Assesment and Prediction of Streambank Erosion in a Southeastern Plains Ecoregion Watershed

Ramirez-Avila, J. J. (2011). Assesment and Prediction of Streambank Erosion in a Southeastern Plains Ecoregion Watershed. Starkville, MS: Mississippi State University. 332.

The Town Creek Watershed (TCW) is a representative area of the Tombigbee River Basin and the Southeastern Plains Ecoregion in Mississippi. The principal channel and four main tributaries have been included for several years within the MS Section 303(d) list of waterbodies biologically impaired due to sediment. The TMDL developed for TCW recommended that streams located near cultivated lands, road crossings and construction activities are a priority for streambank and riparian buffer zone restoration and sediment loads reduction. Development of remedial measures and future BMPs within TCW for reducing water quality impairment and downstream dredging costs requires identification of sediment sources and loads currently transported within TCW. Streambank erosion processes were hypothesized to be an important mechanism driving sediment supply from TCW. The overall goal of this research was to identify mechanisms and the potential effects of streambank erosion processes and to quantify and model the magnitude and rates of these processes within TCW. Research goal and specific aims were addressed in four substudies combining field reconnaissance and detailed data collection, laboratory analysis and computational modeling techniques. The first substudy involved a temporal and spatial analysis of observed suspended sediment transport rates, and determined the stage of channel evolution and identified streambank erosion as an important source of sediment supply for reaches in TCW. Streambank erosion contributions of up to 28.5 Mg per m of streambank were quantified in a second substudy monitoring and determining streambank erosion processes and factors within TCW. Results from a third substudy assessed predictions of the computational model CONCEPTS for time of occurrence and magnitude of streambank failures and top width retreat along a 270-m modeling reach. Empirical and analytical approaches used to estimate rates and depths of fluvial erosion were developed in a final substudy. The rate and depth of fluvial erosion were estimated as a function of hydraulic and hydrologic properties of flow events, vegetation on streambanks, flow induced forces and streambank geometry and soil properties. Reduction of suspended sediment loads should focus on attenuation of geomorphic processes and stabilization of reaches and agricultural lands adjacent to streambanks along incised headwaters within TCW.