Small-scale bedforms and associated sediment transport in a macro-tidal lower shoreface

Guerrero, Queralt; Williams, Megan E.; Guillén, Jorge; Lichtman, Ian D.; Thorne, Peter D.; Amoudry, Laurent O.

doi:10.1016/j.csr.2021.104483

Cited by 4 publications

(4 citation statements)

References 64 publications

(131 reference statements)

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“…When bedforms are present, the main contribution to the roughness is through the form drag associated with their dimensions, as defined by the quantity H 2 /L (for example, k s '' 20H 2 /L in the Chézy coefficient definition of Van Rijn (2006;, where k s '' is the form roughness height of Nikuradse). In certain field settings, waves and currents each have their own roughness, e.g., combined strong waves and weak orthogonal currents over twodimensional bedforms (Guerrero et al, 2021). However, it is reasonable to assume that there is a common wave-current roughness based on the main bedform heights and lengths in the study area, because of the varied wave-current angle, varied relative strengths of the waves and the currents, and the general three-dimensionality of the bedforms.…”

Section: Discussion and Implications: Roughness Predictionmentioning

confidence: 99%

Current- and Wave-Generated Bedforms on Mixed Sand–Clay Intertidal Flats: A New Bedform Phase Diagram and Implications for Bed Roughness and Preservation Potential

Baas

2021

Front. Earth Sci.

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Section: Discussion and Implications: Roughness Predictionmentioning

confidence: 99%

Current- and Wave-Generated Bedforms on Mixed Sand–Clay Intertidal Flats: A New Bedform Phase Diagram and Implications for Bed Roughness and Preservation Potential

Baas

2021

Front. Earth Sci.

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“…The bed-level change pattern of the middle tidal flat was the most dynamic and difficult to predict (Fan et al, 2006). Additionally, there was no clear ripple migration signal in the bed-level series, as sheet flow during wind events tends to wash out ripples (Li and Amos, 1999;Thorne et al, 2018;Guerrero et al, 2021).…”

Section: Intratidal Bed Level Changes Of Sheltered Mudflatmentioning

confidence: 98%

“…This matches the typical ripple migration parameters of mudflats (Baas et al, 2013;Lin and Venditti, 2013;Zhu, 2017). Under dynamic environments with changing currents and waves, reworking and mobilization of bed sediments leads to formation of bed ripples in coastal systems (Catano-Lopera and Garcia, 2006;Thorne et al, 2018;Guerrero and Guillen, 2020;Guerrero et al, 2021;Stella, 2021). Bed ripples preferably occur in the presence of waves (Chakraborty, 2001;Lorenz and Valdez, 2011;Guerrero and Guillen, 2020;Jin et al, 2020).…”

Section: Intratidal Bed Level Changes Of Sheltered Mudflatmentioning

confidence: 99%

Sensitivity of sheltered mudflats to wind events

Zhu¹,

Nie²,

Zhu³

et al. 2022

Front. Earth Sci.

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The impact of waves on the morphological changes of sheltered mudflats is less well studied compared to that on open flats. To investigate the sensitivity of low-energy sheltered mudflats to hydrodynamics such as waves, we carried out in situ measurements of bed level, currents, and waves on the middle flat of a sheltered mudflat in a bay in southern China. Two 1-month measurements, March 26–26 April 2021, and July 8–8 August 2021, were performed for repetition. We found that the sheltered system was not as stable as it appeared. The maximum intratidal bed-level variation, ΔZ, was <5 mm in calm conditions. However, wind speeds slightly highly than 3.0 m/s, under which significant wave height was approximately 0.1 m, triggered significant bed-level variation patterns, with ΔZ reaching up to 2 cm. Intratidal bed-level change patterns depend on the relative dominance of waves and currents: low τc (current-induced bed shear stress) and high τw (wave-induced bed shear stress) promote the generation and migration of bed ripples; comparable τc and τw, with medium-to-high values, lead to non-cyclic bed-level change patterns; high τc and high τw result in bed accumulation/degradation superimposed by bed ripple migration. From a long-term perspective, i.e. in the time scale of month to year, sheltered mudflats are stable systems, and their high sensitivity causes short-term significant bed-level variation. The sensitivity and stability of sheltered mudflats must be further investigated to explore the effects of human intervention and global climate change.

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“…The streaming due to the free surface effect (an onshore boundary layer streaming under the influence of vertical orbital motions in the horizontal non-uniform flow under progressive waves) contributes substantially to an increased onshore sediment transport rate (Kranenburg et al, 2013). Wave-induced currents (as undertow) and the coastal ocean currents (due to tides, winds, and other mechanisms) can also contribute to a net sediment transport rate in the current direction (Guerrero et al, 2021), for example, the experiments conducted by McLean et al (2001) and Dong et al (2013). Dissimilar responses for different size fractions in graded sediment further lead to interactions between fractions.…”

mentioning

confidence: 99%

Analytical Model for Graded Sediment Transport in Velocity‐ and Acceleration‐Skewed Oscillatory Sheet Flow

Chen

2023

JGR Oceans

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At high sediment transport intensities, the oscillatory ripple loses its height and the bed becomes flat, and sediment motion then occurs as a sheet within a few centimeters near the bottom (Hassan & Ribberink, 2010). Sheet flow study is of considerable importance to coastal processes, as it can cause substantial morphological evolutions during severe hydrodynamic conditions over a short time scale (Tan & Yuan, 2021). Sheet flow transport in the coastal area is mainly influenced by the intensity of hydrodynamic forcing and the sediment properties (i.e., size, density, and shape) (Durafour et al., 2015). The heterogeneity of sediment properties is important to sheet flow transport (de Meijer et al., 2002), and this paper only focuses on the heterogeneity of sediment size. Many sediment beds have wide-size distributions, and the distributions may not be lognormal and tend to be negatively or positively skewed (Mohtar et al., 2016). Non-uniform sediments are also generally found in nearshore projects that involve the mixing of multiple types of sediment (e.g., beach nourishment and dredged material disposal) . The non-uniformity of grain size plays a very important role in the sediment movement caused by wave motion (Holland & Elmore, 2008). Massive sediment transport occurs in the surf zone and the swash zone, where graded sediment bed moves primarily under the sheet flow regime (Harada et al., 2015;van der Zanden et al., 2019). Hence, ascertaining the mechanism of oscillatory sheet flow for graded sediment is essential in coastal sediment dynamics.

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Small-scale bedforms and associated sediment transport in a macro-tidal lower shoreface

Cited by 4 publications

References 64 publications

Current- and Wave-Generated Bedforms on Mixed Sand–Clay Intertidal Flats: A New Bedform Phase Diagram and Implications for Bed Roughness and Preservation Potential

Current- and Wave-Generated Bedforms on Mixed Sand–Clay Intertidal Flats: A New Bedform Phase Diagram and Implications for Bed Roughness and Preservation Potential

Sensitivity of sheltered mudflats to wind events

Analytical Model for Graded Sediment Transport in Velocity‐ and Acceleration‐Skewed Oscillatory Sheet Flow

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