Experimental study on the formation and migration of submarine sandwaves under wave-only and combined wave-current conditions

Based on the assumption that the crest lines of sandwaves are perpendicular to the main flow direction, the formation and migration of submarine sandwaves are simulated in a 2 D flume under wave-only and combined wave-current conditions. The effects of various flow parameters, including the wave height and current velocity, on the characteristic dimensions and migration rates of sandwaves are discussed. Measured morphological data indicate that the seabed is composed of both large-scale sandwaves and small-scale sand ripples, and sandwaves are dominant in shaping the seabed form. Starting from a flat seabed, the height of sandwaves increases gradually and tends to become dynamically stable, while the wave length of sandwaves reaches a constant value at the initial stage. Under wave-only conditions, the characteristic wave heights and wave lengths of sandwaves increase with increasing incident wave height. The relative locations of the sandwave peak and trough are almost constant, indicating that sandwaves scarcely migrate under wave-only conditions. Under combined wave-current conditions, the characteristic heights and lengths of sandwaves also increase with increasing current velocity. The migration direction of sandwaves coincides with the direction of the residual current, and the migration rate increases with increasing current velocity. Finally, the characteristic dimensions of sand ripples are also analyzed, revealing that the Reynolds number (based on the particle size) is dominant in determining the size of a sand ripple. Both the characteristic wave lengths and the characteristic wave heights of sand ripples decrease with increasing Reynolds numbers.