Developing a New Parameterization Approach of Soil Erodibility for the Water Erosion Prediction Project(WEPP) Applications on Rangelands

Abstract

The USDA-Water Erosion Prediction Project (WEPP) computer model is a process-based soil erosion prediction technology. WEPP uses three soil erodibility parameters: rill erodibility (K_r, s m^-1), interrill erodibility (K_i, kg s m^-4), and critical hydraulic shear stress, (τ_c,N m^-2). In this study, a new parameterization approach for estimating erodibility was developed for WEPP applications on rangelands. Data from overland flow experiments on disturbed and undisturbed rangelands were used to develop the following empirical equation to predict rill erodibility variation as a function of vegetation ground cover (), and soil texture fractions. For bunch grass: <fig><graphic xlink:href=23063_files/23063-01.jpg id=ID_6037274d-977f-41d5-bd0b-23e26d6baba7></graphic></fig> The regression analysis resulted in similar equations for forbs and sod grass life forms. Critical shear stress values corresponding to the developed rill and interrill erodibility parameters are presented in Table 1. <fig><graphic xlink:href=23063_files/23063-00.jpg id=BC50E069-2A55-41CD-B13F-8AC62EDB86D9></graphic></fig> These values are not necessarily the measured critical shear stress but rather a reference to be used for calibration corresponding to the developed erodibility equations in this study. The proposed critical shear values fall within the range of (τ_c) values recommended for WEPP application (0.3 to 7 N m^-2). The new erodibility predictions were tested by running batch executable files and input file sets with WEPP model v2012.800. The data used to evaluate the new erodibility equations in the model were obtained from independent rainfall simulation experiments. Our results show that the new erodibility approach predicted erosion at the plot scale with a satisfactory range of error (PBIAS = 35.6%). The new approach was used to provide soil erodibility values for the Erosion Risk Management Tool (ERMiT) (Robichaud et al., 2007) which uses WEPP as the runoff and erosion calculation engine. More detailed results can be found in Al-Hamdan et al. (2022).