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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #199268
Title: DEVELOPMENT OF TMDL WATERSHED IMPLEMENTATION PLANS USING ANNUALIZED AGNPS

Author
item YUAN, YONGPING - UNIVERSITY OF MISSISSIPPI
item Bingner, Ronald - Ron
item BOYSTUN, JAN - LDEQ

Submitted to: Land Use and Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2006
Publication Date: 11/15/2006
Citation: Yuan, Y., Bingner, R.L., Boystun, J. 2006. Development of TMDL Watershed Implementation Plans Using Annualized AGNPS. Land Use and Water Resources Research. 6: 2.1-2.8.

Interpretive Summary: The development of management practices used to reduce pollutants produced from agricultural fields entering stream systems is critical in improving overall watershed water quality. The evaluation of the effectiveness of conservation management practices is difficult because of the long-term data collection effort needed for this throughout a watershed system. In order to better assess conservation practices, computer simulation modeling technology has been developed to evaluate the amount of pollutants entering stream systems and what their source is within watersheds. In addition, this technology serves as an aid in determining the most effective conservation practices applied within watershed systems needed to minimize any downstream impacts on water quality. This study describes the development of an implementation plan for Bayou LaFourche that has been designated as one of the sediment and nutrient impaired watersheds within the Ouachita River Basin in northern Louisiana. The USDA Annualized Agricultural Non-Point Source Pollution model (AnnAGNPS) was used to evaluate the amount of water and sediment produced from the watershed with critical source areas identified. Alternative agricultural management practices were identified for implementation on areas that had high sediment production and were evaluated by the model to assess the impact these practices would have on reducing sediment within the watershed. Among the alternative agricultural management practices evaluated, the practice of converting 25 percent of the highest eroding cropland in the watershed to grassland reduced sediment loads by 80 percent at the watershed outlet. The approach of using the watershed modeling technology to assist in the development of implementation plans provides action agencies a tool to evaluate appropriate conservation measures that can implemented to meet their watershed pollutant reduction goals.

Technical Abstract: Section 319 of the amended Federal Clean Water Act requires states to outline management plans for impaired water bodies to address non-point source pollution. When determining the priority for conservation measures within a watershed for non-point source pollution control, models are valuable tools that can provide clues as to where potential sources of water pollution may be and which problems can most easily be corrected. The USDA Annualized Agricultural Non-Point Source Pollution model (AnnAGNPS) is such a model which has been developed to aid in the evaluation of watershed response to agricultural management practices. This paper presents the processes used for developing an implementation plan for Bayou LaFourche, one of the impaired sub-segments of Ouachita River Basin in northern Louisiana. In this study, the AnnAGNPS was used to simulate the amount of water and sediment produced from each user-specified computational area within the watershed and their contributions to the watershed outlet; AnnAGNPS was also applied to simulate the impact of alternative agricultural management options on the water quality. Through AnnAGNPS simulations, high sediment producing areas were identified and those areas were targeted for effective non-point source pollution control. The alternative agricultural management options for reducing non-point source pollution and their impacts on water quality are also presented in the paper. Among all the alternative agricultural management options, scenario G, which converts 25 percent of the highest eroding cropland in the watershed to grassland, would reduce sediment loads at the watershed outlet by 80 percent.