An integrated approach for assessing the impact of urban stormwater discharge on the fecal contamination in a recreational lake near Paris

Abstract : Urban stormwater discharges contribute to the fecal contamination of recreational lakes. It is essential to assess the spatial and temporal distribution of fecal bacterial indicators in the receiving waterbodies, to prevent public health risks. This study develops for the first time in continental waters an integrated monitoring and modelling approach, linking the SWMM and Delft-3D models and including a detailed monitoring of the stormwater discharge and at different points of the lake, for assessing Escherichia coli (E.coli) dynamics in stormwater discharges and the receiving urban lake. This integrated approach is applied to a recreational shallow lake and its adjacent urban catchment, with a single stormwater outlet which discharges into the lake. The SWMM model parameters are calibrated and validated with continuous measurements of the flow rate and mean concentration of E. coli in the stormwater discharge measured during each rainfall event. Using the simulated flow rate and E. coli concentration at the sewer outlet, the Delft3D-FLOW-WAQ model simulates E. coli transport in the urban lake with previously calibrated hydrodynamic parameters and default values of E. coli parameters. Comparing simulations with E. coli concentrations measured at different points in the lake, this integrated modelling approach yields promising results. Further studies will focus on the development of automatic model coupling and parameter optimisation, as well as on the evaluation of long-term impacts and management scenarios.