Waves and Currents at a River Mouth: The Role of Macrovortices, Sub-Grid Turbulence and Seabed Friction

Abstract

Abstract:Numerical experiments of wave-current interaction have been performed to investigate the evolution and dissipation of horizontal large-scale vortical structures generated by differential wave breaking and current shearing at river mouths. Specific focus is on the role played by turbulence of scales smaller than the water depth and by seabed friction on the dissipation of the mentioned macrovortices. The analysis reveals two regions of turbulence generation: at the river mouth, and along the curved seaward boundary of the shoal. In the latter zone, macrovortices are formed due to differential wave breaking induced by the sudden variation in water depth and enhanced by opposing currents which favour wave steepening. Such vortices are then advected towards the shore. Among the dissipative mechanisms, dissipation induced by seabed friction is deemed dominant, in particular in the most shallow waters of the shoal. Sub-grid turbulence dissipation, conversely, is more efficient offshore, although exerting some effect also over the shoal when supported by the continuous action of waves.

Numerical Modelling of a Mussel Line System by Means of Lumped-Mass Approach

“…A different approach was followed in Reference [36], where a turbulent jet current interacting with frontal waves was investigated by means of a 2DH non-linear model based on shallow water equations. A 2DH non-linear shallow water model was also used in Reference [37] to investigate the effects of turbulence and seabed friction on macrovortices generated at a river mouth.…”

Wave‐forced dynamics in the nearshore river mouths, and swash zones

“…In the attempt to better describe the dynamics forced by the sea waves, Melito et al . () run the same cases studied by Olabarrieta et al . () using the intra‐wave NSWE model of Brocchini et al .…”

“…The differential breaking that generates macrovortices is particularly intense at river mouths characterized by seabed shoals. Hence, macrovortices, beyond the river jet expansion, provide a significant contribution to both flow mixing and sediment transport at river mouths (Melito et al, 2018b).…”

“…Right column: results from the wave-resolving solver ofBrocchini et al (2001), averaged over 10 wave periods. Adapted, with permission, fromMelito et al (2018b).…”

Turbulence in River and Maritime Hydraulics

“…Not least, the contents of the papers serve to highlight key priority areas, knowledge gaps, and growth points in research activity in river, coastal, estuarine, and near-shore environments. The 15 papers contained within the Special Issue reflect the range of problems where new high quality data from laboratory and CFD (Computational Fluid Dynamics) modelling studies, and field measurements aid the interpretation of classical flow features in complex flows in: (1) Open channels, river mouths and river canyons [1][2][3][4][5][6][7][8]; (2) breaking waves and wave-current interactions in coastal zones [9][10][11][12][13][14]; and (3) gravity currents in natural channels [15]. Most significantly, the papers provide examples of where emerging problems associated with the disposal of dense brine into the aquatic environment are being tackled by detailed measurements of the turbulence properties of the flows.…”