Bedforms Produced on a Particle Bed by Vertical Oscillations of a Plate

Natural flows are nominally turbulent and predicting the onset of sediment motion in these environments is an ongoing challenge. Traditional sediment transport models utilize the mean shear at the bed to predict the onset of motion. However, these models fail in cases where mean shearing is minimal and turbulence is dominant, such as in a swash zone. We conducted an experiment to observe the formation of a heap in a subaqueous granular bed induced by vertical oscillations of a square plate above the bed. We performed the experiment for oscillation frequencies between 10 and 40 Hz and amplitudes between 0.02 and 0.14 cm to determine how the intensity of these fluctuations influences bed deformation. We observed that the cross-section of the heap is self-similar in time. Its surface contracted and its height grew approximately with the square root of time, in agreement with dimensional arguments predicated on an incompressible viscous coarse-grained analysis of the grain flow in the bed.