Do intertidal flats ever reach equilibrium?

Maan, Cynthia; Prooijen, Bram C. van; Wang, Zheng Bing; Vriend, H.J. de

doi:10.1002/2014jf003311

Cited by 33 publications

(57 citation statements)

References 57 publications

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“…By contrast, a recent study of Maan et al (2015) introduced the possibility of a perpetual imbalance of the tidal flat's Fig. 12 Residual fluxes of silt in the shallow subtidal region for a nowaves case with flood-dominant boundary tide.…”

Section: Residual Transport and Balancing Mechanismsmentioning

confidence: 99%

Net sediment transport in tidal basins: quantifying the tidal barotropic mechanisms in a unified framework

2017

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Net sediment transport in tidal basins is a subtle imbalance between large fluxes produced by the flood/ebb alternation. The imbalance arises from several mechanisms of suspended transport. Lag effects and tidal asymmetries are regarded as dominant, but defined in different frames of reference (Lagrangian and Eulerian, respectively). A quantitative ranking of their effectiveness is therefore missing. Furthermore, although wind waves are recognized as crucial for tidal flats' morphodynamics, a systematic analysis of the interaction with tidal mechanisms has not been carried out so far. We review the tide-induced barotropic mechanisms and discuss the shortcomings of their current classification for numerical process-based models. Hence, we conceive a unified Eulerian framework accounting for wave-induced resuspension. A new methodology is proposed to decompose the sediment fluxes accordingly, which is applicable without needing (semi-) analytical approximations. The approach is tested with a one-dimensional model of the Vlie basin, Wadden Sea (The Netherlands). Results show that lag-driven transport is dominant for the finer fractions (silt and mud). In absence of waves, net sediment fluxes are landward and spatial (advective) lag effects are dominant. In presence of waves, sediment can be exported from the tidal flats and temporal (local) lag effects are dominant. Conversely, sand transport is dominated by the asymmetry of peak ebb/flood velocities. We show that the direction of lag-driven transport can be estimated by the gradient of hydrodynamic energy. In agreement with previous studies, our results support the conceptualization of tidal flats' equilibrium as a simplified balance between tidal mechanisms and wave resuspension.

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Section: Residual Transport and Balancing Mechanismsmentioning

confidence: 99%

Net sediment transport in tidal basins: quantifying the tidal barotropic mechanisms in a unified framework

2017

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“…By including a morphodynamic feedback, Pritchard et al (2002) and Pritchard and Hogg (2003) confirmed the (tide forced only) equilibrium profiles by Friedrichs and Aubrey (1996). More recently, Maan et al (2015) suggested the possibility that mudflats under crossshore tidal forcing, either prograde or retreat while maintaining a migrating, several kilometres long, equilibrium profile shape. Zhou et al (2015aZhou et al ( , 2016 explored the impact of grain sorting and consolidation on mudflat morphodynamics, while Marani et al (2007), Mariotti and Fagherazzi (2010) and Zhou et al (2015b) provide examples on the impact of vegetation and its feedback on morphodynamics.…”

Section: Introduction Frameworkmentioning

confidence: 97%

Mudflat Morphodynamics and the Impact of Sea Level Rise in South San Francisco Bay

Wegen

Jaffe

Foxgrover

et al. 2016

Estuaries and Coasts

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Estuarine tidal mudflats form unique habitats and maintain valuable ecosystems. Historic measurements of a mudflat in San Fancsico Bay over the past 150 years suggest the development of a rather stable mudflat profile. This raises questions on its origin and governing processes as well as on the mudflats' fate under scenarios of sea level rise and decreasing sediment supply. We developed a 1D morphodynamic profile model (Delft3D) that is able to reproduce the 2011 measured mudflat profile. The main, schematised, forcings of the model are a constant tidal cycle and constant wave action. The model shows that wave action suspends sediment that is transported landward during flood. A depositional front moves landward until landward bed levels are high enough to carry an equal amount of sediment back during ebb. This implies that, similar to observations, the critical shear stress for erosion is regularly exceeded during the tidal cycle and that modelled equilibrium conditions include high suspended sediment concentrations at the mudflat. Shear stresses are highest during low water, while shear stresses are lower than critical (and highest at the landward end) along the mudflat during high water. Scenarios of sea level rise and decreasing sediment supply drown the mudflat. In addition, the mudflat becomes more prone to channel incision because landward accumulation is hampered. This research suggests that sea level rise is a serious threat to the presence of many estuarine intertidal mudflats, adjacent salt marshes and their associated ecological values.

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“…However, at the top of the tidal flat, the tidal current velocities fall considerably (Maan et al, 2015;Van Straaten & Kuenen, 1958), see also Figure 2. However, at the top of the tidal flat, the tidal current velocities fall considerably (Maan et al, 2015;Van Straaten & Kuenen, 1958), see also Figure 2.…”

Section: Tides Onlymentioning

confidence: 94%

“…These studies indicate relationships between the SSC in the deeper waters (where longitudinal currents dominate) and the transverse profile slope and progradation velocity of the flats (Friedrichs, 2011;Liu et al, 2011;Pritchard & Hogg, 2003; see Figure 1 for an orientation on the considered domain). In this contribution we use the basis of the "Lagrangian equilibrium state" (Maan et al, 2015) to derive quantitative relationships between the progradation speed, the SSC in the adjacent waters, wave-induced erosion, and SLR. In this contribution we use the basis of the "Lagrangian equilibrium state" (Maan et al, 2015) to derive quantitative relationships between the progradation speed, the SSC in the adjacent waters, wave-induced erosion, and SLR.…”

Section: H(t)u(t)c(t)dtmentioning

confidence: 99%

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Progradation Speed of Tide‐Dominated Tidal Flats Decreases Stronger Than Linearly With Decreasing Sediment Availability and Linearly With Sea Level Rise

Maan

Prooijen

Wang

2019

Geophysical Research Letters

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We use the results of a one‐dimensional morphodynamic model and the basis of the “Lagrangian equilibrium state” (Maan et al., 2015, https://doi.org/10.1002/2014JF003311) to derive a quantitative relationship between the progradation speed of tidal flats and the suspended sediment concentration in their adjacent waters and show that the speed increases more than linearly with the concentration. We also show that horizontally prograding flats rise vertically with sea level rise at the expense of their horizontal speed via a linear relationship. If accretion rates are insufficient to keep up with sea level rise, however, the intertidal flat submerges and retreats landward at the same time. We apply the obtained relationships to the Yangtze Estuary to estimate the critical sediment concentration level below which a shift from progradation to retreat can be expected.

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Do intertidal flats ever reach equilibrium?

Cited by 33 publications

References 57 publications

Net sediment transport in tidal basins: quantifying the tidal barotropic mechanisms in a unified framework

Net sediment transport in tidal basins: quantifying the tidal barotropic mechanisms in a unified framework

Mudflat Morphodynamics and the Impact of Sea Level Rise in South San Francisco Bay

Progradation Speed of Tide‐Dominated Tidal Flats Decreases Stronger Than Linearly With Decreasing Sediment Availability and Linearly With Sea Level Rise

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