Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2004
Publication Date: 10/1/2004
Citation: Dabney, S. M., Shields Jr., F. D., Temple, D. M., Langendoen, E. J. 2004. Erosion processes in gullies modified by establishing grass hedges. Transactions of the American Society of Agricultural Engineers. 47(5):1561-1571.
Interpretive Summary: Gully erosion is a serious problems on sloping land and at the field edges of flat lands next to deep channels and ditches. We conducted an experiment to determine if a series of stiff grass hedges could control concentrated flow erosion on steep slopes and assessed possible mechanisms of failure as a function of soil type, hedge spacing, and flow rate. Our results showed established switchgrass hedges placed with about a 0.5 m vertical interval at slopes less than or equal to 33% steepness were effective in preventing measurable erosion of concentrated flow channels but more research is needed to determine longer-term reliability of the practice. Our results are important to farmers and conservation planners because they demonstrate that growth of small gullies can be controlled with carefully designed vegetative plantings that are less costly than drop pipe structures and have the additional benefits of pollutant filtration and the creation of habitat associated with a stand of native grass.
Technical Abstract: Concentrated flow can cause gully formation on sloping lands and in riparian zones of floodplains adjacent to incising stream channels. Current practice for riparian gully control involves blocking the gully with an earthen embankment and installing a pipe outlet. Measures involving native vegetation would be more attractive for habitat recovery and economic reasons. To test the hypothesis that switchgrass (Panicum virgatum L.) barriers planted at 0.5-m vertical intervals within a gully would control erosion, we established a series of hedges in several concentrated flow channels. Two of the channels were previously eroded trapezoidal channels cut into compacted fill in an outdoor laboratory. The other channels were located at the margin of floodplain fields adjacent to an incised stream channel, Little Topashaw Creek, in Chickasaw County, MS, USA. While vegetation was dormant following two growing seasons, we created artificial runoff events in our test gullies using synthetic trapezoidal-shaped hydrographs with peak discharge rates of approximately 0.03, 0.07, and 0.16 m3 s-1, flow rates similar to those observed during natural runoff events in gullies at Topashaw. During these tests we monitored flow depth, velocity, turbidity, and soil pore water pressures. Flow depths were generally < 0.3 m and flow velocities varied spatially and exceeded 2.0 m s-1 at the steepest points in some tests. Erosion rates remained modest for the conditions tested as long as slopes were less than 3 horizontal to 1 vertical (33%) and step height between barriers was less than 0.5 m. Stability modeling of soil steps reinforced with switchgrass roots showed that cohesive forces were three times greater than shearing forces for 0.5 m step heights, and that therefore mass failure was unlikely even with the surcharge weight of a 0.2 m depth of ponded water. For step heights greater than 1 m, however, mass failure was observed and predicted to be the dominant erosion mechanism.