Acoustic Measurement of Sediment Load

Principal Investigators: Dr. Daniel Wren

Problem:

Measurements of the rate of sand and gravel in transport in streams are difficult and expensive to collect using conventional techniques. Yet this information is critical for determining erosion rates from upstream areas and assessing stability of specific channel reaches. Studies have demonstrated that multiple samples at each location are needed to adequately determine the mean rate of sediment transport for a given flow rate. Currently the best way to obtain sediment transport data is for a sampling crew to be on site during the runoff event with the necessary sampling equipment. Manual sampling, however, is expensive and adequate coverage of the expected range of flows is often difficult due to the uncertainty of predicting runoff events.

Objective:

The goal of this project is to develop automatic samplers to measure depth integrated sand concentrations and the rate of transport of sediment along the bed. An automatic suspended sediment sampler using acoustic backscattering from the sand grains in suspension is currently under development. An automatic sampler to measure the transport rate of bed load using acoustic means is also planned. Samplers of this type have the potential to revolutionize the collection of sediment transport data.

Description of Work:

Currently an acoustic suspended sediment sampler is being developed and tested under controlled laboratory conditions. Recent results have demonstrated that a single frequency instrument yielded excellent information on the temporal changes of suspended sediment concentration over the flow depth in a laboratory flume. Experiments using multiple frequencies to provide information on the size as well as the concentration of sediment are currently in progress. A field version of the suspended sediment sampler will be tested on the Goodwin Creek Experimental Watershed in the near future. The bed load sampler is in the planning stages.

Benefits:

The development of these samplers will provide high quality information on the rate of sediment transport in streams at an affordable cost. This will facilitate the understanding of the processes of erosion and deposition of sediment in agricultural watersheds.