Sensitivity of Tidal Bar Wavelength to Channel Width

T M Hepkema,H M Schuttelaars,H E De Swart

doi:10.1029/2019jf005032

T M Hepkema, H M Schuttelaars + Show 1 more

Open Access

https://doi.org/10.1029/2019jf005032

Copy DOI

Abstract

Tidal bars are repetitive estuarine bedforms with heights of several meters and wavelengths in the order 1–15 km. Understanding their formation and sensitivity to changes in channel characteristics is important as they hamper marine traffic and play a crucial role in the local ecosystem. Recent observations suggest that the local width of the channel is dominant in determining the tidal bar wavelength. However, theoretical studies could not reproduce the sensitivity of the tidal bar wavelength to channel width. This discrepancy between theory and observations suggests that a mechanism is missing. In this study, one of the theoretical models is extended and results in tidal bar wavelengths, lateral mode numbers, and growth rates that agree fairly well with those of natural tidal bars, including the wavelengths dependency on estuary width. An important extension of the model concerns the bed slope induced diffusive suspended load transport of sediments. With this, it is explained why previously, the modelled tidal bar wavelengths depend only weakly on estuary width and why in the extended model it does. This has, from a modelling point of view, general implications for morphological models using a total load sediment transport formulation with a so‐called bed slope parameter.

Highlights

Many tidal channels have a rhythmic bottom topography consisting of so-called tidal bars
The wavelength, mode number, and channel width are obtained from Google Earth (Figure 1)
Mechanism Behind Sensitivity of Tidal Bar Wavelength to Channel Width Here we address the third objective by discussing three important aspects of Figure 4, which shows tidal bar wavelength λpref versus channel width B

Summary

Introduction

Many tidal channels have a rhythmic bottom topography consisting of so-called tidal bars. Examples are the Ord River estuary in Australia, the Exe estuary in England, the Netarts bay in the United States, and the Western Scheldt in the Netherlands (see Figure 1 and Leuven et al, 2016 for many more examples) These bars have wavelengths of 1–15 km and heights of several meters. As tidal bars hamper marine traffic and provide rich feeding grounds for many living organisms, it is important to understand their formation and sensitivity to tidal channel characteristics (i.e., channel width, depth, and currents). These characteristics may change due to, for example, dredging, sea level rise, or land reclamation. The sensitivity of the tidal bars to changes in channel characteristics was previously investigated by measurements, laboratory experiments, idealized models, and complex numerical models

Objectives

Results

Conclusion