SIMULATING HYDROLOGIC AND WATER QUALITY IMPACTS IN AN URBANIZING WATERSHED

The Hydrologic Simulation Program-Fortran, which is a continuous, lumped parameter model that simulates hydrologic and associated water-quality processes on pervious and impervious land surfaces, in streams, and in well-mixed reservoirs, was applied to evaluate the effects of urbanization on water quality and quantity in the Polecat Creek watershed, Caroline County, VA, which is undergoing rapid expansion of residential and commercial land uses. Land-use scenarios were developed and used to develop inputs for the model. For modeling purposes, the watershed was subdivided into 14 subwatersheds and 19 reaches. Land use in the subwatersheds was aggregated into five categories: forest, cropland, pasture, residential, and commercial. The calibrated model simulating the impacts for sedimentation, nitrogen, and phosphorus was applied to each of the future land-use scenarios. Results suggested that, with increasing urbanization, streamflow volume and peak rate will increase dramatically, which could cause increased channel erosion within the watershed. With increased use of fertilizer in residential areas, N loads would increase, but P loadings were predicted to decrease slightly due to a reduction in the agricultural area.