Bedform generation beneath shoaling nonlinear internal waves on a mild slope

Subaqueous sand waves have been observed where nonlinear internal waves (NLIWs) shoal on continental margins. To investigate their generation mechanisms, we propagated periodic NLIWs of depression to shoal upon a sloping bed in a laboratory flume. Following fission of the incident waves, ripple-type bedforms were observed between the point of incipient suspension and interaction point (where the quiescent pycnocline intersects the sediment bed). The largest ripples were centered on the bolus birth point, where the NLIWs of elevation, generated by fission, transform into boluses and maximum near-bed velocities occurred. The ripple height and wavelength were consistent with fluvial scaling. In two experiments, where bedload transport was not predicted, the observations showed resuspension to influence ripple generation. Net upslope sediment movement was observed beyond the turning point.