Sediment source area identification over watersheds: Influence of spatial scale and sediment travel times.

摘要

Sediment yield from a watershed has important implications for water quality and water resources, especially from agricultural areas. Water quality issues arise because sediments serve as carriers for various pesticides, radioactive materials and nutrients. Therefore, it is crucial to identify sediment source areas to design proper abatement strategies and develop TMDL initiatives accordingly. A physically-based watershed-scale surface flow and erosion model, KINEROS was utilized as the modeling tool in this study.; A GIS interface of the KINEROS model was employed to automate the channel extraction and watershed delineation. An important issue of geomorphologic detail was examined here because it influences model predictions of water flow and sediment discharges. The effect of geomorphologic resolution over peak runoff, peak sediment discharge and total sediment load was investigated. It was shown that the required geomorphologic detail is a function of quantity of interest. Empirical relationships were developed relating these quantities to optimal resolution, watershed characteristics and nature of the storm.; Following the study on geomorphologic resolution, two methodologies were developed to identify the source areas and their relative strengths for sediment generation. Both methods rely on hydrograph and sedimentograph data collected at the mouth of the watershed. The first method used a modified unit sedimentograph approach, while the second method relied on optimization techniques. Data over several events were examined over two small watersheds, and a statistical procedure was utilized to assess the erosion vulnerability of different regions in the watersheds. These results were presented in the form of maps to obtain a spatial picture of sediment generating areas. Results from these two independent methods showed good agreement. Because of parameter non-uniqueness that typically confounds the results from these methods, it was suggested that the resolution utilized for source identification be smaller than the one indicated by the study on geomorphologic resolution.