OPTICAL AND ACOUSTIC SURROGATES FOR SEDIMENT MASS CONCENTRATION, PLATTE RIVER NEAR OVERTON, 2012

Despite many main-stem dams and diversions having altered the balance between sediment load and transport capacity, few examples of active sediment-load augmentation are known, except by sediment sluicing or flushing. Hydroelectric tailwater (clear water return) exacerbates the larger scale imbalance caused by dams and diversions well upstream of the central Platte River, Nebraska. In cooperation with the Platte River Recovery Implementation Program, the U.S. Geological Survey operated two temporary, continuously monitoring installations near Overton, Nebr., during September-October 2012 to enhance monitoring of the Program’s pilot sediment augmentation project (sand pump and “island scraping” operations that added about 100,000 tons of sediment to the river channel). Preliminary results from side-looking acoustic Doppler velocimeter, turbidity sensor, and laser diffraction particle-size analyzers are presented, along with results from manually collected samples for gravimetric analyses that may allow calibration of the surrogate measures. Laboratory-analyzed suspended sediment concentrations ranged up to 274 mg/L.