Previous studies have demonstrated that a major source of sediment arriving at sediment basins is erosion from unlined water conveyances. While check dams provide some reduction, lining the diversions and ditches can be highly effective. The typical liner is a rolled erosion control blanket (RECB) made of natural fibers, such as excelsior, jute, or coir. Another material, Posi-Shell, consisting of a spray-on mixture of cement and two proprietary products, has potential to be installed much more quickly and easily, but needed to be evaluated. This project provides an evaluation of four potential lining systems for reducing erosion in water conveyances under both controlled, full-scale conditions and on active construction projects. The four systems included jute mesh, jute mesh + polyacrylamide (PAM), excelsior, and Posi-Shell.
The full-scale model study was conducted at the Sediment and Erosion Control Research and Education Facility at the Lake Wheeler Road Field Laboratory in Raleigh, NC. Plywood flumes were constructed with a trapezoidal shape with 2’ bottoms and a total length of 16’. Three were constructed to have 4, 8, and 12% slopes, and each was packed with soil to a depth of 1’ prior to introducing flows of approximately 0.4, 0.8, and 1.1 cubic feet per second (CFS). Samples were taken at the outlet for turbidity and total suspended solids measurements, and after 10 min the flow was stopped and changes in the channel were measured. At three construction sites, existing diversions were lined with the different materials and samples were obtained during storm events with automatic samplers. Changes in the ditch topography was also measured periodically.
Excelsior performed the best in the flume study, with Posi-Shell and jute+PAM having somewhat more erosion overall. Posi-Shell performance was sensitive to application techniques in both the field and flume. For instance, the hydroseeder used to apply it was unable to produce full power during a field application, resulting in uneven distribution. One application of Posi-Shell to the soil in the flumes did not full cover the soil near the outlet, leading to erosion and failure, which did not occur in all other tests. Jute alone was better than no lining at all, but clearly inferior than the other liners tested. Given the relative ease and speed that Posi-Shell can be applied using standard hydroseeding equipment, and material costs only
