Development and testing of a DRAINMOD-based decision-support tool for designing and evaluating saturated buffers

Authors: ABDALAAL, YOUSEF - Michigan State University; GHANE, EHSAN - Michigan State University; KPODO, JOSUÉ - Michigan State University; NEJAKHASHEMI, A POUYAN - Michigan State University; YOUSSEF, MOHAMED - North Carolina State University; FALASY, ANAMELECHI - Michigan State University; ASKAR, MANAL - The Ohio State University; KATUWAL, SHEELA - Orise Fellow; JOHNSON, GABRIEL - Iowa State University; Rogovska, Natalia; ISENHART, THOMAS - Iowa State University

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2026
Publication Date: 2/18/2026
Citation: Abdalaal, Y., Ghane, E., Kpodo, J., Nejakhashemi, A.P., Youssef, M.A., Falasy, A., Askar, M., Katuwal, S., Johnson, G., Rogovska, N.P., Isenhart, T.M. 2026. Development and testing of a DRAINMOD-based decision-support tool for designing and evaluating saturated buffers. Agricultural Water Management. https://doi.org/10.1016/j.agwat.2026.110201.
DOI: https://doi.org/10.1016/j.agwat.2026.110201

Interpretive Summary: While beneficial for crop production, artificial agricultural drainage promotes nitrate losses from the fields to natural water bodies. Saturated buffer is a promising edge-of-field conservation practice designed to remove nitrate from agricultural tile water by modifying the drainage outlet to allow flow to be diverted through the soil profile of a vegetated buffer. Nitrate is then converted to harmless nitrogen gas by soil microorganisms. Effectiveness of saturated buffers in removal of nitrates from drainage water may vary with soil characteristics and buffer design, therefore there is a need to develop a decision-support tool that would help assess its performance in predicting hydrology and nitrate load. Two Iowa sites that were used for evaluation, showed that the tool provides reasonable estimates of annual and long-term average buffer effectiveness. The percent difference in predicted annual diverted flow and nitrate load removal from measured values were minimal at BC1 site (1% and 2%, respectively), and relatively reasonable at IA1 site (-20% and -16%, respectively), attributed to its limited years of data and uncertainties in drainage area estimates. The use of this modeling tool can aid in estimating the potential nitrate loading reductions due to adoption of saturated buffers at the different watersheds. These results will be of interest to conservationists, land managers or farmers who are considering to install this conservation practice on their land.

Technical Abstract: Saturated buffers (SBs) are an effective edge-of-field practice for reducing nitrate loads from agricultural drainage, contributing to improved environmental water quality. However, no software currently exists to design SBs based on site-specific conditions or to quantify their environmental impact. The objective was to develop and test a DRAINMOD-based tool for predicting drainage discharge and nitrate load removal (NLRSB), incorporating site-specific weather, soil, field drainage, and SB characteristics. We present SBTool, a novel decision-support tool that integrates the DRAINMOD hydrologic model with a nitrate-removal module to simulate SB performance using local weather, soil, drainage, and buffer characteristics. SBTool was validated using field data from two Iowa sites (2014–2022). Model predictions for discharge (QDD), diverted flow (QDP), and NLRSB showed good agreement with observed data. Prediction errors of QDP and NLRSB were only 5.7% and 6.1%, respectively, at the eight-year site, and -17.5% and -13.6% at the four-year site. Unlike existing design methods, SBTool enables site-specific evaluation and design of SBs, supporting conservation planning and nutrient trading through credible quantification of nitrate removal.