# Browsing by Subject "Hydraulic models"

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Item The dynamic response of buoy-supported slender structures to currents and waves(1974) Hicks, James Bryan, 1943-; Clark, Lyle G.Show more Item Estimating uncertainty of 2D hydraulic models used for aquatic habitat modeling studies(2007-05) Osting, Timothy Dennis, 1975-; Hodges, Ben R.Show more Spatially-distributed depth and velocity predictions are required for habitat based instream flow studies. The purpose of this thesis is to estimate uncertainty of two-dimensional (2D) depth-averaged hydraulic models when applied with close spacing of computational nodes. Motivation for close node spacing is discussed from the ecological, aquatic habitat perspective. Model-generated maps of predicted depth and velocity require sufficient resolution to capture spatial variations relevant to aquatic habitat; however, bathymetric variations at that resolution are more complex than strictly applicable for the depth-averaged hydrostatic model equations. Hydraulic model assumptions are discussed and the geometry of a typical model is analyzed to identify areas that do not conform to assumptions. Model input data, including bathymetry, water surface elevation, flow rate, depth and velocity measurements, have accuracy within 5% of actual values. Accuracy of depth measurements conducted with a boat-mounted echosounder approach 15 centimeters and are the greatest source of uncertainty for depth error in model predictions. For model test scenarios using the RMA2 2D depth-averaged finite element code, geometries exhibiting slopes greater than 0.10 (ratio of rise to run) or exhibiting abrupt lateral changes in width are shown to cause changes in continuity (velocity conservation) of greater than 2.5%. For a calibrated model of the Brazos River, Texas, 95% of the model area exhibited low uncertainty with continuity deviations less than 2.5%; remaining areas exhibited higher uncertainty resulting from steep slopes or high Froude numbers.Show more Item Geospatial description of river channels in three dimensions(Center for Research in Water Resources, University of Texas at Austin, 2004-08) Merwade, Venkatesh; Maidment, David R.Show more Item GIS-based hydrologic and hydraulic modeling for floodplain delineation at highway river crossings(Center for Research in Water Resources, University of Texas at Austin, 2000-12) Anderson, David James; Maidment, David R.Show more Item Hydraulics of side-channel weirs for regional detention basins(1989) Tynes, Kevin Allen, 1959-; Holley, Edward R. (Edward Raymond)Show more Side-channel weirs can be used for flood control to divert part of a channel's flow into detention basins, thereby reducing peak discharges and stages. After passage of the flood peak, the stored water can be released back to the channel. The Harris County (Texas) Flood Control District is planning the use of several side-channel weirs which will discharge into regional detention basins. The weirs are being designed to divert approximately 50% of peak flows of up to 25,000 cfs, with accompanying depths of up to 25 feet in the channels. A 1:25 scale model was built to investigate the hydraulic characteristics of embankment-shaped side-channel weirs. This thesis describes the model, its use, and the results obtained from the model study. Particular attention has been given to 1) quantification of the discharge which flows over a side-channel weir for given weir geometries and channel flow conditions, 2) the changes which occur in the channel stage along the length of the side-channel weir as water flows past and over the weir, 3) the effects of submergence on the side-channel weir discharge and channel stages, and 4) the effect of tapering the channel (i.e., progressively reducing its width) along the length of the weir. The standard equation for discharge over a normal broad-crested weir was modified slightly for side-weir applications and a bulk discharge coefficient (C[subscript e]) was used. C[subscript e] was correlated with channel flow parameters and weir geometric parameters. The side-weir discharge causes a head change along the weir in addition to the frictional head loss. This additional head change (h[subscript c]) is needed to determine the change in stage between the ends of the weir. The model results were used to calculate h[subscript c] using the energy equation; h[subscript c] was then correlated with channel flow conditions and weir geometric parameters. Submergence effects were characterized by determining the decrease in the bulk discharge coefficient and in the additional head change along the weir for varying values of submergence. Similar analyses were made to determine the side-weir discharge and stage change for weirs placed in tapered channelsShow more Item The influence of post-spacing density of DEMS derived from LIDAR on flood modeling(Center for Research in Water Resources, University of Texas at Austin, 2004-05) Gueudet, PierreShow more Item The influence of post-spacing density of DEMs derived from LIDAR on flood modeling(2004-05-22) Gueudet, Pierre; Maidment, David R.Show more The primary objective of the research is to determine the optimal post-spacing for LIDAR-derived digital elevation models (DEMs) that is required to achieve different levels of accuracy in the prediction of flood risk using hydraulic models. For the study, high spatial resolution LIDAR data were collected by the University of Texas Airborne Laser Terrain Mapping System and decimated to generate a variety of DEMs with different resolutions for test and evaluation. The data were entered as input to FEMA-approved hydraulic models at varying resolutions to determine the sensitivity of the models to the changes in the densities of the LIDAR ground elevation points. Data were collected in Brownsville, Texas, in the area of the North Main Drain. A flood model was developed using HEC-RAS to delineate the 2-year, 5-year and 25-year floodplains of this drain. For each of the floodplains, 70 simulations were run using different densities of LIDAR-derived ground elevation points. These varying datasets density were also used to delineate watersheds. The work flow sequence needed to produce the flood maps was automated using the ESRI ArcGIS 9 Model Builder. Concerning floodplain delineation, results reveal that below a certain density (5 ground points per 100m² which corresponds to a 4.34 meter post-spacing), the LIDAR data become problematical for use in the creation of accurate flood hazard maps. At lower ground point densities, flow obstructions appear on the 3D cross-sections derived from LIDAR, and the inundation polygons expand to unrealistic proportions. With densities greater than 5 ground points per 100m², the influence of increasing LIDAR point density is weak, and the accuracy of the floodplain resulting from a simulation depends upon the initial conditions of the model run. Concerning watershed delineation, no trend was observed as the density of LIDAR points decreases. This result could be explained by the fact that the area of study is extremely flat.Show more