Do tidal sand waves always regenerate after dredging?

Krabbendam, Janneke M.; Roche, Marc; Lancker, V. Van; Nnafie, A.; Terseleer, N.; Degrendele, Koen; Swart, H.E. de

doi:10.1016/j.margeo.2022.106866

Cited by 4 publications

(6 citation statements)

References 26 publications

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“…This recovery time appears to be longer than was indicated by Katoh et al (1998) and Dorst et al (2011). However, such timescales seem to agree with the observations of Krabbendam et al (2022), who observed partial recovery at one site in the two decades after dredging. Campmans et al (2021) showed that the recovery time is dependent on both the dredged volume and the dredging strategy.…”

Section: Discussionsupporting

confidence: 88%

“…Here, 3D barchanoid sand waves were related to an underlying gravelly bed (van Landeghem et al, 2009a). Krabbendam et al (2022) hypothesised that the lack of recovery of tidal sand waves after dredging on the Belgian continental shelf was related to differences in the availability of erodible sand, because sand waves in a nearby area with sufficient sand supply and similar environmental conditions do recover. Besides the study of Krabbendam et al (2022), there are only a few observations of sand waves after dredging.…”

Section: Introductionmentioning

confidence: 95%

“…Krabbendam et al (2022) hypothesised that the lack of recovery of tidal sand waves after dredging on the Belgian continental shelf was related to differences in the availability of erodible sand, because sand waves in a nearby area with sufficient sand supply and similar environmental conditions do recover. Besides the study of Krabbendam et al (2022), there are only a few observations of sand waves after dredging. Both in the Seto Inland Sea in Japan (Katoh et al, 1998) and in the North Sea (Dorst et al, 2011) sand waves seem to recover within a couple of years after dredging.…”

Section: Introductionmentioning

confidence: 99%

“…The overall aim of this study is to investigate the long-term evolution of tidal sand waves subject to sand supply-limited conditions. Specifically, the objectives are twofold: (1) to quantify the effects of limited sand availability on the saturation time, sand wave height, length and the degree of threedimensionality; and (2) to test the hypothesis of Krabbendam et al (2022) that a limited availability of sand increases the recovery time of sand waves after dredging. To this end, we employ the 3D sand wave model introduced in Chapter 4, to study the evolution of tidal sand waves under limited sand supply conditions on decadal timescales and compare their characteristics with sand waves under unlimited supply conditions.…”

Section: Introductionmentioning

confidence: 99%

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Long-term dynamics of tidal sand waves

Krabbendam

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Tidal sand waves are bedforms that have been observed at the sandy bed of shallow seas all over the world. They have heights (vertical distance between crest and trough) of several meters and lengths (crest-to-crest distance) of hundreds of meters. Sand waves can migrate with several meters per year. Sometimes they move into navigation channels or uncover cables and pipelines, causing them to be at risk to be damaged. Therefore, understanding sand wave dynamics is crucial. Currently, decisions are being made based on the extrapolation of historical trends, which has large uncertainties. In this study, it was investigated whether an existing sand wave model was able to accurately reproduce historical sand wave behaviour. This model gave good results when calibrated with site-specific data. Sand waves are often removed by dredging and it remained unclear whether they can recover after this. The analysis of dredged sand waves in the North Sea revealed that in some areas, they recover within a few decades. In other areas, there was no sign of recovery during the measurement period. This was likely due large water depths, strong currents and/or a lack of sand. Results from a new 3D sand wave model demonstrate that large-scale sand banks influence sand wave patterns, as sand waves on top of sand banks have straight crests, whereas they have curvy crests when banks are not present. Finally, model results show that sand wave patterns are also influenced by the availability of sand: a limited availability results in intermittent crests that are spaced further apart. All of these model results are consistent with observations.

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Section: Discussionsupporting

confidence: 88%

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Long-term dynamics of tidal sand waves

Krabbendam

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“…The self‐organization of sediment particles into bedforms is an ubiquitous process experienced by erodible surfaces exposed to shear stress, extending from planetary bodies to the ocean floors (Andreotti et al., 2021; Cisneros et al., 2020; Duran et al., 2019; Gunn & Jerolmack, 2022; Krabbendam et al., 2022; Lapotre et al., 2016; Lü et al., 2021; Rodriguez‐Iturbe & Rinaldo, 2001). Bedforms grow and move due to continuous erosion and deposition processes that contribute to a net transport of particles in the flow direction (Nittrouer et al., 2008; Simons et al., 1965).…”

Section: Introductionmentioning

confidence: 99%

On the Scaling and Growth Limit of Fluvial Dunes

2023

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Bedforms emerge in a variety of shapes and sizes when a granular erodible surface is subject to a strong enough shear flow, as observed in topographic data from submarine canyons, rivers, deserts, and planetary bodies. The two salient features of bedforms are the ability to collectively transport particles, and to generate form drag thus increasing flow resistance. These two mechanisms are in competition and contribute to force bedforms of increasing size migrating more slowly. In a dedicated large‐scale open channel flow facility, hierarchies of fluvial bedforms were generated and measured in equilibrium conditions. The corresponding scale‐dependent migration velocity and mass flux contributions were quantified in the wave number and frequency domains. Experimental results are paired with a validated set of theoretical models to demonstrate that ripples or dunes reach an equilibrium state when drag partitioning ensures high enough frictional drag to sustain the bedload transport of sediment, and low enough form drag to enable the migration of the largest bedform size. This mechanism is inferred to constrain the growth of bedforms when sediment supply is not the limiting factor.

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