Longshore sediment flux hindcast: spatio-temporal variability along the SW Atlantic coast of France

ABSTRACT Idier, D., Castelle, B., Charles, E. and Mallet, C., 2013. Longshore sediment hindcast: spatio-temporal variability along the SW Atlantic coast of France ! The Aquitanian coast (SW France) is exposed to high-energy waves, and subject to an overall shoreline erosion of 1 to 3 m/year. Engineering practices in this area requires the knowledge of longshore sediment fluxes. The reference values of direction and variability have been estimated 33 years ago with data available at that time. More recent estimations have been done on limited area and time span. The present study aims at: (1) updating and discussing the longshore sediment flux on this coast, (2) comparing the longshore drift spatial variability with measured shoreline evolution, (3) analyzing the interannual variability, in comparison with NAO indexes. Using a recent wave hindcast spanning the period 1958–2001, and the Kamphuis (1991) formula, the obtained gradients in longshore drift appear roughly consistent with the shoreline evolution and previous estimations of residual sediment fluxes. However, the estimated northward oriented fluxes are smaller in the present study than in the 33 year old reference study. The analysis shows a strong interannual variability, slightly smaller than the longshore variability. The interannual variability is not uniform along the coast. The northern section seems to be correlated with NAO indexes. Further analyses are required to better understand the temporal variability of the longshore sediment fluxes.