Sediment Characteristics over Asymmetrical Tidal Sand Waves in the Dutch North Sea

Chiu Hwa Cheng,Bas Wijnand Borsje,Karline Soetaert

doi:10.3390/jmse8060409

Abstract

The behavior of asymmetrical bedforms, which include many tidal sand waves, is challenging to understand. They are of particular interest since they are mostly located within areas prone to offshore engineering activities. Most experimental investigations regarding asymmetrical bedforms consider the riverine environment, are limited to a single sand wave or a few scattered ones, and focus only on differences between crest and trough. Hardly any information is available on sediment compositional changes along asymmetrical tidal sand waves, despite their abundance offshore. An asymmetrical sand wave field located off the coast of Texel Island in the North Sea was studied in June and October 2017. A total of 102 sediment samples were collected over two seasons along a single transect that covered five complete sand waves to measure the grain size composition, organic carbon concentration, chlorophyll-a (chl-a) concentration, and sediment permeability. We found significant variations in these sediment parameters between the sand wave trough, crest, and gentle and steep slopes, including a difference in permeability of more than 2-fold, as well as a difference in median grain size exceeding 65 µm. Based on these characteristics, a sand wave can be divided into two discrete halves: gentle slope + crest and steep slope + trough. Our results indicate a distinct sediment-sorting process along the Texel sand waves, with a significant difference between the two halves of each sand wave. These data could serve as input for process-based modeling of the link between sediment-sorting processes and seabed morphodynamics, necessary to design offshore engineering projects.

Highlights

Tidal sand waves are dynamic rhythmic bedforms, often found in tide-dominated, sandy, shallow coastal regions such as the North Sea, and in many other environments such as straits and tidal inlets around the world [1,2,3,4]
North Sea to be around 0.3, with asymmetry increasing towards the coast and northwards within the the North Sea to be around 0.3, with asymmetry increasing towards the coast and northwards within
We discriminated between different morphological units (MUs) and showed that this leads to measurable changes in the sediment characteristics

Summary

Introduction

Tidal sand waves are dynamic rhythmic bedforms, often found in tide-dominated, sandy, shallow coastal regions such as the North Sea, and in many other environments such as straits and tidal inlets around the world [1,2,3,4]. One prominent feature of sand waves is their ability to migrate as a result of the residual current or tide asymmetry [13,14,15] This movement, which involves up to tens of meters per year, can pose potential hazards to navigation and expose pipelines or buried cables [16].

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