Sediment Modeling of Big Bend Reservoir, South Dakota

Closure of Big Bend Dam in 1963 resulted in changes in the hydraulic regime of the Missouri River and the formation of a delta in the headwaters of Big Bend Reservoir (also known as Lake Sharpe) in SouthDakota. The U.S. Army Corps of Engineers, Omaha District commissioned a study of sedimentation in the headwaters of Lake Sharpe as part of operation and maintenance activities associated with the Missouri River mainstem dams and reservoirs. Questions about the current and future development of the sediment delta in the lake were addressed by developing a calibrated HEC-6T sediment transport model of the Missouri River and Big Bend Reservoir. Cross section geometry was developed using survey data collected by the Corps since dam closure (1968–1997). Sediment inflow from the Bad River, the largest single contributor of sediment to Big Bend Reservoir, was developed from data collected by the U.S. Geological Survey (USGS). A sediment budget was developed for the reservoir, taking into account not only Bad River inflows but also minor tributaries and bank erosion. Both cumulative depositional volumes and average bed elevation statistics were used as criteria in the calibration process. The calibrated model was then used to predict river conditions fifty years into the future.