| The L'Anguille River located in Eastern Arkansas and part of the Mississippi River Delta Eco-region is listed as impaired by the Arkansas Department of Environmental Quality (ADEQ and the United States Environmental Protection Agency (USEPA). The impairment is caused by excessive sediment originating primarily from row crop agriculture. A Total Maximum Daily Load (TMDL) was prepared and accepted listing the causes of the excessive sediment as agricultural row crop production areas, recommending reductions of 48% in spring and 46% in summer to meet in stream turbidity standards of 45 NTU.; A SWAT model was developed to predict flow and sediment concentrations in the L'Anguille River and was calibrated using measured data from two USGS gauging stations located near Colt, AR and Palestine, AR. The calibrated model results were used to develop and analyze targeted agricultural BMP placement to meet TMDL goals in the watershed. The targeted crop in this watershed was soybeans due to the large amount of soybean production area and the relatively larger sediment yield from soybeans as compared to rice and other land uses present. The other targeted critical areas were hydrologic soil group C areas, and those sub-basins that yielded the largest sediment contribution both in total load and in load per unit area. The BMPs used in targeted scenarios included conservation tillage, no till practices, and 10m wide grass filter strips.; It was determined by the SWAT model that targeted implementation of combinations of these BMP's would provide the recommended sediment reduction from agricultural production areas. However, the SWAT model predicted that there was no combination of these BMP's that would result in recommended reductions in the in-stream sediment concentration, due to other sources of sediment present in the watershed. |
