The Determination of Erosion Control Practice C-Factors Under Rainfall Simulation Testing
Large-scale rainfall simulation is used to evaluate the performance of erosion control practices under varying rainfall conditions. The total kinetic energy for each rainfall simulator must be determined to evaluate the impact of the generated rainfall event. The kinetic energy of raindrops is diffused by the soil surface. However, this energy dissipation causes the dislodgement of soil particles from the soil surface resulting in erosion. Erosion control practices are installed on bare soil to prevent erosion and to aid in the establishment of vegetation. The Auburn University Erosion and Sediment Control Test Facility (AU-ESCTF) has constructed a large-scale rainfall simulator following ASTM D6459-19: The Standard Test Method for Determination of Rolled Erosion Control Product (RECP) Performance in Protecting Hillslopes from Rainfall Induced Erosion. This standard specifies a test slope measuring 2.44 m (8 ft) wide by 12.20 m (40 ft) long on a 3H:1V slope. The designed storm event exposes the test slope to three sequential 20-minute rainfall intensities of 51, 102, and 152 mm/hr (2, 4, and 6 in/hr). The flour pan method is used to measure the drop size distribution of each rainfall intensity. ASTM D6459-19 specifies that the kinetic energy and erosion index shall be determined from the drop size distribution and rainfall intensity. Following the calculation of the kinetic energy, the Revised Universal Soil Loss Equation is used to calculate the Cover-factor (C-factor). The C-factor for an erosion control practice is calculated by comparing the total soil loss results of a product to the results of a bare soil control test. A standardized procedure has been developed to quantify the drop size distribution and kinetic energy for the storm event and the C-factor for erosion control product performance.