Last year, Lausanne converted the existing rain water surplusing works Capelard in the southwest of the city. The old plant at the Chemin du Capelard was much too small for the enormous catchment area of the sewage water system, which meant ever larger amounts of untreated combined sewage flowed into Lake Geneva during heavy rain.
The size of the new plant with its special flow configuration (owing to side weir, retention, two grit removal structures and a siphon head) made the project extremely complex. As a result, the City of Lausanne commissioned the local Eidgenössische Technische Hochschule EPFL with the implementation of physical model tests. And ROMAG was able to provide its long-standing experience in storm water treatment and surplusing works in numerous contacts with the participating institutions.
The Laboratoire de Constructions Hydrauliques (LCH) at the EPFL created a full model in the scale 1:15 and analyzed the effective flow configuration. The two storm water screens made by ROMAG RSW 14x8/4 were also replicated true to the model and integrated in the plant. Thanks to scientific studies, the previously highly diverse flow rate estimations - that were partly too high and partly too low - could be established on a realistic basis. The City of Lausanne decided to design the capacity of the storm water screens for the extraordinary rainfalls that can occur every five to ten years, so that the relieved combined sewage will also be cleaned mechanically in future, even during heavy rain. The load on the lake as receiving water is significantly reduced by this. This makes an important contribution to improving the water quality of the lake.
Dr. Michael Pfister, Senior Scientist of the LCH at the EPFL, explained at a professional association convention organized specially for this structure that the simulations as well as the practical tests on the model have made an essential contribution to the sound planning and smooth implementation of the project. Dominique Zürcher of the Service d‘Assainissement Lausanne revealed that the sewage volume that cannot be supplied to any waste water treatment plant is now cleaned more than 60% mechanically even during heavy rain.
The Capelard structure was commissioned in July 2012 and functions without fault.