Hydrologic and Water Quality Modeling of the Spoon River Watershed for Determining Sediment and Nutrient Critical Source Areas

Arash Zaregarizi, E. Getahun

Research output: Chapter in Book/Report/Conference proceedingConference contribution


In the Midwest, non-point source pollution resulting from agriculturally-dominated watersheds remains one of the major causes of water quality impairments. To address this issue in Illinois, a statewide nutrient loss reduction strategy was recently completed, which sets reduct ion goals and provides recommendations for conservation measures. The objective of this study is to dete1mine the critical source areas of sediment and nutrients in the Spoon River watershed. Previous Illinois State Water Survey (ISWS) studies showed that the Spoon River generates the largest sediment per unit area among the major tributaries of Illinois River. To accomplish the study objective, a Spoon River watershed model was developed using the Soil and Water Assessment Tool (SWAT), and it was calibrated and validated for monthly streamflow and sediment at USGS 05570000. For both calibration and validation, the stream.flow NSE and absolute bias were greater than .80 and less than 5 percent, respectively, and an NSE value of at least .57 and absolute bias of less than 14. 5 percent were obtained for sediment simulations. Using the watershed sediment and nutrient outputs at the sub-basin level, three pollution quantifying indices were computed to facilitate the identification and selection of critical source areas for best management. practice (BMP) targeting. The impact indices include a concentration impact index, a load per unit area index, and a load impact index. Each index was used to obtain pollutant-specific rankings of the sub-basins in the Spoon River watershed. A total impact index was derived from these indices and was grouped into low, medium, or high classes using the natural breaks method to prioritize the sub-basins with respect to all pollutants. Using this index, the sediment.- and nutrient-critical source areas were detennined, covering about 9 percent of the Spoon River watershed and accounting for 30, 40, and 36 percent of the overall sediment, nitrate, and total phosphorus loads generated in the watershed, respectively.
Original languageEnglish (US)
Title of host publicationThe Illinois River
Subtitle of host publicationA Watershed Partnership 15th Biennial Governor's Conference on the Management of the Illinois River System
StatePublished - 2015


  • ISWS

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