New Technology Helps Explain Stream Sediment
Movement By Hank
August 8, 2000
New technology is helping scientists demystify erosion dynamics
along stream channels in agricultural watersheds.
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
Scientific contact: Roger A. Kuhnle, ARS National
Sedimentation Laboratory, Oxford, Miss., (662) 232-2971, fax (662) 232-2915,