Development of Techniques to Evaluate the Potential for Flooding, Erosion, and Sediment Transport along the Upper Walker River
AdvisorDennett, Keith E
Civil and Environmental Engineering
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The quality of Walker Lake is degrading due to lowering of the water level in the lake accompanied by increased loadings fine grained sediments and accumulation of dissolved solids. A variety of research projects known collectively as the Walker Basin Project were funded through the United States Bureau of Reclamation in order to identify techniques to minimize the degradation of and gradually restore Walker Lake through the acquisition of additional water rights. This thesis focuses on various aspects of Project E of the Walker Basin Project: "Development of Tools to Quantify Sediment Transport within the Walker River Watershed along with Recommendations to Maximize Water Conveyance and Minimize Degradation of Water Quality in Walker Lake Due to Erosion, Sediment Transport, and Salt Delivery." The results of specific tasks that were completed in order to accomplish various objectives of the project are described. These tasks included: 1) performing a detailed engineering survey along the upper Walker River; 2) developing a hydraulic model of the upper Walker River using the United States Army Corps of Engineers Hydrologic Engineering Center River Analysis System (HEC-RAS) software; and 3) collecting and characterizing sediment samples from selected locations along the upper Walker River.In order to develop the HEC-RAS model, an engineering survey was performed to collect channel cross section data along approximately 100 miles of the river. Bed shear stresses predicted by the HEC-RAS model were used to estimate the potential for erosion and sediment transport with anticipated increases in flow due to the proposed acquisition of additional water rights within the Walker River basin. The output from the HEC-RAS model was used along with results obtained from laboratory flume studies which were performed to determine hydrodynamic conditions resulting in erosion and sediment transport. Sediment samples were collected from several locations and characterized by particle size distribution and mineralogy. The results consistently indicated that the sediments in the upper Walker River are expected to be actively transported under most of the anticipated flow conditions. This was consistent with field observations at the locations where sediment samples were collected. Active sediment transport was visually observed along the bed surface even at relatively low flow conditions.The HEC-RAS model was also used to evaluate the potential for localized flooding due to increased flows. Except for a few areas, the East Walker River can handle flows up to 400 cubic feet per second (cfs), which is higher than the average annual maximum flow. For flows exceeding 400 cfs, localized flooding is predicted at a few locations along the West Walker River. When flows are around the average annual maximum flow of 700 cfs, localized flooding is expected at a number of locations.