Oblique sand ridges in confined tidal channels due to Coriolis and frictional torques

Tjebbe M Hepkema,Abdel Nnafie,Henk M Schuttelaars,George P Schramkowski,Huib E De Swart

doi:10.1007/s10236-020-01413-0

Tjebbe M Hepkema, Abdel Nnafie + Show 3 more

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https://doi.org/10.1007/s10236-020-01413-0

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Abstract

The role of the Coriolis effect in the initial formation of bottom patterns in a tidal channel is studied by means of a linear stability analysis. The key finding is that the mechanism generating oblique tidal sand ridges on the continental shelf is also present in confined tidal channels. As a result, the Coriolis effect causes the fastest growing pattern to be a combination of tidal bars and oblique tidal sand ridges. Similar as on the continental shelf, the Coriolis-induced torques cause anticyclonic residual circulations around the ridges, which lead to the accumulation of sand above the ridges. Furthermore, an asymptotic analysis indicates that the maximum growth rate of the bottom perturbation is slightly increased by the Coriolis effect, while its preferred wavelength is hardly influenced.

Highlights

Tidal bars are rhythmic bottom patterns that occur in many tidal channels
When the Coriolis effect is neglected and only the frictional torque due to lateral bottom slopes is considered, the fastest growing bottom patterns consist of tidal bar patterns, identical to those obtained by Seminara and Tubino (2001), among others
An elaborate explanation of the physical mechanism of the formation of tidal bars is given by Hepkema et al (2019)

Summary

Introduction

Tidal bars are rhythmic bottom patterns that occur in many tidal channels (e.g., the Western Scheldt in the Netherlands, the Exe Estuary in England, the Ord River Estuary in Australia, and the Venice Lagoon in Italy). These bars are several meters high and have wavelengths of 1–15 km. Their characteristics are determined by channel properties (depth, width, tidal amplitude, etc.), which may change due to, for example, dredging, sea level rise, and land reclamation. Seminara and Tubino (2001), Schramkowski et al (2002), and Hepkema et al (2019), among others, studied the physical mechanism that causes tidal bars to form, Responsible Editor: Emil Vassilev Stanev

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