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

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 benefits. The objective was to develop and test a DRAINMOD-based tool for predicting drainage discharge and nitrate load removal (NLRSB) under local 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. 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, field-based quantification of nitrate removal. • A decision-support tool (SBTool) was developed for saturated buffer design and evaluation. • SBTool integrates DRAINMOD and a nitrate-removal model using site-specific input. • Tool predictions of drainage and nitrate removal showed good agreement with field data. • SBTool supports nutrient trading and conservation planning through credible quantification.