Sediment TMDL calculations for Amite River

Abstract

The Amite River is recognized as one of the 15 water bodies impaired by sediments in Louisiana. A sediment TMDL calculation for the Amite River is required by the EPA. Based on EPA’s Protocol sediment TMDL calculations for the Upper Amite River are conducted in this thesis. The sediment TMDL calculations are composed of four parts: (1) Development of a new sediment transport and dispersion model for the Amite River, (2) Estimation of sediment loads (sources) produced by watershed erosion, (3) Flow computation, and (4) Determination of sediment TMDL for the Amite River. Using the mass conservation principle and Reynolds transport theorem a new model has been developed for computation of sediment transport in the Amite River. 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. The calculated soil erosion rate for the Upper Amite River Basin is 5.42 ton/acre/year, producing sediment load of 0.103 kg/ to the Amite River. The flow computation is performed under steady and unsteady flow conditions using the HEC-RAS software developed by the U.S.Army Corps of Engineers. Under the steady flow condition the computed sediment concentration varies in the range of 3-114mg/L. The numeric target criterion was not to exceed 50 NTU or 64 mg/L of suspended sediment. Based on this criterion and the new model developed in the thesis, the sediment TMDL calculations were conducted for steady and unsteady flow. It is found that there is significant difference between TMDLs for steady and unsteady flow due to high sediment loads produced by unsteady flow. It is recommended that (1) sediment TMDL calculation need to take account of the influence of unsteady flow; (2) Sediment criteria for the Amite River can be met by adopting practices such as terraces on the steep slopes, creation of buffer zones along the river. Results indicate that the new model can be an effective tool for sediment TMDL calculations.