Comparative Analysis of Soil Erosion Using Large-, Intermediate-, and Small-Scale Test Plots of Bare Soil and Different Hydromulch Products under Large-Scale Rainfall Simulator

Abstract

A study was conducted to compare the test results of three different size erosion-control plots under rainfall simulation to determine if there is a direct relationship to the size of a tested erosion-control plot and the experimental results of soil erosion. The plots were tested under the same rainfall simulator to minimize the impacts of spatial variability found with different simulators. Three plot sizes (2 ft by 4 ft, 4 ft by 8 ft, and 8 ft by 40 ft for plot width and flow length, which are small-, intermediate-, and large-scale, respectively) were tested for a loam bare soil control condition; and two plot sizes (small- and large-scale) were tested for three different hydromulch products. The large-scale bare soil plots had an average soil loss of 2,333 lb. (7.29 lb./ft^2). The intermediate-scale bare soil plots had an average soil loss of 62.8 lb. (1.96 lb./ft^2). The small-scale bare soil plots had an average soil loss of 2.58 lb. (0.323 lb./ft^2). The large-scale plots experienced significant rill erosion and the early signs of gully erosion; whereas the small-scale plots experienced very limited rill erosion. The flow length of the small-scale plots is inadequate to allow for the transportation of the dislodged sediment caused by splash erosion. However, it was determined that the soil loss for the various plot sizes was related to the horizontal projection of the soil slope length, l (lambda), by the power law function. The experimental soil loss results were comparable to the theoretical results determined from Revised Universal Soil Loss Equation (RUSLE). The theoretical soil erodibility K-factor as determined in RUSLE was calculated to be 0.32 for the loam soil. The experimental K-factor was determined to be 0.28 and 0.24 for the large-scale and intermediate-scale simulations, respectively. However, the K-factor for the small-scale plots was estimated at only 0.06 due to limited rill erosion. For the analysis of the hydromulch (HM) products, the large-scale tests resulted in the cover-management C-factors of 0.44, 0.50 and 0.55 for EcoFibre HM, SoilCover HM, and Terrawood HM, respectively. The small-scale tests however, resulted in C-factors of 0.15, 0.24 and 0.58 for EcoFibre HM, SoilCover HM, and Terrawood HM, respectively. The hydromulch products were tested on small-scale plots for both loam and topsoil. The soil loss from the topsoil plots varied significantly when compared to the loam soil. The average soil loss for the topsoil plots when compared to the loam plots ranged from 30% to 146%. The data gathered over the tested plot sizes indicate the opportunity to utilize flow length and plot area as useful factors to scale up soil loss results, but the plot length needs to be long enough for all soil erosion mechanism to be fully developed. This could provide additional justification for testing on a smaller scale at a reduced cost and scaling the data up to estimate soil losses on a larger area.