Going By the FlowUsing
Listening to a flowing creek may be just the thing for
relaxing on a peaceful afternoon. But ARS
hydraulic engineer Roger Kuhnle listens for a different reason. He's
seeking clues about the overall state of the watershed that feeds the
Kuhnle and colleagues use cutting-edge acoustic technology
to monitor sediment flow, whose speed and concentration may alert researchers
to changes and problems within water systems. The project, undertaken
with the University of Mississippi, is being conducted on a model stream
channel at the ARS Channel and Watershed Process Research Unit's laboratory
in Oxford, Mississippi, as well as in nearby Goodwin Creek.
"Accurate determinations of the rate of sediment
movement by streams are necessary because sediment can fill reservoirs
and reduce their capacities," says Kuhnle, the project's leader.
"It can fill channels and cause flooding, degrade water quality,
and destabilize channel banks, destroying land. Monitoring stream sediment
also helps us evaluate its potential effect on aquatic organisms."
Physical, chemical, and biological damage associated with
sediment flow in North America costs around $16 billion annually, say
ARS and U.S. Geological Survey researchers.
The amount of suspended solid material transported in
rivers and streams is often the main indicator of watershed stabilityas
well as water qualitysays Kuhnle. Ideally, early warning signals
for watersheds will one day trigger effective preventive care and maintenance
strategies. But for now, scientists at the unit are concentrating on
the initial step: developing a mobile sensing system that would make
such improved care possible.
"We need a portable, efficient, automatic system
that doesn't require someone to be on siteone that can provide
better data than what we get today, not only in quantity, but also in
quality," says Kuhnle.
He says years of research indicate that acoustic technology
is one of the most promising sediment-tracking methods among those tested.
"It is more cost- and time-effective than current
methods and the other methods tested," he says. "The short-duration,
high-intensity flows that cause most sediment movement in many streams
are best observed by continuous monitoring systems."
The studies have led to development of the Bedform and
Sediment Information System, or BASIS. Devised by former University
of Mississippi scientist Robert Derrow in close collaboration with ARS
scientists, BASIS emits a pulse of acoustic energy and then gauges the
strength and travel time of the back echo to determine sediment's location
and concentration. Like its predecessorknown as the SedBed Monitorit
locates sediment on a stream's bottom, which can indicate either erosion
or accumulation of sediment there.
But the new system's most important enhancement is its
ability to detect sediment suspended in water. It converts the acoustic
data into a digital image that portrays suspended sediment as a cloud,
in a multitude of colors that signify various concentrations. The main
BASIS unit is compact, and the entire system can run from a laptop computer.
Kuhnle says BASIS technology is now available for use
by private firms and government agencies. More sophisticated technology
under development for total suspended-sediment load sampling will become
available after about 3 to 5 more years of experimentation and field
Pons, Agricultural Research Service Information Staff.
This research is part of Water Quality and Management,
an ARS National Program (#201) described on the World Wide Web at www.nps.ars.usda.gov.
"Going By the FlowUsing Acoustics To Track Stream Sediment" was published in the October 2003 issue of Agricultural Research magazine.