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ARS Home » Midwest Area » West Lafayette, Indiana » National Soil Erosion Research Laboratory » Research » Publications at this Location » Publication #394460
Research Project: Assessment of Sediment and Chemical Transport Processes for Developing and Improving Agricultural Conservation Practices

Location: National Soil Erosion Research Laboratory

Title: A WEPP-Water Quality model for simulating nonpoint source pollutants in nonuniform agricultural hillslopes: Model development and sensitivity

Author
item MCGEHEE, RYAN - Purdue University
item Flanagan, Dennis
item ENGEL, BERNARD - Purdue University

Submitted to: International Soil and Water Conservation Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2023
Publication Date: 2/9/2023
Citation: Mcgehee, R.P., Flanagan, D.C., Engel, B.A. 2023. A WEPP-Water Quality model for simulating nonpoint source pollutants in nonuniform agricultural hillslopes: Model development and sensitivity. International Soil and Water Conservation Research. 11:3(455-469). https://doi.org/10.1016/j.iswcr.2023.02.002.
DOI: https://doi.org/10.1016/j.iswcr.2023.02.002

Interpretive Summary: Runoff and sediment losses from agricultural fields not only negatively affect on-site crop productivity, but also negatively impact off-site water quality. Chemicals in the runoff water (nutrients, pesticides) can contaminant streams, rivers, lakes, and oceans. In particular, soluble and sediment-bound Nitrogen (N) and Phosphorus (P) that leaves agricultural fields can result in major decreases in water quality, that include eutrophication, harmful algal blooms (e.g. in Lake Erie), and hypoxia (e.g. in the Gulf of Mexico). In this research, a computer simulation model was created that allows for better prediction of losses of chemicals from cropland in runoff water and sediment. The effort builds upon earlier USDA-ARS models, including the Water Erosion Prediction Project (WEPP) and the Soil and Water Assessment Tool (SWAT). This paper reports on the WEPP-Water Quality (WEPP-WQ) model structure, science components, and coding, as well as results of sensitivity analysis. The research impacts natural resource agency personnel, extension agents, scientists, students, and others involved in land management to reduce detrimental impacts of agriculture on off-site water quality.

Technical Abstract: The Water Erosion Prediction Project (WEPP) model code was modified extensively to support the simulation of nonpoint source (NPS) pollutant sourcing and transport in nonuniform hillslopes based on NPS science from the Soil and Water Assessment Tool (SWAT). This was accomplished utilizing WEPP’s overland flow element (OFE) in place of SWAT’s hydrologic response unit (HRU) construct which enabled more physically plausible routing within a hillslope. In addition, several improvements to the NPS code base were implemented. These include: free-source format, modern-Fortran conventions, minor enhancements to NPS model science, and code refactoring. This manuscript documents all model development activities, presents a comparison of relevant WEPP and WEPP-WQ code bases, and performs a local sensitivity analysis of the final model code for the most important input parameters and processes. Sensitivity results indicated that the model performed as expected according to its design and provided important insights for potential subsequent validation studies.