Utilisation des outils du système modulaire gradué (SMG) pour estimer les impacts des rejets pluviaux urbains: Avantages et limitations

Today water bodies are suffering from numerous anthropogenic impacts. One of the key players is urban drainage. The directive STORM published by the VSA in 2007 proposes a procedure for an immission oriented strategy for remediation of urban drainage. At the same time the Federal Office for the Environment (FOEN) is developing with the Swiss Federal Institute for Aquatic Science and Technology (Eawag) a new procedure for the assessment of rivers and streams in Switzerland, the Modular Stepwise Procedure (MSP). The MSP proposes different modules to analyse the state of biological (Macroinvertebrates, Fish, Diatoms and Macrophytes) and non-biological (Ecomorphology, Hydrology and Water chemistry) factors as well as the general appearance and ecotoxicology. The goal of this procedure is to give a general appreciation of a river at three different levels of details. The question raised is whether or not the MSP can be used to characterize the impacts of urban drainage. This paper analyses the aptitude of the MSP in urban drainage issues by using a theoretical part and a practical application at the catchment area of the Mèbre and the Sorge in the western part of Lausanne. The modules water chemistry, ecomorphology, macroinvertebrates and general appearance were completed using existing data to locate the problematic zones. As an example, the community of Renens was chosen: the procedure proposed by STORM including modelling with REBEKA II is applied to confirm whether the problems in the Mèbre are due to urban drainage. The example illustrates the advantages and limitations of the MSP in urban drainage management. Altogether the results of the two approaches STORM and MSP are coherent. The hydraulic condition is the most dominant factor in this case. On a broader scale, based on the example, the theoretical reflexions and the methodical approach of the European Union, the synthesis of this paper discusses the integration of a tool like the MSP in the general functioning of urban drainage management. A new proposition of the proceeding based on the two approaches is presented.