Fox River Watershed Investigation: Stratton Dam to the Illinois River, Phase III, Evaluation of Watershed Management Scenarios

This report documents the development and application of two simulation models for the Fox River: a watershed hydrologic model using the Hydrological Simulation Program - FORTRAN (HSPF), and a receiving stream water quality model using QUAL2K. Both simulation models were calibrated with observed data and subsequently used to simulate the impacts of selected watershed management alternatives (scenarios) on water quality in the Fox River. The Fox River HSPF model simulates rainfall runoff processes for watersheds adjacent to the Fox River from Stratton Dam to the mouth of the Fox River at the Illinois River. Runoff is simulated using 31 separate tributary watershed models and two models of the Fox River mainstem. The tributary results are then utilized as an input to the mainstem model. Observed flows at Stratton Dam are used as the upstream boundary condition defining inflow from the Fox River watershed above Stratton Dam. The HSPF model hydrology was calibrated for water years 1991-1999 and validated for water years 2000-2003. The hydrology calibration was verified when the model was expanded to simulate water years 2004-2011. The integrated model adequately simulates flows at the mainstem gages based on specified calibration criteria. The water quality portion of the model was calibrated for water years 2004-2010 with an additional focus on water years 1991-2003 and validated for water year 2011. The QUAL2K model simulates processes affecting the dissolved oxygen regime. Diurnal changes in dissolved oxygen are simulated, although the model is steady state (i.e., flows and other inputs are constant). The QUAL2K model was calibrated using data collected by the ISWS for the Fox River Study Group (FRSG) in June 2012. Calibrated models were used to simulate several watershed management scenarios. The QUAL2K model was used to evaluate the impacts of altering total phosphorus limits at municipal effluents and the removal of selected dams on the mainstem of the Fox River. Even the most drastic scenario of limiting total phosphorus at municipal effluents to 0.1 milligrams per liter (mg/l) did not result in a significant decrease of phytoplankton due to a large portion of the river being impounded. Removing the dams reduced phytoplankton growth but also led to increased growth of benthic algae in some reaches. The HSPF model was used to evaluate the impact of practices that control urban runoff, practices that control agricultural runoff, and stricter limits for municipal effluents. The success in reducing average annual loads by targeting these individual pollution sources varied by pollutant. Changing agricultural practices resulted in the largest reduction of average annual sediment load. Limiting total phosphorus in municipal point sources resulted in the largest reduction of average annual total phosphorus load. Urban best management practices (BMPs) affected the most number of constituents, but the relative impact on the average annual load was not significant due to the small area treated by these BMPs.