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Depositional Patterns of Sediment Trapped by Grass Hedges

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Transactions of the ASAE. 38(6): 1719-1729. (doi: 10.13031/2013.27999) @1995
Authors:   S. M. Dabney, L. D. Meyer, W. C. Harmon, C. V. Alonso, G. R. Foster
Keywords:   Erosion control, Grass hedges, Grass strips, Gully control, Deposition, Sediment characteristics, Vegetative barriers

Stiff-grass hedges can resist, retard, and disperse concentrated flows of runoff; trap suspended sediment; and reduce ephemeral gully development. Flume experiments were conducted at a 5% grade using several combinations of four grass species, four types of sediment, and eight flow rates ranging from 0.33 to 2.66 m3/min-m. Sediment trapping resulted primarily from deposition in the backwater upstream of the grass, rather than by filtration in the grass. Sediment was initially deposited 1 to 2 m downslope from a hydraulic jump transition that formed at the upper edge of the backwater. From this position, a delta of sediment mostly coarser than 125 mm grew back toward the hydraulic jump until flow depth became shallow enough that bedload transport was initiated and the delta began to advance toward the grass. In the flow zone across the delta, slope steepness approached 1 to 2% and the flow was near critical depth. A steady-state model was developed that describes sediment trapping in the backwater area as a settling process controlled by sediment characteristics, flow rate, and backwater depth at the grass. This model underpredicted trapping of fine sediment and overpredicted trapping of coarse sediment in situations where the delta neared the grass.

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