Bed-level changes on intertidal wetland in response to waves and tides: A case study from the Yangtze River Delta

Zhu, Qin; Prooijen, Bram C. van; Wang, Zheng Bing; Yang, S.L.

doi:10.1016/j.margeo.2017.01.003

Cited by 38 publications

(42 citation statements)

References 53 publications

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“…Variations occur on time scales ranging from hourly storms, to intertidal dynamics, century varying sediment supply, and beyond (Friedrichs, 2011). Examples are wave action during storm conditions (e.g., Kohsiek et al, 1988;Zhu et al, 2017), changes in tidal difference due to damming (e.g., Louters et al, 1998, de Vet et al, 2017, neap-spring tidal oscillations (e.g., Kohsiek et al, 1988, Zhu et al, 2017, seasonal variations in presence of biofilms (e.g., Paarlberg et al, 2005), seasonally varying wave climate (Fan et al, 2006) or wind climate (e.g., De Vet et al, 2018), or yearly and decadal changes in sediment supply (e.g., Allison et al, 1995;Jaffe & Foxgrover, 2006). Belliard et al (2019) further suggest that the relative importance of wave forcing compared to tidal forcing varies depending on the location on the flat.…”

Section: Introductionmentioning

confidence: 99%

Morphodynamic Resilience of Intertidal Mudflats on a Seasonal Time Scale

2019

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Intertidal mudflats are morphodynamic features present in many estuaries worldwide. Often located between vegetated shores and deep channels they comprise valuable ecosystems and serve to protect the hinterland by attenuating waves. Although mudflats are persistently present on yearly to decadal time scales, little is known on their morphodynamic adaptation to short-term variations in forcing such as storms, spring-neap tidal cycles, and sediment supply. This study aims to explore the morphodynamic resilience of mudflats to seasonal variations in forcing. First, we compare transects observed in South Bay, California, at 3-to 6-monthly intervals. Second, we present the results of a process-based, morphodynamic profile model (Mflat). Mflat is an open source, Matlab code that describes both cross-shore and alongshore tidal hydrodynamics as well as a stationary wave model. An advection-diffusion equation solves sediment transport while bed level changes occur by the divergence of the sediment transport field. Mflat reproduces the observed South San Francisco Bay profile in equilibrium with significant skill. Short-term variations in hydrodynamic forcing and sediment characteristics disturb the profile mainly at the channel-shoal edge. The modeled profile disturbance is consistent with observations. The modeled profile is remarkably resilient since it recovers to the equilibrium profile within weeks to months. The model results suggest that 3-monthly observation intervals are probably too long to discriminate processes responsible for the profile disturbance. These processes may include variations in sediment supply, mudflat erodibility, and wave action as well as the spring-neap tidal cycle.Plain Language Summary Intertidal mudflats are morphodynamic features present in many estuaries worldwide. Often located between vegetated shores and deep channels, they comprise valuable ecosystems and serve to protect the hinterland by attenuating waves. Mudflats seem to be quite stable features, but their bed level may change due to variations in hydrodynamic forcing, like waves and tides. In this research we explore how a mudflat reacts to changes in forcing like high waves, changing sediment supply, or variations in tides. We first explored observed mudflat profile changes in South San Francisco Bay at 3-to 6-monthly intervals. Next, we developed a model (Mflat) to reproduce observed mudflat profiles. We then imposed varying forcing conditions on the equilibrium profile. Mflat skillfully reproduces observed mudflat profiles in equilibrium. Imposing variable forcing conditions such as storms or periods without waves leads to bed level changes that resemble observed changes. The main bed level changes occur at the channel-shoal edge, while the profiles restore their equilibrium once normal forcing conditions prevail again. Our validated model can be used in future studies to explore the impact of sea level rise and the management of shoals by extra sediment supply.

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Section: Introductionmentioning

confidence: 99%

Morphodynamic Resilience of Intertidal Mudflats on a Seasonal Time Scale

2019

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“…Intertidal areas can be attached to the shore (fringing flats). For example, the Chongming intertidal flats in the Yangtze Estuary, China (Yang et al, ; Zhu et al, ), the flats in San Francisco Bay, United States (Talke & Stacey, ; Van der Wegen M. et al, ), and Baie de Marennes‐Oléron, France (Bassoullet et al, ; Le Hir et al, ). The attachment to the shore has significant consequences for the tidal flow.…”

Section: Introductionmentioning

confidence: 99%

The Importance of Combined Tidal and Meteorological Forces for the Flow and Sediment Transport on Intertidal Shoals

et al. 2018

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Estuarine intertidal areas are shaped by combined astronomical and meteorological forces. This paper reveals the relative importance of tide, surge, wind, and waves for the flow and sediment transport on large intertidal shoals. Results of an intensive field campaign have been used to validate a numerical model of the Roggenplaat intertidal shoal in the Eastern Scheldt Estuary, the Netherlands, in order to identify and quantify the importance of each of the processes over time and space. We show that its main tidal creeks are not the cause for the dominant direction of the net flow on the shoal. The tidal flow over the shoal is steered by the water level differences between the surrounding channels. Also during wind events, the tidal flow (enhanced by surge) is dominant in the creeks. In contrast, wind speeds of order 40 times the typical tidal flow velocity are sufficient to completely alter the flow direction and magnitude on an intertidal shoal. This has significant consequences for the sediment transport patterns. Apart from this wind‐driven flow dominance during these events, the wind also increases the bed shear stress by waves. For the largest intertidal part of the Roggenplaat, only ∼1–10% of the yearly transport results from the 50% least windy tides, even if the shoal is artificially lowered half the tidal range. This dominance of energetic meteorological conditions in the transports matches with field observations, in which the migration of the creeks and high parts of the shoal are in line with the predominant wind direction.

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“…In another study, Zhu et al (2017) reported on the bed level changes on the East Chongming mudflat (see Figure 5 for the location) over a full spring-neap cycle with a mean wind speed close to the yearly average. The forces induced by tides and waves were varying during the field campaign, so that periods of erosion and accretion alternated.…”

Section: An Estimate For Rmentioning

confidence: 99%

“…However, of additional importance are the temporally larger accretion rates after storms, benefitting from the temporarily higher SSCs (S. L. Yang, Friedrichs, et al, 2003;Zhu et al, 2017). These reduce the net effect of the storms.…”

Section: An Estimate For Rmentioning

confidence: 99%

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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Bed-level changes on intertidal wetland in response to waves and tides: A case study from the Yangtze River Delta

Cited by 38 publications

References 53 publications

Morphodynamic Resilience of Intertidal Mudflats on a Seasonal Time Scale

Morphodynamic Resilience of Intertidal Mudflats on a Seasonal Time Scale

The Importance of Combined Tidal and Meteorological Forces for the Flow and Sediment Transport on Intertidal Shoals

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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