New Technology Helps Explain Stream Sediment Movement

New technology is helping scientists demystify erosion dynamics along stream channels in agricultural watersheds.

Agricultural Research Service hydraulic engineer Roger Kuhnle and hydraulic technician John Cox at the National Sedimentation Laboratory in Oxford, Miss., tested an acoustic device called the SedBed Monitor. They used it to measure the rate of sediment movement by measuring the size and speed of dunes that migrate along the bottom of streams. The device was developed by researchers at the University of Mississippi's National Center for Physical Acoustics, in cooperation with Kuhnle.

After lab-testing the SedBed Monitor for several years, Kuhnle field-tested a modified version at Goodwin Creek watershed in northern Mississippi for three years during 12 heavy rains that produced runoff. A special microphone picks up sound that bounces off sediment as it moves along the stream bottom. The data automatically feeds into a computer that only operates when the stream's water depth is above a minimum level.

Kuhnle uses the size and migration rate of the dunes from the records, along with the dune density, to calculate the rate of sediment movement in the test channel. Obtaining this information using conventional sampling methods would take hours because sediment movement is so variable.

For channels in agricultural and other watersheds to remain stable, the amount of sediment moving into the channel must equal the sediment moving out. The roughness of the stream bottom plays a key role in this sediment movement--and this information hasn't often been available for streams that contain sand and gravel.

This technology will help researchers refine and improve current flow and sediment rate prediction methods. It's also critical to engineers in the U.S. Army Corp of Engineers and U.S. Department of Agriculture's Natural Resources Conservation Service responsible for the ecological and environmental stability of watershed drainage systems. ARS is the USDA's chief research agency.

Scientific contact: Roger A. Kuhnle, ARS National Sedimentation Laboratory, Oxford, Miss., (662) 232-2971, fax (662) 232-2915, kuhnle@sedlab.olemiss.edu.