The history of deposition in the White River Reservoir was reconstructed from a study of sediment in the reservoir. Suspended-sediment concentrations, particle size, and streamflow characteristics were measured at gaging stations upstream and downstream from the reservoir from November 1975 through September 1977- Characteristics of the sediments were determined from borings and samples taken while the reservoir was drained in September 1976. The sediment surface and the prereservoir topography were mapped. Sediment thickness ranged from less than 1 foot near the shore to more than 20 feet in the old stream channel.
The original reservoir capacity and volume of deposited sediment were calculated to be 815 acre-feet and 487 acre-feet, respectively.
Sediment size ranged from clay and silt in the pool area to large cobbles and boulders at the upstream end of the reservoir. Analyses of all samples averaged 43 percent sand, 40 percent silt, and 17 percent clay, and particle size typically increased upstream. Cobbles, boulders, and gravel deposits were not sampled. The average density of the deposited sediments was about 80 pounds per cubic foot for the entire reservoir.
The reservoir was able to trap about 80 percent of the sediment entering from upstream early in its history. This trap efficiency has declined as the reservoir filled with sediment. Today (1976) it traps only sand and silt-sized sediment, or only about 20 percent of the sediment entering from upstream. Data collected during this study indicate that essentially all of the clay-sized sediment (
