Overland Flow and Rainfall Simulation Studies on Ornamental Vegetation, Compost, and Jute Netting

摘要

The literature is replete with studies quantifying erosion control effectiveness from raindrop impact on various vegetation types and erosion control products. However, there is little published overland flow research documenting the effectiveness of ornamental vegetation and erosion control products in filtering sediment and nutrients from stormwater runoff. The California Department of Transportation and the Office of Water Programs, California State University, Sacramento, has conducted two studies at the Erosion Control Research Facility at Cal Poly State University, San Luis Obispo addressing the use of ornamental vegetation as an erosion control treatment. The first study addressed how well ornamental vegetation, jute netting, and a combination of jute netting and vegetation decreased soil erosion and runoff during rainfall simulation. The second study compared the performance of ornamental vegetation, 0.5 inches of compost, and jute netting treatments in decreasing sheet erosion due to overland flow. Both studies used sandy loam soil in test boxes set at a southwest aspect with 2:1 and 3:1 slopes, respectively. Treatments were evaluated by measuring the runoff quantity, sediment load, sediment concentration, pH, total dissolved solids (TDS), electrical conductivity (EC) and turbidity of the runoff. Ornamental plant species included Lonicera japonica, Lantana montevidenses, Carpobrotus edulis, Hedera helix L., Myoporum parvifolium, Rosmarinus officinalis L. and Vinca major. Rainfall simulation trials yielded significant reductions in total runoff and sediment by any treatment compared to bare soil, with 100 % vegetative cover yielding 98.6 % and 99 % reductions, respectively. Turbidity was significantly reduced by all treatments, while TDS and EC were not significantly different among trials. Average pH values for bare soil were significantly higher than those of jute netting and/or vegetation. In overland flow experiments, compost reduced runoff, sediment, and turbidity by greater than 96 % and increased EC by 430 % when compared to bare soil. Jute netting reduced runoff, sediment, turbidity, and EC by 43 %, 99 %, 97%, and 65 %, respectively, when compared to bare soil. Higher pH and salt concentrations were detected in runoff from boxes treated with compost; however, levels were not substantial enough (1673.9 μS) to be harmful to plants. Since no runoff was produced in overland flow trials, ornamental vegetation treatments were 100 % effective in controlling overland flow under test conditions. Differences among the plant species will be elucidated with future research involving steeper slopes and increased flow rates.