A watershed modeling approach using the Soil and Water Assessment Tool (SWAT) was developed to simulate the transport of pesticide residues in runoff and spray drift originating from use sites throughout the California Central Valley, an intensively farmed region draining to the important California Bay-Delta estuary region. Model customizations were developed to incorporate the impacts of flood control structures and irrigation diversions on hydrology and to geospatially account for the potential contribution of spray drift to pesticide load in streams. U.S. Geological Survey and California Department of Water Resources gage data was used to model freshwater outflows from reservoirs and for hydrology calibration and validation. A program was created to generate random pesticide application scenarios varying application spatial extent and timing based on California Pesticide Use Report data. Probability distributions of pesticide concentrations were generated from the Monte Carlo simulation results and were found to be consistent with available monitoring data.

Modeling pesticide fate and transport through flowing water bodies for endangered species assessment in the California Central Valley

248th National Meeting (2014)

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