Potential influence of sea-level rise in controlling shoreline position on the French Mediterranean Coast

We analysed the rates of relative sea-level rise (RSLR) and the variations in shoreline position over more than a century on pocket-beaches in Provence and on open beaches of the Camargue (France). Our objective is to quantify the role of sea-level rise in the shoreline retreat, and evaluate this retreat in terms of future sea-level rise. The methodology did not use the classical Bruun rule but the principle of active flooding which combines the RSLR with the slope of the beach profile. This slope is averaged between the shoreline and the upper and lower part of the active profile. On the wave-dominated open-beaches of the Camargue, the sea-level rise between 1895 and 1977 yields a theoretical averaged retreat of -34.8 m along eroding beaches, but this value eventually represents only a small proportion (8%) of the total historical distance of shoreline retreat. On open-beaches exposed to the swell, (Camargue), rising sea level enhances the erosion, which is itself ultimately dependent on the action of the waves (longshore transport, cross-shore processes) and the sedimentary budget. In other words, sea-level rise is not the major cause of coastal erosion and does not represent the most severe risk along this type of shore. Moreover, the cross-shore processes of overwash "assist" the shoreline retreat by compensating for sea-level rise. On the other hand, since sea-level rise is one of the principal factors influencing shoreline retreat, the acceleration in sea-level rise predicted for 2100 will play an important role in the future position of the shoreline on pocket-beaches protected from wave action and with limited back-shore areas (i.e. the beaches of Provence). The width of the beaches is going to decrease significantly with the increasing risk of disappearance of some beaches. Indeed, if we integrate the low rates of long-term retreat, and taking account of the morphology of the back beach, then the pocket-beaches appear to be threatened by disappearance due to sea-level rise. Under these conditions, sea-level rise will have important socio-economic impacts on the pocket-beaches of Provence. (c) 2008 Elsevier B.V. All rights reserved.