Abstract

Abstract. Tidal bars in estuaries are poorly understood compared to fluvial bars. There is limited theory that predicts tidal bar dimensions. Moreover, where fluvial channels bifurcate around bars, tidal channels around bars often develop either flood- or ebb-dominance which remains unexplained. Tidal experiments are rare and have not reproduced these phenomena to date because these are usually highly ebb-dominated. Here we report preliminary experiments in a novel setup that produce tidal bars from an initial situation with flat bed and exactly symmetrical ebb- and flood-related sediment mobility. The bars initially develop in a saw-tooth pattern with mutually evasive ebb- and flood channels. The tips of the bars evolve further into lobate bars built up from sediment from excavating channels. The bar tips form steep and high obstructions for the opposing flow direction, which then diverges into evasive channels. The bars develop into a diamond shape as channels bifurcate and deepen around it. We further found that bar height correlates well to bar width but not with bar length, whilst bar length correlates well to the tidal excursion length. As the experiment progressed scour holes developed that affected the channel and bar pattern and are considered artifacts of the experiment. We conclude that the mutually evasive ebb- and flood-dominance of channels emerges simultaneously with the onset of tidal bar formation, and that these preliminary data confirm results from linear stability analyses. The results are proof of principle for the novel experimental setup for tidal systems.

Highlights

  • ObjectivesOur objective is to understand formative processes and shapes of tidal bars in sandy estuaries

  • Tidal bars in estuaries are poorly understood whereas for rivers there are adequate empirical and theoretical predictors for bar length, bar mode

  • The tidal excursion length, here estimated as the maximum tidal surface flow velocity multiplied with half the tidal period, is the same order of magnitude as the flume length, which means that the experiments represent a short reach within an estuary

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Summary

Objectives

Our objective is to understand formative processes and shapes of tidal bars in sandy estuaries

Results
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Conclusion
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