Field and theoretical investigation of sediment mass fluxes on an accretional coastal mudflat

Shi, Benwei; Wang, Ya Ping; Du, Xiaoqin; Cooper, James R.; Li, Ming Liang; Yang, Yang

doi:10.1016/j.jher.2016.01.002

Cited by 30 publications

(15 citation statements)

References 61 publications

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“…Based on Soulsby (), the wave friction coefficient f wr depends on the hydraulic regime, and can be expressed as

f_{w r} = ({|, \begin{matrix} left \\ {2 R e}_{w}^{- 0.5}, {R e}_{w} \leq 10^{5} (|, normall normala normalm normali normaln normala normalr) \\ {0.0521 R e}_{w}^{- 0.187}, {R e}_{w} > 10^{5} true(smooth turbulent true) \\ 0.237 r^{- 0.52}, true(rough turbulent true) \end{matrix})

where

{R e}_{w} false(= \frac{Û_{δ} A_{δ}}{v} false)

is the wave Reynolds number and r (=

\frac{A_{δ}}{k_{s}}

) is the relative roughness. Based on the recommendations of Davies and Thorne () and Shi et al (), the equivalent bed roughness was estimated from k s = 25 η 2 /λ (Davies & Thorne, ), where η is the ripple height and λ is the ripple wavelength. The ripple heights and wavelengths, measured by a ruler during bed exposure after ebb, ranged from 1.5 to 2.3 cm and 5.5 to 7.4 cm, respectively (Table ).…”

Section: Methodsmentioning

confidence: 99%

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Erosion and Accretion on a Mudflat: The Importance of Very Shallow‐Water Effects

et al. 2017

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Understanding erosion and accretion dynamics during an entire tidal cycle is important for assessing their impacts on the habitats of biological communities and the long‐term morphological evolution of intertidal mudflats. However, previous studies often omitted erosion and accretion during very shallow‐water stages (VSWS, water depths < 0.20 m). It is during these VSWS that bottom friction becomes relatively strong and thus erosion and accretion dynamics are likely to differ from those during deeper flows. In this study, we examine the contribution of very shallow‐water effects to erosion and accretion of the entire tidal cycle, based on measured and modeled time‐series of bed‐level changes. Our field experiments revealed that the VSWS accounted for only 11% of the duration of the entire tidal cycle, but erosion and accretion during these stages accounted for 35% of the bed‐level changes of the entire tidal cycle. Predicted cumulative bed‐level changes agree much better with measured results when the entire tidal cycle is modeled than when only the conditions at water depths of >0.2 m (i.e., probe submerged) are considered. These findings suggest that the magnitude of bed‐level changes during VSWS should not be neglected when modeling morphodynamic processes. Our results are useful in understanding the mechanisms of micro‐topography formation and destruction that often occur at VSWS, and also improve our understanding and modeling ability of coastal morphological changes.

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“…Based on Soulsby (), the wave friction coefficient f wr depends on the hydraulic regime, and can be expressed as

f_{w r} = ({|, \begin{matrix} left \\ {2 R e}_{w}^{- 0.5}, {R e}_{w} \leq 10^{5} (|, normall normala normalm normali normaln normala normalr) \\ {0.0521 R e}_{w}^{- 0.187}, {R e}_{w} > 10^{5} true(smooth turbulent true) \\ 0.237 r^{- 0.52}, true(rough turbulent true) \end{matrix})

where

{R e}_{w} false(= \frac{Û_{δ} A_{δ}}{v} false)

is the wave Reynolds number and r (=

\frac{A_{δ}}{k_{s}}

Section: Methodsmentioning

confidence: 99%

“…The coastal hydrodynamics are influenced by a large radial sand‐ridge system in the southern Yellow Sea off the Jiangsu coast, and characterized by a radial current field and high turbidity due to abundant sediment supply from the Yangtze River estuary and the abandoned Yellow River mouth (e.g., Shi et al, ; Wang, ; Zhang et al, ).…”

Section: Study Areamentioning

confidence: 99%

Erosion and Accretion on a Mudflat: The Importance of Very Shallow‐Water Effects

et al. 2017

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“…A 6 MHz Nortek acoustic Doppler velocimeter (ADV), i.e., vector, was used to record the near-bed 3-D velocity and intratidal bed-level changes and was set up in autonomous mode at 16 Hz in 5 min bursts (4096 Journal of Geophysical Research: Oceans 10.1002/2016JC011902 points per 5 min time series), with its probe installed at a height of 0.22 m above the bed ( Figure 2). The ADV can measure not only the boundary 3-D velocity but also intratidal bed-level changes [Salehi and Strom, 2012;Shi et al, 2015Shi et al, , 2016.…”

Section: Methodsmentioning

confidence: 99%

“…With increased human activity, such as river damming [e.g., Xu et al, 2006;Yang et al, 2007;Dai et al, 2011Dai et al, , 2013 and large-scale land reclamation [e.g., French et al, 2000;Chung et al, 2004;Wang and Gao, 2012], intertidal mudflats are subject to tremendous pressure and even complete removal in some regions of the world [Gornitz et al, 1994;Chen and Chen, 2002;Yang et al, 2005Yang et al, , 2011Abuodha and Woodroffe, 2006]. Nonlinear interactions between tidal currents and wind waves control sediment erosion, deposition, transport, and mixing processes [Janssen-Stelder, 2000;Herman et al, 2001;Shi, 2012;Shi et al, 2016] and are directly responsible for the morphological development of intertidal mudflats [Widdows et al, 2008;Hunt et al, 2015]. However, it is not clear how these interactions result in morphological change on intertidal mudflats.…”

Section: Introductionmentioning

confidence: 99%

Role of wind in erosion‐accretion cycles on an estuarine mudflat

et al. 2017

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Wind is an important regulator of coastal erosion and accretion processes that have significant ecological and engineering implications. Nevertheless, previous studies have mainly focused on storm‐generated changes in the bed level. This paper aims to improve the understanding of wind‐induced erosion‐accretion cycles on intertidal flats under normal (nonstormy) weather conditions using data that relates to the wave climate, near‐bed 3‐D flow velocity, suspended sediment concentration, and bed‐level changes on a mudflat at the Yangtze Delta front. The following parameters were calculated at 10 min intervals over 10 days: the wind wave orbital velocity (Ûδ), bed shear stress from combined current‐wave action, erosion flux, deposition flux, and predicted bed‐level change. The time series of measured and predicted bed‐level changes both show tidal cycles and a 10 day cycle. We attribute the tidal cycles of bed‐level changes to tidal dynamics, but we attribute the 10 day cycle of bed‐level changes to the interaction between wind speed/direction and neap‐spring cyclicity. We conclude that winds can significantly affect bed‐level changes in mudflats even during nonstormy weather and under macro‐mesotidal conditions and that the bed‐level changes can be predicted well using current‐wave‐sediment combined models.

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“…However at other sites, tidal currents have been shown to have a greater impact on landward sediment transport than wave activity (Janssen-Stelder, 2000;Zhu et al, 2014). Furthermore, some studies have emphasized the importance of longshore and cross-shore sediment advection for SSC and tidal mudflat topography (Wang et al, 2012;Shi et al, 2016). However, these advection terms have been shown to be most pronounced in the lower (seaward) parts of tidal mudflats (Le Hir et al, 2000;Wang et al, 2012), with wind and current-induced sediment resuspension becoming more important towards the upper (landward) part of the tidal mudflat (Green, 2011;Ma et al, 2018).…”

Section: Drivers Of Intertidal Sediment Resuspensionmentioning

confidence: 99%

Coupling between tidal mudflats and salt marshes affects marsh morphology

2019

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It is generally assumed that coastal salt marshes are capable of adapting to moderately fast rising sea levels although local sediment availability crucially affects this capability. Whilst there is an increasing awareness that the local sediment availability is inherently related to sediment dynamics on the adjacent tidal mudflat, our current understanding of the interactions between salt marshes and tidal flats is very limited. To address this knowledge gap, we measured suspended sediment concentrations alongside hydrodynamic, morphological and sediment deposition measurements over a total period of 16 weeks in a wave-exposed macro-tidal mudflat-salt marsh system on the UK east coast (Tillingham). Our results show that local sediment supply to the salt marsh is strongly linked to intertidal sediment dynamics and that the vast majority of suspended sediment deposited on the marsh originates from windwave induced intertidal sediment resuspension in very close vicinity (< 130 m) to the seaward marsh margin. Vertically the salt marsh grows at rates >5 mm yr-1, thereby increasing the slope of the tidal mudflat-salt marsh transition and making the salt marsh susceptible to lateral erosion. Consequently, the marsh edge retreats at a rate of approximately 0.8 m yr-1. Our study shows that the response of coastal salt marshes to climate change is a function of the coupled tidal mudflat-salt marsh system, rather than their vertical sediment accretion rates alone. Therefore, the idea that salt marsh adaptability relies on local sediment supply needs to be expanded, incorporating the morphology and long-term evolution of the adjacent tidal mudflats.

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Field and theoretical investigation of sediment mass fluxes on an accretional coastal mudflat

Cited by 30 publications

References 61 publications

Erosion and Accretion on a Mudflat: The Importance of Very Shallow‐Water Effects

Erosion and Accretion on a Mudflat: The Importance of Very Shallow‐Water Effects

Role of wind in erosion‐accretion cycles on an estuarine mudflat

Coupling between tidal mudflats and salt marshes affects marsh morphology

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