|Shields Jr, Fletcher|
Submitted to: International Journal of Sediment Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2005
Publication Date: 12/15/2005
Citation: Shields Jr, F.D., Dabney, S.M., Langendoen, E.J., Temple, D.M. 2005. Control of gully erosion using stiff grasses. International Journal of Sediment Research. 20(4):319-332.
Interpretive Summary: Gully erosion is a serious world wide problem, destroying arable land, and contributing excessive amounts of sediment to water bodies. Gully erosion may become particularly severe when overbank runoff passes over high streambanks adjacent to an incised channel, and traditional structural controls are costly. The use of dense hedges of planted switchgrass for controlling gully erosion was tested in a series of pumped and natural flow tests involving four gullies in two different soils. All gullies were stabilized with a series of mature switchgrass hedges that were planted and maintained using standard procedures. Erosion between hedges was negligible during the pumped flows, but hedges failed during over a several month period when exposed to natural flows. In addition, hedges were not effective in stabilizing gully mouths where vertical steps in the gully bed exceeded about 3 ft. These findings will support future research and development regarding alternatives to structural methods for gully erosion control.
Technical Abstract: Current practice for riparian gully erosion control involves blocking the gully with a structure comprised of an earthen embankment and a metal or plastic pipe. Measures involving native vegetation are more attractive for habitat recovery and economic reasons. To test the hypothesis that switchgrass (Panicum virgatum L.) hedges planted at 0.5-m vertical intervals would control gully erosion, we established a series of hedges in four channels. Two of the channels were previously eroded trapezoidal channels cut into compacted fill in an outdoor laboratory, and the other two were natural gullies in highly erodible soils. While vegetation was dormant, we created artificial runoff events in the two laboratory gullies and one of the natural gullies. During these tests we monitored flow depth, velocity, turbidity, and soil pore water pressures. The fourth gully was subjected to a series of natural runoff events over a five-month period. Flow depths in all tests were generally < 0.3 m, and flow velocities exceeded 2.0 m s-1 at the steepest points of the gullies. Erosion rates were negligible for controlled flow experiments, but natural flows in the fourth gully resulted in 1 m of thalweg degradation, destroying the central portions of the grass hedges. Geotechnical modeling of soil steps reinforced with switchgrass roots showed that factors of safety > 1 for step heights < 0.5 m, but instability was indicated for step heights >1 m, consistent with our observations.