THE DYNAMICAL BALANCE OF FLOW IN THE MENAI STRAIT

Observations of sea surface slope and along-channel current from two e xperiments are used to explore the dynamical balance in the tidally en ergetic Menai Strait. A regression analysis is used to deduce a new va lue for the sea-bed frictional drag coefficient which achieves a close balance of the forces involved. The regression results are consistent between the two experiments and highly significant (over 90% of the v ariance is explained), and indicate that the friction coefficient for the Menai Strait is significantly larger than that usually employed fo r shelf sea flows but consistent with values of the Chezy coefficient for open channel flow. The tidal cycle of along-channel flow is highly distorted as a result of shallow water (frictional) effects and there is a net transport of water to the south-west of the order of 25-30 m illion tonnes per tidal cycle. The non-linear (advective) acceleration term in the dynamical balance is shown to be small (<5%) compared to the leading (surface slope) term. (C) 1998 Academic Press Limited.