Effects of Wave Streaming and Wave Variations on Nearshore Wave-Driven Circulation

Abstract

Wave streaming is a near-bottom mean current induced by the bottom drag on surface gravity waves. Wave variations include the variations in wave heights, periods, and directions. Here we use numerical simulations to study the effects of wave streaming and wave variations on the circulation that is driven by incident surface waves. Wave streaming induces an inner-shelf Lagrangian overturning circulation, which links the inner shelf with the surf zone. Wave variations cause alongshore-variable wave breaking that produces surf eddies; however, such eddies can be suppressed by wave streaming. Moreover, with passive tracers we show that wave streaming and wave variations together enhance the cross-shelf material transport.

Cross‐Shore Distribution of the Wave‐Induced Circulation Over a Dissipative Beach Under Storm Wave Conditions

“…A similar circulation patern in the vicinity of the surf zone was found by Wang et al. (2020). The magnitude of the Lagrangian circulation then decreases relatively rapidly within zone I (Figure 8d).…”

“…In addition, Kumar et al (2012) also reproduced the results from Lentz et al (2008) seaward of the surf zone using the same data set. In a recent model-based study following Uchiyama et al (2010), Wang et al (2020) further discussed the effect of the bottom wave streaming, which is the stress along the direction of wave propagation that accompanies the wave energy dissipation by bottom friction. Most notably, their results tended to show that the Lagrangian overturning circulation within the surf zone could be substantially weakened by an opposite overturning cell arising seaward of the surf zone and extending within it, associated with the bottom This study aims to explore the cross-shore distribution and the driving mechanisms of the wave-induced crossshore circulation within the shoreface and the surf zone of a dissipative beach.…”

Wave Dissipation and Mean Circulation on a Shore Platform Under Storm Wave Conditions

“…Wang et al. (2020) suggested that a high bottom roughness, which enhances the dissipation of short waves by bottom friction, can result in a stronger bottom streaming that can weaken the undertow close to the surf zone. A similar behavior was observed in our study, in which both the undertow and the wave setup were found to be sensitive to the vertical distribution of the bottom streaming (Equation 12), and particularly to the decay length k wd .…”

“…Wave dissipation by friction at the bottom also affects the nearshore circulation through the generation of a near-bottom streaming along the wave propagation direction (Longuet-Higgins, 1953). Wang et al (2020) suggested that a high bottom roughness, which enhances the dissipation of short waves by bottom friction, can result in a stronger bottom streaming that can weaken the undertow close to the surf zone. A similar behavior was observed in our study, in which both the undertow and the wave setup were found to be sensitive to the vertical (c and d) H m0 , (e and f) rates of wave energy dissipation by depth-induced breaking and bottom friction normalized by the water density, and (g and h) their contribution to total wave energy flux dissipation along the transect from the subtidal to the intertidal zone, in fair weather and storm wave conditions.…”

Wave Enhanced Overtides in an Idealized Tidal Inlet System

“…The radiation stress is caused by covariances in surface‐wave orbital velocities, whose divergence (or gradients) imparts a momentum flux to the dynamics (Longuet‐Higgins & Stewart, 1964; Mellor, 2015). The 3‐dimensional vortex force representation separates phase averaged conservative wave‐current interactions and non‐conservative wave effects on currents (WEC), which have been well studied in both deep and shallow water environments (Craik & Leibovich, 1976; Longuet‐Higgins, 1953; Longuet‐Higgins & Stewart, 1964; McWilliams et al., 2004; Wang et al., 2020; Xu & Bowen, 1994). The conservative vortex force (per unit mass) results from the interaction between Stokes drift velocity and the vorticity of the mean flow; and includes a pressure adjustment to accommodate incompressibility, known as the Bernoulli head (Craik & Leibovich, 1976; Lane et al., 2007; McWilliams et al., 2004).…”