INTEGRATION OF A BASIN-SCALE WATER-QUALITY MODEL WITH GIS

Geographic Information Systems (GIS) have been successfully integrated with distributed parameter, single-event, water quality models such a s AGNPS (AGricultural NonPoint Source) and ANSWERS (Areal Nonpoint Sou rce Watershed Environmental Response Simulation). These linkages prove d to be an effective way to collect, manipulate, visualize, and analyz e the input and output date of water quality models. However, for cont inuous-time, basin large-scale water quality models, collecting and ma nipulating the input data are more time-consuming and cumbersome due t o the method of disaggregation (subdivisions are based on topographic boundaries). SWAT (Soil and Water Assessment Tool), a basin-scale wate r quality model, was integrated with a GIS to extract input data for m odeling a basin. This paper discusses the detailed development of the integration of the SWAT water quality model with GRASS (Geographic Res ources Analysis Support System) GIS, along with an application and adv antages. The integrated system was applied to simulated a 114 sq. km u pper portion of the Seco Creek Basin by subdividing it into 37 subbasi ns. The average monthly predicted streamflow is in agreement with meas ured monthly streamflow values.