Storm surges in the North Sea, 11 to 30 December 1954

Abstract
The disturbances produced by the stormy conditions of December 1954 have been analyzed. The basic data used were tidal observations at ten British and fifteen continental stations in the North Sea and English Channel, together with records of the mean flow of water through the Straits of Dover as represented by electromagnetically induced currents in a telephone cable running from St Margaret’s Bay to Sangatte. The main purpose of the investigation has been to determine the relative magnitudes of the various factors contributing to the phenomena. The effect of westerly winds has been shown to depend upon whether the wind system is confined to the North Sea, or to the north-western approaches to the sea, or is a broad airstream covering both areas. Evidence has been put forward for the existence of a 'return’ surge, or southward return of water previously expelled from the North Sea, on 15 December. Co-disturbance charts have been constructed for the large surges of 20 to 25 December, and the water movements thus deduced exhibit marked geostrophic effects in all cases. An example of an external surge has been noted. Representing the sea by a rectangle, a correlation of 0-96 was found between the longitudinal water gradient and the geostrophic wind; this analysis led to a value of the wind stress coefficient, y 2 , of 2-7 x 10- 3 . The transverse gradient has been shown to be composed of a direct wind effect and a larger geostrophic effect. Estimates have been made of the mean level of the sea which, during surge peaks, was some 2-5 ft. above normal, and these have been represented satisfactorily by winds in and to the north of the sea. The cable measurements throughout the whole period have been analyzed at intervals of 25 h, and, after Bowden (1956), provided estimates of y2 (2-1 x 10- 3 ) and the bottom friction coefficient k (3-5 x 10- 3 ). A similar analysis of the data at 3 h intervals gave values of 2-3 x 10~3 and 4-5 x 10“3, respectively. The subject of the oscillatory development of storm surges has been reviewed with particular reference to the North Sea, and the conclusion reached that for this area the motion appears to be so heavily damped that positive surges may be represented, for practical purposes, by equilibrium conditions modified by a time lag. Negative surges, however, exhibit a strong tendency towards oscillations, as evidenced by the existence of return surges

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