Coupling of statistical and numerical modelling approaches to multi-scale storm surge dynamics at coastal zones: case of the English Channel

Extreme events are considered for the main cause of dynamical changes at coastal systems. In the context of increased coastal hazards due to variability in storm frequency patterns, the danger of coastal damages and/or morphological changes is related to the total impact of sea level conditions, storm surges and wave heights. This research examines the multi-scale dynamics of storm surges along the English Channel coasts combining statistical and numerical approaches with the aim to develop an integrated prediction tool of storm surges and flooding close to coastal zones. The first approach uses the continuous and multi-resolution wavelet techniques in order to investigate the spectral content of surges from the interannual to the interdecadal scales and identify their connection with the atmospheric circulation. The second approach focuses on the physical behaviour of surges and their evolution within the channel and close to the coastlines of the British and the French sides by the use of numerical modelling. Results have shown that the effect of driving forces induced by the climate patterns (North Atlantic Oscillation, Sea Level Pressure, Atlantic Multidecadal Oscillation) are significantly different at all time scales and extremely significant to explain the multiscale variability of storm surges. At small scales, 2018 Elanour storm was numerically simulated within the English Channel and water levels of the event were compared with 15 tide gauges in order to investigate the spatial variation of the storm during the event. The results show that the wave energy shifts from French to British coasts with changes in the spectral content of the signal showing smaller surges from Weymouth to Dover and bigger fluctuations along Brest, Cherbourg and Dunkirk. The assessment of the storm dynamics also revealed complex variations at storm currents, flux and energy fields, particularly at intertidal zones. These findings will be used to understand the impact of sea level rise on dynamics of the storm surge modulation.