Hydrobiochemical modeling of the Saint-Charles watershed. 2: Water quality

This paper presents the application of a biochemical modelling study to the Saint-Charles watershed using available data. The objective of the study i s to assess the behaviour of the receiving waters of the watershed. Water q uality modelling is performed with the physically based water quality model QUAL2E, using a real situation as well as various scenarios. A sensitivity analysis was performed on the degradation parameters and input data. Gener ally, qualitative comparison with observed data showed that upstream water quality simulations (BOD and fecal coliform) provide a good representation of what actually occurs. However, QUAL2E did not accurately reproduced the observed downstream data. A multiscenario approach provides better results for fecal coliform and BOD. This approach also provides the basic informati on for estimating potential reductions of pollutant inputs to comply with e nvironmental standards. Results suggest that unconsidered fecal coliform an d BOD contamination sources, possibly sewer network leaks, are responsible for the downstream water quality degradation.