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Woody Debris Structures Help Rehabilitate Streambed ChannelsBy Jennifer Arnold
July 24, 2001
Interlocking piles of felled trees anchored to a streambed and adjacent banks can help protect eroding streambanks and cost less than current control measures.
Many stream corridors in agricultural watersheds suffer from accelerated erosion. For years, researchers have tried to stabilize streambanks with planted vegetation. This technique is usually cheaper, better for the environment and more aesthetically pleasing than traditional artificial control measures that use structures made from costly stone and concrete. However, vegetation is hard to establish in rapidly eroding channels.
Now, Agricultural Research Service hydraulic engineer Doug Shields at the National Sedimentation Laboratory, Oxford, Miss.--in cooperation with the USDAs Natural Resources Conservation Service, U.S. Army Corps of Engineers and local landowners--has designed and constructed an experimental erosion control system. It uses interlocking piles of felled trees anchored to the streambank.
These felled-tree structures are designed to induce sediment deposition at the toe--the place where the streambank intersects the streambed--of eroding banks. This reverses erosion-driven channel enlargement. Data and observations indicate that the structures create hydraulic conditions favorable to stream habitat restoration and induce sediment to be deposited in areas formerly subject to erosion.
About a year after construction, water depths near the structures had doubled, reducing severe stress on the aquatic community caused by extremely shallow conditions associated with channel erosion.
Additional components of the project include planting willow cuttings and switchgrasses. Results could provide the technical basis for future applications that cost only about one-third of current approaches featuring the use of quarried stone and other artificial materials to stabilize streambanks.
This technology will help to create forested riparian buffer strips, control streambank erosion and restore the nations 3.5 million miles of rivers currently considered degraded by erosion, sedimentation and excess nutrients.
ARS is the U.S. Department of Agricultures chief scientific research agency.