LES RISQUES D’éROSION SUR LES RIVES DES éTANGS, LE CAS DU DéMAIGRISSEMENT DES PLAGES

Ponds shore management and beach erosion risk. Ponds are very small water bodies where shore erosion mainly depends on wind waves. In Central-Western France (departments of Indre, Vienne, Haute-Vienne and Creuse) some fifty ponds present artificial beaches for tourism. Maps of effective lengths and fetches allow to estimate the beach erosion hazard. The example of the Rochegaudon pond (municipality of Chaillac), which is an oblong pond from north to south with a crescent form, shows that the theoretical maximum erosion (effective length calculation) occurs in the extremities and on the convex shore. The compass card of the meteorological station adds some information aboutsouth-western dominant winds. We suggest new morphoclimatic indicators such as asymmetric effective fetch and coefficiented fetch, whose computing and mapping show a maximum shore erosion in the north-east of the pond. This part of the shore just coincides with the beach of Rochegaudon, which took place on ancient micro-cliffs buried under a big artificial input of granitic sand. The choice of the beach location previously depended of criteria such as the nearness of the camping site, the road and the car park. At the present time the municipality manages the beach erosion by supplying every year the beach with sand.