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Emin C. Dogrul, Hafzullah Aksoy and M. Levent Kavvas Identification of the sources of sediment and nutrients that eventually affect the clarity of Lake Tahoe has recently been an important issue. Until now, most studies have concentrated on the identification of such sources in watersheds of Tahoe basin and the zones that intervene the watersheds have been ignored. The goal of this study is to analyze the effect of urbanization on sediment and nutrient loads in an intervening zone located between Carnelian Bay and Kings Beach. 49.9% of this intervening zone is urbanized and the rest of it is rural. The U. S. Environmental Protection AgencyÕs (EPA) Storm Water Management Model (SWMM) is used to simulate the quantity and quality of urban storm water runoff. The UC Davis Hydrologic Research LaboratoryÕs rural watershed hydrology and erosion model is coupled with SWMM in order to model the runoff in the rural part of the intervening zone. The coupled model can simulate runoff quantity and quality due to snowmelt as well as rainfall events. For this study, the storm drain network was mapped and the major outlets were identified. Then the areas draining into these outlets were obtained by the analysis of digital elevation maps (DEM) using GIS (Figure 1). GIS was also used in order to obtain other parameter values regarding soil characteristics, topography, road and storm drain network. At this point in time, the model is being calibrated for several snowmelt and rainfall events that were observed in the year 1999. After the calibration is completed, the percentage of urbanization in the intervening zone will be modified and the runoff quantity and quality will be simulated. It is expected that the analysis of the results obtained for different percentages of urbanization will lead to the understanding of the effect of urbanization on the sediment and nutrient loads transported to Lake Tahoe.  |