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METHODOLOGY FOR DETERMINING EFFECTS OF EXTENT AND GEOMETRY OF IMPERVIOUS SURFACE ON HYDROLOGIC BALANCE
Citation:
Warnemuende,E, W. Shuster**, D. Smith, AND J. Bonta. METHODOLOGY FOR DETERMINING EFFECTS OF EXTENT AND GEOMETRY OF IMPERVIOUS SURFACE ON HYDROLOGIC BALANCE. Presented at National Interagency Conf. on Research in Watersheds, Benson, AZ, October 28 - 30, 2003.
Impact/Purpose:
To inform the public
Description:
In the urbanization of watersheds, impervious surface is the primary agent of hydrologic change. The impact of impervious surface on hydrology and sediment transport is understood only in terms of unverified models not specifically adapted for urban watersheds. Therefore, in this study we explore experimental methods to better understand how the extent and geometry of impervious surface affect hydrology and sediment transport at the rainfall simulation-soil box scale, and to screen methods to simulate urbanization for larger scale studies. We used a 4 x 4 m soil box with rainfall simulation of varying intensity and duration to produce runoff from a 100 percent pervious surface; and from 5, 10, 20, 30 and 40 percent impervious surface cover. Impervious cover was simulated with 45 cm square sections of aluminum that each represented 1.25 percent of the total surface. Results from preliminary trials with rainfall simulation of 20, 30, and 40 mm hr-1 run until steady state; on a soil bed configured with 40 percent impervious surface showed that time of concentration was decreased twenty-fold, compared to a similar trial with 100 percent pervious cover. Mass curves of flow showed that once runoff had begun, it was produced similarly from the contrasting landscapes, until the highest-intensity rainfall began. Total sediment losses were increased nearly three-fold with 40% impervious cover and peak erosion rates were nearly doubled, compared with the pervious cover. Further experimentation will yield a more detailed quantitative view of the relationships between impervious surface and correspondent runoff and sediment loadings.