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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


Shelf Sands and Sandstones — Memoir 11, 1986
Pages 121-132
Storm-Dominated Shelves - Processes

Processes Affecting Sand Transport on a Storm-Dominated Shelf

Christopher E. Vincent

Abstract

On continental shelves, where tidal and regional currents are weak and unable to initiate sediment transport, storms play an important role in generating waves and wind-driven currents which, acting together, can move sand-sized sediment. Storms may also be the physical event that dominates sediment transport on shelves where there are moderately strong tidal currents. The processes important to sediment movement are described using the Middle Atlantic Bight of the U.S. A. as the major example. Local wind-waves and swells have different influences on transport, and dominate in different regions of the shelf; the swell is largely unrelated to wind-driven currents and results in an essentially diffusive transport of sand into deeper water. In addition to longshore currents, which may be concentrated into coastal jets with speeds in excess of 60 cm/s, winds over the shelf result in upwelling and downwelling events, all of which affect the transport of sand. During storms, this may be part of an efficient mechanism for transferring sand from the surf zone several kilometres offshore. Waves do not simply lift sediment into suspension but interact with currents to alter the boundary layer that the current experiences and to change the direction and rate of the bed load transport from that of a steady current alone. Bedload transport rates under combined waves and currents are still a matter of some contention. During such transport events, fine sediment in the mobile bed load layer is released into the water column and fine sediment below this mobile layer can also be released by the action of wave ‘pumping’. Such mechanisms can result in the ‘cleaning’ of sand bodies and are particularly effective in the presence of active bed forms.


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