New erodibility parameterization for applying WEPP on rangelands using ERMiT

Authors: AL-HAMDAN, OSAMA - Texas A&M University; Pierson Jr, Frederick; ROBICHAUD, P - Us Forest Service (FS); ELLIOT, WILLIAM - Us Forest Service (FS); Williams, Christopher - Jason

Submitted to: American Society of Agricultural and Biological Engineers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2021
Publication Date: 2/15/2022
Citation: Al-Hamdan, O.Z., Pierson Jr., F.B., Robichaud, P., Elliot, W.J., Williams, C.J. 2022. New erodibility parameterization for applying WEPP on rangelands using ERMiT. American Society of Agricultural and Biological Engineers. 65(2):251-264. https://doi.org/10.13031/ja.14564.
DOI: https://doi.org/10.13031/ja.14564

Interpretive Summary: The USDA-Water Erosion Prediction Project (WEPP) computer model predicts soil erosion using three soil erodibility parameters: rill erodibility, interrill erodibility, and critical hydraulic shear stress. In this study, a new parameterization approach for estimating soil erodibilities and critcal shear was developed for WEPP applications on rangelands. Extensive experimental data from disturbed and undisturbed rangelands were used to develop empirical equations to predict rill and interrll erodibilities from readily available vegetation cover and soil texture information. Appropriate critical shear values corresponding to the developed rill and interrill erodibility parameters were also provided. Model testing results show that the new parameterization approach predicts erosion with a satisfactory range of error useful for making management decisions. These newly developed WEPP parameter estimation procedures were used to estimate updated soil erodibility values for the Erosion Risk Management Tool (ERMiT) utilized extensively by land managers for post-fire assessment and management decision making.

Technical 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 (Kr), interrill erodibility (Ki), and critical hydraulic shear stress, (tc). 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 empirical equations to predict rill erodibility variation as a function of vegetation cover and soil texture. Data from rainfall simulation experiments were analyzed by piecewise regression to develop empirical equations for predicting variability of interrill erodibility before and after disturbance and across a wide range of soil textures as a function of vegetation cover and soil texture. Critical shear values corresponding to the developed rill and interrill erodibility parameters were proposed. Our results show that the new erodibility approach predicts erosion at the plot scale with a satisfactory range of error (PBIAS =35.6 and Nash-Sutcliffe efficiency = 0.47). The new approach was used to provide soil erodibility values for the Erosion Risk Management Tool (ERMiT) which uses WEPP as the runoff and erosion calculation engine.