Shoreline Erosion Rates and Processes Along Lake Sharpe Near Lower Brule, South Dakota

The U.S. Geological Survey in cooperation with the Lower Brule Sioux Tribe is monitoring shoreline retreat along the western boundary of Lake Sharpe near the Lower Brule, South Dakota. Lake Sharpe is a reservoir along the Missouri River impounded by the Big Bend Dam. Construction of the Big Bend Dam began in 1959 and reservoir filling was initiated in 1963. During 2013–14, operation of the hydroelectric plant at Big Bend Dam is reflected in a cycle of reservoir water levels lowering during weekdays and rising during the weekend. An analysis of aerial photos and topographic maps since 1966 indicates truncation of several shoreline spurs by 1976, and subsequent shoreline retreat (aerial photographs since 1991). Aerial photo analyses complement Light Detection and Ranging (LiDAR) surveys of recent bank erosion from 2011–2013 near Lower Brule which indicated erosion rates of up to 9 meters per year. Time-lapse cameras have been installed at three locations to qualitatively examine shoreline changes: the Lodge site approximately 4 kilometers (km) north of Lower Brule, the Playground site along the shoreline east of Lower Brule, and the Lagoon site approximately 1 km southeast of Lower Brule. Images were taken four times per day. Soils at these sites are the Opal-Chantier clay, Bullcreek clay, and Fairlo silt loam, respectively. The Lodge site has a more complex stratigraphy with aeolian deposits underlying the Opal-Chantier clay. Soil samples have been collected at each location to determine soil properties and strength. A goal of this research is to identify the key factors, such as reservoir operation, wave erosion, ice scour, shallow groundwater movement, and soil properties that influence shoreline erosion. Once identified, these results can be used to inform the selection and development of strategies to mitigate shoreline erosion.