Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | MAY 2015 | 19 Project focus T he UNESCO World Heritage site of Mont St Michel, Normandy is the second most important tourist attraction in France, attracting more than 2.5 million visitors each year. Built on a rocky outcrop one Pumps and pumping systems Effluent pumps boost Abbey restoration Project focus ● Mont St Michel restoration project required wastewater solution ● Effluent pumping system housed in subterranean chamber ● Variable flow rate capabilities ensure energy efficiency By Bryan Orchard Europe. However, over many decades the maritime character surrounding the abbey has changed dramatically. A combination of manmade and natural forces has resulted in much of the bay silting up and the sea has been pushed back to such an extent that the abbey is now almost marooned in a salt marsh. Fortunately, this regrettable situation is being addressed through a major project with the aim of restoring the degraded environment and renewing tourist appeal that will be completed by the end of 2015. The project, which commenced in 2005, has taken in the construction of a new dam on the Couesnon river close to the estuary in order to increase hydraulic capacity, the removal of the 130-year-old causeway between the mainland and the abbey and its replacement with a foot bridge, removal of sand surrounding the base of the rock to create improved hydraulic seawater flows and the development of enhanced visitor facilities and infrastructure. One particular aspect of the improvements to the abbey's infrastructure has been to address the removal of wastewater and effluent in a safe, effective and environmentally acceptable manner from Mont St Michel to a treatment plant located 2.5km along the coast. Instigated by Synicat Mixte Baie du Mont St Michel, the project involved the construction of a pumping station that would accommodate the considerable fluctuations in effluent flow that are associated with times of the year when visitor numbers can be both high and low. In addition, it had to be insulated from the effects of high spring tides. The contract for designing, equipping and constructing the pumping station was awarded to Sogea North West Construction (Vinci Group) and KSB. Design challenge In order to satisfy the many technical, environmental, performance, economic and security challenges, both contractors had to come up with an almost unique solution. The result was a dry pit on-line li– pumping station discreetly positioned below sea level at the approaches to the main entrance to Mont St Michel, equipped with four KSB Amarex KRT pumps. Several factors influenced the choice of a submersible dry pit pumping station, not least of which The abbey of Mont St Michel kilometre offshore between the mouth of the Couesnon River and the English Channel, the 1000-year-old abbey overlooks one of the largest bays in the world where the tidal rise of up to 15 metres is one of the highest in

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