A validation of WEPP water quality in uniform and nonuniform agricultural hillslopes

Authors: MCGEHEE, RYAN - Purdue University; Flanagan, Dennis; ENGEL, BERNARD - Purdue University; Gilley, John

Submitted to: International Soil and Water Conservation Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2023
Publication Date: 11/30/2023
Citation: McGehee, R.P., Flanagan, D.C., Engel, B.A., Gilley, J.E. 2023. A validation of WEPP water quality in uniform and nonuniform agricultural hillslopes. International Soil and Water Conservation Research. https://doi.org/10.1016/j.iswcr.2023.11.005.
DOI: https://doi.org/10.1016/j.iswcr.2023.11.005

Interpretive Summary: Runoff and sediment losses from agricultural fields can negatively impact off-site water quality, and in particular chemicals in the runoff and sediment can contaminate streams, rivers and lakes. Computer simulation models are often used to estimate the amount of nitrogen (N) and phosphorus (P) that leaves crop fields from storm runoff events. In this research, we tested how well the Water Erosion Prediction Project – Water Quality (WEPP-WQ) model could predict N and P losses measured in experimental field studies. We found that that the calibrated model could satisfactorily estimate the N and P lost in both runoff water and associated with sediment. These results impact natural resource agency personnel, extension agents, scientists, students, and others involved in conserving soil and water resources, and reducing negative impacts of agriculture on off-site water quality.

Technical Abstract: Current watershed-scale, nonpoint source pollution models do not represent the processes and impacts of agricultural best management practices on water quality with sufficient detail. A Water Erosion Prediction Project-Water Quality (WEPP-WQ) model was recently developed which is capable of simulating nonuniform hillslopes such as those with BMPs or other nonuniform conditions. However, WEPP-WQ has not been validated for these conditions, and prior validation work only evaluated calibrated performance rather than uncalibrated performance, with the latter being most relevant to model applications. This study evaluated uncalibrated and calibrated model performance in two plot-scale, artificial rainfall studies. 179 observations were compared to corresponding WEPP-WQ simulations of runoff, sediment yield, and soluble and particulate nutrient forms for both nitrogen and phosphorus. Uncalibrated validation results were mixed for the different field conditions, model configurations, and prediction variables. Performance was improved substantially for all prediction points with calibration.