Effect of Uncertainties in the Results of Soil Particle Size Test Due to Methods and Operators on WEPP Erosion Analysis

Abstract

In the Water Erosion Prediction Project (WEPP) simulation model, soil particle size distribution is employed in numerous calculation processes. To elucidate the impact of soil particle size distribution on the outputs of WEPP analysis, three methods of particle size test were utilized: the specific gravity method, the integral suspension pressure method, and the laser diffraction/scattering method. The results were characterized differently depending on the test method and the operator. Soil erodibility parameters and effective hydraulic conductivities of WEPP were calculated using the measured soil particle size distribution, organic matter, and CEC. The amount of erosion was then subsequently calculated using WEPP. The estimated soil erodibility parameters and effective hydraulic conductivities varied depending on the soil particle size distribution. The calculated amount of erosion exhibited differences by a factor of up to approximately three, depending on the test method, and by a factor of up to approximately two, depending on the operator. In order to properly estimate the amount of erosion using WEPP, it is essential to ensure proper dispersion treatment and washing process in the soil particle size test.