Some observations of currents in shallow water during a storm surge

Abstract

Observations of currents in a shallow coastal embayment, Swansea Bay in the Bristol Channel, U.K., have indicated that during a storm surge residual flows may be five times higher than during quiescent flow periods. In particular near-bed residuals of the order of 10 cm s −1 were observed during the storm surge of 11 November 1977. While the effect of waves on these measurements cannot be eliminated entirely, correlation analyses and comparisons of wave and current records suggest that the effect is likely, in this case, to have been minimal. The observed flow regime suggests that while the residual circulation in Swansea Bay may be influenced by strong SW. winds blowing onshore, offshore winds from a NW. direction have a more significant effect, possibly as a result of wind induced set down in the Bay head. Calculations show that the observed bottom currents can be predicted by a simple constant eddy viscosity model in which tidal mixing is dominant.