Sediment TMDL Development for the Amite River

Abstract

The Amite River is recognized as one of the 15 water bodies impaired by sediments in Louisiana, USA. Based on US EPA’s Protocol sediment TMDL (Total Maximum Daily Load) development is conducted for the Amite River and described in this paper. The TMDL development consists of four components: (1) development of a new model for cohesive sediment transport, (2) estimation of sediment loads (sources) due to watershed erosion, (3) river flow computation, and (4) determination of sediment TMDL for the Amite River. Using the mass conservation principle and Reynolds transport theorem a new 1-D model has been developed for computation of suspended cohesive sediment transport. Sediment erosion in the Amite River Basin is calculated by combining the USLE (Universal Soil Loss Equation) model with GIS and the digital elevation model of the Amite River Basin. Digital elevation data was imported into the GIS which generated inputs for USLE. The calculated average annual rate of soil erosion in the Amite River Basin is 13.368 tons per ha, producing a nonpoint sediment load of 103 mg/L to the Amite River. The flow computation is performed using the HEC-RAS software. The computed sediment concentration in the Amite River varies in the range of 3–114 mg/L and sediment TMDL is 281.219 tons/day. The reduction necessary to support beneficial uses of the river is 55% or 275.946 tons/day. Results indicate that the combined application of the new 1-D sediment transport model, GIS, USLE model, and HEC-RAS is an efficient and effective approach to sediment TMDL development.