Browsing by Subject "impervious cover"

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Analog Computer Simulation of the Runoff Characteristics of an Urban Watershed
(Utah State University, 1969) Narayana, V.V. Dhruva; Riley, J. Paul; Israelsen, Eugene K.
In the syntheses of hydrograph characteristics of small urban watersheds, the distribution of water among the various phases of the runoff process is attempted by the concept of equivalent rural watershed. The urban parameters considered in the study are percentage impervious cover and characteristic impervious length factor. A mathematical model is developed for the equivalent rural watershed with precipitation as input. The hydrograph of outflow is obtained by chronologically deducting the losses due to interception, infiltration, and depression storages from precipitation and then routing through the watershed storage. This mathematical procedure is programmed on an analog computer and is tested with data from the Waller Creek watershed, at Austin, Texas. In the verification process, watershed coefficients representing interception, infiltration, and depression storage are established by trial and error such that the simulated and observed hydrographs are nearly identical with a high statistical correlation. Sensitivity studies indicate the relative influence of the watershed coefficients on the runoff process. The watershed coefficients determined by model verification for each year of study are related to corresponding urban parameters.
Linking Biologic Metrics to Hydrologic Characteristics in Austin, Texas Streams
(City of Austin Watershed Protection Department, 2011) Richter, Aaron
Urbanization can alter the hydrology of creeks as land use changes as represented by increases in impervious cover. Flow regime change is modeled directly on the basis of impervious cover in the City of Austin; however, it would be helpful for planning purposes if other aspects of the environmental integrity of urban creeks could be modeled on the same basis. Benthic macroinvertebrates and diatoms are used as biological indicators of creek health, but an adequate direct relationship between the impervious cover and these biological metrics has not been found. Relationships between flow and biological health were investigated in order to form an indirect link so that changes in biological health could be predicted by changes to impervious cover. Pearson correlations and step-wise regression was performed on 35 hydrologic metrics and 25 biological metrics using sub-daily and daily flow data from the US Geologic Survey in 14 creeks in Austin, Texas. Data were grouped by impervious cover period or water year. The sub-daily flow data grouped by impervious cover period created the best model using mean--area (avg neg flowrate changes/watershed area),FHn (avg times mean flow > 75%-tile), and TQmean (fraction of time daily mean flow > mean for period) as the predictive hydrologic metrics to describe biological health of the creeks. Correlations were strongest between hydrology and the sensitive taxa biologic metrics. As the hydrology becomes flashy, one result of an increase in impervious cover, the sensitive taxa decrease at a site thereby decreasing the overall biological health of a site. It is recommended that this indirect link be used in water quality improvement projects to predict how the biological health of a creek in Austin will be affected by changes in land use.