Abstract
Abstract. The English Channel is characterised by strong tidal currents and a wide tidal range, such that their influence on surges is expected to be non-negligible. In order to better assess storm surges in this zone, tide-surge interactions are investigated. A preliminary data analysis on hourly surges indicates some preferential times of occurrence of large storm surges at rising tide, especially in Dunkerque. To examine this further, a numerical modelling approach is chosen, based on the 2DH shallow-water model (MARS). The surges are computed both with and without tide interaction. For the two selected events (the November 2007 North Sea and March 2008 Atlantic storms), it appears that the instantaneous tide-surge interaction is seen to be non-negligible in the eastern half of the English Channel, reaching values of 74 cm (i.e. 50% of the same event maximal storm surge) in the Dover Strait for the studied cases. This interaction decreases in westerly direction. In the risk-analysis community in France, extreme water levels have been determined assuming skew surges and tide as independent. The same hydrodynamic model is used to investigate this dependence in the English Channel. Simple computations are performed with the same meteorological forcing, while varying the tidal amplitude, and the skew surge differences DSS are analysed. Skew surges appear to be tide-dependent, with negligible values of DSS (<0.05 m) over a large portion of the English Channel, although reaching several tens of centimetres in some locations (e.g. the Isle of Wight and Dover Strait).
Highlights
Recent events like Katrina (2005) or Xynthia (2010) illustrate the potentially devastating effect that storm surges can have on the coasts
Preliminary data analysis on the scale of several decades indicates that the largest instantaneous storm surges occur preferentially at low and rising tide at Dunkerque, whereas this tendency is less pronounced at Saint-Malo and barely detectable at Le Conquet
It appears that the elevation due to tide-surge interaction is on the order of tens of centimetres in the eastern part of the English Channel, decreasing towards the west, and is practically inexistent offshore Brittany
Summary
Recent events like Katrina (2005) or Xynthia (2010) illustrate the potentially devastating effect that storm surges can have on the coasts. Vivid memories of severe coastal disasters attach to the 1953 and 1962 storm surge events, which caused flooding over broad coastal areas in the south-western Netherlands and eastern England (Gerritsen, 2005) and in northern Germany (von Storch et al, 2008), respectively. These examples illustrate the need for a better understanding of storm surge phenomena, as well as for improved water level forecast systems and land planning with respect to coastal flood risk
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