Modeling a Large, Dynamic, Urban Drainage Systemby Nick N. Adelmeyer, U.S. Army Corps of Engineers, Los Angeles, United States,
Kerry Casey, U.S. Army Corps of Engineers, Los Angeles, United States,
Abstract: Impacts of progressive urbanization on peak streamflow are often difficult to quantify due to the dynamic, but subtle changes from year-to-year. In this instance urbanization impacts are further complicated by upstream regulation -- debris basins, water supply dams, and flood control dams and channels -- constructed during this period. The system operation requirements make use of a rainfall-runoff model to compute reservoir inflow and simultaneous runoff in downstream subareas a virtual necessity. The rainfall-runoff model is linked to a reservoir routing model to determine reservoir releases and combine these with downstream runoff. Discrete event rainfall-runoff analysis provides estimates of a range of peak floodflows throughout the basin, and also makes available flood hydrographs at any location of interest. The basis of this approach - frequency rainfall and sub-area runoff calibrated to observed flow - provides a sound basis for computation of frequency runoff. The dynamics of urbanization are quantified by establishing a 'current' discharge-frequency relationship for observed flow for urbanized locations. The rainfall runoff model linked to a reservoir operation model was able to replicate these floodflow trends, especially in the downstream reaches.
Subject Headings: Hydrologic models | Rainfall-runoff relationships | Runoff | Urban areas | Reservoirs | Rivers and streams | Floods | Hydraulic models
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