Surge-Tide Interaction in the Southern North Sea

Abstract

Abstract Observations of storm surges in the River Thames show that surge peaks tend to occur on the rising tide and seldom, if ever, occur on high tide. This tendency has been attributed to the interaction between tide and surge propagation as described by the non-linear terms in the associated hydrodynamic equations. A recent study by Prandle and Wolf (4) examined the mechanics of interaction within the River Thames and showed that an important component of it originates outside of the river; this component is investigated in the present paper. A method of identifying interaction in the southern North Sea is developed involving the use of two hydrodynamic numerical models, one simulating tidal propagation and the other surge propagation. Operating these models concurrently, the coupling between tide and surge is introduced by perturbation terms which represent the influence in either model of sea levels and velocities computed by the other. This approach has been used to simulate the pattern of interaction which occurred during the disastrous storm surge of 30 January to 2 February 1953. It is shown that interaction in the southern North Sea results primarily from the quadratic friction term, developing significantly in the coastal region off Lowestoft as far south as the Thames estuary due to the high velocities associated with both tide and surge propagation in that area. Changes in the surface elevation of tide and surge due to the effects of interaction may develop rapidly in certain localised regions such as the Thames estuary. There may also be longer period changes of the order of the duration of the storm due to a systematic displacement of the M 2 tidal regime.