Nonpoint source pollution management enhancement using geographic information system

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AWRA Conference

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The Little Bear River Watershed (384 sq km) in Northern Utah has been identified by USDA as a national high priority watershed for reduction of sediment and nutrient inputs to downstream water bodies. Watershed managers in this and other impacted areas are using distributed parameter models, such as the Agricultural Nonpoint Source model (AGNPS), to simulate sediment and nutrient outputs. This paper describes the use of a geographic information system (GIS) to improve AGNPS model input/output for a 9.5 sq km sub-watershed of the Little Bear River. The objectives were to: (i) obtain a spatially distributed approximation of landuse, soils and slope, (ii) determine the difference between outputs from spatially distributed versus traditional lumped parameter inputs, and (iii) assess the influence of pixel size selection on model output. Watershed landuse, soils and slope coverages were manipulated using GIS (Arc/Info) to extract input parameter values. Grid cell size was adjusted from the standard 16 ha cell to finer resolutions of 8 and 4 ha. This resulted in significant improvement to output estimation and improved efficiency in data management.

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