Assessment of TMDL Implementation Strategies for Nitrate Impairment of the Raccoon River, Iowa: Supplemental Material Section

This supplemental material section contains detailed information on the input data assumptions for the SWAT modeling as well as the model calibration and validation results. The data sources listed in Supplemental Table 1 were used to build the SWAT TMDL modeling system for the Raccoon River watershed, most of which are accessible in the Iowa Department of Natural Resources (IDNR) on-line digital data library (IDNR, 2008). The subwatersheds were selected to match the 12-digit HUC watershed boundaries (see USDA-NRCS, 2008b for an explanation of different standard hydrologic units) plus additional subwatersheds were created at the gage station locations (Fig. 1) to facilitate comparisons of model output with measured data. The process of watershed delineation and HRU creation was performed using the ArcView SWAT interface (AVSWATX) which is described by Di Luzio et al. used to burn the stream network into the DEM. The resulting watershed configuration consisted of 112 subwatersheds (Fig. 1).