USGS Washington Water Science Center
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WA303 - Rainfall-Runoff Models for Small Basins in Metropolitan Areas of Western Washington - Completed FY1989
Problem - Most new population growth in King and Snohomish Counties is occurring in the mid and upstream parts of small drainage basins. Land-use changes in upland areas and encroachment of development on natural marshes and wetlands have caused more frequent and costly flooding in the small basins. These changes are also having a negative impact on the anadromous fish resources, and accelerated bank erosion and the increase in fine-sediment load are reducing the amount of good spawning habitat. There is a rapidly growing need to mitigate the urbanization and runoff impacts in these small unincorporated basins.
Approach - Apply the Hydrological Simulation Program-FORTRAN model to a number of small basins to determine: rainfall-runoff parameters; effects of land use on high flows, low flows and runoff parameters; effects of retention dams or other channel structures; and relationships between basin characteristics, degree of urbanization and runoff parameters that may be used to calibrate the model for ungaged basins. After calibration and verification, the impact on runoff of potential changes in land-use and channel structures will be evaluated. Finally, an attempt will be made to develop regression relationships between optimized-model parameters, extent and type of land use, and measurable basin characteristics.