I. Introduction
Wave and currents often are simultaneously present in coastal areas, giving rise to a complex non-linear superposition that characterizes the mutual interaction of such forcings. As a consequence, several researchers in the last decades paid attention to understand the effects that take place when waves superpose to currents with an angle ranging from 0 to 90°. For instance, collinear waves and currents were investigated, among others, by [1]–[4]; in particular [2] showed that the ratio between the current and the wave orbital velocities strongly influenced the bed shear stresses depending on the nature of the bottom boundary layer. More recently [3] observed that the superposition of a steady current over an oscillatory flow reduced both the current directed velocity and the intensity of the vortex shedding.