Cost-Effective Watershed Modeling Approach to Achieve TMDL Targets

Abstract

Prioritizing the watershed areas that should be targeted for implementing BMPs, rather thanrandom or first-come, first-serve methods, shows promise for improving cost-effectiveness ofwater-quality improvement efforts, yet more work needs to be done to test targeting methods. Theobjective of this study was to demonstrate the use of Soil and Water Assessment Tool (SWAT) totarget areas for effective adoption of best management practices. The study area, Kanopolis LakeWatershed, has a High-Priority TMDL designation for eutrophication. To reduce eutrophicationrates, lower pollutant-load targets must be established for contributing pollutants such as sediment,nitrogen (N), and phosphorus (P). ArcView GIS coupled SWAT was used to identify target areasand model the watershed response due to targeted and random BMP adoption. The impact ofconverting cropland from conventional tillage (CT) to reduced tillage (RT) BMP for 0, 10, 26, 52,and 100% of total cropland area within the watershed was estimated using random and targetedselection methods. For the targeted method average sediment yield estimates were used as the solecriteria for selecting the subbasins for BMP. With 100% BMP adoption, 29.5% reduction in annualaverage overland sediment yield and 8% reduction in annual average sediment yield at thewatershed outlet was achieved. A 10% reduction in overland sediment loss was achieved withabout 17% of cropland area by the targeting approach compared to 36% by random approach. A5% reduction in sediment yield at the watershed outlet was achieved with BMP adoption in about17% of targeted cropland area as compared to 81% randomly selected area. A targeted watershedmodeling approach using SWAT was found to be effective in reducing the sediment load. Thisstrategy could be extended to other landuse types, and other appropriate BMPs.