Improving and verifying channel erosion simulation in the Water Erosion Prediction Project (WEPP) Model

Authors: GUO, TIAN - Purdue University; SRIVASTAVA, ANURAG - University Of Idaho; Flanagan, Dennis

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2021
Publication Date: 5/5/2021
Citation: Guo, T., Srivastava, A., Flanagan, D.C. 2021. Improving and verifying channel erosion simulation in the Water Erosion Prediction Project (WEPP) Model. Journal of Environmental Management. 291. Article 112616. https://doi.org/10.1016/j.jenvman.2021.112616.
DOI: https://doi.org/10.1016/j.jenvman.2021.112616

Interpretive Summary: Soil erosion and sediment loss in runoff from fields and small agricultural watersheds is a continuing problem within the U.S. and throughout the world. Sediments and associated chemicals (nutrients, pesticides) can pollute off-site water bodies and lead to eutrophication and harmful algal blooms. In order to determine potential soil loss from farms, soil conservationists most often utilize erosion prediction models, due to wide model applicability, ability to simulate many different crops and land management scenarios, and limited resources for on-site monitoring. This research involved improvement of a process-based soil erosion model to better account for soil loss from channels in farm fields, by incorporating daily updating of soil erodibility (soil’s resistance to detachment) parameters. We tested how well the original and modified model performed using observed field data from six small watersheds. The updated model did a better job of representing soil erosion and sediment loss from the channels and watersheds examined. This research impacts soil conservation agency staff, farmers, and others involved in reducing soil erosion and protecting natural resources. Improved soil erosion prediction models will allow for better management of agricultural lands to minimize sediment losses.

Technical Abstract: The Water Erosion Prediction Project (WEPP) model has been widely used to assess the impacts of management practices and climate change on runoff and soil loss at both hillslope and watershed scales. However, the representation of channel erosion processes in WEPP has not been changed significantly since it was first publicly released about 25 years ago. This research was to improve the channel sediment detachment capacity estimation in the model, which is calculated based upon two soil parameters: a channel erodibility factor and a channel critical shear stress. The current (WEPP v2012.8) and previous WEPP versions assume that these channel input parameters are constant through time, which may lead to erroneous channel detachment predictions, especially for cropland with substantial tillage operations. In this research, the temporally constant values of channel erodibility and critical shear stress were replaced by daily updated values, using the same temporal erodibility and critical shear stress adjustments that are applied in hillslope profile simulations for rill detachment. Observed watershed-scale runoff and soil erosion data from six agricultural watersheds were used to validate and compare the WEPP model performance in simulating channel runoff volumes and soil losses before and after the modification. The research showed both WEPP v2012.8 and the modified WEPP model (WEPP_CE) could satisfactorily simulate event-based hydrology and soil erosion at the watershed outlets after calibration. The WEPP_CE model with temporally varying channel erodibility factor and critical shear stress values improved the representation of the physical processes in channel soil detachment. Continued improvement in representation of channel erosion processes in WEPP and other process-based models is needed. The improved WEPP model can be used to evaluate the effectiveness of soil conservation practices on hydrology and erosion in further research.