Formation dynamics of sand bedforms under solitons and bound states of solitons in a wave flume used in resonant mode

This paper reports the results of an experimental study of the formation of sand bedforms under solitons and bound states of solitons in a wave flume used in resonant mode. A numerical modeling of Boussinesq equations is carried out to simulate the generated flow and a good agreement is obtained between the measured and calculated fluid velocities. An original method based on image processing is developed to obtain the morphology of the sandy bed over large areas. The size and the shape of ripples which form on the bed significantly change from one end of the flume to the other end. Accretion zones are observed beneath the nodes of the standing harmonic wave. These bed features result from the variation of the amplitude of the first harmonic of fluid velocity, and of the time interval between the passage of contra-propagative solitons and bound states of solitons, with the distance from the wave paddle along the flume. An equation obtained from a phenomenological analysis is proposed for the description of the temporal growth of the ripples.