Development of a Storm Runoff Simulator: Part 3 – Sediment Mixing Device

Abstract

Runoff simulators used in plot research have not effectively represented a natural hydrograph and sediment graph. Therefore, an improved runoff simulator is needed to better evaluate the performance of conservation buffers and similar practices. The objective of this study was to design, build, and test a prototype sediment mixing device that could be incorporated into the final design of a storm runoff simulator. Based on an engineering analysis, the simulator design constraints were a maximum water volume of 7580 L, a peak flow rate of 7.3 L s-1, a maximum sediment load of 882 kg, and peak sediment rate of 1.15 kg s-1. The sediment mixing device consists of an impeller agitated mixing tank to create a homogeneous slurry of fine silica sand and water. Slurry outflow is measured and controlled by an output control system operating under gravity flow conditions. A time-compressed 5-yr, 2-h SCS design storm with an eroded sediment mass of 442 kg and a peak sediment rate of 1.3 kg s-1 was used to verify performance. When reproducing the design sediment graph using a slurry concentration of 0.30 kg L-1 comparable efficiencies among repetitions were maintained; with root mean square error (RMSE) representing less than 4% error between the RMSE and the peak flow or sediment rate. Peak sediment rates were within 7% of the target rate. The prototype sediment delivery system uses fine silica sand to represent clay and silt sized particles, and is capable of producing varying sediment rates that match a design sediment graph.