Evaluation of Erosion Control Practices Under Large-Scale Rainfall Simulation Following ASTM D6459 Standard Test Methods

Abstract

Land development and construction activities remove vegetative cover, exposing bare soil to the erosive forces of rainfall. Stormwater causes dislodgement of soil particles through splash, sheet, and rill erosion, resulting in soil particles being transported off-site causing pollution in local water bodies and water conveyance systems. Erosion control practices are installed to minimize the amount of erosion caused by erosive forces and to aid in the establishment of vegetation. A rainfall simulator has been constructed at the Auburn University Erosion and Sediment Control Test Facility (AU-ESCTF) following the ASTM D6459-19: The Standard Test Method for Determination of Rolled Erosion Control Product (RECP) Performance in Protecting Hillslopes from Rainfall Induced Erosion requirements. The rainfall simulator was constructed to produce 2, 4, and 6 in. per hr (51, 102, and 152 mm per hr) rainfall intensities and has test plot dimensions of 8 ft (2.4 m) wide by 40 ft (10.1 m) long on a 3H:1V slope. Each rainfall experiment was an hour long with three sequential 20 minute rainfall intervals of increasing rainfall intensities of 2, 4, and 6 in. per hr (51, 102, and 152 mm per hr). Calibration testing was performed on each rainfall intensity to verify rainfall drop size distribution, intensity, and uniformity. Bare soil control, loose straw, loose straw with tackifier, and crimped straw were evaluated under rainfall simulation. The mulch practices and bare soil installations were evaluated under initial and longevity performance testing. Following the completion of the straw mulch testing, the soil type of the test slope was changed from a sandy loam to a loam soil, which better followed the soil classification stated in ASTM D6459 standard. During this time, the test procedure was altered to calculate the product C-factor. Three hydraulic mulches, three erosion control blankets, and bare soil control tests were evaluated under the new test procedure. Following the completion of testing, the Revised Universal Soil Loss Equation (RUSLE) was used to calculate the product C-factor from incremental rainfall depth and soil loss results. Rainfall simulation tests performed on the sandy loam soil resulted in an average soil loss of 738 lb. (335 kg) for bare soil, 143 lb. (64.9 kg) for loose straw, 97 lb. (44 kg) for loose straw, and 169 lb. (76.6 kg) for crimped straw. Longevity testing was performed on the straw applications following the initial product test resulting in a total soil loss 611 lb. (277 kg) for bare soil, 287 lb. (130 kg) for loose straw, 131 lb. (59.4 kg) for loose straw with Tacking Agent 3, and 82 lb. (37.2 kg) for crimped straw. The initial and longevity test results were combined to determine which practice reduced the overall soil loss. The loose straw with Tacking Agent 3 resulted in the highest reduction in soil loss of 83%, which was closely followed by the crimped straw with an improvement of 81%. This concluded that anchoring the straw mulch reduced the overall soil lose better than the non-anchored straw applications. Hydraulic mulches and erosion control blankets were evaluated on a loam soil with a new test procedure that allows for the calculation of product C-factors. The loam soil had higher total soil loss rates than the sandy loam soil with a total soil loss of 2,333 lb. (1,058 kg). The hydraulic mulches resulted in C-factors of 0.55 for Eco-Fibre, 0.46 for Soil Cover, and 0.53 for Terra-Wood. All three hydraulic mulches experienced high erosion rates caused by the product washing from the test plot. Erosion control blankets tests resulted in C-factors of 0.05 for Curlex I, 0.14 for S150, and 0.12 for ECX-2. The blankets resulted in lower C-factors than the hydraulic mulches. The Curlex I blanket provided the best test plot coverage resulting in the lowest C-factor.