Modelling the Rollovers of Sandy Clinoforms from the Gravity Effect on Wave-agitated Sand

Clinoforms on coasts exposed to ocean waves form from sand exported from the shoreface during extreme wave conditions and deposited where wave action diminishes. Elsewhere, it is shown that, during upper 5-percentile wave conditions, wave-induced shear stresses exceed the sediment threshold of motion to below the clinoform rollovers. Experiments and theory suggest that, where bed sediments are agitated by waves, the effect of gravity should move particles down-slope with a flux proportional to the slope. Combined with considerations of continuity, this implies a diffusion of the sediment topography, a property that would explain the smooth seabed morphology found at sandy rollovers where recorded with multibeam sonar. For situations where this gravity effect dominates, a simple analytical expression