followed by the Arthropoda with 25 percent, and the Mollusca with 20 percent. '!be remaining three Iilyla, the Bryozoa, Rhyn chocoela, and Chordata, comprised a total of six percent of the species identified. Mean monthly densities ranged from a high of 1,463 individuals/m2 in September 1975 to a low of 409 individuals/m2 in August 1976. The OITerall mean density for the 12-rnonth study was 945 individuals;m2. Occasional peak populations in individual samples precluded any correlation between samples. For example, standing crops ranged from 129 individuals;m2 at station 5 to 2,222 individuals/m2 at nearby station 6 in May 1976 (Figure 7-11). Bottcxn salinities generally followed the pattern of river discharges during the year with highest values recorded during the fall and winter \>hen sustained freshwater inflows were low. In almost all months the lowest salinities were recorded at stations, 3, 4 and 5, presumably because of the more direct river influence. The polychaetes dominated benthic collections at all stations (Figure 7-12). Seventy-four percent of the OIlerall collections were canprised of polychaetes; the molluscs accounted for 15 percent, and others, including arthropods, rhynchocoels, chordates, and bryozoans, accounted for 11 percent. Stations 3, 4 and 5 exhibited greater numbers of molluscs than the stations farthest removed fran the mouth of the river. While the lIOlluscs and "others" comprised 34 percent of the total standing crop at stations 3, 4 and 5, they only accounted for 14 percent at stations 1, 2 and 6. Conversely, the rely chaetes dominated stations 1, 2 and 6 with 86 percent of the catches and accounted for only 61 percent of the collections at stations 3, 4 and 5. vrr-20 3Z00 3600 3200 3600 SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG 4000 4000 400 800800 400 2800 Z800 """'OJ ~ "-- 2400 Z400 V) "'I i§ ~ ZOoo ZOoo:::,. .... ~ .... ~ V) 1600 1600 0 ~ ~ ~ 1Z00 1ZOO o 0 SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG (SEPTEMBER 1975 - AUGUST 1976) LEGEND o ~ ST%I'JON 1 "~ST%I'JON Z += ST.KFION 3 X·:o:. ST.AT/ON 4 'l ~ ST%I'JON , ,,- ST%I'JON 6 Figure 7-11. Mean Monthly Benthos Densities in Trinity Bay. September 1975-August 1976 VII-21 STATION I 80 100 60 STATION 2 20 o I VZ////A VA 40 w u Z f- :: 60 40 20 Sept Oct Nov. Dec Jan. Feb. Mar. Apr May June July Aug. r~;i~if~~§lPOLYCHA ETA 1"""'''''''1 MOLLUSCA............. DOTHER Figure 7-12. Relativ.e Abundance of Major Benthic Groups in Trinity Bay, September 1975-August 1976 STATION 3 Aug.JulyJuneMayAprMarFebJon. ~ « o a z Dec.Nov.Oct.Sept. o ! V/////A V/////4 kI 20 20 STATION 4 o I W4/1! W/#/J W/ffi W/ff/A ~ 80 80 60 60 40 40 100 100 ~0 w u z « 0 z ::::> CO « w <: >H H f- I « N ...JW W a:: .POLYCHAETA II MOLLUSCA DOTHER Figure 7-12 Cont. STATION 5 STATION 6 o ! tf/P/A I I l/ Aug.JulyJuneMayApeMar.Feb.Jan.DecNov CD H f-I '" 0.05) were disoovered between Trinity Bay standing crop and river flow or bottom salinities. Benthic populations at stations 3, 4 and 5, under direct influence of the Trinity River, comprised 51 percent of the total standing crop during the study; stations 1, 2 and 6, exposed to tidal exchange or discharge of the Houston Ship Channel, comprised 49 percent (Figure 7-13). VII-25 Table 7-4. Nurrt>er of M:::nths in Iotlich Each Benthic Organism Constituted 30 Percent or More of the Total Standing Crq:> in Tdnity Bay, September 1975 August 1976 VII-26 SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG 100 100 90 80 70 70 zo VJ 0 60 roo ~ ~Q:l "'l ~ ~ r-0ht., 0 h oo~ F O~1:; I . , .' "~ t:l, 30 30 ·r 10 0 ] J'" ~--r,---,,---r,---,'---r,--.",---.,--.",---.,--" 0 SEP OCT NOV DEC JAN FEB MAR APR MAY fUN' JUL AUG (SEPTEMBER 1975 - AUGUST 1976) LEGEND 0..: STATIONS 1,2,6 .6. "" STA:I'IONS 3,4-".") Figure 7-13. Percentage Representation of Benthos Standing Crops in Trinity Bay, September 1975·August 1976 VII-27 Although oot statistically correlated with inflows or salinity, it appears likely that the benthic cxmnunity structure _s influenced by these factors nevertheless. For example, low standing crops in October through November 1975 and June through August 1976 probably occurred in response to the low salinity regime resulting from greater 'river inflows (Figure 7-14). SlIIlIlIary The cxmnunity CXJIIIPOsition, distribution, abundance, and seasonality of the P'lytoplankton, zooplankton, and benthic invertebrates' of the Trinity-San Jacinto estuary were employed as "indicators" of primary productivity. The estuarine communities were typical in that they were composed of a mixture of endemic species (Le., species restricted to the estuarine zone) and marine species plus several species with the osmoregulatory capabilities for pene trating fran the freshwater envirorunent. The upper Texas bays have never been dlaracterized by high plankton p::>pu lations (253, 32). High plankton counts observed in SOUth Texas bays are pre sumably influenced by higher salinities and shallow, clearer waters (23). Seven P'lytoplankton divisions represented by 132 taxa were collected from Trinity Bay. The diatoms were the nost taxonomically dominant group, account ing for 41 percent of the total number of P'lytoplankton species collected. 'A clear distinction in cxmnunity CXJIIIPOsition was discovered between stations 3', 4 and 5, directly influenced by the Trinity River, and the nore, saline sta tions 1, 2 and 6. A ,total of 70 zooplankton species representing nine P'lyla were identified during the 12-month study. The Arthropoda accounted fur 55 percent of the organisms identified. Regression analysis revealed 00 statistically signifi cant correlations between zooplankton standing crops and freshwater inflows. However, these factors did exhibit a regulating influence on species composi tion, seasonal occurrence, and distribution of zooplankton in Trinity Bay as evidenced by comparing stations. Six phyla represented by 72 benthic species were collected from Trinity Bay. The polychaetes, P'lylum Annelida, were the nost prominent organisms collected. Although not statistically correlated with inflows or salinity, the benthic cxmnunity appears to be influenced by these factors. The phytoplankton, zooplankton, and benthic assemblages in any body of water respond to a combination of physical and dlemical seasonal controlling factors. Thus, it is difficult to single out the influence of anyone of these factors on the entire corrmunity. Most estuarine organisms can be classified by salinity tolerance as oligohaline, mesohaline, polyhaline, or euryhaline. That is, there is always an assemblage of species which will be capable of maintaining high standing crops, regardless of the salinity, as long as it is relatively stable, and provided that other P'lysical and dlemical requirements for that particular assemblage are met. If freshwater inflow is decreased, either partially or totally, the oammunity composition will merely shift toward the neritic or marine (polyhaline and euryhaline) forms. The primary question, then, is how this shift affects the food dlain and the environment of those economically important organisms which, during rome stage of their life cycle, depend on freshwater inflow. VII-28 SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG 1:500 1~ 1ZOO 13.5 12 1.5 3300 1~0 1000 10.5 ,--.. C\l ~ 900 9 >... "- t/J .., '"'I ~~ ....'"'I ~ 7ro 7.5 ~::. .... ~ . ~ 0.., .... .., ~ 0 t/J 600 6 ~0 ~ ~Q:j ~O 4-.5 o 0 SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG (SEPTEMBER 1975 - AUGUST 1976) LEGEND O~BENTHOS "-SALINITY Figure 7·14. Mean Monthly Benthos Densities and Mean Monthly Bottom Salinities in Trinity Bay, September 1975-August 1976 VII-29 OJAPI'ER VIII FISHERIES Introduction Virtually all (97.5 percent) of the coastal fisheries species are con sidered estuarine-dependent (93)." During the five year period, 1972 through 1976, conmercial landings of finfish and shellfish in Texas averaged 97.3 million pounds (44.2 million kg) anrlually (475-479). Approximately75 percent of the harvest was taken offshore in the Gulf of Mexico and the remainder was taken inshore in" the bays and estuaries. COnputed on the basis of two general fisheries components, the finfish harvest distribution was approximately 28 percent offshore and 72 percent inshore, lItlile the shellfish harvest was of an j oppdsite distribution with abOut 21 percent inshore and 79 percent offshore. Specifically, the offshore harvests. accounted for about six percent of the total Texas red drum (redfish) landings, 17 percent of spotted seatrout land ings, 60 percent of lItlite shrimp landings, and 95 percent of brown and pink shrimp landings. With respect t9 commercial Texas bay l~dings from 1972 to 1976, bays of the Trinity-San Jacinto estuary contributed an average 11.0 percent of finfish landings and 45.4 percent of shellfish landings made from Texas bays. The estuary is the largest of eight major Texas estuarine areas and ranks first in shellfish and fourth in finfish. Based on the five year inshore-Qffshore com mercial laildings distribution, the. average oontribution of the Trinity-San Jacinto estuary to total (bays and Gulf) Texas commercial landings is estimated at 827,700 pounds (375,440 kg) of fish and 40,792,500 pounds (18.• 5 million kg) of shellfish annually. In crldition, the commercial fish harvest has been estimated to account for only aoo.ut 14.1 percent of the total fish harvest in the estuary, with the remainder (85.9 percent) <;ping to the sport or recreational catch (295r. " Thus, an crlditional 5,042,400 pounds (2.3 million kg) of sport catch can be computed lItlich raises the estimated average annual" fish harvest contribution from the estuary (both inshore and offshore) to 5,870,100 pounds (2.7 million kg). The average harvest contribution of all fisheries species (fish and shellfish) from the estuary is therefore estimated at 46.7 million pounds (2;.2 million kg) annually. Previous research has described the general ecology, utilization and management of the coastal fisheries (360, 180, 178, 88, 222, 218), and has provided information of Texas tidal waters (341, 346, 480, 202) and the re lationship of freshwater inflow to estuarine productivity (501). Also, prior studies in the Trinity~San Jacinto estuary have covered a wide range of topics dealing with the estuary's fish (361, 352, 130, 299, 324, 209, 208, 350), shrimp (500, 21,. 329), oysters (76, 300), and the effects of man-induced dis turbances and pollution (334, 292, 161, 158, 335, 518, 288, 316, 184, 206, 241). For a IIOre comprehensive listing of studies, the· reader is referred to Christman, Kochman, and Lippencott' s recent annotated bibliography of Galves ton bay fish and wildlife resources (494) which contains Oller 1,600 scien-" tific, engineering,. and economic references to the estuary. VIII-l 'I11e fluctuating contributions of freshwater inflow am associated nutri tive and sedimentary constituents from the Trinity River and Delta have been of continuing interest because of their P'lysical, cnemiCal, and biological effects on the estuary, particularly Trinity bay. In this regard, Diener (498) concludes that the q>timum salinity range in the bay is 10-17 ppt and that an estimated 2,000 cubic feet per second (118,800 acre-feet per nonth) of Trinity River inflow during March through OCtober is necessary to maintain the habitats. Copeland et al. (317) estimated that the upper Trinity Bay habitats were up to 72 percent dependent upon river-borne organic matter to, support the observed high secondary productivity of the area. More specifically, Parker et al. (23) conclude that a minimum 1.3 million acre-feet (1.6 billion m3) per year of Trinity River inflows may provide sufficient nutrients to sustain a low level of P'lytoplankton and marsh plant production in the Trinity Delta and Bay area. However, Soloman and Smith (25) suggest that I>.bile the bay is highly dependent upon the river inflows for salinity gradient maintenance, the bay may not be as dependent upon river-borne nutrients. Although an inverse correlation has been reported between' Trinity River flows and the bay's density of crustaceans (255), Coq>er (31) notes that excessive retardation of freshwater flow acted as a stress I>.bich hcrl synergis-: tic effects with increased effluent loading. Using 1958 through 1968 COIlIIler cial fisheries statistics, Parker and Blanton (24) hypothesize a reduction in seafood landings I>.ben average winter salinities exceed summer salinities as a result of high spring/sumner freshwater inflows to the estuary. In another attempt to correlate fisheries with inflows, Armstrong and Hinson (336) report an analysis of 1959 through 1964 records indicates that Galveston Bay dis placement rates exceeding twice per year apparently cause a decrease (Le., negative correlation) in total commercial harvests. Recognizing this analysis as rather gross, they further suggest that the estuarine system would produce larger comnercial catches with Galveston Bay water volume displacement rates less than 2.0 per year, estimating the maximum fisheries production to be near 0.5 per year or about 1.2 million acre-feet (1.5 billion m3) annually. Powell (264) examined the seasonal distributions of freshwater inflow at Trinity Delta and found several dichotanies in seasonal inflow distributions associated with the "best" versus "worst" five harvest years in the 1962 to 1976 comnercial fisheries records. Additionally, negative correlations ~re reported between oyster harvests and September-october inflow, and brown am pink shrimp harvests and March-May inflow (264). However, multivariate equa tional models of fisheries production fran several important species as a function of the effects of seasonal freshwater inflows have not been previous ly constructed. Data and Statistical Methods Direct analysis of absolute fisheries bicrnass fluctuations as a function of freshwater inflow is not possible because accurate bicrnass estimation requires either considerable experimental calibration of current sampling methods (141) or the developnent and application of higher technologies such as the use of high resolution, a:xnputer interpreted, oonar soundings for estimation of absolute fish abundance (41). Therefore, rome indirect or relative measure of the fisheries must be substituted in the analysis. In terms of measurement, precision is a major consideration of relative estimates, I>.bile accuracy is of paramount importance to absolute estimates of abundance (14 1) . VIII-2 Prior research has dem::mstrated that variations in rainfall and/or river discharge are associated with variations in the catch of estuarine--dependent fisheries, and can be used as an indicator for finfish and shellfish production (115, 96, 95, 423, 238, 237). Therefore, oomffiercial harvest can be useful as a relative indicator of fisheries abundance, especially if the harvest is not critically limited below the production available for harvest on a long-term basis (Le., the surplus production) by market conditions. Similarly, annual harvest variations can provide relative estimates of the fisheries biomass fluctuations occurring from year to year. In Texas, commercial harvest data are available from the Texas Landings, publications (481-487, 472-479) which report inshore harvests from the various bays and offshore harvests from the Gulf of Mexico. Since the offshore har vests reported in Texas Landings represent collective fisheries production from the western Gulf region's estuaries, it is the inshore harvests reported by estuarine area that provide fisheries data related to a particular estuary. In addition, the offshore shrimp fishery is partitioned into shrimp fishing grid wnes in the Gulf tted Finfish c/: Seatrout Red Drum Black Drum ;:i H H I ... 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 5,254.1 6,736.8 9,534.1 10,599.6 7,382.2 6,227.8 7,203.1 9,438.0 12,097.7 11,196.4 9,485.0 9,184.4 6,634.8 7,855.9 10,058.2 3,324.4 3,027.2 4,700.7 3,066.2 1,260.0 1,038.8 2,514.0 3,809.6 4,069.5 2,963.8 2,956.7 4,063.4 2,392.4 3,927.2 3,358.2 868.5 600.8 717.0 1,132.2 681.1 1,148.5 307.8 475.5 1,556.0 2,050.1 1,398.5 951.6 1,422.6 828.4 1,802.0 311.3 977.5 1,195.6 1,817.9 1,357.8 1,047.9 1,542.6 1,705.7 2,622.0 2,160.8 1,870.1 2,040.0 1,983.1 1,863.5 1,599.5 749.9 2,131.3 2,920.8 4,583.3 4,083.3 2,992.6 2,838.7 3,447.2 3,850.2 4,021.7 3,259.7 2,129.4 836.8 1,236.8 3,298.8 59.9 159.0 411.0 413.4 350.5 635.1 333.4 278.1 264.7 155.3 ·295.8 498.6 446.2 452.9 445.4 17.0 142.9 176.9 277.0 161. 7 280.4 174.2 55.7 89.2 75.9 128.4 232.8 272.9 221.0 181.5 2.6 1.3 25.7 32.2 29.8 45.0 21.2 38.1 35.3 18.1 33.6 49.6 34.9 79.5 97.5 11.9 7.9 62.4 23.9 29.1 124.9 54.4 44.6 39.0 25.2 72.7 93.0 27.6 46.4 47.4 Mean 8,592.6 +S.E. 31 +516.1 3,098.1 +206.6 1,062.7 +129.4 1,606.4 +146.0 2,825.4 +306.6 346.6 +38.7 165.8 +21.3 36.3 +6.5 47.4 +8.1 a! Estuary ranks first in shellfish and fourth in finfish colTlTlercial harvests of eight Major ~xas--estuar1ne areas b/ Mul ti-species fisheries corrponent includes blue crab, bay oyster, and white, brown, and pink shrimP harvests c/ Multi-species fisheries conp::ment includes croaker, black drum, red drum, flounder, sea catfish, spotted seatrout, - and sheepshead harvests 31 Standard error of mean; two standard errors provide approximately 95 percent confidence limits about the mean Table 8-2. Offshore Conrnercial Penaeid Shrimp Harvests in Gulf Area No. 18 ai, 1959-1976 (503-512, 519-526) - White Shrimp b/ Brown and pink Shrimp c/ All Penaeid Shrimp d/ Year Harveste/: Effo_rt_ f/ Harvest Effort Harvest Effort ;:i ..... 7 Ul .1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 . 1974 ··1975 1976 Mean 2:S•E• sI 2,279.1 2,344.8 1;372.6 .1,409.8 1,988.2 2,513.1 1,851.8 2,018.5 2,049.8 2,515.3 3,445.7 3,822.1 3,851.0 3,195.9 4,064.7 4,893.6 3,287.5 3,482.4 2,799.2 +234.0 4,209.9 6,210.3 3,929.1 3,445.2 3,595.1 4,124.2 4,176.7 4,591.1 6,992.7 4,170.6 5,049.9 4,754.4 7,009.6 6,315.3 5,613.2 8,149.0 6,238.4 5,260.2 5,213.0 +317.3 8,222.7 11,831 .6 4,022.2 3,520.3 5,655.3 4,404.6 6,630.0 4,543.2 17,740.1 ·3,426.4 3,716.3 4,591.1 11,637.2 6,811.4 2,988.0 13,019.2 6,482.9 10,015.7 7,181.0 +970.0 4,520.7 6,389.6 4,192.4 3,763.7 3,933.2 4,344.4 4,410.7 4,692.6 7,294.4 ·4,436.7 5,399.7 5,192.9 7,355.9 6,851.9 6,191.9 9,002.2 6,660.2 6,192.9 5,601.4 +344.0 10,502.7 14,176.8 5,403.9 4,930.6 7,684.2 6,921.9 8,484.7 6,572.8 19,790.1 5,945.1 7,162.0 8,416.2 15,492.7 10,027.1 7,059.6 18,070.6 9,.776 .1 13,498.1 9,995.3 2:1 ;042.4 4,520.7 6,389.6 4,192.4 3,763.7 3,933.2 4,344.4 4,410.7 4,692.6 7,294.4 4,436.7 5,399.7 5,192.9 7,355.9 6,851.9 6,191.9 9,002.2 6,660.2 6,192.9 5,601.4 +344.0 , a/ Gulf-shrimp ffShfng -giidArea No.--fS-lies -directly offshOre· fran the Trinity-San - Jacinto estuary 15j-White shrimp harvest and fishing effort at depths < 20 fathans "2/ Brown and pink shrimp harvest and fishing effort at all depths recorded d/ White, Brown, and pink shrimp harvest and fishing effort at all depths recorded e/ Whole Shrimp harvest. weight in thousands of pounds estimated by tail weight X - 1.54 (White shrimp), i 1•.61 (Brown shrimp), and X 1.60 (pink shrimp) f/ Fishing effort in number of fishing trips by.shrimp vessels ~ Standard error of rean; t~ standard errors provide approximately 95 percent confidence limits about the mean " ... Linnaeus), and brown and pink shrimp {Penaeus aztecus Ives and P. duorarum Burkenroad, mostly P. aztecus}. Other fisheries components are generally given as a single sPecies or species group of interest. Freshwater inflow' to the estuary is discussed in Chapter IV and is tabulated here on the basis of three anayltical categories: (1) freshwater inflow at Trinity Delta (Table 8-3), (2) freshwater inflow from San Jacinto River basin (Table 8-4), and (3) combined freshwater inflow to Trinity-San Jacinto estuary from all contributing river and. coastal drainage basins (Table 8-5). Each inflow category is thus specified by its historical record of seasonal inflow volumes. The effects of freshwater inflow on an estuary and its fisheries produc tion involve intricate and imperfectly understood physical, chemical, and bio logical pathways. Moreover, a complete hypothesis does not yet exist from which an accurate structural model can be constructed that represents the full spectrum of natural relationships. As a result, an alternative analytical procedure must be used which provides a functional model, that is, a procedure which permits estimation of harvest as a unique function of inflow. In this case, the aim is a mathematical description of relations arrong the variables as historically observed. Statistical regression procedures are nost 0 ~ ~ WOO ~ •~ 7000 0 ~ 1000 •E E ~OOO 0 U '00' 3000±:--"I-~-~~-,~-~-~-~---,-~--I ~ ~ ~ m U~ = ~ ~~ 2QO 27m = Mean Monthly Inflow (1000 ac-f!) APR-JUN A. regression coefficient (slope) =-2.43, standard error = ±1.01 13000 0'''' n 11000 0 0g .,'" · · ~,> 0 ~ ~ ~, ·~ · ~ 7000~ 0 ~ 1000 •E E woo 0 U 4000 13000 12000 · n 11000 0 0g 10000 ·: ."', 0 ~ ~ '00' •~ '''''~ 2 '''''~ E E '''''0u ."', '00' ±,,,,:--c:pr.,-~,~..:-~,":--:,:Cw:--.",~,-~":C'-~'''oo:--,..r,-~,~,"-,--1,oo l.4eon Monthly Inflow (1000 oc-ff) JUl-AU~ B. regression coefficient Islope) = +8.55, standard error = ±2.82 ,"oo:!--~--".:--,c--,-c-~-~-~---,-~--J ICO 3~O ISO no 1260 e:lC (5.1,0 21~ H20 2710 3000 Mean 1.401"1 t h IY Inflow (1000 oc- If) APR-JUN 1-yr. on t eceden t C. regression coefficient (slope) = +1.33, standard error =±0.46 Figure 8-1. Inshore Commercial Shellfish Harvest as a Function of Each Seasonal Inflow From Combined River and Coastal Drainage Basins, Where all Other Seasonal Inflow in the Multiple Regression Equation are Held Constant at Their Mean Values VIII-14 - 0= '$ 11000 0 0 t 10000 · ~ooo> 0 ~ ~ "'~ •£ ,,~ ~ 0 0 .= •E E ,~, 0 u ,~. - 0= ~ _. g t ... . ttoOO .. ~"'"" ~ 7000 ,~, ~~ .:±:-,-CV',---=-,.r,---=-,."-,""'"-,O"',---:,"'",----=-,T"':---=-_,-O,,!:.--~:J iolean l.4onlhly Inflow (1000 at-H) JUL-AUG l-yr. anhcedent D. fllgrlluion coefficient islopel :;:: -12.16, standard error:;; ±2.04 .~, 12000 '" ~ -0 0 t ..., ·~ .= 0 ~ ~ "'.. •£ ,~. ~ 0 ~ -•E E ""'.0 u ..~ ~.. 4m,---,"",----=,T..:---=...,-,c""'r:--:Vo.'-,-C,"..=.-o""o.-o,"'r.-,=."..=_-,::!... toloxlmum Monthly Inflow (1000 ac-tt) NOY-DEC 1-yr. antecedent E. See Tobie 8-7 for regression coefficient" and .tondord error ..~.J-.-~--~-~--~-~-~--:T-""'--~-~ tOO S!lO 1000 uso lIOO 23!M1 2100 :521)0 5700 ~':lO 4fl10 Ioloxlmum t.lonlhiV Inflow (1000 at-til APR-JUN F: See Tobl. 8.7 for regression coefficienh and standard .rrors Figure 8-1. (Continued) VIII-1S of 157.0 thousand acre-feet per nonth to its observed upper rounds of al:x:>ut 3.0 million acre-feet per nonth. Thus, the negative (-) sign on the regres sion coefficient (a2) for the Q2 inflow term in the equation is illus trated as a line of negative slope relating increasing spring season inflow to a decreasing estimate of annual harvest. It is noted that this line can be shifted upward or downward in a parallel manner fran that ~ich has been graphed by holding any of the other rorrelating seasonal inflow terms in the equation at specified levels of interest other than their mean observed. values. For instance, if the p:>sitively rorrelating July-August (Q3) inflow term is specified at some level lower than its mean of 334.6 thousand acre feet per nonth ~ile the other inflow terms in the equation remain at their mean observed values, then the estimated harvest response to April-June (Q2) inflow w::>uld be similar to that shown in Panel A (Figure 8-1) and w::>uld have the identical negative slope;. however, the o::JIIIputed line w::>uld be shifted downward and parallel to that ~ich is graphed. Analogous circumstances exist for each of the harvest responses illustrated, but to facilitate o::JIIIparisons only the seasonal inflow of interest in each panel graph is varied, ~ile all others in the equation are held ronstant at their respective mean values. Panel B (Figure 8-1) exhibits the positive response of shellfish harvest to summer season freshwater inflow from the same year as harvest. The esti mate of harvest increases 1.9 times (from al:x:>ut 6.7 to 12.5 million pounds annually) as the July-August (Q3) inflow increases fran its observed lower rounds of 112.5 thousand acre-feet per IlDnth to its observed upper bounds of 798.0 thousand acre-feet per nonth. Panel C (Figure 8-1) shows another positive harvest response to fresh water inflow. In this case, the estimate of shellfish· harvest increases 1.5 times (from al:x:>ut 7.2 to 11.0 million p:>unds annually) as the 1-year ante cedent April-June (Q2) inflow increases fran 157.0 thousand acre-feet per month to about 3.0 million acre-feet per IlDnth. Canparing Panel A to Panel C indicates that ~ile spring season inflow fran the same. year as harvest are negatively related to shellfish harvest, spring season inflow fran 1-year antecedent to harvest are positively related to shellfish harvest; however, the rombined effect of both inflow terms in the equation is negative since the negative regression coefficient is larger than the p:>sitive one. The dicho tomy in harvest response to spring season inflow is probably due to the ron tent of the multi-species fisheries =ponent for shellfish, since the component rontains species that may be greater affected by inflows during the same year as harvest (e.g., brown shrimp) and species that may be greater affected by inflows 1-year antecedent to harvest (e.g., bay oyster). Summer season inflow 1-year antecedent to harvest (Q-3) exhibits a strong negative relationship to shellfish harvest and the harvest estimate declines 72.7 percent (from about 11.5 to ··3.1 million p:>unds annually) as July-August inflow increases from 112.5 thousand acre-feet per nonth to 798.0 thousand acre-feet per nonth (Panel D, Figure 8-1). similar to the previous example, a CXlllIparison of Panels B and D indicates differential responses of harvest to the timing of this season I s inflow. Again, a probable explanation for the estimated positive harvest response to inflow in the same year, and negative response to 1-year antecedent inflow in the same season, may be found in the multi-species =position of the shellfish fisheries o::JIIIponent ~ere divergent species responses to inflow appear (also see Table 8-16). VIII-16 A slight negative relationship of shellfish harvest to the square of the l-year antecedent maxiJm.un llOnthly inflow in the late fall season (Max Q-5) suggests a negative effect of high inflow events (Le., floods) fran this season on harvest. Panel E (Figure 8-1) illustrates this effect as a 47 percent decline in the estimate of harvest (fran about 9.1 to 4.8 million pounds annually) as the maximum llOnthly inflow in the November-December seasonal interval increases fran 191.0 thousand acre-feet to about 3.2 million acre-feet. Panel F (Figure 8-1) displays the effect of the last two inflow terms (Max Q2) and (Max Q2)2 in the shellfish harvest equation (Table 8-7). These are considered together because they both relate to the effect of maxi mum llOnthly inflow in the spring season on shellfish harvest. The effect is quadratic (Le., the highest p;:>wer of the variable is a square, thus (Max Q2)2 is a second degree term) and is illustrated as a convex curve with its maximum harvest estimate of about 10.5 million p;:>unds annuapy occurring at a maximum llOnthly spring· season inflow of about 2.3 million acre-feet. The computed relationship indicates that while llOderate allOunts of spring (April June) inflow are beneficial , high inflows appear detrimental to shellf ish canponent harvests. All Penaeid Shrimp Analysis of the inshore fisheries component for bay landings of all penaeidshrimp.(Le., white, brown, and pink shrimp) did not yieldany signi ficant relationships, However, analysis of the offshore penaeid shrimp har vest (Gulf Area No. 18) results in a highly significant (ex = 1.0%) multiple regression equation (Table 8-8), where harvest is expressed as a function of the offshore fishing· effort (Eo) and the seasonal freshwater inflows to Trinity San-Jacinto estuary from all contributing river and coastal drainage basins (FINC inflow category). The equation accounts for 87 percent of· the observed harvest variation and includes regression variables for winter, spring, and summer inflow, .as well as.for offshore fishing effort. The effect of each of the correlating terms in the highly significant equation is illustrated by using the previously discussed procedure of holding all other correlating terms in the equation constant at their respective mean values, while varying the term of interest over its observed range and comput ing the estimated harvest response (Figure 8-2). The estimate of offshore shrimp harvest is thus shown to decline 41. 1 percent (fran about 12.0 to 7.0 million pounds annually) as January-March (Ql) inflow increases fran its observed -lower bounds of 80.3 thousand acre-feet per llOnth to its observed upper bounds of about 2.0 million acre-feet per IIDnth (Panel A, Figure 8-2). Panel B (Figure 8-2) exhibits the negative relationship of harvest to spring season inflow. In this case, the estimate of offshore shrimp harvest declines 34.9 percent (from about 11.4 to 7.4 million p;:>unds annually) as April-June (Q2) inflow increases fran 157.0 thousand acre-feet per llOnth to about 3.0 million acre-feet per llOnth. The p;:>sitive effect of summer inflow is shown in Panel C (Figure 8-2), where the harvest estimate increases 1.4 times (fran about 8.9 to 12.6 million pounds annually) as July-August (Q3) inflow increases fran 112.5 thousand acre-feet per llOnth to about 1.2 million acre-feet per llOnth. VIII-17 Table 8-8. Equations of Statistical Significance Relating -the All Penaeid Shrimp Fisheries Component to Freshwater Inflow Categories 51 _Trinity-San Jacinto EstuaJ:Y All Shrimp Harvest = f (seasonal FINTD!?j) (no significant equation) Trinity-San Jacinto EstuaJ:Y All Shrimp Harvest = f (seasonal FINSJ EI) (no significant equation) Trinity-San Jacinto All shrimp Harvest = f (seasonal FINC !¥) (no significant equation) Trinity-San Jacinto EstuaJ:Y Offshore All Shrimp Harvest = f (seasonal FINC +Eo) Very Highly Significant Equation (C/.= 0.1%, r 2 = 87%, S.E.Est. = ;!:1,832.0) OH as = -1,484.3 - 2.57 (01) ( 1. 06) - 1.42 (02) (0.63) + 3.56 (03 ) (1.87) + 2.46 (Eo) (0.31) upper bounds lower bounds mean Where: OH =as E =o o = OHas 0 1 O2 03 Eo ---------- ._----~-------------- 19,790.1 1,996.3 2,962.0 1,150.0 9,002.2 4,930.6 80.3 157.0 112.5 3,763.7 -=..9L:.'9:.:9;.::5.:...3=--_..c8:.:3:.::8.:...3=--_-.:,11-'1:..:2::::9.:...9:::- 4~1:.:7.:... ::.3_ 5, 601•4 ----------------------- offshore commercial penaeid shrimp harvest (Area #18), in thousands of p:>unds; offshore harvest effort (Area #18), in nUllDer of fishing trips; mean nonthly freshwater inflow, in thousands of acre-feet: 01 = Jan.-Mar. 02 = Apr.-Jun. 03 = Jul. -Aug. 04 = Sept.--{)ct. 05 = Nov. -Dec. 51 Standard error (+) of each regression roefficient is shown in parentheses beneath the coefficients of the regressioo equations bl FINTD = Freshwater inflow at Trinity Delta(51 FINSJ = Freshwater inflow from San Jacinto River ~ FINC = Combined freshwater inflow to the estuaJ:Y fran all contributing river and coastal drainage basins VIII-18 •.,,----------------------, •., ~ lU o :::I: 13.4 !t5 12.0 "• ••~ a •.,,------------------, j U.6 ., ~ 14.6 o ::r: 13.4 ~ {j; 12.0 ~ Q> 10.6 ! a •., ,.• ... •., *,"O.,--C,700"O.,-.7":c.,,---.,,,,:c.,'---.:J00':c"'---~=MC:-tl=00c:-:.o,---,,,:r,"O.,--C.:r,,"0.'--=."'00"0.,-:12\)00.0 Mean Monthly Inflow (1000 oc-H) JAN-MAR A. regreuion coefficient (slope) ::::-2.57, standard ~rror =±I.06 o ~ •E, u •• ,., +,"O.,-,:Joo~.~, __:,,~,"O.,-.',~,.,,---"Otl:r,,-:.,---:,,~,=,.~, -,,=,:r,=.,--:,~'oo~.,,---,=,,","O,~,,"',~,.,--=,::\ooo.o Meon Monthly Inflow (1000 ac-f!) APR-JUN B. regression coefficie.nt [slope) ::: -1.4f, 'standard error::: 1:0.63 18.0 ~ o. ., g " u. •t 0 Z G.' ~ E L 12.0 ~ " 1M ·~ a "~ 0 c ,. •E E 0 u .. ,., -1:'00=.:-'"O,"MC:-"O""'.:-'---::"CCo.o:-c,"..::;.,---::.7,,=.,--=,",oo"O.,--=~",.:-,--=.",>::.,:-C.:J.:c,.,:-::i1200.0 Mean Monthly Inflow (1000 ac-H) JUL-AUG C. regression coefficient {slope) ::: +3.56, stondard error::: ±1.87 •., " 0.' D ., 0 v " ,.. · > 0 Z 13.J ~ E L 0.' ~ " 10.6 ·! a •., ~ 0 • ,..E E 0 u ... ,., +--~-~--~-~---:=.,__=___:=___:___:'CC__:T"__=::1 3~()ll.OI100.0 .700.0 5300.0 51100.0 6500.0 7100.0 7700.0 8300.0 8900.0 li500.0 Annual Numb~r' of FishIng Trfps D. regression c,?efficient (slope} .= +2.46, standard error = ±O.31 Figure 8-2. Offshore Commercial Penaeid Shrimp Harvest as a Function of Fishing Effort and-Each Seasonal Inflow From Combined River and Coastal Drainage Basins, Where all Other Seasonal Inflows in the Multiple Regression Equation are Held Constant at Their Mean Values VIII-19 As might be anticipated, fishing effort appears p:>sitively related to shrimp harvest (Panel D, Figure 8-2). Specifically, the estimate of harvest increases 3 •3 times (fran about 5.5 to 18.4 mill ion p:>unds annually) as fishing effort increases fran about 3.8 to 9.0 thousand fishing trips per year by shrimp vessels. White Shrimp Analysis of the inshore mite shrimp a:xnponent also did not yield any significant relationships. However, analysis of the offshore mite shrimp harvest (Gulf Area No. 18; catch at < 20 fathoms depth) gives a highly signi ficant (ct = 1.0%) equation (Table- 8-9) that explains 61 percent of the observed harvest variation as a function of offshore fishing effort (Eo) and spring, SllllU1ler, and autumn season freshwater inflows to the estuary from all contributing river and coastal drainage basins (FINC). The effect of spring season inflow is a:xnputed to be p:>sitive and the estimate of, offshore mite shrimp harvest increases 1.4 times (from about 2.5 to 3.4 million pounds) as April-vune (Q2) inflow increases aver .its observed range (Panel A, Figure 8-3). On the other hand, Panel B (Figure 8-3) shows the harvest estimate declining 35.1 percent (from about 3.1 to 2.0 million pounds annually) as July-August (Q3) inflow increases aver its, observed range. Another p:>sitive relationship of harvest to inflow is shown in Panel C (Figure 8-3), mere the harvest estimate increases 1.5 times (from about 2.5 to 3.8 million pounds annually) as September-october (Q4) inflow increases from 85.0 thousand acre-feet per month to about 2.1 million acre-feet per month. Again, fishing effort (Ee) is p:>stivily related to harvest with the harvest estimate increasing 2.1 times (from about 2.0 to 4.2 million pounds annually) as effort increases from about 3.4 to 8.1 thousand fishing trips per year (Panel D, Figure 8-3). Brown and Pink Shrimp Analysis of the fisheries oomponent for brown and pink shrimp results in four significant regression equations (Table 8-10). The best significant equation (fourth equation, Table 8-10) accounts for 80 percent of the observed variation in offshore harvest (Gulf Area No. 18) and is very highly signifi cant ( ct = 0.1%) for correlation of harvest to fishing effort (Eo) and winter, spring, summer, and autumn season freshwater inflows to the estuary from all contributing river and coastal drainage basins (FINC). The effects of each of the variables in the best significant equation are shawn in Figure 8-4. A negative relationship of harvest to winter inflow is shawn in Panel A (Figure 8-4), mere the estimate' of harvest declines 44 per cent (from about 8.7 to 4.9 million pounds annually) as January-March (Ql) inflow increases aver its observed range. Panel B (Figure 8-4) also displays a negative relationship of harvest to spring season inflow. Here, the harvest estimate declines 56.4 percent (from about 8.9 to 3.9 million p:>unds annually) as April-vune (Q2) inflow increases aver its observed range. On the other hand, the estimate of harvest increases 1.9 times (fran about 5.6 to 10.9 million pounds annually) as July--August (Q3) inflow increases aver its observed range (Panel C, Figure 8-4). Another negative relationship, in this case with autumn season inflow, is illustrated in Panel D (Figure 8-4), mere VIII-20 Table 8-9. Equations of Statistical Significance Relating the Vl1ite Shrimp Fisheries Coop:>nent to Freshwater Inflow Categories !y ---------------- Trinity-San Jacinto Estuary White Shrimp Harvest = f (seasonal FINTO!?I) (no equation) Trinity-San Jacinto Estuary White Shrimp Harvest = f (seasonal FINSJ Ell (no equation) Trinity-San Jacinto Estuary White Shrimp Harve9t = f (seasonal FINC 9() . (no equation) Trinity-San Jacinto Estuary Offshore White Shrimp Harvest = f (seasonal FINC +~) . Highly Significant Equation «1= 1.0%, r 2 = 61%, S.E. Est. = .:!:. 710.5) O~s =102.5 + 0.32 (Q2) (0.23) - 1.06 (Q3) (0.75) + 0.63(Q4) (0.41) + 0.47 (Eo) (0.13) , upper bounds lower bounds mean O~ Q2 Q3 Q4 Eo 4,893.6 '---2,-962.0 ---f;-150.0-"2;fll.5·-----8","149.0 1,372.6 157.0 112.5 85.0 3,445.2 .::;2.<..,7;.,;9;.;;9;.;;•.",2__-,-1.!-';.,;12;.,;9...:•.;,.9 417 •~_ 532.~ 5 , 213 •0 Q ----_._---------_._-----------------------------_._------- --- Where: OHws =. offshore conmercial white shrimp harvest, « 20 fathoms, Area#18 ), in thousands of p:>unds; - Eo = offshore harvest effort « 20 fathoms, Area #18), in nUllber of fishing trips; - = mean monthly freshwater inflow, in thousands of acre-feet: Ql = Jan.-Mar. Q2 =Apr.-Jun. Q3 = Jul.-Aug. Q4 = Sept.-oct. Q5 = Nov. -Dec. !y Standard error (+) of each regression coefficient is shown in parentheses beneath the coefficients of the regression equations b/ FINTO = Freshwater inflow at Trinity Delta c/ FINSJ = Freshwater inflow from San Jacinto River 'd/ FINC = Combined freshwater inflow to the. estuary fran all contributing river an~ 90astal drainage basins VIII-21 ~200.0 '970.0 "~ 0 '740.0 0 ~ 35jO.0 · > 0 3290.0r 0 E '050.0 ~ ~ · 2920.0 ~ 0 2590.0 0 E 2'80.0 E 0 0 2130.0 4200.0 " '970.0 ~ 0 '740.0 0 ~ " '510.0 · > 0 '280.0r "E " '050.0 ~ ~ • 2820.0~ " <; 25110.0 ~ • 2360.0E E 0 0 21,o.0 1900.0 j'-OO-.O~"OO-.O'---C..COc.O-C"rO-.O~,-"rO-O~""'CO.-O~'~~O.Co'---"'"=.o'---,=,r,,-.o'---,=,r,,c.o---',,.Iooo.o Mean Monthly Inflow (1000 oc-fl) APR-JUN .' 1900.0 j,=ooc.o---"'ro=.o-C"O:oC.o-,c.,r:o.=o-'c,C"o.:,-;.J"C,o;-~,~oo~.';-:""o~,,;'-~..~o~,O~'~M:;O~,'-;o~oo,o Mean Monthly Inflow (1000 o<:-ft) JlJl-AUG A. reg.ression coefficient (slope) :: +0.32, standard error:: ±0.23 8. re'gression coefficie'nt (slope) =-'1.06, standard 'error ~ ±0.75 ,'r I 2130.0 3970.0 o 3TMJ.0 o ~ · :!: 2920.0 ~ ", 2"0.0 4200.0 3970.0 " ~ 0 3740.0 0 ~ 3510.0 ~ C' 0 3290.0 ,r 0 E .. ' ~ ;J050.a ~ · 2920.0 ~ ~ 2590.0 0 E 2'60.0 ~- E 0 u '510.0 3290.0 4200.0,-------~~~~~~~~~ ~, " · > o r 2590.0~ o E 2360.0 .! , aoo.o +oc.o,---c"co=,o,---c,,'-o=.o-'=''="O.cO---'M"OC.O:-c,'oo=.o:-c,,:r,,=.o:-,="roCo'---v=.ro=.o'---.=.co.=o'---,,~oo.o Mean Monthly Inflow' (1000 ac-:-f1) SEP-QCT ,r, 1900.0 +,=,Coo=.•=.",c,.c,-.C,:roC,.o:-,=.Too=.,:-':,=,rooC.,---'.CooC,=.,,---~:r:o,C,--::,,"oCo:o -.,=.:roo=.,:-~CToo="---:,,.Iooo.o Annual Number of rlshlng Trips C. regression coefficient (slope,) = +0.63, standard error = ±0.41 D. regression coefficient (slope) :: +0.47, standar~ error:: ±0.13 Figure 8-3. Offshore Commercial White Shrimp Harvest as a Function of Fishing' Effort and Each Seasonal Inflow From Combined River and Coastal Drainage Basins, Where all Other Seasonal Inflows in the Multiple Regression Equation'are Held Constant at Their Mean Values VIII-22 Table 8-10. Bquations of Statistical Significance Relating the Brown and Pink Shrimp Fisheries Conp:>nent to Freshwater Inflow Categories a/ TrinitrSan Jacinto Estuary Brown and Pink Shrimp HaJ'Vest = f (seasonal FINTDb/) , Significant Natural Log EqUation ( Cl= 5.0%; r 2 = 44%; S.E. Est. = + 0.4225) In,Hbps = 8.6836 - 0.4365 (In Q2) + 0.1~53 (In Q) (0.1461) (0.1221) upper bounds lower bounds mean In Hbps 7.6256 5.7295 6.8526 7.4487 4.0553 6.1312 5.8985 1,6094 4.3296 --------------------------------------------------------, , Trinity-San Jacinto Estuary Brown and Pink Shrimp Harvest = f (seasonal FINSJc/) , Significant Natural Log Equation, ( ci= 2.5%, r =:.64%, S;E. Est. = + 0.3685 In Hbps ~ 7.9740 ~ 0.5585 (In Ql) (0.1552) + 0.2653 (In Q5)' (0.1556) , , - 0.5740 (In Q3) + 0.6573 (In Q4) (0.4133) (0.2311) In. ~bps In Q1 In Q3 'lnQ " 4 upper bounds 7.6256 5.9330 5.6595 6.4077 lower bounds 5.7295 3.4563 4.2268 3.7842 mean 6.8526 4.8498 4.7077 4.6592 6.3483 3.4012 4.6256 -------------------------------------------'----~ Trinity-San Jacinto Estuary Brown and pink Shrimp Harvest = f (seasonal, FINed/) ; Significant Natural Log Equation ( Cl= 5.0%, r = 61%, S.E. Est = + 0.3834) In Hbps ~ 6.8224 - 0.4977 (In Ql) (0.1597) + 0.3160 (In Q5) (0.1749) - 0.2995 (In Q3) (0.2060) + 0.4955 (In Q4) (0.1618) upper bounds lower bounds mean 7.6256 5.7295 6.8526 7.3000 4.3858 6.3280 ,6.6821 4.7230 5.6339 7.6552 4.4427 5.8689 7.8665 4.9053 6.1993 -----------------------------.-----------------------------------_.(continued) VIII-23 Table 8-10. Equations of Statistical Significance Relating the Brown and pink Shrimp Fisheries COmponent to Freshwater Inflow Categories a/ (cont'd) - Trinity-San Jacinto Estuary OffShore Brown and pink ShrliiP Harvest = f----- (seasonal FINC + Eo) Very Highly Significant Equation (Ct = 0.1%, r 2 = 80%, S.E. Est. = 2:2194.0) OHbps = -1836.6 - 1.99 (Ql) (1.40) + 5.03 (Q3) (2.33) - 1.67 (Q4) ( 1.43) + 2.05 (Eo) (0.38) 9002.2 3763.7 5601.4 2111.5 85.0 532.4 1150.0 112.5 417.3 2962.0 157.0 1129.9 1996.3 80.3 838.3 OHbpS Q1 Q2 Q3 Q4 Eo-~_=._-------------------------- 17,740.1 2,988.0 7,181.0 upper bounds lower rounds mean -------_. Where: In Hbps = OHbps = Eo =Q = In Q = natural log, inshore carmercial brown and pink shrimp harvest, in thousands of pounds; offshore rorrmercial brown and pink shrimp harvest (Area #18), in thousands of pounds; offshore harvest effort (Area #18), in number of fishing trips; mean monthly freshwater inflow, in thousands of acre-feet; natural log of Q: Ql = Jan.-Mar. Q2 = Apr. -Jun. Q3 = Jul. ~Aug. Q4 = Sept.-oct. Q5 = Nov. -Dec. y Standard error (+) of each regression coefficient is shown in parentheses beneath the coefficients of the regression equations b/ ·FIN'ID= Freshwater inflow at Trinity Delta c/ FINSJ = Freshwater inflow from San Jacinto Rivery FINC = Combined freshwater inflow to the estuary fran all contributing river and coastal drainage basins VIII-24 1~.0,---------_-------------, ~ a.' a •t "" 0 ~ 0 E 10.2 ~ ~ ~ •.,, ~ ~ '"0 ", ••~ ro 0 ... ~ •E .., E 0 u ,., 4,c.,c.-=,~"c,:-C,oo"',:-c"',c.,-,c,r,.c,-=,c,,c,~.,-.',~,.~,~,,",~,.~, -""T,~.,-,~.T,,~.,-,-jooo.o Mean Monthly Inflow (1000 ac-H) JAN-MAR A. regression coefficient (stope} =-1.99, standard error =±1.401~.0 ,-------=-..::.:-=-::-'-'''-''"--~-=-'-------, ~ 12.6 a ·t a.0 ~ 0 ~ 10.2 ~ t .., ~ ~ ,.. "0 ", ...0 ro 0 ... ~ E '"E 0 u " 100.0 210.0 '20.0 .30.0 3.0.0 630.0 760.0 570.0 i50.0 10iO.0 1200.0 Mean Monthly Inflow (1000 ac-f!) JUl-AUG C. regression coefficient (slope} = +5.03, stondard error =±2.33 1~.0'----- ·'::"' ~1 13.8 13.0,-------------------- , 13.8 ~ ... •t 11.40 ~ 0 E m.' < ~ ~ •.,, ~ ~ ,.• 0 ", ..•~ ro 0 .., ~ •E .., E 0 u ,., 4,C.,:-C,T"=.,:-C"T,=.,-C"",c.,-,c,,c:,c,-=,c,,c,c,-=,,",c,.c,-="""c.,:-,C.T"C.,:-,=,T"C,:-,::!ooo.o Mean Monthly Inflow (1000 ac-f!) APR-JUN B. regression coefficienf (slope) =-1.79, standard error = ±0.7513.0 , ...:.:..::.:..::.:'-''-'CC::-_~-=-.::... , 13.6 ~ 12.6 · > 0 ""~ 0 E 10.2 < ~ ~ •.,, ~ ~ ,.• 0 ", ••~ ro ~ ,. 0 E .0 E 0 u 3.0·~,.,:-C"o:,=.,-.'.C...:-C..O:,C.,---:"",C,:-C",',C,--="",C,,:-,C..C:,C.,-=,:i"C.,:-.C.c:,.C'--:::!2200.0 Mean Monthly Inflow (1000 ac-ft) SE:P-OCT D. regression cpefficient (slope} =-1.67, standard error = ±1...43 g-- 10.2 ~ · > o ~ •.. ,.• .., •• ... .., " +,c"=,c.cmc:,c.,-=":c"c.,:-:~~,=,C.,-:::"T,,C.,:-:.,,,c,c,-:::,m",c.,--="~,,c.c,c.=,c:,,=.,--=,,:c,c"':-:'::!300.0 Annual Number of FishIng TrIps E. regression coefficienf (slope) = +2.05, standard error = ±0.38 Figure 8-4. Offshore Commercial Brown &·Pink Shrimp Harvest as a Function of Fishing Effort and Each Seasonal Inflow From Combined River and Coastal Drainage Basins, Where all Other Seasonal Inflows in the.Muitiple Regression Equation are Held Constant at Their Mean Values VIII-25 the harvest estimate declines 42.8 percent ,(from about 7.9 to 4.5 million pounds annually) in response to increasing September--october (Q4) inflow over its observed range. Similar to previous shrimp analyses, fishing effort (Eo) exhibits a strong positive relationship to harvest (Panel E, Figure 8-4). Specifically, the increase in effort from about 3.8 to 9.0 thousand fishing trips per year results in the estimate of annual harvest increasing 4.2 times (from about 3.4 to 14.1 million p::>unds). Blue Crab Analysis of the fisheries oornponent for blue crab bay landings yields a significant equation (Table 8-11) for harvest as a function of seasonal fresh water inflows to the estuary from all oontributing river andooastal drainage basins (FINC). The equation is statistically significant ( a. = 2;5%) for correlation of harvest to 1-year antecedent spring, sumner, and autumn season inflows, and explains 58 percent of the observed harvest variation. The estimate of harvest is shown to increase 2.4 times (from about 1.1 to 2.5 million pounds annually) as April--0une ,(Q2) inflow increases over its observed range (Panel A, Figure 8-5). Panel B (Figure 8-5) displays a strong decline (87.8 percent) of the estimated annual harvest (from about 2.3 million pounds to 282.3 thousands p::>unds) as July-August (Q3) inflow increases CNer its observed range. The positive relationship of harvest to autumn inflow results in the harvest 'estimate increasing 1.7 times (from about 1.4 to 2.4 million pounds annually) in response to increasing September--october (Q4) inflow over its observed range (Panel C, Figure 8-5). ~Oyster Analysis of the bay oyster fisheries component gives a significant equation for each of three inflow categories (Table 8-12). The best significant equation (seoond equation, Table 8-12) involves natural log (In) transformation of the regression variables, accounts for 79, percent of the observed harvest variation, and is highly significant ( a. = 0.5%) for correlation of harvest to 1-year antecedent winter, spring, sumner, and late fall season freshwater inflows to the estuary from San Jacinto River (FINSJ). The responses of harvest to each of the inflow variables in the best significant equation are computed similar to previous examples; however, the results are graphed in non~transformed units to show the curvilinearity of harvest responses (Figure 8-6). A weak negative response to winter inflow is illustrated in Panel A (Figure 8-6), where the estimate of annual harvest declines 32 percent (from about 3.1 to 2.1 mill ion p::>unds of oyster meat) as January-March (Q1) inflow increases over its observed range. The estimate of annual harvest increases 1.7 times (from about 2.0 to 3.3 million p::>unds) in response to increasing April--0une (Q2) inflow over its observed range (Panel B, Figure 8-6). A strong negative response to increasing July-August (Q3) inflow over its observed range results in a 7S.9.percent decline in the harvest estimate (from about 4.0 to 1.0 million pounds annually) and is shown in Panel C (Figure 8-6). Another negative, harvest response, in this case to late fall inflow, is exhibited in Panel D (Figure 8-6) where the estimated annual harvest decl ines 41 percent (from about 3. 1 to 1.8 mill ion pounds) as November-December (QS) inflow increases over its observed range. vrlI-26 Table 8-11. Equations of Statistical Significance Relating the Blue Crab Fisheries COmponent to Freshwater Inflow Categories !y . ---------- Trinity-San Jacinto Estuary Blue Crab Harvest = f (seasonal FINTD £I) (no significant equation) Trinity-San Jacinto Estuary Blue Crab Harvest = f (seasonal FINSJ EI) (no significant equation) Trinity-San Jacinto Estuary Blue Crab Harvest = f (seasonal FINC d/) Significant Equation ( a = 2.5%, r 2 = 58%, S.E. Est. = + 416.0) - Hbc = 1773.4 + 0.52 (Q2) - 2.96 (Q3) + 0.49 (Q4) (0.16) (0.80) (0.27) Hbc Q2 Q3 Q4 upper oounds 2622:0 2962.0 798.0 2111.5 lower oounds . 311.2 157.0 112.5 85.0 mean 1606.4 1168.3 351.3 537.6 ---- -------- -----------~----- where Hbc = inshore commercial blueQ = mean IlOnthly freshwater Q1 = Jan.-Mar. Q2 = Apr.~un. Q3 = Jul.-Aug. crab harvest, in thousands of p:>unds; inflow, in thousands of acre-feet: Q4 = Sept.:-Oct. Q5 = Nov. -Dec. a/ b/ c/ ~ Standard error (+) of each regression coefficient is shown in parentheses beneath the coefficients of the regression equations FINTD = Freshwater inflow at Trinity Delta FINSJ = Freshwater inflow from San Jacinto River FINC = Combined freshwater inflow to the estuary. from all contributing river and coastal drainage basins VIII-27 21tlQ.0 2510.0 4 2120.0 0 0 ~ 1580,0 ,. lUO.O 0 ~ ~ 1~00.0 U ~ 1110.0 m ~ 120.0 u E 110.0E 0 U HO.O 200.0 4,~,"~,:-:-"r"~,-:,~,"~,.-:~,,r.,~.-:"T,"~,,-:,~,,"r,~.-:"T.,~,.-:,~,,~.,~.-,~.r"~"-:,,,,.~,,-:~c400.0 Mllon Monthly Inflow (1000 ac-ft) APR-JUN A. regression coefficient (slope} ;; to.52, stondord error;; ±0.16 2&00.0 2:lo10.0 '0 4 2120.0 0 0 ~ 18BO.O · > II~O.o 0 ~ 4 I-(tlQ.O0 U •, 1110.0 m 0 no.o u •E 680.0E 0 U HO.O 21tlQ.0 2360.0 · 4 2120.0 0 0 ~ 18BO.O ·•t II~O.O 0 ~ 4 1-(00.0~ u · , ~,. m 0 t20.0 .' u E &80.0§, u ~~O.o 200.0-1---~~~-~-~-~--:-~-~~=-:-,-I 100.0 170.0 2~0.0 3m.o :580.0 ~IO.O '20.0 ,to.O $$0.0 750.0 IDO.O l. • C 3360.00 ~ · 21150.0 · ~ 0 ~ 25'0.0 0 00 0 2130.0 u •E 1720.0 E 0 U 13to.0 1I00.0+--~--~-~-~--~-~--~-~--~-~ 0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0 '00.0 '50.0 SOO.O !.lean !.lanttlly Inflow (1000 oc-ft) JAN-MAR A. regression coefficient =-0.1407, $Iandord error = ±0.1355 SOOO.O 45110.0 '" ~ "60.0 0 0 ~ 3770.0 " · > 0 3360.0 ~ · 21150.0 · ~ O. ~ 25'0.0 0 00 0 2l:J0.0 u E 1720.0~. U 1310.0 1100.0 .oC.o'---,"oC,o-C.,",Co-Co"o,:,-:"Co,Oo-',OooC,Oo-"c"C,,:-:,~.,c",--:"io:,o'--~»"o:,o-,;;!o'o.o Meon Monthly Inflow (1000 oc-ff) JUL-AUG C. regression coefficient =-0.9168, stondord error = ±0.2434 5000.0 'SIIO.O "~ '180.0 0 0 ~ 3770.0 · · > 0 H60.0 ~ · 21150.0 "~ 0 ~ 25'0.0 0 00 0 2130.0 u E • E 1720.0 0 U 1310.0 too.O +-,---:!-:--r-~:--~-~-~--,-~--~--j 0.0 80.0 160.0 240.0 320.0 '00.0 '80.0 560.0 6.0.0 720.0 800.0 !.leon !.lonthly Inflow (1000 ac-fl) APR-JUN B. regression coefficient,= +0.1873, stondord error = ±0.1288· ,OQO.o 4511Q.O ~ '160.0 0 0 ~ 3770.!? " ·t 3360.00 ~ · 21150.0 · ~ 0 ~ 25'0.0 0 00 ~ 2130.0 ~ E 1720.0 E 0 U 1310.0 '00' +::_-:c:--,cc-C'C:-~:-:_~-~--~-~--~-~ 0.0 60.0 120.0 180.0 2,o.0 300.0 360.0 '20.0 '80.0 5'0.0 600.0 !.leon Monthly Inflow (1000 <:IC-ft) !'l0V-DEC D. regression coefficient =-0.1792, standord error = ±0.1207 Figure 8-6. Commercial Oyster Harvest as a Function of Each Seasonal Inflow From the San Jacinto River, Where all Other Seasonal Inflows in the Natural Log Multiple Regression Equation are Held Constant at Their Mean Values VIII-31 Finfish Analysis of the multi-species fisheries canponent for bay landings of finfish results in two significant regression equations (Table 8-13). The best significant equation (second equation, Table 8-13) also involves loga rithmic (In) transformation of the regression variables, explains 51 percent of the observed harvest variation, and is significant ( Cl = 5.0%) for correla tion of harvest to 3-year average antecedent surrmer, autumn, and late fall season inflows to the estuary from San Jacinto River (FINSJ). Again, the effects of each of the correlating seasonal inflows are graphed in non-transformed units to show the curvilinearity of the estimated harvest responses (Figure 8-7). The negative relationship between harvest and summer inflow is illustrated in Panel A (Figure 8-7), \\here the harvest esti mate declines 97.3 percent (fran about 1.4 million to 36.7 thousand pounds annually) as July-August (03) inflow increases fran its lower to upper observed bounds. On the other hand, the estimate of annual harvest increases 5.6 times (fran 117.3 to 651.3 thousand pounds) as September~tober (04) inflow increases over its observed range (Panel a, Figure 8-7). Another positive harvest response, in this case to late fall inflow, is shown in Panel C (Figure 8-7), \\here the annual harvest estimate increases 2.2 times (fran about 224.7 to .489.0 thousand pounds) as November-December (05) inflow increases over its observed range. ~ted Seatrout Analysis of the spotted seatrout fisheries canponent yields a significant harvest equation for each of the three inflow categories (Table 8-14). The best significant equation (first equation, Table 8-14) accounts for 70 percent of the observed harvest variation and is highly significant ( Cl = 0.5%) for correlation of the bay landings to 3-year average antecedent winter, SUlTl11er, and autumn season inflows to the estuary at Trinity Delta (FIN'll). The effects of each of the seasonal inflows in the best significant equa tion on spotted seatrout harvest are shown in Figure 8-8. The response to winter inflow is negative and the estimate of annual harvest declines 74.2 percent (from about 257.6 to 66.5 thousand pounds) as January-March (01) inflow increases over its observed range (Panel A, Figure 8-8). Also, the annual harvest is estimated to decline 54.5 percent (fran about 229.3 to 104.3 thousand pounds) as July-August (03) inflow increases over its observed range (Panel a, Figure 8-8). The positive response to autumn inflow results in the harVest estimate increasing 3.4 times (fran about 97.9 to 335.9 thou sand pounds annually) as september~ober (Q4) inflow increases over its observed range (Panel C, Figure 8-8). Red Drum Analysis of the red drum fisheries canponent also results in a signifi cant harvest equation for each of the three inflow categories (Table 8-15). The best significant equation (first equation, Table 8-15) explains 69 percent of the observed harvest variation and is significant (Cl = 5.0%) for correla tion of the bay landings to freshwater inflows at Trinity Delta (FIN'ID) fran all seasonal intervals (Q1 through Q5)' VIII-32 r?ble 8-13. Equations of Statistical Significance Relating the Finfish Fisheries Gomponent to Freshwater Inflow Categories 51 rr~flity-San Jacinto Estuary Finfish Harvest = f (seasonal FINTD b/) Significant Equation «X= 2.5%, r 2 = 50%, S.E. Est. = 2:. 114.6) - Hff= 540.1 - 0.67 (Q1 ) + 0.71 , (Q4) (0.20) (0.25) Hff Q1 Q4 upper bounds 635.1 912.2 581.7 tower POu.nds 59.9 229.7 96.0 !JleEgl 346.6 547.2 240.5 --------~~--------~---------------------------------------------------------- Trinity-San Jacinto Estuary Finfish Harvest = f (seasonal FINSJ c/) Significant Natural Log Equation' (et = 5.P%, r 2 = 51%, S.E. Est. ~ +'0.4721) , - ' In Hff = 11.3076 - 2.5766 (In Q3) + 0.9008(ln Q4) + 0.4976 (In Q5)(9. 8314 ) (0.4877) (0.3902) In Hff In Q3 In Q4 In Q5 upper pound? 6.4538 5.6630 5.8046 5.8061 lower bounds 4.0927 4.2556 3.9020 ,4.2437 mean 5.7197 4.8412 4.9617 4.8561 Trinity-San Jacinto Estuary Finfish Harvest = f (seasonal ,FINC 3/) , (no significapt equatiol1) .. Where: Hff = insnore oorrrnercial finfish harvest, in thoqsands of ]X>unds; In b.f~ : :~):"~n~ qh:~fi~ater inflow in thousands of acre-feet; . .... _.....Y ....... ', ......_ ." ".or., ""', ..;., In Q =natqral log of Q: Q1 = Jan.-Mar.Q2 = Apr.-Jun~Q3 = Jul~-Aqg. Q4 = pept.-oct.Q5 = !'/OV. -Dec. 51 Standard error (+) of each regression roefficient is shown in P"lrentheses beneath the roefflcients of the regression equations b/ FrNrD = Freshwater inflow at Trinity Delta ' c/ FINSJ' = Freshwater iTifiow fran San Jacinto River 0/ FINC = cOmbin~'freshwater'infiow to the estuary fran all contr~buting river arid 'ooastal' drainage basins ", " .. '~ .. ,- . , . VIII-33 1400.0 1260.0 ~ "20,0 0 0g 1180.0 . . 8~0.0> 0 ~ ~ 700,0 "~ C ~ '60.0 2 u ~20.0 E E 280.00 U 140.0 O.~ +--~-~-,---."r:--:r:c-=:-"",-:-~:-:---,-r-:-."crc-,--j 0.0 ~O.O 80.0 120.0 160.0 200.0 2~0.0 280.0 320.0 ~.o ~oo.o ~eon ~onthly Inflow (1000 oc-ft) JUL-AUG A. regression coefficient =-2.5766, standard error = ±0.831.4 «OOD 1.250.0 '" '~D~ 0 0 1180.0g ". 3<10.0> 0 ~ > 'OOD , !la0.0~ "0 u ~20.0 E E 280.00 U 1~0.0 1.00,0 1280.0 ~ "20.0 0 0g 1180.0 . a.o.o> 0 ~ > 700.0 , ~., 0 ~ ~20.0 •E E 280.00 U 140.0 M -I--~-~-~----~-~-,--...".:-:--."r:--.,,:r:c--j. 0.0 ~o.o 80.0 120.0 l6O.0 200.0 2~O.0 280.0 uo.o ~.o ~oo.o ~eQn ~Qnth!y Inflow (1000 oc-H) SEP-OCT 8. regression coefficient = +0.9008, standard error = ±0..4877 M+,C".,---"'M:-c"~".,---''',~:-:.,---'.:O:'C"D-:,T.OOC"D-::'''-O.:-o ---=""O.O:-'''~:-:D---'''"~:-:D--,-j~oo.O ~eon ~onthly Inflow (1000 oc-H) NOV-DEC C. regression coefficient = +0..4976, standard error = ±0.3902 Figure 8-7. Inshore Commercial Finfish Harvest as a Function of Each Seasonal Inflow From the San Jacinto River, Where all Other Seasonal Inflows in the Natural Log Multiple Regression Equation are Held Constant at Their Mean Values VIII-34 Table 8-14. Equations of Statistical Significance Relating the Spotted Seatrout Fisheries OOrnponent to Freshwater Inflow Categories ~ Trinity-San Jacinto Estuary Seatrout Harvest = f (seasonal FINTD b/) Highly Significant Equation (a= 0.5%, r 2 = 70%, S.E. Est. = + 5e1) Hss= 272.3 - 0.28 (Ql) - 0.50 (Q3)- + 0.49 (Q4) (0.11) (0.28) (0.11) Hss Q1 Q3 Q4 " upper bounds 280.4 912.2 265.2 581.7 lower bounds 17.0 229.7 15.3 96.0 mean 165.8 547.2 136.4 240.5 ---------------------------------------------"--------------------------- Trinity-San Jacinto Estuary Seatrout Harvest = f (seasonal FINSJ- c/) Highly Significant Natural Log Equation Equation (a = 1.0%, r2 = 67%, S.E. Est. = 2: 0.4886) ln H = 12.0028 - 3.8511 (In Q3)ss (0.8606) + 1.2948 (lnQ4) + 1.0583 (ln Q5) (0.5048) (0.4039) ln Hss ln Q3 ln Q4 ln Q5 upper bounds 5.6362 5.6630 5.8046 5.8061 lower bounds 2.8332 4.2556 3.9020 4.2437 mean 4.9221 4.8412 4.9617 4.8561 ---------------- ------ -------------------- Trinity-San Jacinto Estuary Seatrout Harvest = f (seasonal FINC d/) Significant Equation (a = 2.5%, r 2 = 66%, S.E. Est. = :!:. 56.9) - HSS = 281.2 - 0.23 (Q,) - 0.21 (Q3) + 0.15 (Q4) + 0.11 (Q5) (0.11) (0.15) (0.14) (0.11) Hss Q 1 Q 3 Q4 Q5 ----- upper bounds 280.4 1356.7 831.2 1127.2 1148.7 lower bounds 17 .0 423.9 122.5 185.2 307.8 mean 165.8 849.1 370.0 542.1 708.5 (Continued ) VIII-35 Table 8-14. Equations of Statistical Significance Relating the SPotted Seatrout Fisheries Component to Freshwater Inflow Categories a/ (Coot'd) - Where: Hss = inshore a:mnercial spotted seatrout harvest, in thousands of pounds; In H ss = natural log of H ss ; Q = mean nonthly freshwater inflow, in thousands of acre-feet; In Q = natural log of Q: Q1 = Jan.~Mar.Q2 = Apr.-Jun.Q3 = Jul.-Aug• Q4 = Sept.-oct.QS = Nov. -Dec. ~ Standard error (+) of each regression coefficient is shown in parentheses beneath the coefficients "of the regressIon· equations b/FIN'ID "= Freshwater inflow at Trinity Delta cl FINSJ = Freshwater inflow from San Jacinto River d/ FINC = Combined freshwater inflow to the estuary frem all contributing river and coastal drainage basins "' VIII-36 10.0 350.0,----------------------, I 280.0 ,., +,,=,.:-,::,,",.:-,--:o":c,.,:-.",,:-;.,,...-;~"-,::.,---::,,",.:-, --::"",.,:-:o,,:c,.,:-.",,:-:.,,...-;,"-,,::.,--::J1oo0.0 Mean I.lanthly Inflow (1000 ac-f1) JAN-t.AAR A. regression coefficient (slope) =-0.28, standord error = ±0.11 3'0.0 '" 31'.0 D 0 0 200.0~ ;; ~ "0 17'.0 :. 1: 1~0.0 o b:" 10M o o I o u 5'0.0 " 3T,.0 D 0 0 280.0~ " H'.O · > 0 ~ 210.0 , ~ 17'.00 •~ ~ 140.0!;; ~ ~ 10'.0 ~ 0 70.0 ·E E 0 3'.0U ,., -!;-;-":::----:r:-=---:o.::---::c-;:---::,;:::--=:-=----::=-::!,0.0 50.0 &0.0 10.0 120.0 1,o.0 180.0 210.0 2~0.0 270.0 300.0 Mean I.lanthly Inflow (1000 oc-H) JUL-AUG 8. regression coefficient {slope) =-0.50, standard error = ±0.28 ,.,+----.:~-~~~~-~-~---~-_-I 0.0 &0.0 120.0 180.0 HO.O 300.0 3&0.0 ~20.0 ~8o.0 '~O.O &00.0 Mean Monthly Inflow (1000 ac-ft) SEP-OCT C. regression coefficient (slope) = +0.49, standard error = ±0.11 Figure 8-8. Inshore Commercial Spotted Seatrout Harvest as a Function of Each Seasonal Inflow at Trinity Delta, Where all Other Seasonal Inflows in the Multiple Regression Equation are Held Constant at Their Mean Values VIII-37 Table 8-15. Equations of Statistical Significance Relating the Red Drum Fisheries Component to Freshwater Inflow Categories sI --------- Trinity-San Jacinto Estuary Red Drum Harvest = f (seasonal FINTO b/) Significant Equation ( Cl = 5.0%, r 2 = 69%, S.E. Est. = + 17.6) - H = 10.6 - 0.04 (Ql) + 0.04 (Q2) - 0.18 (Q3) + 0.10 (Q4) + 0.05 (Q5)rd (0.04) (0.01) (0.11) (0.07) (0.05 ) H rd Q1 Q2 Q3 Q4 Q5 ---,--_.- upper bounds 97.5 912.2 1217.3 265.2 581.7 993.3 lower bounds 1.3 229.7 196.4 15.3 96.0 173.7 mean 36.3 547.2 682.9 136.4 240.5 456.6 Trinity-San Jacinto Estuary Red Drum Harvest = f (seasonal FINSJ c/) Significant Equation ( Cl = 5.0%, r 2 = 59%, S.E. Est. = ~ 19.2) - H = 38.5 + 0.09 (Q2) - 0.58 (Q3) + 0.15 (Q4) + 0.19 (Q5)rd (0.06) (0.18) (0.15) (0.14) ~d Q2 Q3 Q4 Q5 -------._--- upper bounds 97.5 420.0 288.0 331.8 332.3 lower bounds 1.3 76.3 70.5 49.5 69.7 mean 36.3 267.2 137.7 173.0 151.0 Trinity-San Jacinto Estuary Red Drum Harvest = f (seasonal FINC d/) Highly Significant Equation ( Cl = 1.0%, r! = 65%, S.E. Est. = + 17.0) H = 5.5 + 0.03 (Q2) - 0.12 (Q3) + 0.06 (Q5) rd (0.01) (0.04) (0.02) H rd Q2 Q3 Q5 --------- upper bounds 97.5 1896.0 831.2 1448.7 lower bounds 1.3 336.5 122.5 307.8 mean 36.3 1133.9 370.0 708.5 (Continued) VIII-38 Table 8-15. Equations of Statistical Significance Relating the Red Drum Fisheries Component to Freshwater Inflow Categories a/. (cont'd) --------------------- where: ------_._------- H rd = inshore commercial red drum harvest, in thousands of pounds:° = mean nonthly freshwater inflow, in thousands of acre-feet: 01 = Jan.-Mar. Q2 = Apr.--vun.Q3 = Jul.-Aug. 04 =Sept.-oct. 05 = Nov. -Dec. a/ bl cl dl Standard error (+) of each regression coefficient is shown in parentheses beneath the coefficients of the regression equations FINTO = Freshwater inflow at Trinity Delta FINSJ = Freshwater inflow fran San Jacinto River FINC = Canbined freshwater inflow to the estuary fran all contributing river and coastal drainage basins VIII-39 Harvest responses to seasonal inflows in the best significant equation are illustrated in Figure 8-9. Panel A (Figure 8-9) shows the estimate of annual harvest declining 53.4 percent (from about 51.1 to 23.8 thousand pounds) as January-March (Q1) inflow increases over its observed range. The positive response to spring season inflow results in the harvest estimate increasing 3.2 times (from about 18.9 to 59.7 thousand pounds annually) as April-.June (Q2) inflow increases over its observed range (Panel B, Figure 8-9). Panel C (Figure 8-9) shows a strong negative relationship of sumner inflow to harvest and the estimate of harvest declines 74.8 percent (from aoout 60.2 to 15.2 thousand pounds annually) as July-August (Q3) inflow increases over its observed range. The estimate of annual harvest increases 3.0 times (from about 23.9 to 72.5 thousand pounds) as September-october (Q4) inflow increases over its observed range, indicating' a positive response to autumn season inflow (Panel D, Figure 8-9). Panel E (F igure 8-9) exhibits another positive harvest response, in this case to late fall season inflow, and the' estimate of harvest increases 2.7 times (from about 24.2 to 65.2 thousand pounds annually) as November-December (Q5) inflow increases over its observed range. Black Drum Analysis of the fisheries component for black drum did not result in any significant regression equations for harvest as a function of seasonal fresh water inflows to the estuary. Fisheries Component 'Summary The fisheries analysis involves ten 'fisheries components and three fresh water inflow source categories in the analytical design, allowing a maximum 30 potentially significant equations. The analysis results in 19 equations of statistical significance. Although each of the three inflow categories can potentially produce ten significant equations, the analysis yields five equa tions with freshwater inflow at Trinity Delta (FIN'ID), five equations with freshwater inflow from San Jacinto River (FINSJ), and nine equations with combined freshwater inflow to Trinity-San Jacinto estuary from all contribut ing river and coastal drinage basins (FINC). Seasonal inflow needs are similar for fisheries components when the signs (positive or negative) on the regression coefficients in the harvest equations are the same for a season of interest (Table 8-16). Therefore, the seasonal inflow needs of' the fisheries components can reinforce each other. However, where seasonal inflow needs are of opposite signs, the fisheries components' become competitive in terms of inflow management. Altogether, these results support the hypothesis that seasonal freshwater inflow has a significant im pact on the estuary's fisheries, and by ecological implication, on the "health" of the ecosystem. Freshwater Inflow Effects Introduction The hydrologic importance of both tidal inlets and freshwater inflow for ecological preservation of estuaries has been recognized (154,317). Since the 'JIII-40 0.0 +o::.o---:'O".~o -:0"0.'-0-:~,-.0:-,".,-0.0:-~20::.0-:"T.0-::.-:,,~0.-::0---::,'O".o:-''',":::.o:-::!~·.o htean Monthly Inflow (1000 ac-tl) SEP-OCT O. regression coefficient (slope} = to.lO, standard error = ±O.07 M 4~::-:.0:-::,,"0.~0---:~~0~.0---:~.'Oc.~0---:~r:.0---:,~OO~0=-~,,~0~.0-:.~'"~0---:'=M!:0~.0---:O~'O~.0---:0:!00.0 Mean Monthly Inflow (1000 ac-H) APR-JUN B. regression coefficient (slope) = +0.0.4, standard error =±O.Ol 75.0,-----------------------, o o ~ o u 75.0 57.5 '" ~ 50.0 0 0 ~ 52.5 ·•t ~5.0 0 X E ",, a ~ 30.0 • 0 22.5 ~ •E 0.0E 0 u " 2&0.0 ~70.0 UO.O 5~.0 540.0 no.o e20.o ~10.0 lOOQ.o htean Monfhly Inflow (1000 ac-H) JAN-MAR A. regression coefficient (slopel =-0.0.4, standard error = iO.O.4 50.0 10.0 t20.0 l5O.0 ISO.O 210.0 2~0.0 270.0 $00.0 Mean Monthly Inflow (1000 ac-H) JUL-AUG C. regression coefficient (slope) =-0.18, stondard error =±0.11 75.o,---------------=--------, 75.0 ." ~ '0.0 0 0 ~ 52.5 · ·t ~5.0 0 X § ,,, a ~ 50.0 • • 0 22.5 ~ •E 15.0E 0 u ,., M 0.0 ~. 75.0 n.5 · ~ '0.0 0 0 ~ 52.5 · > ~5.0 0 X § 57.5 a ~ 50.0 • 2 22.5 0 E 15.0E 0 u ,., M 100.0 1~0.0 · · > o x ~ a ~.o 22.5 Figure 8-9. Inshore Commercial Red Drum Harvest as a Function of Each Seasonal Inflow at Trinity Delta, Where all Other Seasonal Inflows in the Multiple Regression Equation are Held Constant at Their Mean Values 15.0 o.o+--~-~--~~~-~-~-~--~~~-_I 100.0 l~O.o 2&0.0 570.0 ~SO.O 550.0 540.0 730.0 e20.o ~10.0 1000.0 Mean Monthly Inflow (1000 oc-II) NOV-DEC E. regression 'coeffiCient (slope) = to.05, standard error = iO.05 VIII~41 Table 8-16. Positive (+) and Negative (-) Correlation of Fisheries Components to Seasonal Freshwater Inflow Categories -,-_-,-I%L__: (~L_ Winter ----:----Spr[ng-·--·---:--S~-r----:-Auturnn----- Inflow: Inflow : Inflow : Inflow Fisheries Q,: Q2 : Max Q2:(Max Q2)2: Q3 : Q4 : Q5 Canponen.1:. : (Jan.-Ma~L-,- (~r.-Jun. L ~ (Jul.-Aug. L : (Sept.-- are potenti?l11y explainable by divergent aspects of their life histories and ecology, l:?Uch as the timing of migration .into the estuary and the timing of recrui~nt of maturing shrimp to their -'respective a:'Iult populations, the differing responses of inshore and offshore : harvests from the same species (Le., brown and pink shrimp fisheries o::m- ponent) are IIDre difficult to explain. It is fX)ssible, oowever, that ,an increase in a particular seasonal inflow may be locally detrimental to -shrimp harvests in the bays, \rtant and have stimulated considerable research o Finfish SIXJtted Seatrout Red Drun OFFSHORE: White Shrimp Brown and pink Shdrrp 346.6 165.8 36.3 296.3 116.2 27.4 (-14.5) (-29.9) (-24.5) 352.1 (+ 1.6) 161.3 (- 2.7) 21.6 (-40.5) 304.8 137.3 36.3 329.4 (+ 8.1) 145.6 (+ 6.0) 37.5 ( +3.3) 332.5 ( +9.1) 147.9 (+ 7.7) 28.7 (-20.9) 165.8 36.3 2799.2 7181.0 130.4 29.7 2801.7 6999.9 (-21.4) (-18.2) (+ 0.1) (- 2.5) 150.7 (- 9.1) 20.4 (-43.8) 2709.0 (- 3.2) 7705.4 (+ 7.3) All Shrimp 9995.3 9790.0 (- 2.1) 10,365.8 (+·3.7) al Freshwater inflow Trinity Delta bl Freshwater inflow from San Jacinto River cl CCxTbined freshwater inflow fran all oontributing dver and coastal drainage basins dl EF "" exceedance frequency; 50% EF reflects the tl2ffi[X)ral median inflCM to the estuary el Average harvest, in thousands of poundsII Shift in percent increase (+) or decrease (-) of harvest fisheries equations involves using aritlunetic mean seaonal inflows as input to the linear equations and geometric mean seasonal inflows as input to ,the natural log (In) equations. There are 13 positive and 23 negative shifts of the harvest estimates from exercise of the equational rrodels. Long-term mean inflows are associated with five positive and 13 negative shifts of the harvest estimates, \>hen can pared to the fisheries harvest levels resulting fran the observed short-term interval, and there are eight positive and ten negative harvest shifts in response to long-term 50 percent exceedance frequency (EF) inflows. The harvest shifts are variable arrong the fisheries canponents and range fran an estimated +13.5 percent shift of oyster harvest in response to 50 EF inflows (FINSJ inflow category), to an estimated -43.8 percent shift of red drum harvest in response to 50 percent EF inflows (FINC). The results reflect not only differences in inflow quantity, but also differences in the seasonal distributions of inflow from the freshwater oource categories. In addition, they suggest that fisheries harvests based on the long-term mean inflows lIOuld . be lower OITerall because of the greater nunt>er of asoociated negative harvest shifts; however, long-term 50 percent EF inflows appear notably beneficial to inshore oyster and finfish canponents, and offshore all shrimp and brown and pink shrimp canponents. While management policies could favor the specific seasonal inflow needs of preferred fisheries canponents, it is in reality difficult and in many cases impossible to maximize the harvests fran nore than one fisheries arn ponent at the same time because of arnpetitive seasonal inflow needs arrong the species. Nevertheless, management scenarios for inflow can be developed that predict good harvest levels from several of the fisheries arnponents simul- taneously (see Chapter IX). ' Surrmary Virtually all of the Gulf fisheries species are estuarine-dependent. Ccmnercial inshore harvests (1962-1976) fran bays of the Trinity-San Jacinto estuary rank first in shellfish and fourth in finfish of eight major Texas estuarine areas. In addition, the Sport or recreational finfish harvest has been estimated at six times larger than the arnmercial finfish harvest in the estuary. For the 1972 through 1976 interval, the average annual sport and ccmnercial harvest of fish and shellfish dependent upon the estuary is esti mated at 46.7 million'pounds (21.2 million kg; 87 percent shellfish). Although a large portion of the fisheries production fran each Texas estuary is harvested offshore in collective association with fisheries pro duction from' other regional estuaries, inshore bay harvests are useful as relative indicators of the year to year variations in an estuary's surplus production (Le., that portion available for harvest). These variations are affected by the seasonal quantities and oources of freshwater inflow to an estuary through eoological interactions involving salinity, nutrients, food (prey) production, and habitat availability. The effects of freshwater inflow on the Trinity-San Jacinto estuary are also reflected in the offshore harvests of the penaeid shrimp fishery. Therefore, the fisheries species can be viewed as integrators of their environment's conditions and their harvests used as relative ecological indicators, insofar as they reflect the general pro ductivity and "health" of the estuarine ecosystem. VIII-51 A time series analysis of the a:xnmercial bay fisheries landings (1962 through 1976) and the a:xnmercial offshore penaeid,shrimp harvests (Gulf Area No. 18, 1959 through 1976) produces 19 ,statistical equations: that-- estimate harvest as a function of seasonal freshwater inflows to the estuary. ,These equational llDdels provide numerical estimates of the effects of variable seasOnal inflows, contributed' fran the major' freshwater sources,' on the production of seafood· organisms dependent' on the estuarine ecosystem. The analysis also supports' existing scientific information on the seasonal importance of freshwater inflow to the estuary. All ,significant inshore cand offshore harvest responses to winter ,(January-March) inflow are estimated to. be negative for increased' inflow in this season. with, exception 'of the inshore 'brown ar1d pink shrimp canponent' s positive response to Trinity Delta sumner,' inflow (FIN'ID inflow category)" all .other significant inshore harvest responses 'are estimated to relate' negatively to increased sllllllller (July-August) inflow._ Offshore all shrimp and brown, and ,pink shrimp fisheries components also' relate positively to increased sumner inflow, _but negatively -to increased spring (April-June) inflow. However, offshore vklite shrimp and inshore red drum, oyster and blue' crab harvests relate positively, to increased spring season inflow. Significant harvest 'responses to increased autumn (September-october) ;inflow are all positive, except for the negative responses of the oyster and offshore brown and ,pink shrimp fisheries components. Increased late fall (November-December) inflow 'relates positively_ to several fisheries components (e.g., finfish, spotted ,seatrout, and red drum), but nents are similar" the components reinforce each other; however, ,mere canponents are - competitive by exhibiting, opposite seasonal inflow needs, a management deci sion must be made to balance the divergent needs or, to -give preference to-the needs of a particular fisheries canponent. A dloice could be made on the basis of vklich species' production is more ecologically dlaracteristic and/or econanically important to the estuary. Whatever the decision, a freshwater inflow management regime can only provide an cpportunity for the estuary to be viable and productive because· there, are no guarantees for estuarineproouctiv - i ty based on inflow alone, since mariy other biot ic and abiot ic factors are _capable of influencing this- production. However, most of these other factors are largely, beyond human ,control, vklereas freshwater inflows ,can be restricted by man's activities so _that fish' and wildlife resources are a::lversely af fected. , ' " ,.. ' VIII-52 QiAPl'ERIX ESTIMATED FRESHWATER INFI.OO NEEDS Introduction In previous chapters, the various physical, chemical and biological factors affecting the Trinity-San Jacinto estuary have been discussed. 'I1lere has been a clear indication of the importance of .the quality and quantity of freshwater inflows to the maintenance of a viable estuarine ecology. The purpose in Chapter IX is to integrate the elements previously described into a methodology for the purpose of establishing estimates of the estuary's fresh water inflow needs, based upon historical data. Methodology for Estimating Selected Impacts of Freshwater Inflow Upon Estuarine Productivity The response of an estuary to freshwater inflow is subject' to a nurrber of factors and a variety of interactions. These include changes in salinity due to mixing of fresh and saline water, fluctuations in biological productivity arising from variations in nutrient inflows, and many other phenomena. The methodology presented here incorporates major. interacting elements described in previous chapters (Figure 9-1). The methodology includes the use of data bases and certain analytical processes described herein. Data for these analyses include six groups: (1) salinity data for finfish and shell fish, (2) commercial fisheries harvest data, (3) hydrologic data of freshwater and sal ine water, (4) water qual i ty data, (5) aquat ic food chain data, and (6) terrestrial and aquatic geomorphic data of the estuary and the surrounding coastal area. In this section data and results of previous sections, including (1) statistical analysis of relationships among freshwater inflow, commercial fishery harvest, and estuarine salinity;· (2) estimates of marsh freshwater inundation needs; (3) estimates of nutrient exchange; arid (4) records of historical freshwater inflow, are used in an Estuarine Linear Programning (LP) Model to compute estimates of the monthly freshwater inflows needed to achieve specified objectives. 'I1le tidal hydrodynamic and salinity transport models are then applied to comPute salinity levels and circulation patterns through out the estuary for a set of computed freshwater inflow needs. Application of the Methodology to canpute Estimates of Freshwater Inflow Levels Needed to Meet Selected Objectives The schematic indicated in Figure 9-1 shows the sequence of steps utilized in computing the freshwater inflow needs to achieve specified objec tives as expressed in terms of salinity, marsh inundation, and productivity. The six data bases developed for the Trinity-San Jacinto estuary provide the IX-1 r- I I I I I I I I I I I I L_ ODD :;;!!; ~i :;,.i , n i;;:~ i",. ~~~ ~'i! "" Ii~~ ;;('S::'i ~'1., .. ,I :0>::1"n~g m g§i~ ~~~;:;§g i~~1~~~ ~M'5'" -",, 5.:1 g ~i~ ~t;; i, , ~~i ~~ , .' I's "" , IX-2 fUndamental information of the system. These data were used in previous sections of these analyses. The relationships and results are incorporated into the Estuarine Linear Programming Model to oampute estimates of effects of various levels of llOnthly freshwater inflows upon salinity, marsh inundation and fisheries harvests in the estuary. This I!Ddel uses an cptimization 'tech nique to select the optimal or "best" llOnthly inflows for the objective speci fied. The estimated llOnthly inflows are then used as data inputs in the tidal hydrodynamic and salinity transport I!Ddels to simulate the effects of the inflows upon circulation and Salinity patterns in the entire estuary. Should the computed salinity conditions in certain critical areas of the estuary be unsatisfactorily high or low, then the freshwater inflow estimates w::>uld require appropriate I!Ddification. This revision of the estimates (indicated by the dashed line in Figure 9-1) would necessitate a recomputation of the freshwater need by the Estuarine Linear Programming Model under a modified set of contraints. The data bases and analytical processes utilized in this chapter have been described in detail in previous chapters. Only the procedures necessary to establish salinity bounds, estimate marsh inundation needs, and apply the Estuarine Linear Programming Model are presented in this chapter. '.. . ... . Salinity Bounds for Fish and Shellfish ~i~ The effects of salinity on estuarine-dependent fisheries organisms are fundamentally physiological, and influence growth, survival, distribution, and ecological relationships (see Chapter VIII). Specific information on salinity limits, preferences and/or cptima for selected fisheries species has been tabulated from the scientific' literature and Texas Department of Water Resources research data (Table 9-1). The cpti mum condition for llOst of these species lies between 25 percent and 75' percent seawater (8.8-26.3 ppt). Young fish and shellfish commonly utilize estuarine "nursery" habitats that are below 50 percent seawater (less than 17.5 ppt), while adults seem to prefer salinities slightly higher than 50 percent sea water. In general, and within the tolerance limits, it is the season, not salinity~ se, that is llOre important because of life cycle events such as spawning and migration. While the salinity limits for distribution of the species are ecologically informative, they are often physiologically too broad. COnditions encouraging good growth and production are commonly re stricted to a substantially narrower range of salinity than are simple survi- val needs. . Data on salinity effects, CXJ!11bined with life cycle information, were utilized to provide seasonal bounds on estuarine salinity within ~ich fish and shellfish can survive, grow, and maintain viable populations (Table 9-2). Since universal consensus is not evident for precise viability salinity limits, the llOnthly salinity bounds were established subjectively based upon the results available from scientific literature (Table 9-1). It is important to note that these limits are site specific and adjusted to tw::> rontrol p:>ints' IX-3 ! s • a , , ! • E , , " • • , , , , ! ,, , , , , , 2 , , , 0 . 0 . • . " l • l ~fil!!!, , , " " , • • • § • ; ; " , ~ , , ;;: ~ i l ~ ., . " , ~ il ~ z ~ , ~ , , ~ , , ~ ll ~ , " ! " ,0& , i , , ,.t~ j , , , , , , , , , j . , , ; . 1~ , , i " 0 " " " " 0 ., " ! l~ l~i~ i ~ ~ " ~ , , k ~ • • , , 1~~ , . " 0 0 " 0~ ! I '"(lJ ~ IX-4 ~ • , • l • • , ; • , ., . , • 'r , • ~, , , , I , ~ ;:i ., i , , e, ~ • , 7" ; 1 ~ ~ ~• , ; , , • • l ~. , b l 1 •., I , , " " , , l , • i HI, Fa ~ ,j ~ - 1 ! ll~X jli j , . '0 .w 8 IX-5 Table 9-2. Salinity C1aracteristics of Upper Galveston Bay and Upper Trinity Bay salUiity in - Upper Trinity Bay a/ (ppt) - Salinity Tii--·--,----- Upper'Galveston Bay b/ (ppt) - Month Upper E;T:I1::1viirE!= Median --i-uppe=r~cl'-~"'Lowe=:C-r:-c""Ir---;Median--- Viability Viability: Historic Viability Viability Historic Limit Limit Salinity Limit Limit Salinity January February March April May June July August September October November December 20 20 20 15 15 15 20 20 15 15 20 20 10 10 10 5 1 1 10 10 5 5 10 10 5 4 4 4 4 3 5 11 13 12 11 7 30 30 25 20 20 20 25 25 20 20 30 30 10 10 10 5 5 5 10 10 5 5 10 10 13 13 14 14 12 13 17 16 17 18 21 15 ar-Represented1!Y-samplID:l sfte -llOOlinesite-23()(FrgureF9f------- ----- b/ Represented by statewide IIOnitoring network station 1005.1, Morgan's Point. - (Figure 3-9) sf These values estimate the limits of long-term viable species activity at control points in the estuaries, and not individual organism survival limits (Table 9-1) IX-6 in the estuary below the "Null Zone" .v: (1) in upper Galveston Bay at Morgan's Point, and (2) in upper Trinity Bay near the Trinity River delta . .The·limits are. expressed- as mean (average) IlDnthly salinities for ,general limits of viability. From· both locations, salinities generally increase towards the Gulf inlets (Bolivar Pass and San Luis Pass) and eventual~y attain seawater concentration (35 ppt). The salinity gradient in the estuary is thus steeper during seasons of higher inflow (e.g., the ,spring) and ~ess distinct during seasonal low inflow (e.g., the summer). Moreover, ,the estuarine dependent species have adapted their life cycles to' the 'natural freshwater, inflow regime and are today productively associated. with local and State economies. '. " Although the fisheries species can generally tolerate salinities-9reater' or less than the IlDnthly specified viability range, foraging for food and production of body tissue (growth) becomes increasingly IlDre difficult· under 'extreme salinities, and may eventually cease altogether because body mainte nance requirements consume an increasing arrount of an organism's, available energy under unfavorable conditions. High IlDrtality -and low production are expected during prolonged extremes of primary environmental factors such as ,salinity and temperature. 'Monthly Salinity COnditions The salinities within an estuarine system fluctuate with variations in freshwater inflow. During periods of flood or drought, salinity regimes nay be so altered from normal conditions that IlDtile. species canrronly residing in an estuary may migrate to other areas I>bere the environmental conditions ·are more suitable. Generally, however, estuarine-dependent species will remain. in the system during normal periodic salinity fluctuations. Should the normal salinity conditions be altered. for prolonged periods due to,.natural or ~de causes, the diversity, distribution· and productivity of species within·" an estuary will be depressed. ' .. The median IlDnthly Salinity is a measure of the normal IlDnthly salinity condition of the estuary. The median IlDnthly salinity is that value for I>bLch one-half of the observed average IlDnthly salinities exceed the value and one half are less. The median IlDnthly salinity thus reflects an ."expected'! salinity in the estuary ·and represents a numerical value exceeded 50 percent .of the' time. Median historic salinities have been bich the salinity regression equations were developed in Chapter v. Marsh Inundation Needs The periOdic inundation of deltaic marshes serves to maintain shallow protected habitats for postlarval and juvenile stages· of several irnJ:lortant 1/- Nulf-Zone: The general area' I>bere the net landward flow creates the - phenomenon of landward and seaward density currents being equal but cp- posite . in effect. . The nullification of net bottom flows in this area allows suspended materials to accumulate and has also been termed the entrapnent zone, the critical area, the turbidity maxima, the nutrient trap, and the sediment trap (109, 7). ( IX-7 estuarine species, provides a suitable fluid medium for nutrient exchange processes, and acts as a transport rrechanism to IIDve detrital food materials from the deltaic marsh into the open estuary. The areal extent of deltaic marsh inundation 'is a function of the channel capacity, discharge rate and volume, wind direction, and tidal stage. Historically, the discharge rates of Texas rivers have fluctuated on a seasonal basis. Monthly freshwater inflows usually peak in the spring and early fall, reflecting the increased rainfall and surface runoff that normally occur during these' IIDnths. The cyclic periods of high and low freshwater discharge have influenced the life history of estuarine-dependent organisms, especially the early life stages which are dependent upon marsh inundation and nutrient processes for biological productivity. Two river deltas of the Trinity-San Jacinto estuary (the San Jacinto and Trinity River deltas) are periodically inundated.1/ The Trinity delta is subject to periodic inundation by freshwater due to discharge fran the Trinity River system. The areal extent of deltaic inundation is a function of wind, tide, and discharge rate and volume. If high tides are present, the area of delta inundated by a given peak flood discharge is greater than that occurring with normal or low tides. The San Jacinto River delta is much smaller in areal extent than the Trinity delta, and was not considered of sufficiently significant area to warrant extensive analysis of its inundation characteristics. To formulate a water management program that incorporates deltaic inun dation as an objective, it is necessary to determine both the frequency and magnitude of historical flood events for the Trinity delta. If what has happened naturally iri the past has been sufficient to maintain the prO- ductivity of the estuary, incorporation of historical patterns into a manage ment plan will IIDSt likely provide inundation sufficient to maintain productivity in the future. Historical deltaic inundation was canputed through the use of a hydro dynamic rrodel for Trinity delta (62, 61). A series of peak discharges ranging from 10,000 to 35,000 ft3/sec (283 to 991 m3/sec) for low and high tidal regimes were used in the analysis and the areal extent of deltaic inundation was canputed for each tide/discharge combination. With low tides (-0.9 feet to 0.8 feet above MSL), a peak discharge of 20,000 ft3;sec (566 m3/sec) would be sufficient to begin inundation of the delta. During high tides (range 0.6 feet to 2.4 feet above MSL), the rrodel predicted that a 20,000 ft3/sec (566 m3/sec) peak discharge from the Trinity River loOuld result in inundation of 44 percent of the delta. Since historical tide stages are un known for a large portion of the period of record, a daily peak discharge of 20,000, ft3/sec (566 m3/sec) or greater was selected as a potential inunda tion event. 17--Delfa--rc1nundation is defined as sutmergence of a portion of the river ,- delta by water to a depth of at least 0.5 feet for a period not less than 48 hours. These values are based upon TDWR supported research (310, 311). Studies indicate that maximum rates of nutrient release from the sediment of a discrete inundation event, following a prolonged period of emergence drying. IX-8 Daily gaged discharge data for the period of record (1924-1977) were examined to arrive at IlDnthly and seasonal distributions of discharge events with daily peak flows of .20,000 ft3/sec (566 m3/sec)or greater (Table 9-3). It was apparent that IlDre inundation events have occurred in the spring months of March, April, and May than during any other seasonal period. The data suggest that inundation events in the Trinity delta have occurred IlDre often in the winter and spring than in the sumner and fall. According to the biological evidence, spring inundation events are necessary for (1) adequate physical wetting of the marsh plant COImlunities, (2) nutrient exchange and biogeochemical cycling of carbon, nitrogen and {i1osphorus, (3) transport of detrital food materials, and (4) reduction of salinity to suit the needs of juvenile, estuarine-dependent organisms utilizing the "nursery" habitats of the marsh and adjacent shallow water areas. In the tropical-storm dominated fall season, less frequent inundation events occur, however, maintenance benefits are still provided to the estuary and dependent· species such as the redfish. If historical inundation events (peak daily flows greater than 20,000 ft3/sec or 566 m3/sec) are grouped into those that occur in spring (March, April, and May), those that occur in the winter (December, January and February), and the total that occurs during the year, it is evident that an average of three inundation events have occurred per year in the Trinity delta over the period of record (Table 9-4). In order to maintain the historical inundation frequency, the Trinity River delta \'Puld need to receive three flood events per year with flows greater than 20,000 ft3/sec (566 m3jsec) in half of the years in any period. Ideally, inundation events should occur at times which \'Puld provide the most benefit to estuarine organisms. The importance of at least one spring and one fall event has been discussed previously, therefore, flood events are specified for May and October. Since low salinities and shallow habitat (for protection of the young) are primary requisites during the spring,· any inun dation events occurring during this period will provide the greatest benefit to the organisms. '!herefore, the third inundation event is specified for April and is expected to extend favorable habitat conditions for larval and juvenile stages of many estuarine-dependent organisms. The median daily peak discharge for flood events (peak flows g:r:eater than 20,000 ft3/sec) over the period of record has been 29,500 ft3/sec (835 m3/sec). '!he Trinity delta hydrodynamic model canputed a delta inundation volume of 750,000 acre-feet (921 million m3), for this peak discharge of 29,500 ft3/sec. The percent of marsh inundated will vary with wind direc tion and tide stage. With a low tide (range -0.9 feet to 0.8 feet above MSL) and a peak discharge of the magnitude mentioned above, the model predicts that 'about 21 percent (Figure 5-46) of. the delta area will be inundated to a depth of at least 0.5 feet for a minimum of 48 hours. Under a "high tide" (range 0.6 to 2.4 feet above MSL) similar peak discharges will result in inundation of 98 percent of the Trinity delta. Estuarine Linear Programming Model Description The combination of specified objectives and environmental and physical constraints relating the interactions of freshwater inflows with selected estuarine indicators is termed the Estuarine Linear Programming Model. The model relates the conditions of the estuary, in terms of a specified criteria, IX-9 Table 9-3. Peak Gaged Discharges for Discrete Flood Events Greater than 20,000 ft3/sec in the Trini.ty River at Romayor, 1924-1977 ----.-.-:------:----.-- --;-------:----:------:-----;------:-------:-·-r Jan. : Feb. : Mar. : Apr. : May : Jun. : JuL : Aug. : Sep. : Oct. : Nov. : Dec. : : : : -- ft3/sec 59,300 50,800 47,700 104,000 107,000 94,200 44,100 33,500 40,200 49,000 60,800 46,600 48,100 48,800 47,000 52,200 93,000 57,700 36,300 20,000 26,800 45,300 52,400 40,200 37,700 47,000 44,100 50,600 69,000 49,400 22,700 25,100 31 ,100 51,200 38,700 36,500 45,800 41,300 46,600 66,800 48,700 28,500 46,600 35,100 36,400 41,700 39,000 43,800 66,200· 40,600 23,000 45,600 27,400 32,600 34,500 37,800 41,800 61,600 33,200 42,200 26,300 30,500 29,800 37,600 41,500 58,200 27,300 33,500 25,200 28,800 28,900 34,700 40,600 51,500 26,300 30,800 24,000 28,400 28,500 33,600 40,400 48,000 25,600 21,200 23,800 H 28,000 27,700 30,900 39,700 47,200 23,400 23,500 x 26,500 27,400 30,700 33,000 46,600 22,500 23,200I ~ 24,600 27,000 27,200," 32,400 45,200 22,3000 24,200 26,600 26,800 31,600 42,400 22,200 23,800 25,700 26,000 29,000 40,000 21,200 23,200 25,200 25,000 27,400 37,600 20,100 22,200 24,300 24,000 26,800 37,200 20,000 21,800 24,000 24,000 24,700 35,800 20,800 22,500 23,800 21,700 35,100 20,500 21,600 21,600 21,300 28,500 20,100 21,600 21,300 20,200 26,400 20,000 21,200 21,000 19,600 25,900 21,000 21,000 25,500 20,300 24,400 23,000 22,800 22,700 21,400 20,800 Mediarl-peakTIwnstream Stream Gage b/ Trinity River Basin Inflow Needs from Drainage Area of the Basin.Upstream,fram the Last D::>wnstre&~ Stream Gage c/ Total Inflow Fran Coastal Basins ~ Combined Inflow ~ Thousands of Acre-Feet January 249.4 '181.5 135.9 96.1 103.0 488.3 February 215.1 153.0 136.9 97.1 128.0 480.0 March 164.2 110.6 115.8 81.4 85.0 365.0 April 217.• 0 154.5 750.0 691.2 109.0 1,076.0 May 268.0 197.0 750.0 702.2 144.0 1,162.0 June 180.5 124.1 450.7 429.9 129.0 760.2 July 134.1 85.4 49.2 56.5 54.0 237.3 August 132.8 B4.4 62.7 59.0 60.0 255.5 September 149.2 98.0 86.5 70.2 97.0 332.7 October 99.9 57.0 750.0 670.2 89.0 938.9 November 95.0 52.9 133'.5 94.8 76.0 304.5 December 198.3 139.0 159.6 119. 1 94.0 451. 9 H - ._--- ._--- ---- X I Annual ·2,103.5 1,437.4 3,580.8 3,167.7 1,168.0 6,852.3~ lJ1 al All inflows are mean rronthly values S/.These values computed using regression equations relating monthly river basin inflow to the estuary with monthly gaged inflows at -. USGS Stations #08074000,08074500, 08075500, 08076000, and 08076500 .: cl These values oomputed~ using regression equations relating monthly river basin inflow.to the estuary with monthly gaged flows at - USGS station at Romayor, with historic diversions between the stream gage arid the estuary removed dl The ooastal basins are the Neches-Trinity, Trinity-San Jacinto, and San Jacinto-Brazos; ~ Includes all freshwater inflow to the estuary except direct precipitation on the estuary's surface (see Chapter IV for definition) ,. ' .. 30,..---------.....--------------------, 25················································· -:;::- 20 a. a. '-' >- 15 -c o(/) 10 f!.•.••...•.f!.•.•..... ·A:············ :f!r ·eo: ... . ,f!r········eo . . .: 'A f!. fj,: . . .. .f!........•...e,.,. decaug(un (ul Month mayaprmar sep r---"o"'CT\t=.i.n..,o,,-,Ve-, LEGEND ~=PREDICTED 0= UPPER BOUND l>= LOWER BOUND Average Monthly Salinities in Upper Galveston Bay Under Alternative IFigure 9·2. 0+--......--..,..-......--..,..-......--.....-...,--.....-...,....- .....-_...._ ... . (on feb 30,..------------------------------...... 25 ... ~ 20 --- - - - -- . a. a. '-' >- 15 == 5 . c e5l 10 t!f-------t!f-------i!l . , , , , ............ .ec c· •. -- -e .- - - - " --8-_. ...!'>••.•••.• i!i . fan ·6 .....f, o~-~-_--....--..,......;;....,.....;;~......,....,...-~-_--....--..,..--I feb mar apr may (un lui Month Figure 9·3. Average Monthly Salinities in Trinity Bay Under Alternative I IX-16 and October provide salinities lower than the upper limit as a ronsequence of meeting marsh inundation .requirements f,?r the Trinity delta. The upper and lower salinity limits are the same in Trinity Bay for the nonths of December through March and JUly since the median salinities were less than the lower viability limit. ' .. Comparisons between the mean 1941 through 1976 historical combined inflows and the estimated freshwater inflow needs are made for each nonth (Figure 9-4 and 9-5), for the San Jacinto and Trinity River Basins. For the San Jacinto River Basin, the inflow needs are less than the mean nonthly 1941 through 1976 inflows, with the exceptions of the nonths of January, March, August and December. For the Trinity River Basin, the mean 1941 through 1976 IlIOnthly inflows exceed the inflow need except for the nonths of April and. September when marsh inundation events are scheduled. The distribution of the 'freshwater inflow needs between rontributing basins is illustrated in Figure 9-6. The inflow from the three adjacent coastal basins is a significant ron tribution accounting for approximately ,17 percent of the total annual inflow. Implementation of Alternative I for the Trinity-San Jacinto estuary under the inflow regime indicated in Table 9-6 is projected to result in a general increase in commercial fisheries harvests from average historic levels (Figure 9-7); The finfish category is predicted to have an annual harvest of 500.8 thousand pounds (227 thousand kg), or a 44 percent increase above average; total shellfish harvest (including the harvest of shrimp from offshore Gulf Area No. 18), a 15 percent increase above average historic levels; and bay oyster, a predicted 14 percent above average historic levels. Only the bay harvest of red drum is predicted to be lower than the mean 1962 through 1976 mean historic harvest (26 thousand pounds or 12 tho.usand kg versus 36 thousand pounds or 16 thousand kg). Alternative II: Maintenance of Fisheries Harvests. The objective of Alterna tive II (Maintenance of FiSherIes Harvests) is to minimize 'combined inflow to the estuary while providing freshwater inflows sufficient to generate pre dicted annual commercial harvests of red drum, spotted seatrout, shrimp, blue crab, and bay oyster at levels no less than their mean 1962 through 1976 historical values, satisfying marsh inundation needs, and meeting rounds for' salinity. . The optimal set. of nonthly freshwater inflow needs derived by the Estuarine Linear progranuning Model for Alternative II (Table 9-7) amounts to· 7.19 million acre-feet (8,865 million m3) annually, of v.hich 10 17· million acre-feet (1,443 million m3) are rontributed from the coastal basins. The computed annual.contributions of the San Jacinto· and Trinity River Basins are 2.42 thousand (2,984 million m3) and 3.60 million acre-feet (4,439 million m3), respectively. The yearly inflow volume from the San Jacinto River Basin is slightly greater (seve~ percent) than the average historical inflow, while the inflow specified from the Trinity River Basin is 40 percent less than the historical average annual inflow of 5.962 million a=e-feet (7,351 million m3) over the period 1941 through 1976. Relatively little additional inflow (340 thousand acre-feet or 419 million m3) above that required for Alternative I is needed to satisfy the constraints of this. alternative since only one of the predicted species har vests (red drum), under Alternative I inflows, fails to be at least as great as its historical average harvest. The additional inflows occur in the IlDnths of November and December. All but cipproximately 20 thousand acre-feet (24 mill ion m3) of the 340 thousand acre-feet (419 million m3 ) is required IX-17 San-Jacinto River Basrn Inflow to Estuary ,...... l-t 1200-r--~-~--~--~--~--~-""'--"",--"""---:---~-"" U « o 1000 . o o ~ '-' 800 . .......... - . · . · ... __ - __ -. · . . · . · . · . 600 .. dec HISTORIC ESTll/ATED NEEDS sep o D augfun lui Month Trinity River Basin Inflow to Estuary '. ". --_.- ----- - -. , .' . . . . . mayaprmar . . '. . , .................. - -- .. __ . febfan 400 ....... 200 ... 600 400 .. 200 800 .~ o ;:;:: c ... Q) -o ~ .r: Ul Q) ... ... > .r: -c o ~ ,...... I- ... 1200I U « 0 1000 0 0 ~ '-' ... Q) -o ~ .r: Ul Q) ... ... > .r: -c O~......-r...."""'"...,,,I,,,O~..I.io~:I........""-l_y."""'..-r...."""'"-O'....""'-..I.io"-'.........""'-l_y.~..-r.,.............. o~ [lin feb mar apr may fun lui aug sep oct nov dec Month 0 ESTIl/ATED NEEDS D HISTORIC Figure 9-4. Comparison Between Mean Historical Freshwater Inflow and Inflow Needs Under Alternative I for the Trinity-San Jacinto Estuary From the San Jacinto River Basin Figure 9-5. Comparison Between Mean Historical Freshwater Inflow and Inflow Needs Under Alternative I for the Trinity-San Jacinto Estuary From the Trinity River Basin IX-18 fon' feb; mor. opr moy. lun lui oug sep oct nov dec Month rzJ TRINITY RIVER BASIN _ .. " D SAN JACINTO RIVER BASIN rzJ COASTAL BASINS 900 . '. 300 600 . 1200r---~~----;~::;::;;-----------~-:-----, ... '0> . ... o .~ .s:. ., ., ... ... > .s:. ... 'c o ~ ~ o ! .:;::: C o ... ... 0> ... o .. -0( o o o ~ ~ Figure 9-6. Estimated Freshwater Inflow Needs for the . 'Trinity-San Jacinto Estuary Under Alternative I 0· ., .D , . .'. ..,.... 0 all sp c c -0( o 8 22000 -r--------------~---------------..,...--....,~ ~ ... ., .s:. ., ... .... ., "I» .. ~ 16500 o :z: ., . ., ., . 0> o ... ., > -0( Figure 9-7. Comparison Between Trinity-San Jacinto Historical ., ,', ' . Fisheries Harvests and Predicted Harvests Under Alternative I IX-19 from the San Jacinto River Basin since salinity bounds limited oclditional inflow from the Trinity Basin. Monthly freshwater inflow needs generated for Alternative II provide salinities which oorrespond. to those under Alternative I (Figure 9-8), except for the nonths of November and December in upper Galveston Bay and November in upper Trinity Bay (Figure 9-9). Comparisons between the mean historical ccmbined inflows and estimated freshwater inflow needs are made for the San Jacinto and Trinity River Basins (Figures 9-10 and 9-11). The average 1941 through 1976 historical inflows from the San Jacinto River Basin are higher than the freshwater inflow needs under this alternative for about half of the nonths. Fran the Trinity River Basin, inflows larger than historical average values are needed only in April and October. The Estuarine Linear Programming Model distributes nonthly inflows to achieve Alternative II (Maintenance of Fisheries Harvests) as indi cated in Figure 9-12. Implementation of Alternative II for the Trinity-San Jacinto estuary under the inflow regime indicated in Table 9-7 results in a projected increase in comnercial fisheries harvests fran average historical levels for all har vest groups except red drum (Figure 9-13). The red drum harvest is predicted to be equal to the 1962 through 1976 average historic harvest of 36.3 thousand pounds (16.4 thousand kg) annually. Alternative III: Shrimp Harvest Enhancement. The obj~ive of Alternative III (Shrimp Harvest Enhancement) is to maximize the annual offshore can mercial harvest of shrimp in the offshore region ocljacent to the estuary (Gulf Area No. 18) while observing salinity limits and marsh inundation needs, and utilizing annual San Jacinto and Trinity River Basin inflows 00 greater than there respective average historical annual inflows. The Estuarine Linear Programming Model was utilized to deteDlline an optimal set of nonthly river basin inflows to meet the stated objective (Table 9-8) . The annual canbined inflow 11 fran freshwater sources needed to maximize the offshore shrimp harvest is estimated at 7.02 million acre-feet (8,656 million m3). The total annual contribution fran the Trinity River Basin is estimated at 3.59 million acre-feet (4,426 million m3), while the corresponding San Jacinto River Basin contribution is limited to' the histori cal average of 2.26 million acre-feet (2,787 million m3). Additional inflow from the San Jacinto River Basin loOuld have increased the predicted harvest without violating Salinity limits. The remaining annual freshwater oontribu tion of 1.17 million acre-feet (1,443 million m3 ) is the historical average annual inflow fran the contributing coastal basins. Salinities in the upper Galveston Bay are the same under both Alterna tives II and III, except in July, August, NovernbEir, and December (Figure 9-14). Monthly freshwater inflow needs generated for Alternative III provide salinities which are lower than those under Alternative II only in, the nonth of August in Trinity Bay (Figure 9-15). In November, OOwever, upper Trinity Bay salinity is slightly higher than that under Alternative II. 17--CCinbfne- 15 =:. c oVl 10 5 .. &-- - .. , , , , ......'t7.:.:.:..". - -8-_ . :'6' .-._." - .... .:'6 ....... 1!!.o~~..,........;...;..,.--.,....- ......-.:;;....,....:::....,,....-..,...-.....--....,--.,....-..,..-_l jan feb, .' mar ,'.. apr may lun rul Month aug sep ~-'o"c;.t'-=d,n!-'o~v'......, dec LEGENO ~= PREDICTED 0= UPPER aOUND l:>= LOWER BOUND Figure 9-9.-' Average'Monthly Salinities in Trinity Bay Under Alternative II IX-21 San-Jacinto River BasIn 1000 Inflow to Estuary ~ I- 't 1200 -r---"--"",--"""--"---""'--"--""'--"""--"---""'--"---' o < o o o '-' ~ o ;;:: c 800 .. · . ....... _-.- - -.- . · ., . ., . · . · . · . . . . -.. -- - "" - - . L CD .... o ~ L: III CD L ... > L: .... C o :::E 600 400 ...... 200 Ian feb mar apr may [un lui Month aug sep o oc t nov ESTlIlATEO NEEDS dec · . . , . ..................................................................._-.- - . · . . . . D HISTORIC Figure 9-10. Comparison Between Mean Historical Freshwater Inflow and Inflow Needs Under Alternative II for the Trinity-San Jacinto Estuary From the San Jacinto River Basin 200 .... decoct nov ESTlIlATED NEEDS sep o augfun lui 'Month TrInIty River Basin . Inflow to Estuary mayaprmarfebIan ................. -..... · . · . · . 400 ~ I- ... 1200I 0 < 0 1000 0 0 -'-' ~ 800 0 ;;:: c 600 L CD .... o ~ L: III CD L ... > L: .... C o :::E D HISTORIC Figure 9-11. Comparison Between Mean Historical Freshwater Inflow and Inflow Needs Under Alternative II for the Trinity-San Jacinto Estuary From the Trinity River Basin IX-22 feb mar apr may lun lui aug sep oct nov dec Month [2] TRINITY RIVER BASIN D SAN JACINTO RIVER BASIN fZJ C9ASTAL BASINS 600 . Ion 300 ... '" -o ::l ~ III .. ... .... > ~ c: o :::; r;- .... .. t 1200 T------------;:;::;::;:;;------------:---------..., -e( o o oV 900 r; III .0 Figure 9-12. Estimated Freshwater Inflow Needs for the Trinity-San Jacinto Estuary Under Alternative II o g 22000 -r----------------------------------, III .. ~ 16500 o ::r: III .. ... .. ~ III .... II> Ol o ... .. > -e( 11000 . 5500 .. 0 all spotted red all all whTte brown blue boy ffnflsh a.otrout drum shellffsh shr(mp shrimp shrImp crab oyster 0 PREOICTEO D HISTORIC Figure 9-13. Comparison Between Trinity-San Jacinto Historical Fisheries Harvests and Predicted Harvests Under Alternative II IX-23 Table 9-7. Freshwater Inflow Needs of the Trinity-San Jacinto Estuary mder -Alternative II ~ Total Inflow Needs· Trinity River Basin Month San Jacinto River Basin Inflow Needs from Drainage Area of the Basin upstream from the Last Downstream Stream Gage b/ Total Inflow Needs Inflow-Needs fran Drainage Area of the Basin Upstream fran the Last Downstream Stream Gage c/ Total Inflow Fran Coastal Basins 9i Combined Inflow Y "a/ All inflows are mean rronthly values. bl These values computed using regression equations relating monthly river basin inflow to the estuary with monthly gaged inflows at - USGS Stations #08074000, 08074500, 08075500, 08076000, and 08076500. c/ These values computed using regression equations relating monthly river basin inflow to the estuary with monthly gaged flows at - USGS station at Romayor, with historic diversions between the stream gage and the estuary removed. d/ The roastal basins are the Neches-Trinity, Trinity-San Jacinto, and San Jacinto-Brazos.31 Includes freshwater inflow need fram the basin distributed according to San Jacinto River Basin historical monthly freshwater inflow (1941-1976) in the season (November and December). y Total seasonal freshwater inflow need from the basin distributed according to San Jacinto River Basin historical ITDnthly freshwater inflow (1941-1976) in the season (November and December). H ~ '"~ Thousands January 249.4 181.5 February 215.1 153.0 March 164.2 110.6 April 217.0 154.5 May 268.0 197.0 June 180.5 124.1 July 134.1 85.4 August 132.8 84.4 September 149.2 98.0 October 99.9 57.0 November 308.2 i/ 230.5 December .300.~ y -224.4 Annual 2,419.3 1,700.4 of Acre-Feet 135.9 96.1 • 103.0 136.9 97.1 128.0 115.8 81.4 85.0 750.0 691.2 109.0 750.0 702.2 144.0 450.7 429.9 129.0 49.2 56.5 54.0 62.7 59.0 60.0 86.5 70.2 97.0 750.0 670.2 89.0 154.4 114.2 76.0 159.6 119. 1 94.0 3,601.6 3,187.1 1,168.0 488.3 480.0 365.0 1,076.0 1,162.0 760.2 237.3 255.5 332.7 938.9 538.5 554.5 7,188.9 ! H ~ N U1. I Table 9-8. Freshwater Inflow Needs of the Trinity-San Jacinto Estuary under Alternative III ;y' San Jacint9 River Basin : Trinity River Basin : Total Inflow : Canbined Inflow Needs fran : : Inflow Needs fran : Fran Coastal : Inflow ry Month : Total Inflow : Drainage Area of the : Total Inflow : Drainage Area of the : Basins 31 Needs : Basin upstream from : Needs : Basin Upstream fran .. : the Last Downstream : : the Last Downstreai1\ Stream Gag" bl : : Str,,~am Gage c/ Thousands of Acre-Feet January 249".4 181.5 135.9 96.1 103.0 488.3 February 215.1 153.0 136.9 97.1 128.0 480.0 March 164.2 110.6 115.8 81.4 85.0 365.0 April 217 .0 154.5 750.0 691.2 109.0 1,076.0 May 268.0 197.0 750.0 702.2 144.0 1,162.0 Juri.e . 180.5 124.1 450.7 429.9 129.0 760.2 July 250.6fl 182.5 49.2 56.5 54.0 353.8 August 172.81/ 117 .5 73.9 69.4 60.0 306.7 September 149.2- 98.0 86.5 70.2 97.0 332.7 October "99.9 57.0 750.0 670.2 89.0 938.9 November 95.0 52.9 133.5 94.8 76.0 304.5 December ~~:1 139.0 159.6 119. 1 94.0 451.9 ---- Annual 2,260:0 1,570.6 3,592.0 3,178.1 1,168.0 7,020.0 Oaf ':"All -iTIflows are mean rronthly -values. -------- --------.-"- . 5/ These values computed using regression equations relating monthly river basin inflow to the estuary with mOnthly gaged inflows at - USGS Stations #08074000, 08074500, 08075500, 08076000, and 08076500. c/These values cOmputed using regression equations relating monthly river basin inflow to the estuary with monthly gaged flows at - USGS station at ROmayor with historic diversions between the 'stream gage and the estu~ry removed. dj'The coastal basiqs are the Neches-Trinity, Trinity-San Jacinto, and San jacinto-Brazos. ej Includes all freshwater .inflow to the estuary except direct precipitation on the est-tiary's surface (see Chapter IV for definition). II Total seasonal freshwater . inflow need from the San Jacinto River Basin distributed August according to the river basin (1941-1976) - average monthly ~flow distribution in the season (JUly and August). 30 25 ,...., 20 -0- 0- -..J >- 15 ==c -0 10(f) ..- . ',13----13---- - . --- '" . ... .. . " ;,/... ....... . . .. . _. -'" . , ... -& ..••••• •f!,•..••••.•f!,.: .... ............•.................. ':b"'" f!, ······················:b .-c-----is . 5···················· ......... :·:'is········is······· -fJ.'-:"." .": :f!,··-------a:"··· . 0+--...,..-.....,.--,...---.....--......--,....-.,....-...,..-......--.....- .....- ...... ron feb mar apr may [un lui Month aug sep r--"o""c;,;t"",,",npo,-,v., dec LEGENO ~= PREDICTED 0= UPPER BOUNO t.= LOWER BOUND Figure 9·14. Average Monthly Salinities in Upper Galveston Bay Under Alternative III 30-r-------------------------------, 25 ~ 20 - -- -- . 0 0 -..J ................. 'a..---·.. ~ 10 ···.--.--ft····································· _---O~ _.. -. ............. - . 5 >- 15 ==c '6' ... -I!i. 0 ......-...,..-......--.....- .........;;;......,..-;;;.....---.....- ......--,....-.._-.....-:-..... fan run lui Month aug sep oct nov dec LEGEND ~= PREDICTED 0= uPPER BOUND t.= LOWER BOUND Figure 9-15. Average Monthly Salinities in Trinity Bay Under Alternative III IX-26 COmparisons between inean 1941 through 1976 historical oombined inflows:' and' estimated' freshwater inflow needs under Alternative III have I:i!enmadefor the San Jacinto and Trinity River Basins (Figures 9-16 and 9-17). The average historical inflows from the San Jacinto River Basin are higher than the fresh water inflow needs under Alternative III 'for all llDnths except January, March, July, August and December. Historical inflows from the Trinity River Basin are higher than the estimated needs under Alternative III for all llDnths except April and october. The Estuarine Linear Programming Model distributes monthly inflows to achieve Alternative III (Shrimp Harvest Enhancement) as indicated in Figure 9-18. , According to this analysis, implementation of Alternative III for the Trinity-San Jacinto estuary under the inflow regime indicated in Table 9-8 Would result in an estimated 12 percent increase in total offshore (GiJlf Area No. 18) shrimp harvest above the 1962 through 1976 mean historical level (Figure 9-19). This increase OCcurs when the inflow level is equal to 100 Percent of mean historical ,inflow from the San Jacinto River Basin and 60 percent of ,the mean historical inflow from the Ti:-inity River Basin.. Pro jected ,changes m individualharv-est categories under Alternative III include' . a ' 1s percent increase' in the overall shellfish harvest, (including offshore shrimp), a' very 'slight increase '(0.5 percent) in blue crab harvest, a four' percent' increase iri" offshore white' shrimp harvest, and a seven percent increase in offshore brown shrimp harvest. An increase in annual bay oyster harvest of four percent is also projected. In the finfish categories, projected manges from, 1972 through 1976 historical harvests in the estuary include a 19' percent increase' in 'the overall finf ish harvest, a 49 percent increase in spottedseatrout' harvest, and a 57 percent decrease in red drum harvest. Application of Tidal Hyqrodynamic and Salinity Transport Models The determination of preliminary estimates of freshwater inflow needs, described above, must be followed by ooditional steps in the methodology in order to insure that the resulting salinity distribution throughout the estuary is satisfactory (Figure 9-1). The Estuarine Linear programming Model considers salinities only at two p:>ints in the Trinity-San Jacinto estuary' near the major'sOurCes of freshwater 'inflow. 'Ib determine circulation' and Salinity patterns throughout the estuary it is ,necessary to apply the tidal hydrodynamic arid' salinity mass transport nDdels (described in Chapter V) using' the estiinates of llDnthly freshwater, inflow needs obtainoo from the Estuarine Linear Programming Model. If the circulation patterns and salinity gradients predicted by the hydrodynamic and transport nDdels are acceptable, then the tentative llDnthly freshwater inflow .needs may 'be accepted. ' Should. the estimated estuarine COnditions not be satisfactory" then :the constraints upon the Estuarine Linear Pr09ramming Model must be nDdified, and the J!Odel' used agai~to .compute new:e~timates. Salinity patterns' of the estuary are of primary importance for insuring that predicted salinity gradients provide a suitable environment for the estuarine organisms. For high productivity, it is estimated that mean llDnthly mid-bay salinities in Galveston Bay should not exceed 20 parts per thousand (ppt) in any ./lDnthunder. tI1eprojected llDnthly, freshwater inflow needs. The lowest annual inflow to the estuary from any of. the three alternatives con sidered here is provi.<;led. by Alternative I; thus, if the salinity conditions IX-27 ~ I- .... 1200I· (.) « 0 1O00 .. 0 0 - ....., ;l 800 0 .... <: San- J ac i n toR I ve r Bas rn Inflow to Estuary .... _. . ---...-_. .. -......... ................ .... · . · . 400 . 600 . . . .-........ ...... ............. .. ...-.. . . . · . . · . · . · . .decoct nov HISTORIC ESTIlIATED NEEDS sep o o augjun Ju I Month mayaprmarfebjan 200 I. '".... o ;l .l: '" '"I.- .... > .l: .... <: o ::::l: Trinity River Basin Inflow to Estuary Figure 9-16. Comparison Between Mean Historical Freshwater Inflow and Inflow Needs Under Alternative III for the Trinity-San ;::- Jacinto Estuary From the San Jacinto River Basin 't 1200,...--.,....----...,.---:---.,..----.....,--...,.--...,..--...,.--.,....--, (.) « o 1O00 o o ....., ;l .800 . o ;;:. <: aug sep oc t nov dec o EST IliATED NEEDS .0 HISTORIC -.. .. -... .. ........ . · . · . · . fun ful Month · . . . feb mar apr mayjan 400 ... 600 .. 200 ,...... I. '"....o ;l .l: '" '"I.- .... .l: .... <: o ::::l: Figure 9-17. Comparison Between Mean Historical Freshwater Inflow and Inflow Needs Under Alternative III for the Trinity-San Jacinto Estuary From the Trinity River Basin IX-28 aug sap oct nov dec rzJ TRINITY RIVER BASIN D SAN JACINTO RIVER BASIN ~ COASTAL BASINS (un (u I Month Ian 600 ~ o .... <: .... Q) -o ~ .£ III Q) .... " > .£ -<: o :::; Q) ~ 1200 T------------;:;;:~:;_--------------------..., o o o '-'" Figure 9-18. Estimated Freshwater Inflow Needs for the Trinity-San Jacinto Estuary Under Alternative III III .n III Q) ~ 16500 o :I: o o S! '-'" III Q) .... Q) .£ III 22000 -r--------------------------..,..------, 5500 Q) Ol o .... Q) > .q: O+"=---...,..---,---.,....u.......¥.u...........,.....I-l......roi'-''''"-l........"r"'-~.L-..,.'"-'I ....."''''i all' spotted red all all whlh brown blue boy flnffsh seatrout drum shll!lllffsh shrimp shrImp shrfmp crab Q other alternatives considered should also satisfy the condition (since they specify higher inflows). A lower limit on salinity in Galveston Bay is not evaluated since it was not anticipated that the IlDnthly inflows under the three alternatives \>Quld give salinities lower than 10 ppt. Simulation of Mean Monthly Circulation Patterns. The estimated IlDnthly fresh water inflow needs of the Trinity-San Jacinto estuary under Alternative I are used as input conditions to the tidal hydrodynamics IlDdel, along with typical tidal and meteorological conditions for each IlDnth, to simulate average circulation patterns in the Trinity-San Jacinto estuary for each IlDnth of the year. The output of the tidal hydrodynamics IlDdel consists of a set of tidal amplitudes and net flows computed for each cell in the 46 x 32 computational matrix representing the Trinity-San Jacinto estuary. 'The computed net flows are the average of the instantaneous flows calculated by the IlDdel O'ler the tidal cycle. Thus, the circulation pattern represented by these net flows should not be interpreted as a set of currents that can be observed at any time during the tidal cycle, but rather as a representation of the net IlDVe ment of water created by the combined action of the Gulf tides, freshwater inflow, and meteorological conditions during the tidal cycle. The resultant circulation patterns can best be illustrated in the form of vector plots, ~erein each vector (or arrow) represents the net flow through a computational cell. The orientation of the vector represents the direction of flow, and the length of the vector represents the magnitude of flow, with one inch corresponding to a flow rate of 11,000 ft3/sec (310 m3/sec). The simulated IlDnthly circulation (Figures 9-20 through 9-31) patterns in the estuary can be divided into t\>Q groupings based uPJn similarities: (1) March, June, August and October, and (2) all the remaining IlDnths. The flow characteristics exhibited by the munerical simulations in each of these cases are discussed below. (1) Simulated March, June, August and October Circulation Patterns. The flow cirCUlations in the Trinity-San Jacinto estuary are simulated for historical average meteorological conditions and estimated freshwater inflow needs for Alternative I for the IlDnths of March, June, August and October. The predominant wind speed and direction of 10.6 miles per hour (mp"!) (4.7 m/sec) fran the south-southeast varies only slightly among these IlDnths. The most obvious circulation pattern evident in the estuary during the indicated months is a northwesterly-directed current in the Houston Ship Channel toward Morgan's Point. The magnitude of the net flow in the Ship Channel is exceeded only by -the flow rate in the vicinity of Bolivar Pass. The daninant pattern in Trinity Bay is a clockwise circulation induced by prevailing winds. The current in West Bay is predominantly directed in a northeasterly direction from San Luis Pass to Galveston Bay. The IlDvement of water in East Bay is generally in an easterly direction from Galveston Bay through Rollover Pass at the eastern end of Bolivar peninsula. IX-30 DOUBLE BAYOU , " ' ... ..... ...... -+ .. "y... " ... . _/' , .. .. ~ ~ .. .. .. . 'I OYSTER 'I I' , , 'i--I: I :¥r" .~ ROLLOVER PASS .' .. BOLIVAR ROADS . , ,. , ,. ,. ,. • '. ~ ~ ~ l' ?< '" '" '" -'< 1- to ,. 10 J< .... .. .. .. r ~ , ....I I! CEDAR: "--. "- \/ J';J BAYOU ,/ / ." \ \\.1 ////~.'i\~ ",,-~,,---,( '.,( I j ,t 11.•••• "'\\ A/II' .. \'.,~/ ~ ~ , .~ '~ , f J' • • f f ~ ........ -/'/ ! ~ ~ J' t , "- " '. " '. :1 , , .. , , , t t , • , , • . , , t " \ , HOUSTON SHIP ~ __ . CHANNEL' .~- . / BARRIER ISLAND + + + + + ~ GULF OF MEXICO .. GALVESTON BAY I" .. , MOSES BAYOU .... - ...... -------r-, I DICKINSON BAYOU CLEAR CREEK ,I I~' I . , CHOCOLATE BAYOU MUSTANG, BAYOU HALLS BAYOU ~ ---,'" .I ..... _ 4-- - ..-. '\ ~ ~ ~ ~ ~ + ? ~ , ~ ... ......... _t.~ , SAN LU IS PASS ~ ,. • ~ n n m n ~ n n 0' m • " n • n HX ,.,. V> " n " • • ,0 U l~ lJ )~ IS !.s n l~ l~ cO ~! ~~ ~l :.. ~5 ,S /n ~, h 10 ,,' n n )' j", ,~ j~ ,'j ]~ ~o 4; 4~ n ,4 45 .~ NAUTICAL MILES Figure 9-20. Simulated Net Steady.State Flows in the Trinity-San Jacinto Estuary Under January Freshwater Inflow Needs, Alternative I DOUBLE BAYOU ;" ;') ~~ 4~ '1 4~ n .. -l~ lS , · . . , · , • .. io 11 .'" .., • • . . • ~, .. , • . .... ~ t • .. ~ ~ o· r '-. • ~ ~ ~ ~ , . . '. ~ . . IOYSTER BAYOU • ; . I, • ~ ~ f , , " l' ~ • n ~'i ~.; • I • .......,.-/ ! ... I I • HOUSTON SHIP:-_ CHANNEL ~I "_ .. / ----;::::: "'. "I .. < •. / CEDAR .-.... '" \ .~ ~ .\ '1 BAYOU /-:: ' \ \ "" . ---/// \i\~ I . "'._~.~. .. .. i I I • tIl \ \ ,\. • • • 0 • I • \ \ , ~ ! !/1 .. " .. \,'-.,,-....~/ . ~ - ... + ... ... BARRIER ISLAND GULF OF MEXICO GALVESTON BAY f" ~ • '" 'l. , ~I ---+\J'" . "···~D:l\,,... -. '>0. .~ .. I f> - ~ , '. "'~ ,h~. BOLIVARROADS. -, , ." ,,,,,,,,,,,,,,.,, .. MOSES BAYOU DICKINSON BAYOU CLEAR CREEK-r- I :D 11 l~ 11 )4 ~, !_~ l? l~ l~ ~c ~l n • <~ 1 < ,I I~' . .... --_ ....... .-.. '\ < I .. .. CHOCOLATE BAYOU ,MUSTANG BAYOU HALLS BAYOU ~ ~ ~ ~ ~ ~ ~ - ~ ~ . 'SAN LUIS PASS a • • • N n ~ • " n ~2 ., m w w n " HX ~ I CO H N n w " m NAUTICAL MILES Figure 9-21. Simulated Net Ste'ady-State Flows in the Trinity-San Jacinto Estuary Under February Freshwater Inflow Needs, Alternative I OYSTER BAYOU:n .~ ~ ROLLOVER PASS · ~ ./ . BOLIVAR ROADS " '" ---: '."'~ , ! \ , , , ! ~ --", , r ! .' ..• .- .- · t , t I t, , • , , · I , I I ~ .. .. · \ , , · t • I . ~ /\ , , • , \ • • I I I • \ ~ DOUBLE,I I I , , , / BAYOU J I I ~ < , I I I I i I , I I I \ J~\ . , ~I ~ • • • • , .I '" ...... ....- I? • ... // I I I I I , j j I ,/ I , I '. \ \ ' \ 0 , \. \ /' ............ -'1 \ I \ '\. "" ... GULF OF MEXICO BARRIER ISLAND MOSES BAYOU ~. I . I ,/ , 'j / 1"---'--- / / ~ //"rll/I 1 \ \ .. \ ~'-"''-... DICKINSON *'- . . . . t LV/~1 BAYOU CLEAR CREEK~"':-.---- . . ' HOUSTON SHIP _ CHANNEL ~ I ~ .... &" ~ ",. ~ ,I I~' CHOCOLATE BAYOU ,MUSTANG BAYOU HALLS BAYOU ~ ~ ~ . I .I .. .. ,. ~ '>t " ,;,,··,. ..,. 10 ! SAN LUIS PASS E 0. m ~ n ~ ~ ~ ,. n 22 2! W " " ,. u "H X "I CO ,. CO " " • HI II 12 !3 II 15 16 l? 16 IS 20 21 n 23 c~ 25 26 27 2'3 N lC 31 10: 3l II % 36 )7 38 3S 10 II 42 43 H (5 '6 NAUTICAL MILES Figure 9-22. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary Under March Freshwater Inflow Needs, Alternative I OYSTER BAYOU DOUBLE BAYOU 'y . t • . ., ~ , , • • _. .. .....-------Y .- ....... ....... '\ .. ..-./'''' ........... . . OLiVAR ROADS '. • 28 ;'S )0 31 n :n l' )5 35 17 36 39 ~o H 42 ~3 U 45 46 · . · . ~I \ --.. t /' ~ - ~ '\ t ,. Itt j t • --- I 1Y I J' , \ HOUSTON SHIP __ CHANNEL .." - 1 .. .. .. .. .. t .. .. .. .. .. BARRIER ISLAND -----_./' / ~ :'~;~BAY·O~_I' //-"'"' \[/ l;~"~'/I---'-\~~//~, '~//I/~\\ 1,,--,,/1 ~_::::'-///II",\\-. It", ~~~"' '-/~III·i\,! GALVESTON BAY---J\".. '" i . . ~ ~ - - I ,( I ' , .-" I~~/\il'~/ · ... .. ... .. ~~ I , MOSES BAYOU DICKINSON BAYOU CLEAR CREEK ~ ... ,. .... -..-" ,I I~' /' -+ ..... ." .J' ... ..... ..... ..... .I' .... CHOCOLATE BAYOU MUSTANG BAYOU HALLS • • "I BAYOU 1 t • ~ '-. --.~--./' ~ (~ V SAN LUIS PASS GULF OF MEXICO I ;: 1 S f; 7 ~ 9 JO Il I;: 11 H IS 15 17 13 15 ;:0 Z! ;:0: ;:) ;:4 25 ;:5 • ., m • " n m B ., B • ., m n n " n g~ ,.I CO n~ " " " NAUTICAL MILES Figure 9-23. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary Under April Freshwater Inflow Needs, Alternative I OYSTER BAYOU DOUBLE BAYOU ~ ... ·r· . . • • - ~ " ........... • ,/ .. .. .. ~ ~ . • . - -- " ,..'------ ¥' ...- ,,/ ./'/- -. '\ ~--/--///-'''--~ ~--/~//*'" --- -- , ~ .. ~ ~ , OLiVAR ROADS , '" ............. - II" ~ - "n ; \ /.-'~'~! ,. ~t ~' I ,/'/ , ... , \ ~ ... ~ - - "- . - ~ I ' , . :1 - • ~ - , , , .. • · • t t · • t • · , /' J' ~ , ~ , \ \ I i '- ... , GULF OF MEXICO BARRIER ISLAND .... .. .. .. .. .. GALVESTON BAY p!' __ MOSES BAYOU DICKINSON BAYOU CLEAR CREEK HOUSTON SHIP _ CHANNEL:--' I ,I I~' CHOCOLATE BAYOU ,MUSTANG BAYOU HALLS I "1 BAYOU I ~~--~~--~/_/-----/? /' -. _ ~ ..... ... .A / _~---" /1. '" / / / 1 I / \ ~ - ~ -.~~.--' I , SAN LUIS PASS • " • n n n n • u n • u • • • n • •HX ,. I W nen • " m 10 11 lZ 13 I' IS 16 17 IS 19 ~ 21 n 23 Z' 25 ~ ~ n " )0 31 12 11 ]4 15 3S ]' ~ w .0 41 .2 .) •• 45 '5 NAUTICAL MILES 'Figure 9-24. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary Under May Freshwater Inflow Needs, Alternative I " OYSTER BAYOU • DOUBLE BAYOU , ~ ........................... 1 ... ~ ~ ... t ~ --. .. t , ,. t 1 '\ . .,. '\ ........... , ~ t. , . ." . • • t BOLIVAR ROADS l 1 • II ... .. I , ... , . I , , I I , • l I j ~ , ~ J I , .. ~ r J I I ... ~ ... J 1 I \ I i I I I \ . , ......... ./ ,.. ..... c'" ~ " GULF OF MEXICO BARRIER ISLAND i I .- ·····,1 11" I '1'--'--// ;'-'-"f1""\ " .........~................ .. ,,\.7 ~ \1 1-~~\1\ ~ I II , ~ , i GALVESTON BAY MOSES BAYOU DICKINSON BAYOU CLEAR CREEK H~~~:~~~HIP~=-~__---, " II~' ~.~''' ./' .". - CHOCOLATE BAYOU ,MUSTANG BAYOU HALLS BAYOU , . Ii' • ~ .. .1 "... ./' ... .... ", .. t' ' .. /" I I SAN LUIS PASS· " " " " " " " " " " " " " '< " " " " " " " " H ~ W '" 10 1I 12 n H IS l~ 11 l!l l~ 213 II Zl 23 ... 2S 26 /n 28 2':1 lC 31 ,.. 33 J~ 35 35 l~ 3" 19 10 '1 .2 13 H .5 .6 NAUTICAL MILES Figure 9-25. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary Under June Freshwater Inflow Needs, Alternative I , DOUBLE' BAYOU , · • , , · • , · . ·r . ~ -- · , . · . , . . . • IOYSTER . BAYOU • --- ~ , :~~, I ~ ~ ... , / -_ .... \ . .- " \ .... ..... ...... +. ./ ,/ /,,-- ~ '" ,/ \ \ '" I I , - ... - ~ I .- 1 , I , , • 1 ~ ~ - ~ I • I , ~ . , • , ~ /'1 ~ ~ • . . . . GULF OF MEXICO BARRIER ISLAND GALVESTON BAY ~.', dI_ HOUSTON SHIP CHAN NEL '-'-,~,---~ MOSES BAYOU DICKINSON BAYOU I I • \! __ t CLEAR -f~ ~ ~ ~ ~ ,I 11 J' ~ t CREEK " / ~ ~ / /' ~ ,1 ___ // 1 _ r t t ~ \ ~ __ .A_ .... .I' " II~' I' ~ CHOCOLATE \ • BAYOU H'uHLAI'U' L-.' I t ~ , MUSTANG BAYOU /' - _ '\.LI f \ ~, ~ BAYOU I --- '-.=:\1 HALLS /' , 'D l 1L BAYOU ~ : =__ , .. \ \~ ......... - !'\ .........~ ~ ~ ?I ....... .?' ..... _ ......... ~ - J' __ ~ I t ~ ~(~I/ , SAN LUIS PASS R ., • • • n • • n n • 0' W g g " m g H ~ ,. I W n~ g " w • 9 10 1l lZ 11 1. 15 16 II IS 19 ~o 21 ZZ 21 Z' 2'; 2& 27/ za 29 )0 1) .;" 33 J< l5 ;5 ]7 30 39 '0 H .Z 4J H 45 ,6 NAUTICAL MILES Figure 9-26. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary Under July Freshwater Inflow Needs, Alternative I OYSTER BAYOU •ROLLOVERPASS ~ DOUBLE BAYOU • , Y: . . ~ - , . , .' - . • • • . ~ " . . ~ ~) l~ 1S ~ l' ]~ 39 .0 41 42 4} •• 45 46 . - • 29 JO Jl. 12 • , , , , 'II ~ " '~ fBOLIVAR ROADS ~ t • " 25 n 28 - ~ ~ ~ ,. - , I , 23 24 25 .. \ '0' .. -' .. ... ... t " • . . " , 19 ::'0 Zl ::'2 HOUSTON SHIP. CHANNEL :-.~----, GULF OF MEXICO BARRIER ISLAND 16 17 Ie . . \ • 1 I .. ~ , ~ ~ ~ ~ ~ '1 1J " \~ I • - - ~ , ':w. I / -- ,./ / 1J \. .. .. .. II. .., .... ... /' ... "r(.;. 7. .I'~.I'". ... ~ ~ - ~ ! ':w. .. ~ ~ ~ ~ GALVESTON BAY ,I 'c ~ r \. II '- "'.. 1, .. .. .. \ I , \ I \ ,i,<, ... ~ r \ J .;. \ • , <' \ , , 1 • 1 • 1 \ . ... • ... of' ... • MOSES BAYOU DICKINSON ... BAYOU ------, CLEAR CREEK 10 II l~ n H IS , , ~ ~ ... • tI' I ...... - ...... ~ ~ . " II~' , . ... .. ~ CHOCOLATE BAYOU ,MUSTANG BAYOU HALLS nAYOU • , . , SAN LUIS PASS 1 ~ 1 • 5 n " • • • n • • p n • ., • g g ,. g H 7 g co ,. 00 " n " g NAUTICAL MILES Figure 9-27, Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary Under August Freshwater Inflow Needs, Alternative I DOUBLE BAYOU •1 ~ ~ ~ ~ l' t ~_ ..... '\. '"t ,, • ....... ~ ... ~ • • • . ~ • . ~ , ~ . • I , .. .. .. ... .... ... ... • BOLIVAR ROADS • • • \ • • • " ...... +---- +- , , , . . ~ .... - . . I \ 1 'Ii j 1 J J 1 I I I I I , , ~ ~ ~ • , • , . , • .... -~ " ~ • I ... ~ .. ; 'D. " -.. ~ ... - . " . · , ... ~ ,/ \ \ ,,, HOUSTON SHIP ~ CHANNEL ~~ ~ BARRIER ISLAND GULF OF MEXICO .......... .. '>tIL~__---.J GALVESTON BAY I. 4 •• ..... ~ ... .. .. MOSES BAYOU DICKINSON BAYOU CLEAR CREEK , ,I/0, 't .• I ,/-_ ...... - ..... CHOCOLATE BAYOU )VIUSTANG BAYOU HALLS BAYOU I ~ • ,-- '01 \ ........ J'I ...--"' _ ... ; . ..., ... f' \ ...... i - ... , SAN LU IS PASS 32 n • n • n • • H • n 0' n g d n d U H 7 " co ""' ~ " u ,0 11 12 13 H 15 16 I? 18 1S 20 21 n 23 2~ 25 25/27 2B 2S 30 31. ':,:: 3) 3. 35 36 37 3B )~ .0 _.1 .2 43 H .'5 ~6 NAUTICAL MILES Figure 9-28. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary Under September Freshwater Inflow Needs, Alternative I OYSTER BAYOU •ROLLOVERPASS DOUBLE BAYOU ......................... • ... ... \0 ~ " \ ., / , \ , 'I / ..... ~ "-V// '\ .. 'I. .. _. / / I<,. ~......... ~ /' "',/v' , , .. + + .. l ... ... \. .. ;. J ,r .. ~ ~ ~ ,r J ,t ... J l , J " " J , , ~ ~ r , , I .r .r ... }// ........ /<' .... I I J I J I ' I ! I \ I j " " \'1 i\ i ~ 1 j 1 \ '- \ ..... r HOUSTON SHIP:-•• CHANNEL ., GULF OF MEXICO BARRIER ISLAND " I .' I ' ••••• ·1 Ii ~ i v,..-- / / / " ..- I I 1 • • ';, \ '-. MOSES BAYOU DICKINSON BAYOU .-.---------, CLEAR CREEK \ j '~--Il' \D\L~ •• , •••••• ~ ~i \ __~~ 'Ii~ . JO II l~ !~ l' IS l~ n " j9 Z~ Zl z: n ;'l ZS ;'5 /Z1 Z'l Z~ l{\ 1.' 1: 11 H 1S ]', n 11 .,~ ~o 41 'Z H H '5 _6 , . ~ ~ t .. >I" .... , ~ " II~' ~~~ .... Jf_... CHOCOLATE BAYOU ,MUSTANG BAYOU HALLS BAYOU ~ ... .. ... .. SAN LUIS PASS ! ~ } • S ~ 1: • :~ ~ ",. ~~ ~ " ~: " m g " " " lSH ~. " I .. " 0 " n " NAUTICAL MILES Figure 9-29, Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary Under October Freshwater Inflow Needs. Alternative I DOUBLE BAYOU ,----;Y .-- --. .... , /'/_ .... " " -///-,\\ /'/<11'\\\ ,\\,/11 , .. """,/1 ...... _--/ , , • , , , , , ., t ~ ~ . . , , , , '-_'f--.. "- • , I ~ ~ , ~ --.. ~ • r • • I I • ~ --'.~ • ~ ... ... - ~ I , • • ~ ~ , . . . • I OYSTER BAYOU • • , • • , , , , • , , . , ... , :\ .... f • , . , . . , .--.- ...- . , . • , I - - - ..... ... \ ~~~~'D' ............ \ .. ~" HOUSTON SHIP CHANNEL -- ~ BARRIER ISLAND HIGHLAND BAYOU .. ~ F···· ·1 I; , • I ... II:., , - ......... .-// ! .... _ .--" t " GALVESTON BAY ~•• ~ , ~ .• MOSES BAYOU DICKINSON BAYOU CLEAR CREEK " ,/I~' CHOCOLATE BAYOU MUSTANG BAYOU HALLS I "I BAYOU ,// ..... _---+-' . , " \, . • • ? ~ , < r I • , ' \ ~ ~ ,/ I ~ < • " • • • n • • • n • 0' n n • n • •H ~ u .. n --' n " u , SAN LUIS PASS GULF OF MEXICO BOLIVAR ROADS, 10 11 12 13 H IS 15 17 1':1 IS 20 21 22 2, 24 25 25 27 ;>5 2~ JO 31 12 31 H 35% ;7 35 ,g 40 41 42 0 H 4S 46 NAUTICAL MILES Figure 9-30. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary Under November Freshwater Inflow Needs, Alternative I OYSTER BAYOU DOUBLE BAYOU / ~ .. , \ /~ ..... ,\ //,\\ /1,11, I"ll .---=- " ~ .--x / ... •ROLLOVERPASS _....... "" ... . ~ . , , . . t • -. • • l' • • , t t • · , , • • · , ..- '" "- \ ~I , I' -" \ I , r I I r I t ! ! , '\ \ , HOUSTON SHIP CHANNEL ".---, ~/ , .. .- I' I ". ~ t r • • • • • • I I f ?~~ I \ LI.-.-, • .. ? ...- _/ / '" .... I ./' .-" / ! W ~ , ~ ! tit "\ l\ .. BARRIER ISLAND GALVESTON BAY I"" " MOSES BAYOU DICKINSON .-L' . . . BAYOU CLEAR CREEK " II~' CHOCOLATE BAYOU ,MUSTANG AYOU HALLS BAYOU ". ~ ~ , . . • , - .-" ./' ~ / ". ~ ~ ... ~ ~ ~ ". t t ~ ~ ...... --.. ...... -...-"'" /". I' \ R 0' m n n n " n n n n n " " n n g ~ g I ~ ,. N n g " w SAN LUISPASS I ~ 1 l 5 GULF OF MEXICO 10 II l~ 11 14 15 16 17 16 19 ~O 21 22 B 24 25 26 27 26 29 10, 11 J2 JJ ]. 35 36 " 38 39 ~O 41 42 n U 45 46 NAUTICAL MILES Figure 9-31. Simulated Net Steady-State Flows in the Trinity-San Jacinto Estuary Under December Freshwater Inflow Needs. Alternative I 'lbe dominant flow pattern in Galveston Bay is a novement of water up the Houston Ship Channel toward Morgan's Point. This northwesterly novement of water along the Ship Channel induces return currents on either side of the Channel noving in the opposite direction: thus, there is a net routheasterly current along the western shore of Galveston Bay. The simulated net circulation of water anong the various bays is pre daninantly fran Trinity Bay into Galveston Bay and fran Galveston Bay into East Bay. Limited exchange occurs between Galveston Bay and West Bay. The net flow through Bolivar Pass during these nonths is out of the estuary into the Gulf. (2) Simulated January, February, April, May, July, September, November and December Circulation Patterns. The flow circulations in the Trinity':san Jacinto estuary simulated under historical average rreteorological and esti mated freshwater inflow needs for Alternative I indicate similar flow patterns for the nonths of January, February, April, May, July, September, November and December (Figures 9-20, 9-21, 9-23, 9-24, 9-26, 9-28, 9-30 and 9-31). The average wind speed is 11.2 mph (5.01 rrilsec) for the IlDnths, with the wind direction predominantly from the north and west. The nost evident circulation pattern in the estuary during these inch cated nonths is a routheasterly-directed current in the Houston Ship Channel. The magnitude of the simulated current in the Ship Channel is generally exceeded only by the flow rates in the vicinity of Bolivar Pass. The daninant flow in Trinity Bay is a rounter-clockwise rotating circulation in the upper bay. The circulation patterns in West Bay indicate that an internal current rotating rounter-clockwise predominates in the upper end, with the net water movement fran Galveston Bay near Bolivar Pass through the Galveston Ship Channel into west Bay, and from West Bay through San Luis Pass into the Gulf of Mexico. The simulated net flow of water in the western p::lrtion of East Bay is dominated by a northerly current fran Galveston Bay into Trinity Bay. A secondary net flow in East Bay noves water fran Galveston Bay through Rollover Pass at the·eastern end of .Bolivar peninsula. The circulaion pattern for Galveston Bay shows a' net IlDvement of water down the Houston Ship Channel toward the Gulf. The novement of water along the Ship Channel induces return currents on either side noving in the opposite direction. The circulation patterns simulated for the various bays in the estuarine system indicates, as with the nonths of March, June, August, and October, that the predominant net flow is from Trinity' Bay into Galveston Bay and then into East Bay. Only limited net exchange occurs between Galveston Bay and West Bay. Also, the net flow through Bolivar Pass during these nonths is directed toward the estuary from the Gulf. Simulated Mean MonthlcI ~alini.;a ~~terns. The tidal amplitud.es and flows calculated by the ti al hydr ynamc nodel for the nonthly mflows under Alternative I were utilized as input to operate the salinity transport nodel to simulate the salinity distributions in the Trinity-San Jacinto estuary for each nonth. The resultant salinity distributions are illustrated in the form of salinity rontour plots wherein lines of uniform salinity are shown in IX-43 increments of five· parts per thousand (ppt). The evaluation of the simulated monthly salinities in the Trinity-San Jacinto estuary resulting fran these model. operations (Figures 9-32 through 9-43) revealed two distinct salinity distribution patterns: one evident during July and. the high inflow lIOnths of April, May, June, and October, and the other during the remaining IIOnths of -the year. . (1) Simulated Agril, May, June, July and OCtober Salinity Patterns. The simulation of estuarme salinities under April, May, June, July and October inflow needs and average meteorological conditions results in salinities over the Trinity-San Jacinto estuary varying fran less than five parts per thousand in Trinity Bay to slightly over 25 ppt near San Luis and Bolivar Passes (Figures 9-35 through 9-41). The salinity simulations for these IIOnths- reveal that salinities in Trinity Bay are less than five parts per thousand over a1Irost all of the bay. Salinities in Galveston Bay range fran between five and ten parts per thousand in its upper p:>rtion to 25 ppt at the IIOuth of the bay near Bolivar Pass. The simulated salinities in west Bay range between 20 and 25 ppt. The simulated salinity distributions for East Bay during these months range between 10 and 15 ppt. The simulated salinities in the estuary are lowest for the spring IIOnth of May. For the IIOnths during this period an intrusion of· IIOre highly saline water is evident along either side of the Houston Ship Channel. This simu lated condition corresp:>nded to observed variations in salinity. The intru sion of IIOre saline water along the Houston Ship Channel is -due to its 4Q-foot depth, compared to the adjacent shallow areas in Galveston Bay. (2) Simulated November thro1t March, ~ust and September Salinity Patterns. Simulated saIinity distrlutions in e Trinity-San Jacinto estuary for Alternative I inflows show relatively similar patterns for the remaining months of the year (Figures 9-42, 9-43, 9-32, 9-33, 9-34, 9-39, and 9-40). For Trinity Bay the simulated salinities are at a minimLUll near the Trinity River delta with concentrations lower than five parts per thousand during the seven remaining IIOnths. MaximLUll simulated salinities in Trinity Bay are between 10 and 15 ppt, except in the IIOnths of February, March and September when the maximLUll salinities are less than 10 ppt. The simulated salinities for Galveston Bay range fran less than ten parts per thousand in the upper p:>rt ion of the bay near Morgan's Point to over 25 ppt near Bolivar Pass. Simulated concentrations for west Bay range fran a maximLUll of aver 25 ppt near Bolivar Pass to less than 20 ppt in the ~stern end of the bay. East Bay salinities have a minimLUll value of less than 10 ppt near the eastern end of the bay and a maximLUll level of between 20 and 25 ppt at the boundary between East and Galveston Bays. Simulated salinities are greater than 10 ppt at Rollover Pass, the intermittent channel between East· Bay and the Gulf of Mexioo. In all of the IlVnths, the salinities in the middle p:>rtion of Galveston Bay were simulated at under 20 ppt, thus, meeting the criterion given pre- viously. Further refinement of the estimated IIOnthly freshwater inflow needs for the three Alternatives is therefore not considered necessary at this time. IX-44 DOUBLE ....... BAYOU ROLLOVER PASS TRINITY RIVER EAST.BAY 6 TRINITY BAY CEDAR BAYOU MOSES BAYOU DICKINSON~ BAYOU 20 WEST SAl I ., . -.' MUSTANGf BAYOU (~ HALLS/~/BAYOU o 8 16 KILOMETERS ! I~, I 10 MILES50 ~25~P- ~ 25~'\ SAN LUIS PASS . \ BOLIVAR \ ROADS \ 2 U1 Figure 9-32. Simulated Salinities in the Trinity-San Jacinto Estuary Under January Freshwater Inflow Needs, Alternative I (ppt) ,0 DOUBLE ~ BAVOU ROLLOVER PASS TRINITY RIVER TRINITY BAY .CEDAR BAYOU I ALVEST~N BAY I I I I MOSES BAYOU DICKINSON~/ BAYOU I 16 KILOMETERS8 ,I I~' MUSTANGf BAVOU I '::"'\ HALLS~/BAYOU CHOCOLATE BAYOU o o 5 10 MILES I , I 6~~-'~,,","e= ~"BOLIVAR' \ROADS \ H ~ .. 0\ Figure 9-33. Simulated Salinities in the Trinity-San Jacinto Estuary Under February Freshwater Inflow Needs, Alternative I (ppt) SAN JACINTO RIVER TRINITY RIVER TRINITY RIVER DOUBLE ~ BAYOU ROLLOVER PASS 6 EAST BAY TRINITY BAY ,CEDAR BAYOU 10 I I GALVESTON BAY I MOSES BAYOU DICKINSON~ BAYOU WEST BAY MUSTANGf BAYOU I HALLSBAYOU ,I I~' a 5 10 MILES I , o 8 16 KILOMETERS I , ~ SAN LUIS PASS ~ ..,. --.I Figure 9-34. Simulated Salinities in the Trinity-San Jacinto Estuary Under March Freshwater Inflow Needs, Alternative I (ppt) o 5 10 MILES I I I DOUBLE ~ BAYOU ROLLOVER PASS TRINITY AIVER TRINITY BAY BOLIVAR ROADS MOSES BAYOU DICKINSON~ BAYOU 16 KILOMETERS MUSTANG , BAYOU I HALLS BAYOU 8 --!I' CHOCOLATE BAYOU I I o ~ SAN LUIS PASS H ~ .... CO Figure 9-35. Simulated Salinities in the Trinity·San Jacinto Estuary Under April Freshwater Inflow Needs, Alternative I (ppt) ,D DOUBLE ___ BAYOU ROLLOVER PASS TRINITY RIVER TRINITY BAY MOSES BAYOU DICKINSON~ BAYOU HIGHLAND BAYOUt WEST BAY 20~ ,I I~' MUSTANGf BAYOU I HALLS~ BAYOU SAN JACINTO RIVER CHOCOLATE BAYOU o 5 10 MILES I ! ! o 8 16 KILOMETERS I I 25 V" ~ ~ 1I1r ~ • '""-J =---..3",,-rS'~::~,:lO~ BOLIVAR \ ~ ROADS \ SAN LUIS PASS H :;< ..,. '"" Figure 9~36. Simulated Salinities in the Trinity-San Jacinto Estuary Under May Freshwater Inflow Needs, Alternative I (ppt) SAN JACINTO RIVER TRINITY RIVER H :;: LT1 a ~I' a 5 10 MILES I I a 8 16 KII.OMETERS ! I CHOCOLATE BAYOU MUSTANGrBAYOU I HALLSBAYOU ~3fJ ~ SAN LUIS PASS DICKINSON~ BAYOU MOSES BAYOU TRINITY BAY ,D DOUBLE ~ BAYOU ROLLOVER PASS Figure 9-37. Simulated Salinities in the Trinity-San Jacinto Estuary Under June Freshwater Inflow Needs, Alternative I (ppt) ,0 ROLLOVER PASS TRINITY RIVER ~ ~ DOUBLE ". ...- BAYOU 6 ,CEDAR BAYOU MOSES BAYOU DICKINSON~ BAYOU MUSTANG , BAYOU I HALLSBAYOU ,I I~' ~-..." V .. ~ - • 25" '" BOLIVAR \ ROADS \ SAN LUIS PASS CHOCOLATE BAYOU o 5 10 MILES I I I o 8 16 KILOMETERS I ! H T U1 Figure 9-38. Simulated Salinities in the Trinity-San Jacinto Estuary Under July Freshwater Inflow Needs, Alternative I (ppt) SAN JACINTO RIVER TRINITY RIVER TRINITY BAY ROLLOVER ~ASS MOSES BAYOU DICKINSON~ BAYOU WEST BAY 10 MILES 16 KILOMETERS MUSTANG , BAYOU I HALLSBAYOU ~I' 5 8 SAN LUIS PASS ~'1r - ~ ~ '3"" BOLIVAR \ ROADS CHOCOLATE BAYOU o o H :;< lJl '" Figure 9-39. Simulated Salinities in the Trinity-San Jacinto Estuary Under August Freshwater Inflow Needs, Alternative I (ppt) SAN JACINTO RIVER DOUBLE ...- BAYOU ~ V1 W --!I' o 5 10 MILES I ! o 8 16 KILOMETERS I I ! SAN LUIS PASS ,uDICKINSON~ BAYOU MOSES BAYOU BOLIVAR ROADS .CEDAR BAYOU TRINITY RIVER TRINITY BAY 6 15 EAST BA ROLLOVER PASS ,0 Figure 9-40. Simulated Salinities in the Trinity-San Jacinto Estuary Under September Freshwater Inflow Needs, Alternative I (ppt) .D DOUBLE ~ BAYOU ROLLOVER PASS TRINITY RIVER 6 TRINITY BAY CEDAR BAYOU MOSES BAYOU DICKINSON~ BAYOU MUSTANG , BAYOU I HALLSBAYOU o 8 16 KILOMETERS , ! I ,I I~' 0 5 10 MILES ~ ::S'"25 ........---v .... - . '\~ BOLIVAR \ ::::::..----' ROADS SAN LUIS PASS H ~ U1 .. Figure 9-41. Simulated Salinities in the Trinity-San Jacinto Estuary Under October Freshwater Inflow Needs, Alternative I (ppt) DOUBLE ~ BAYOU ~ lJ1 lJ1 --!I' o 5 ·'0 MilES o 8 16 KILOMETERS I SAN LUIS PASS I, I, (, I I GALVESTpN BAY I DICKINSON~ BAYOU MOSES BAYOU BOLIVAR ROADS TRINITY AIVER 10 6> 20 ROLLOVER PASS ,0 Figure 9-42. Simulated Salinities in the Trinity-San Jacinto Estuary Under November Freshwater Inflow Needs, Alternative I (pptj SAN JACINTO RIVER ,0 DOUBLE ~ BAYOU ROLLOVER PASS TRINITY RIVER 6 TRINITY BAY MOSES BAYOU DICKINSON~ BAYOU MUSTANG , BAYOU I HALLSBAYOU -" "3 "~Y - - BOLIVAR \\ ROADS \ SAN LUIS PASS o 8 16 KIL.OMETERS I I ,I I~' 0 5 10 MILES~ U1(j) Figure 9-43. Simulated Salinities in the Trinity-San Jacinto Estuary Under December Freshwater Inflow Needs, Alternative I (ppt) Interpretation of the Physical Significance of the Estimated Freshwater Inflow Needs 1be IlOnthly freshwater inflows, estimated in the Trinity-San Jacinto estuary report, from the San Jacinto and Trinity River Basins represent the best statistical estimates of IlOnthly inflows needed to satisfy selected specified objectives for the major estuarine factors of marsh inundation, salinity distribution, and fisheries harvests. These estimates'cover a range of potential factors and illustrate the comPlexity of the estuarine system. Freshwater inflows approximately equal to the estimated needs may give estuarine responses which are indistinguishable, on a statistical basis, from the desired conditions. COnfidence limits can be obtained for manges in estuarine conditions, such as salinity, using statistical techniques. It is not clear, however, as to the proper temnique for determining conf idence bounds on the actual IlOnthly inflow estimates for those nOnths where the individual confidence limits on the inflow needs for salinity, harvest and inundation must be combined into a single confidence interval. A wide variability of freshwater inflow occurs in Texas estuaries from year to year, through drought and flOod cycles. The IlOnthly freshwater inflow levels received by the estuary fluctuate about the average inflow due to natural hydrologic variability. Such fluctuations are expected to continue to exist for practically any average level of inflow that might occur or that might be specified. It is not likely that sufficient control can be exerted to completely regulate the inflow extremes. In fact, to do 00 may be detri mental to the process of natural selection and other aspects of this vast living system. However, some proVision may be needed to prevent an increase in the frequency of periods of low flows. Such a provision could specify minimum IlOnthly inflows required to keep salinities below the upper viability limits given for the key estuarine-dependent species (Tables 9-1 and 9-2). Summary A methodology is presented which combines the analysis of the component physical, memical and biological elements of the Trinity-San Jacinto estuary into a sequence of steps which results in estimates of the freshwater inflow needs for the estuary based upon specified salinity, marsh inundation and fishery harvest objectives. Monthly mean salinity bounds are established at locations in the estuary near the inflow points of the San Jacinto and Trinity River Basins. ' These u);pE!r and lower limits on IlOnthly salinity provide a salinity range within which viable metabolic and reproductive activity can be maintained and normal historical salinity conditions are observed. Marsh inundation needs, for the flushing of nutrients from riverine marshes into the open bays, are computed and' specified for the Trinity 'River delta. The San Jacinto River delta is limited in areal extent and far smaller than the Trinity delta. As a result, no inflow requirements for inundation of the San Jacinto River delta are specified from the San Jacinto River Basin. The Trinity River delta is frequently sutmerged by floods from the Trinity River. Based upon historical conditions and gaged streamflow records, fresh water inflow needs for marsh inundation are estimated and specified at 750 IX-57 thousand acre-feet (924 million m3) in each of the nonths Jil, May, and OCtober. 'I1lese vollUl1E!s correspond to flood events with peak daily flow rates of 29,500 ft3/sec (836 m3/sec). Estimates of the freshwater inflow needs for the Trinity-San Jacinto estuary are, cono, Pennsylvania. 1977. 7. Arthur, J. F. and M. Ball. "Entrapnent of Suspended Materials in the San Francisco Bay-Delta Estuary." U. S. Dept. Int., Bureau of Reclamation. Sacramento, California. GPO 789-115/78-5., 106 p. 1978. 8. Bayly, 1. A. E. "Salinity TOlerance and Osrrotic Behavior of Animals in Athalassic Saline and Marine Hypersaline Waters." Ann. Review Ecol. and Syst., Vol. 3, W. 233-268. 1972. 9. Beadle, L. C. "The Effect of Salinity on the Water Content and Respira tion of Marine Invertebrates." J. Exp. BioI., Vol. 8 , W. 211-277. 1931. 10. , ' Blum, U., et al. "Photosynthesis ,Salt Marshes in North Carolina: 228-238. 1978. and Respiration of S~tina' an~ Juncus Some M:Jdels." Estuar~es, Vol. 1, w. 11 • Brezonik, P. L. Waters." In: J. R. Kramer. "Nitrogen: Sources and Transformations in Natural Nutrients in Natural Waters, edited by H. C.· Allan and W. 1-50. ,John Wiley & Sons, New York. 1972. 12. Burrell, D. C., and J. R. Schubel. In: sea~rass Ecosystems, edited pp. 195-2 2. Marcel Dekker, Inc., X-l "Seagrass Ecosystem Oceanography." by C. P. McRoy and C. Helfferich. New York. 1977. BIBLIOGRAPHY (cont' d) 13. Bursey,C. R. and C. 'E. duroarum Burkenroad." 1971. Lane. cane· "Osnoregulation in the Pink Shrinip Penaeus Biochem. Physiol., Vol. 39 A, W. 483-493, 14. Butler, P. A. "Gametogenesis in the Oyster under Conditions of Depressed Salinity." BioI. Bull., vol. 96, W. 263-269. 1949. 15. Butler, P. 'A. Gradients." "Oyster Growth as Affected by Latitudinal Temperature Cbmm. Fish. Rev., Vol. 15, W. 7-12. 1953. 16. Califorriia, University of. "BMD Biomedical Canputer Programs," edited by W. J. Dixon, Publications in Automatic Canputation, No.2. University of California at Berkley. 600 p. 1970. 17. California, Univ. Instit. of Marine graphy: Citations to Documents on Impact Assessment," by J. SOrensen TR-43 Sea Grant Publication No.8. 1973. Resources. "Coastal Zone Biblio Planning, Resources Management and et al. 133 p. in 2 Fiche. 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Cronin, Vol. 1, pp. 420-427. Academl.c Press, New York. 1975. 47. Eleuterius, C•. K.. "Location of the Mississippi Sound Oyster Reefs as Related. to Salinity of Bottom Waters during 1973-1975." Gulf. Res. Repts., Vol. 6, pp. 17-23. 1977. 48. Espey, Huston and Associates, Inc. "Developnent and Application of a Hydrodynamic Model of the Lavaca and Guadalupe Deltaic Systems," by L. M. Hauck et al. Report to the Texas Water Development Board. EH&A 0163-01. 88 p. 1976. 49. Espey, Huston and Associates, Inc. "Ecological Studies in Sabine Lake, 1974-1975," by J. M. Wiersema et al. Technical Report to the Texas Water Development Board,EH&A Ibcument No. 7644, 242 p. 1976. 50. Espey, Huston and Associates. "Galveston Bay Project; Addendum to Compilation of Water QUality Data Through August, 1972." R. J. Huston et al. Subnitted to Texas Water Quality Board. 1973. [628.168/ ES6GA.j 51. Espey, Huston and Associates. 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