Chapter 8 - Influences of Inherited Structures, and Longshore Hydrodynamics Over the Spatio-Temporal Coastal Dynamics Along the Gâvres-Penthièvre, South Brittany, France

Abstract

Beach profile surveys and a set of spatial analyses were used to examine, respectively, the short-term and long-term evolution of the beaches of the Gâvres-Penthièvre beach dune system. The long-term coastline variations were analyzed based on aerial photographs of the years 1952, 1985, 1999, and 2004. Spatial data include sediment cover, coastline orientation, morphology, and bathymetry data. Simulations of nearshore currents were obtained by the MARS S4 model set up by SAFEGE in 2008. The spatial distributions of both short and long-term coastal changes within the sediment cells were then assessed, leading to an investigation of sediment transport dynamics over different temporal and spatial scales. Over the short term, morphological changes displayed by variations in profiles were interpreted to be the results of offshore wind and wave climate changes. Results suggest that at a regional scale, the Gâvres-Penthièvre coastline behaves as a vast sediment cell in which sediment transport is controlled by SE-directed longshore drift. It is also inferred that the sites of dune accretion and erosion fit with the sink and source sites, respectively. At a finer spatial scale, the distribution of emerged rocks and bedrock controls the morphological responses of beach profiles to seasonal wave and wind climate variations, and also interferes with longshore sediment transport.