In the context of rising sea level, many estuaries and bays show an overall trend to sedimentary infilling. Among these coastal environments, the Bay of Somme is a hypertidal tide and wave-dominated estuary, filled in by marine sands, with a superficy of 70 km². This study proposes a spatial zonation of the intertidal area of the bay based on the combination of information on sediments, seabed morphology and dynamics. Data come from a surficial sediment sampling campaign and six airborne LiDAR topographic surveys, acquired over the period 2011–2013, providing information on grain size, carbonate content, bedform occurrence and seabed dynamics. The Main Map shows the morpho-sedimentary and -dynamic zonation used as a basis to describe infilling stages in the bay.

This research was carried out in the framework of the Surface Water and Ocean Topography (SWOT) program of the French National Centre of Space Studies (CNES). In the context of global climate change, increases in frequency and intensity of extreme events are considered potential threats. Hence, many efforts have been devoted to acquiring a better understanding of the natural processes driving the hydrodynamics’ multiscale variability in order to produce a more accurate estimation of their fluctuations. In this situation, and in the framework of Normandy’s coastal risk management, the dynamics of extreme events were investigated from regional scales (the English Channel basin) to local scales (the Normandy beaches in Etretat and Hautot-sur-Mer). Offshore wave data were obtained and hourly wave data were simulated for two years using the SWAN (Simulating WAves till Nearshore) model, including ten highly energetic stormy events selected by their different physical characteristics. Spectral analysis was conducted to compare the transformation in frequencies of the wave spectra from the Channel to shallow waters. A special focus was given to the hydrodynamics close to Normandy during these extreme events depending on their duration, their strength, and the persistence of the maximum wave height.