DECISIONS model: A GIS-based tool for watershed nutrient planning

Abstract

Community DECISIONS is a decision support system for evaluating watershed nutrient planning strategies. The system centers around stakeholders in the watershed and is comprised of several components: a nutrient loading model, a treatments database, and objectives-setting and strategy selection processes for stakeholders. This paper focuses on the nutrient loading model, which is a GIS-based tool developed to assess the effects of alternative strategies. A watershed is overlaid with a grid of 30-m by 30-m cells. Based on each cells characteristics, the tool computes total loadings from both point and nonpoint sources and estimates reductions in nutrient loadings due to nonpoint source treatments. Nutrient losses are calculated using the GLEAMS model for agricultural and forest land. Nutrient loads from urban areas are estimated based on relationships used in the GWLF model and the Simple Method. Calculated nutrient losses from each cell are routed overland to the receiving stream by accounting for the landuse and topography of each cell along the pathway. Different nutrient reduction strategies were modeled to describe nutrient reductions and the estimated costs associated with each strategy. Strategies included point source upgrades, tillage, cover crop, riparian buffers, fencing on pastures and bio-retention filters on urban land. Results of this study indicate that the GIS-based tool can assist stakeholders in ranking and choosing strategies to achieve watershed management goals.