Experimental Investigation of the Effect of Wave-Current Interactions on the Morphology and Dynamics of Subaqueous Dunes

Abstract

Dunes in natural marine environments are subject to various complex and unsteady hydrodynamic forcings. In shallow waters and intertidal environments in particular, subaqueous dunes are strongly influenced by waves which combine with unidirectional or reversing currents. Understanding and predicting their morphology and dynamics is crucial because bedform-related roughness strongly influences sediment transport. In this article, we investigate in a flume tank the impact of monochromatic waves combined with a unidirectional current on the geometry of migrating dunes as well as the associated flow field. The influence of the wave steepness and dispersion on the bathymetry temporal evolution, the streamwise velocity, the vertical velocity, the turbulence intensity, and Reynolds shear stress above migrating dunes were examined. Furthermore, higher order moments related to the streamwise velocity were calculated in order to evaluate the flow non-Gaussian behavior above migrating dunes. Our experiments confirm that the presence of migrating dunes can produce non-Gaussian statistics related to the streamwise velocity. The skewness and the kurtosis of the horizontal velocity have different trends. Skewness has a local maximum on the top of the stoss shallower region of the dune, whereas the kurtosis has a local maximum on the dune's lee side.