Improvement of the Water Erosion Prediction Project (WEPP) model for quantifying field scale subsurface drainage discharge

Authors: REVUELTA-ACOSTA, JOSEPT - Purdue University; Flanagan, Dennis; ENGEL, BERNARD - Purdue University; King, Kevin

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2020
Publication Date: 11/3/2020
Citation: Revuelta-Acosta, J.D., Flanagan, D.C., Engel, B.A., King, K.W. 2020. Improvement of the Water Erosion Prediction Project (WEPP) model for quantifying field scale subsurface drainage discharge. Agricultural Water Management. 244. Article 106597. https://doi.org/10.1016/j.agwat.2020.106597.
DOI: https://doi.org/10.1016/j.agwat.2020.106597

Interpretive Summary: Crop growth can be impeded by too little as well as too much water. Subsurface tile drains are often installed in agricultural fields in the Midwest US and elsewhere to remove excess water in the soil profile, allowing farmers earlier access to their land, and providing a better growing environment for crops. Water leaving tile drains does not contribute to surface runoff or soil erosion on fields, but can add to off-site flows, pollutant transport, and channel erosion. In this research we modified a computer simulation model used to predict cropland soil erosion to better account for tile drainage and water leaving fields from subsurface drains. Different equations and logic were used, and the model predicted tile drainage was compared to measured values from four field sites in northwestern Ohio and northeastern Indiana. We found that the enhanced model using the new equations and approach did a better job of estimating the amount of water leaving the four fields through the tile drains. This research impacts scientists, students, conservation agency personnel, and others involved in soil and water conservation efforts, and use of computer simulation models to predict runoff, tile drainage, and soil loss from agricultural fields. As the use of tile drains becomes more widespread, being able to simulate their effects becomes more important as well.

Technical Abstract: In the poorly drained regions of the world, subsurface drainage systems are required to remove excess water for crop growth. Plastic drains alter a field’s hydrology by lowering the water table, reducing surface ponding, and reducing surface runoff. One significant concern with the use of subsurface drainage systems is adverse environmental effects because of the modification of the soil water dynamics. Some effects include the reduction of ecological services since wetlands change to croplands, water quality concerns, particularly sediment, nitrogen, and phosphorus losses in agricultural subsurface discharge water, as well as changes in the volume and timing of off-site discharges. Hydrological simulation models predict surface and artificial subsurface flow at different scales. Often in these models, Hooghoudt-based expressions are adapted in their internal algorithms. In this study, the Water Erosion Prediction Project (WEPP) model, developed by the United States Department of Agriculture - Agricultural Research Service (USDA-ARS) for soil and water conservation planning activities, was tested and improved to simulate surface and subsurface discharges. The modified WEPP model was tested and validated on an extensive dataset collected at four experimental sites managed by USDA-ARS within the Lake Erie Watershed. Predicted drainage discharges show Nash-Sutcliffe Efficiency (NSE) values ranging from 0.50 to 0.70, and Percent Bias ranging from -30% to +15% at daily and monthly resolutions. Evidence suggests that the WEPP model can be used to produce reliable estimates of subsurface flow with minimum calibration. Future work includes the extension of the model for quantifying subsurface drainage under controlled water table and watershed-scale simulations.