Interaction of internal waves with the seabed on continental shelves

Large-amplitude internal waves generated by tidal fluctuations at the outer edge of the continental shelf propagate shoreward and interact with seabed sediment. A crude mathematical model describing the propagation of such internal waves is used to predict wave-induced sediment flux and thereby to provide a possible explanation of sand-ridge formation on continental shelves. The ocean over the shelf is modelled as a two-layer system and it is assumed that the internal waves are generated at the shelf edge. Field measurements indicate that the very low frequency tidal fluctuations create a train of internal oscillations of periods between 15 and 20 min. Because of nonlinear effects these wave trains generate differential sediment fluxes and, in the model, this leads to the creation of seabed topography. The predictions of the model are tested against field data collected on the eastern Canadian continental shelf and in particular on Sable Island Bank and the Grand Banks of Newfoundland. The comparisons between predictions and measurements are encouraging especially in light of the fact that the model has no free parameters.