Sea Bottom Velocity Profiles on the Continental Shelf south-west of England

Abstract

THE peak velocity of tidal currents on the Continental Shelf around the British Isles varies greatly from place to place, nowhere more markedly than in the south-west (Fig. 1). In this area the grade of the superficial sediment and the geometry of the sea floor are both highly variable^1,2 and grain size tends to decrease as tidal current strength weakens^1,3 along certain sediment transport paths¹. It is usually considered^4–6 that the bulk of this sediment can be redistributed by tidal currents only when they are augmented by storm-induced oscillatory water movement. But it is still thought that the regular, essentially horizontal and reversing, mass water movements associated with tidal flow exert the principal, long term control on the areal distribution of sediment. We are interested in quantifying this dependency, and hope to show whether any relationship connects the median sediment grade Md and the peak horizontal shear stress τ_0max exerted by tidal flow at the sediment/water interface.