WAVE ENTRAINMENT OF SAND FROM A RIPPLED BED

Malcolm O. Green, Christopher E. Vincent

Abstract


Wave-orbital velocities at 20 cm above the bed and continuous vertical profiles of near-bed suspended-sediment concentration were measured seaward of the surfzone over a rippled bed. Sand was intermittently entrained from the bed and ejected upwards in discrete clouds. The typical sequence of events in the entrainment cycle, with sand being rolled up in a thin near-bed layer and ejected into the flow on alternating wave strokes, is attributed to the action of vortices shed from the bed ripples by the reversing flow. The orderly cycle of events causes a time-domain correlation between the wave fluctuations of velocity and concentration, and the resulting sediment flux is comparable in size, and at some elevations directed opposite to, the mean sediment flux.

Keywords


rippled bed; sediment entrainment

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