Simulation approaches and potential improvements of ephemeral gully erosion prediction in the Water Erosion Prediction Project (WEPP) Model

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

Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: 12/1/2022
Publication Date: 1/8/2023
Citation: Guo, T., Flanagan, D.C., Srivastava, A., and LaPlante, N.H. 2023. Simulation approaches and potential improvements of ephemeral gully erosion prediction in the Water Erosion Prediction Project (WEPP) model. In: (Flanagan, D.C. and Thompson, A.M., eds.). Proceedings Soil Erosion Research Under a Changing Climate International Symposium, January 8-14, 2023, Aguadilla, Puerto Rico, Paper No. 23009. 8 pp.

Interpretive Summary: A gully is an eroded channel in a farm field that is formed by large flow concentrations of surface runoff water. When gullies are small enough, farmers will usually operate tillage equipment (e.g. plows) to fill them back in with soil, to allow normal cropping practices where they were located. However, if a large rain storm event occurs, the gully can form again in the same location of flow concentration, and is thus known as an “ephemeral” gully (larger gullies that cannot be farmed across are known as “classical gullies”). While ephemeral gullies occupy relatively small areas in farm fields, they can in some cases erode large amounts of sediment (e.g. up to 40% of sediment lost from a field). This paper reviews research and approaches to mathematically estimate the amount of soil eroded from ephemeral gullies, discusses needed future research and monitoring of these channels, and proposes possible improvements to a USDA soil erosion prediction computer simulation model. This information impacts other scientists, students, and soil conservation agency staff that are involved in soil conservation efforts, and evaluation of various management practices to control and reduce soil erosion from agricultural fields. Incorporation of improved approaches and equations to predict soil lost from ephemeral gullies in process-based USDA soil erosion modeling tools will enhance conservation agency efforts to protect the soil natural resource.

Technical Abstract: Soil losses caused by ephemeral gully erosion (EGE) have been considered a major soil erosion source around the globe, which negatively impact soil quality, agricultural economy, downstream water quality, and ecosystem health. However, few studies have thoroughly investigated the status, needs, and opportunities of EGE research. It is unclear how much and where monitoring EGE data is available to improve our understanding of EGE processes, and to support model validation of EGE simulation in various regions. Moreover, the simulation of ephemeral gullies (Figures 1-2) in hydrologic and soil erosion models is still in early stages and needs major improvements to represent EGE processes accurately. For example, the Water Erosion Prediction Project (WEPP) has broadly been used to estimate runoff and soil losses at various spatial scales worldwide. There is a need to improve our understanding of current EGE research and enhance the representation of EGE simulation processes in WEPP and the model’s performance in simulating EGE. This paper is to review the status of monitoring and modeling research on EGE, identify the research needs and opportunities of EGE, and discuss the potential improvements of EGE simulation in the WEPP model. Collection of more EGE monitoring data is needed, especially data directly from these eroding channels in the field. Relevant components in the model, such as variable non-erodible layers, cross-sectional shapes, and dimensions of ephemeral gullies, can be considered. Enhancing soil erosion parameters, considering rock fragments in the soil, and improving soil freezing and thawing cycles induced soil erosion also may benefit EGE predictions. It is also important to improve the representation of EGE conservation practices in the model to support selecting the most suitable erosion control technologies. The conclusions from this study can guide further monitoring and modeling research on EGE processes to better understand and control this important soil erosion source.