Tidal bar accretion by mudflat sedimentation

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Authors

Lisanne Braat , Wout Matthijs van Dijk , Harm Jan Pierik , Wietse van de Lageweg, Muriel Bruckner , Friederike Wagner-Cremer, Maarten G. Kleinhans

Abstract

Mud plays a pivotal role in estuary ecology and morphology. Effectsof mud are often ignored in morphodynamic studies due to longer compu-tational times and limited field data. This study aims to understand thespatial distribution of mud layers in tidal bars, their formative conditions,preservation potential and their effects on the morphology of tidal bars inhigh-energy, sand-dominated estuaries. We use complementary numericalmodelling outcomes of a Delft3D schematisation, and field data, includ-ing historic bathymetry, biomorphological maps and sediment cores, ofa tidal bar (shoal of Walsoorden) in the Western Scheldt, the Nether-lands. We distinguish two types of mud layers: 1) drapes, 2–20 mm thickburied layers that are preserved under high energy conditions; and 2)thick beds,>10 cm layers at the surface associated with high elevationsand slow accumulation. We conclude that mud accumulation is mostlycontrolled by elevation, flow velocity and flow field. Specifically, mudflatsaccumulate mainly on the highest landward side of the shoal just afterhigh water slack, shielded from high flood velocities. Mud accumulationincreases shoal elevation, potentially to supratidal levels, providing a posi-tive hydrodynamic feed by further reducing flow over the shoal, decreasingchute channels, stabilising the bar and decreasing tidal prism. This sup-ports more mud deposition and eventually vegetation settling. While mudcover at the surface is relatively high (20–40%), only a small percentageis preserved in the stratigraphy (∼5%). Due to this preservation bias, in-terpretations of estuary stratigraphy risk underestimating the importanceof mud at the surface.

DOI

https://doi.org/10.31223/osf.io/gq9pt

Subjects

Earth Sciences, Geomorphology, Physical Sciences and Mathematics

Keywords

bar accretion, estuary morphology, marsh development, mud accumulation, mudflat, mud layers, tidal bar, tidal shoal

Dates

Published: 2019-08-29 15:55

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License

CC BY Attribution 4.0 International

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