Author(s): Vanessya Laborie; Philippe Sergent
Linked Author(s): Philippe Sergent
Keywords: Numerical modeling; Tide/surge interactions; Seine Estuary; Marine submersions; Surge levels
Abstract: Within the Technical Commission for the Study and the Evaluation of Maritime Submersions in the Seine Estuary (Ctee SMES) ,whose aim is to improve the collective knowledge on physical processes related to maritime surge levels, a numerical model of the Atlantic French Coast based on TELEMAC2D was used to study the evolution of surge levels from the ocean to the harbour area of Le Havre and to evaluate the interactions between tide and surge levels in the Seine Bay. The numerical model was specifically calibrated on JOHANNA and XYNTHIA storm events, which respectively occurred in March 2008 and in February 2010. To calibrate the global signal (tide+surge levels) ,measurements available on seven outputs of the Atlantic coast were used to optimize the coefficient for wind influence and for bottom friction. Maritime boundary conditions were provided by the North East Atlantic Atlas (LEGOS) .Winds and pressure fields were CFSR data. Once the numerical model had been calibrated both for tide and surge levels, it as been possible to draw the evolution of surge levels from the ocean to Le Havre (quai Meunier) and then to compare the signal obtained at each point of the Seine Bay with that obtained without taking into consideration tide for each event. That also allowed us to evaluate the contribution of interactions between tide and surge levels inside of the Seine Bay for Xynthia and Johanna events, but also for other events in the slice[1979-2010]. To improve the knowledge about tide/interactions on the French Atlantic Coast and specifically in the Seine Bay, data analysis and modeling approaches with a numerical model of storm surges in the Seine Bay were used. A preliminary data analysis based on 15 years at several harbours' locations highlighted that the largest instantaneous storm surges occur preferentially at low and rising tide at Le Havre. That is why, to better quantify tide/surge dependence, specific numerical computations with the shallow-water model TELEMAC2D were carried out for two events: Johanna and Xynthia. The existence of strong interactions explained by strong tidal currents and shallow water depths in the Seine Bay were put in evidence. Finally, skew surges were also studied for Xynthia event, but further investigations must be done on other events or spring tides to conclude about the necessity to take into account the dependency in extreme water level analyzes in the Seine Bay.
Year: 2015