Quelques principes d'aménagement pour lutter contre l'envasement des zones conchylicoles

Most shellfish farms are located in sheltered areas which enable farmers to work whatever the weather is like as well as to limit the damages caused by storms. But these areas get some important natural sediment deposits. Looking at the height of some muddy elevations which can ruin traditional on-bottom oyster farms, overelevation techniques have spread rapidly. Showing numerous advantages (easier handling, reduced carrying out by the sea, better oyster growth...), off-bottom culture is more and more used and tends to substitute completely on-bottom culture. However, this technique poses some important silting problems. Indeed, if these elevated cultures enable farmers to avoid mud deposits in the short-term, they quickly lead to a new sediment increase. Numerous shellfish culture areas face more or less important silting issues (Sornin, 1979). And they often tend to get worse. Indeed, if there is not any change in the current sediment balance, muddy elevations will keep increasing, leading to a gradual burying of the cultures, even off-bottom cultures or "bouchots" pilings, as has already happened in the past (bay of the Aiguillon, Vilaine estuary... ). Therefore, it seems necessary to set up some emergency devices in the endangered areas and to conduct preliminary studies on the future farming areas.