Tour Stop #13: Developing Erosion Control Technology and Examining Channel Adjustment Using a Model Basin

Experimental facilities provide unique opportunities to systematically investigate the processes of sediment erosion and deposition, to develop design criteria for grade-control structures, and to examine the performance of erosion control technology. The model basin, originally constructed in 1974, has been used to study a variety of different problems germane to the Agricultural Research Service, and three of these are briefly described below.

1. Low Drop Grade Control Structures. W. C. Little and J. B. Murphey. Rapid migration of head-cuts through the incised streams of the Mississippi River Valley produced an urgent need for an economical grade stabilization structure to halt the channel bed incision. Design criteria were established for low-drop structures constructed of rip-rap where the drop in bed elevation is relatively low. The resulting structure design dissipates 80% of the energy gained in the drop in bed elevation on site. The structure design has been widely accepted and used in the mid-South saving an estimated $200 million in construction costs.

2. Stage-Discharge Relationship for Unsubmerged Stiff-Grass Hedges. S. M. Dabney, G. H. Dunn, K. T. Krishnegowda, and C.V. Alonso. Grass hedges, narrow strips of stiff grass planted across concentrated flow zones, can retard surface runoff, cause deposition of sediment and prevent ephemeral gully development The model basin was used to develop an equation to predict backwater depth as a function of flow and grass hedge characteristics, and several different types of grasses were evaluated. This information has been incorporated into a USDA-NRCS Interim Practice Standard as the basis for erosion control in agricultural areas.

3. Impact of Large Woody Debris on Channel Morphology. N. Wallerstein, C. V. Alonso, S. J. Bennett and J. B. Murphey. Field investigations indicate that large woody debris severely impacts channel processes by locally controlling grade, by increasing flow resistance and thus flood risk, and by causing channel erosion and widening. Using a field prototype, a flume model study was conducted to determine the effect of debris orientation and height above the bed on the depth and extent of bed scour, and to assess the time variation of the force acting on the element as erosion and deposition ensued. On-going work will use this information to model channel adjustment to large woody debris.

Key Words:

Grade control, Vegetative barriers, Large woody debris.

Publications:

Little, W. C., and J. B. Murphey, 1982, Model study of low drop grade control structures. J. Hydr. Div., ASCE, 108,1132-1146.

Dabney, S. M., L. D. Meyer, W. C. Harmon, C. V. Alonso, and G. R. Foster. 1995. Deposition patterns of sediment trapped by grass barriers. Trans. ASAE, 38, 1719-1729.