Effectiveness of selected erosion control covers during vegetation establishment under simulated rainfall
Type of Degreethesis
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Soil erosion on unprotected roadside slopes generates significant soil loss during storm events. Proper surface protection to reduce erosion is promoted by water protection agencies including the United States Environmental Protection Agency (USEPA) and the United States Department of Agriculture (USDA). In the present study, selected seeded and non-seeded covers were evaluated on a sandy clay soil transported from an earthen roadside embankment in Russell County, AL. The selected cover treatments were polyacrylamide (BS+P), wheat straw with and without seed (WS+P+S, WS+P), and engineered fiber matrix with and without seed (EFM+S, EFM). Cover treatments were evaluated using 1.2 m x 0.6 m (47 in x 22 in) test plots on a 3:1 slope subjected to 15 minutes (2.9 cm depth) of simulated rainfall. Annual ryegrass (Lolium multiflorum) and browntop millet (Panicum ramosum) were planted on seeded plots in spring and summer test periods, respectively The objectives of the study were to quantify reduction of runoff volume (ml), turbidity (NTU), and modified total suspended solids (MTSS) compared to the bare soil control, and to determine the most cost-effective temporary cover treatment for similar soil, rainfall, and slope conditions. The seeded EFM+S and WS+P+S treatments were observed to be the most effective in terms of runoff volume with 68% and 49% reduction, respectively, as compared to the bare soil control. The most effective treatment with respect to turbidity and MTSS was EFM+S, with 98.7% and 99.8% reduction, respectively, as compared to the bare soil control. Water quality response of seeded treatments combined (EFM+S, WS+P+S) were negatively correlated with days after seeding (DAS) (r = -0.48,-0.47, and -0.63 for runoff volume, turbidity, and MTSS, respectively), as compared to a flat correlation of corresponding responses in non- seeded treatments (r = 0.10, 0.01, and 0.02, respectively), indicating important water quality benefits of seeding. The EFM+S treatment resulted in 39% less MTSS delivery per hectare than WS+P+S but the WS+P+S treatment (cost of $1.03 kg-1 sediment reduction) was found to be 84% less expensive per hectare than the EFM+S treatment (cost of $6.36 kg-1 sediment reduction). The WS+P+S treatment can therefore be recommended over EFM+S as a cost effective method for sediment delivery reduction under conditions similar to this study. Results confirm the cost effectiveness of vegetation in conjunction with other temporary covers to reduce erosion and sediment loss, and provide a method to quantify environmental benefits of erosion control in terms of economic cost.