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EVALUATION OF URBANIZATION IMPACTS ON HYDROLOGY - LABORATORY AND FIELD APPROACHES
Citation:
Shuster**, W., Warnemuende,E, D. Smith, AND J. Bonta. EVALUATION OF URBANIZATION IMPACTS ON HYDROLOGY - LABORATORY AND FIELD APPROACHES. Presented at 11th National Nonpoint Source Monitoring Workshop, Dearborn, MI, September 08 - 11, 2003.
Impact/Purpose:
present information
Description:
Although urbanization has a major impact on watershed hydrology, there have not been many studies to quantify how basic hydrological relationships are altered by the addition of impervious surface under controlled conditions. In addition, few studies have been conducted to quantify these effects under controlled conditions and standard rainfall simulation methodologies have not been established. The USDA-ARS and USEPA have jointly initiated a pilot research program to study the impacts of simulated impervious surfaces on hydrology, sediment, and water quality in small experimental watersheds located at the North Appalachian Experimental Watershed, Coshocton OH. This paper outlines the approach and rationale for using rainfall simulation to predict basic differences in the extent and arrangement of impervious surfaces on hydrology and erosion processes; the use of experimental watersheds subjected to natural precipitation regimes; and modeling approaches. In particular, the results from laboratory rainfall simulation will help guide the implementation of impervious surfaces in the watersheds. Percent imperviousness is planned from 0% to 40% under two spatial arrangements of imperviousness - stream-channel-connected and stream-channel-disconnected imperviousness. Analysis of the Coshocton baseline runoff data shows that, during the time of constant land use since 1975, annual runoff depths are similar and runoff regimes have been constant. We found that 2-dimensional laboratory rainfall simulations yielded inconsistent runoff and sediment yield data, which was attributed to hydraulic similarities between the different geometric arrangements of impervious surface and difficulty in creating a consistent surface from one rainfall run to another. However 1-dimensional simulations yielded differences in both hydrograph and sediment losses, with the most clear differences in sediment losses. The upper impervious treatment yielded initially less runoff than when impervious surface was set in the downgradient location. However, this pervious zone also became more quickly saturated than the upslope impervious treatment. As a result, the upper impervious treatment yielded generally higher runoff and sediment after the usual initial wetting period. This one-dimensional slope rainfall simulation approach appears to be sensitive to impervious treatments. However, transition points between the impervious and pervious sections were prone to scouring and undercutting at higher rainfall intensities. Field implementation of impervious surface will begin Spring 2004.
