Coastal Artificialization and Public Policies: The Example of the Beach of Marennes (Seudre Estuary, France)

ABSTRACT

This study deals with practical issues induced by public policies that have led to coastal artificialization. Problems of management of artificial coastal features are illustrated with the example of Marennes-Plage (French Atlantic Coast), a sand barrier built in 1997 to protect an artificial saltwater lagoon. This lagoon allows safe bathing at any time of the tide cycle and the sand barrier acts as a buffer against storm floods. But from now on, the sustainability of Marennes-Plage becomes questionable and has shown signs of frailty. Present storm damages turn out to be more important than 10 years ago and the maintenance costs have dramatically increased. The main problem is to anticipate storms effects. Which storm is able to damage the sand barrier? When will it happen? To help the local managers we have built a tool for storm damage prediction : it is a locally tuned erosion index. This index is based on historical data, field work before and after storms and on online data (wind speed, waves, tides). It allows to sort out which combination of surge/wind speed and wave is likely to erode the artificial barrier. It also allows to anticipate the amount of lost material. This index has been tested for several storms and has proved its efficiency and its accuracy but in practice, the relevancy of our index will entirely depend of mitigation strategies and financial stakes. It could be efficient if managers get prepared for costly fast interventions on the dune/beach just before each damaging storm. It will not be really useful if replenishment is considered has a “one year time” event (just before tourists arrival) and low cost solution.

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