Instream Water Quality

Building on the SWMM quantity model, a riverine water quality model of the Lower, Middle, Upper and Main Rouge River branches was developed using the Water Quality Analysis Simulation Program (WASP) EUTRO model (Ambrose et. al., 1993). While the model was originally developed and calibrated as a continuous model of eight pollutants, it has evolved to its current, primary role as an event model to simulate the CBOD-DO interaction which results from CSOs, including the sudden transitory DO drops which have been observed in the Rouge River. The model is currently being used to addresses the following questions:

• Will various CSO control alternatives eliminate the transitory DO drops caused by high CBOD in CSO discharges?
• What wet weather DO impairment will remain after all CSO controls are in place?
• How much will dry weather DO improve after controls eliminate most of the sediment oxygen demand (SOD) contributed by CSOs?

The water quality model developed is shown schematically below.

Stormwater inputs are simulated with the SWMM RUNOFF build-up/washoff algorithms. CSO inputs are assigned concentrations based on the time from when overflow begins, based on typical “pollutograph” shapes from monitoring data. The Rouge Project also developed a new model code linking the SWMM TRANSPORT river hydraulic output to the WASP model. Portions of the model have been calibrated to several heavily-monitored wet weather events.

The model of the Main Rouge River was utilized to evaluate the impact of treated effluent from three demonstration CSO basins on instream DO. The model showed that the basins were not causing violations of the DO standard at times of discharge. This analysis, along with analysis of instream monitoring data, ultimately resulted in formal acceptance of the demonstration basins by the Michigan Department of Environmental Quality as meeting water quality standards. For further information see the paper Monitoring and Modeling of DO Impacts from CSO Facility Effluent and the technical report Main Rouge DO Modeling Status/Observations.

The model of the entire main branch of the Rouge was also used to simulate dry weather DO, which is primarily driven by SOD and reaeration. For the first phase of CSO control and also for complete control, model SOD was reduced to approach that of in-situ SOD measurements made in river reaches which were not CSO impacted. The results in showed that CSO controls will provide a significant benefit to dry weather DO, but that some DO impairment will remain in selected river reaches which are somewhat impounded.

Please address all comments and suggestions about the contents of this Web page to rougeweb@co.wayne.mi.us.

The Rouge River National Wet Weather Demonstration Project is funded, in part, by the United States Environmental Protection Agency (EPA) Grants #XP995743-01, -02, -03, -04, -05, -06, -08 and C-264000-01.