Identifying Priority Subwatersheds in the Illinois River Drainage Area in an Arkansas Watershed using a Distributed Modeling Approach
This article describes a modeling approach for prioritizing 12‐digit hydrologic unit code subwatersheds in the Illinois River Drainage Area in Arkansas (IRDAA) watershed utilizing the soil and water assessment tool (SWAT) model output for sediment, total phosphorus (TP), and nitrate‐nitrogen (NO3‐N). The model was calibrated and validated at seven locations for total flow, base flow, and surface runoff and at three locations for water quality outputs. A multi‐objective function consisting of percent relative error (RE), Nash‐Sutcliffe efficiency (NSE), percent bias (PBIAS), coefficient of determination (R2), and ratio of the root mean square error to the standard deviation of measured data (RSR) was used to guide model evaluations. The resulting priority subwatersheds comprised only 24% of the total area of the watershed but contributed 49% of sediment, 33% of TP, and 27% of NO3‐N simulated loadings. Statistical relationships between priority subwatersheds and their various characteristics assisted with supporting the prioritization results. For the IRDAA, this approach produced results that could assist watershed management agencies in optimizing allocation of limited resources in addressing water quality issues.