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Publication Abstract

The Role of Streambank Erosion in Contributing to Sediment Loads in the Town Creek Watershed in Mississippi

Ramirez-Avila, J. J., McAnally, W. H., Langendoen, E. J., Ortega-Achury, S. L., & Martin, James L. (2011). The Role of Streambank Erosion in Contributing to Sediment Loads in the Town Creek Watershed in Mississippi. Proceedings of the International Symposium on Erosion and Landscape Evolution. Anchorage, Alaska: American Society of Agricultural and Biological Engineers (ASABE).

A combination of in situ monitoring, geomorphic characterization methods and modeling was performed on different locations along the principal channel of the Town Creek watershed (Figure 1) in Northeastern Mississippi to quantify the contributions of streambanks to stream sediment loads and better understand the processes of streambank erosion. Estimated annual suspended sediment load at the watershed�s outlet averaged about 1,100,000 Mg over a 29 year period of existing data. Temporal analysis of suspended sediment loads suggests an increase in time of sediment availability, transport capacity, and suspended sediment loads in the watershed and channel system with increasing flow. However, the suspended sediment load under low or base flow conditions was reduced. Both observations can be explained by the difference in stages of channel evolution along Town Creek. Streambank instability is widespread and the highly erodible streambank materials make streambanks an important potential source of sediment along the entire watershed. Streambanks predominantly lost materials through gravitational failures and removal of failed sediments by hydraulic forces along the watershed headwaters, commonly represented as incised channels near agricultural areas. Headwaters contributed up to 70% of the total sediment load exported from the entire watershed. Annual sediment loading to the stream from streambank retreat was estimated as 28.5 Mg per m-stream based on repeated cross section surveys. Changes in channel morphology, vegetation and streamflow patterns favored significant amounts of sediment deposition (up to 20% of headwaters� sediment load) observed along the middle length of the principal channel. The computational model CONCEPTS (Conservational Channel Evolution and Pollutant Transport System) was used on an incised reach to assess model performance and capability to simulate spatial and temporal streambank changes along the study reach. CONCEPTS was able to accurately predict the time of occurrence and magnitude of top bank retreat and failures of streambanks along the modeled reach. Results from field measurements and modeling offer important insights into the relative effects of land and streambank erosion on the sediment budget for Town Creek watershed, stream water quality, and how management measures can effect improvements. Reduction of suspended sediment loads should focus on the attenuation of geomorphic processes and stabilization of reaches and agricultural lands near streambanks at the headwaters within the watershed. Additional research should focus on the significance of subaerial processes on incised headwater channels.