Control of wave climate and meander dynamics on spit breaching and inlet migration

Abstract

Chaumillon E., Ozenne F., Bertin X., Long N., Ganthy F., 2014. Wave climateand inlet channel meander bend control spit breaching and migration of a new inlet: La Coubre Sandspit, France. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 109–114, ISSN 0749-0208.This study focuses on the mid-term (infra annual and pluri annual; over the period 1999–2013) morphological evolutions of a sandspit (La Coubre Sandspit, West coast of France), with a particular emphasis on spit breaching, new inlet opening and migration. Morphological evolutions are observed from a large number of aerial photographs and satellite images and are compared with wave parameters and extreme events (periods where significant wave height exceeds the 1% largest waves with water level exceeding the 90% highest water level) obtained from a high resolution hindcast wave modelling. It appears that extreme events are likely to be responsible for spit breaching and new inlet opening. Once opened, the new inlet migrates downdrift, but its migration rate is not correlated with the wave climate variations. Detailed geomorphological observations suggest that the main control on downdrift inlet migration is related to orientation of the meander bend of the tidal inlet main channel. When the meander bend is convex in an updrift direction, it counteracts the littoral drift and slows the inlet migration. Oppositely, when the meander bend is convex in a downdrift direction, the meander-induced transport is in the same direction as wave-induced longshore transport, which allows the inlet to migrate much faster.