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Cost-Effective Watershed Modeling Approach to Achieve TMDL Targets

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Watershed Management to Meet Water Quality Standards and Emerging TMDL (Total Maximum Daily Load) Proceedings of the Third Conference 5-9 March 2005 (Atlanta, Georgia USA) Publication Date 5 March 2005  701P0105.(doi:10.13031/2013.18065)
Authors:   P. Tuppad and K. R. Mankin
Keywords:   Nonpoint source pollution, SWAT, Watershed modeling, TMDL, Agricultural Best Management Practices

Prioritizing the watershed areas that should be targeted for implementing BMPs, rather than random or first-come, first-serve methods, shows promise for improving cost-effectiveness of water-quality improvement efforts, yet more work needs to be done to test targeting methods. The objective of this study was to demonstrate the use of Soil and Water Assessment Tool (SWAT) to target areas for effective adoption of best management practices. The study area, Kanopolis Lake Watershed, has a High-Priority TMDL designation for eutrophication. To reduce eutrophication rates, 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 areas and model the watershed response due to targeted and random BMP adoption. The impact of converting 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 targeted selection methods. For the targeted method average sediment yield estimates were used as the sole criteria for selecting the subbasins for BMP. With 100% BMP adoption, 29.5% reduction in annual average overland sediment yield and 8% reduction in annual average sediment yield at the watershed outlet was achieved. A 10% reduction in overland sediment loss was achieved with about 17% of cropland area by the targeting approach compared to 36% by random approach. A 5% reduction in sediment yield at the watershed outlet was achieved with BMP adoption in about 17% of targeted cropland area as compared to 81% randomly selected area. A targeted watershed modeling approach using SWAT was found to be effective in reducing the sediment load. This strategy could be extended to other landuse types, and other appropriate BMPs.

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