Morphodynamic Feedback Loops Control Stable Fringing Flats

Maan, Cynthia; Prooijen, Bram C. van; Zhu, Qin; Wang, Zheng Bing

doi:10.1029/2018jf004659

Cited by 14 publications

(25 citation statements)

References 45 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Figure 7a shows the tidally averaged flow (τ c ), wave (τ w ), and maximum (τ max ) shear stresses for tidal cycle TCini (at an early development stage) and TCeq (at equilibrium). The shear stress distribution for TCeq shows good resemblance with observations and modeling results presented by Maan et al (2018) for a similar fringed shoal setting in the WS.…”

Section: Intratidal Dynamicssupporting

confidence: 81%

“…Other studies implemented a process-based approach without underlying assumptions of equilibrium (e.g., Pritchard et al, 2002;Pritchard & Hogg, 2003). Roberts et al (2000) and van der Wegen et al (2017van der Wegen et al ( , 2019 showed modeled 1-D profiles similar to observed mudflat profiles; 2-D/3-D processed-based models provided skillful reproduction of observed morphodynamic developments in entire estuaries such as San Francisco Bay (Ganju et al, 2009;van der Wegen et al, 2011;Elmilady et al, 2019), Western Scheldt (Maan et al, 2018), and Yangtze Estuary (Guo, 2014;Luan et al, 2016Luan et al, , 2017.…”

Section: Modeling Intertidal Flatsmentioning

confidence: 99%

“…This idealized approach allows for reducing the system's complexity. The setup is inspired by fringing shoals found along the edges of the WS (e.g., Maan et al, 2018). The initial bathymetry comprises a flat submerged 850 m wide shoal (−3 m MSL) adjacent to a 150 m wide channel (−15 m MSL).…”

Section: Model Setup and Forcingmentioning

confidence: 99%

“…Although the previous section suggests that shoal formation is primarily associated with tidal currents, waves play an important role when shoals become shallow and intertidal (e.g., Kohsiek et al, 1988). Observations and modeling studies suggest that tidal flats tend to evolve toward a morphologically steady-state maintained by a balance between sediment supply, wave action, and tidal forcing (Friedrichs, 2011;Friedrichs & Aubrey, 1996;Hu et al, 2015;Maan et al, 2015Maan et al, , 2018Roberts et al, 2000;van der Wegen et al, 2017van der Wegen et al, , 2019. Tidal forcing is usually associated with deposition while erosion tends to be associated with wind-wave activity (e.g., Allen & Duffy, 1998;Christie et al, 1999;Janssen-Stelder, 2000;Yang et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Morphodynamic Evolution of a Fringing Sandy Shoal: From Tidal Levees to Sea Level Rise

et al. 2020

View full text Add to dashboard Cite

Intertidal shoals are vital components of estuaries. Tides, waves, and sediment supply shape the profile of estuarine shoals. Ensuring their sustainability requires an understanding of how such systems will react to sea level rise (SLR). In contrast to mudflats, sandy shoals have drawn limited attention in research. Inspired by a channel-shoal system in the Western Scheldt Estuary (Netherlands), this research investigates governing processes of the long-term morphodynamic evolution of intertidal estuarine sandy shoals across different timescales. We apply a high-resolution process-based numerical model (Delft3D) to generate a channel-shoal system in equilibrium and expose the equilibrium profile to variations in wave forcing and SLR. Combined tidal action and wave forcing initiate ridge formation at the seaward shoal edge, which slowly propagates landward until a linear equilibrium profile develops within 200 years. Model simulations in which forcing conditions have been varied to reproduce observations show that the bed is most dynamic near the channel-shoal interface. A decrease/increase in wave forcing causes the formation/erosion of small tidal levees at the shoal edge, which shows good resemblance to observed features. The profile recovers when regular wave forcing applies again. Sandy shoals accrete in response to SLR with a long (decades) bed-level adaptation lag eventually leading to intertidal area loss. This lag depends on the forcing conditions and is lowest near the channel and gradually increases landward. Adding mud makes the shoal more resilient to SLR. Our study suggests that processes near the channel-shoal interface are crucial to understanding the long-term morphodynamic development of sandy shoals.Plain Language Summary Intertidal area is the coastal zone that undergoes a rhythm of wet-dry cycles under the influence of tidal action. Intertidal shoals are vital components of the estuarine environment. They have high ecological value but also help in reducing flood risk by wave attenuation. It is important to understand how these shoals will react to sea level rise in order to plan sustainable management strategies. We developed a high-resolution model to investigate the long-term evolution of an intertidal sandy channel-shoal system. The model describes tidal flow, wave action, and associated sediment transports and generates an intertidal sandy shoal in equilibrium. Changes in equilibrium forcing lead to morphodynamic adaptation. A drop in wave height causes the formation of small-scale tidal levees at the channel-shoal edge, which are also observed in reality. High wind-wave activity causes shoal erosion. Shoals accrete in response to imposing sea level rise, but the accretion rate is smaller than the sea level rise rate leading to the loss of intertidal area and increased inundation. Inclusion of mud makes the shoal more resilient to sea level rise. Our study suggests that processes near the channel-shoal edge are crucial to understanding the long-term morphodynamic evolution of sandy shoals...

show abstract

Section: Intratidal Dynamicssupporting

confidence: 81%

Section: Modeling Intertidal Flatsmentioning

confidence: 99%

Section: Model Setup and Forcingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Morphodynamic Evolution of a Fringing Sandy Shoal: From Tidal Levees to Sea Level Rise

et al. 2020

View full text Add to dashboard Cite

show abstract

“…Numerical, process-based modeling has shown reproduction of observed mudflat profiles in equilibrium for various 1-D and 2-D case studies (e.g., Maan et al, 2015Maan et al, , 2018Pritchard & Hogg, 2003;Roberts et al, 2000;Van der Wegen & Jaffe, 2014;Van der Wegen et al, 2017). In a 2-D setting Gong et al (2012) and Wang et al (2019) explored the impact of additional longshore currents on a prograding mud coast and recognized the considerable impact of the suspended sediment concentration boundary conditions on the profile development.…”

Section: Introductionmentioning

confidence: 99%

Morphodynamic Resilience of Intertidal Mudflats on a Seasonal Time Scale

2019

View full text Add to dashboard Cite

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.

show abstract

Observed and modelled tidal bar sedimentology reveals preservation bias against mud in estuarine stratigraphy

Braat

Pierik

Dijk

et al. 2022

The Depositional Record

View full text Add to dashboard Cite

Mud plays a pivotal role in estuarine ecology and morphology. However, field data on the lateral and vertical depositional record of mud are rare. Furthermore, numerical morphodynamic models often ignore mud due to long computational times and simplifications of mixed depositional processes. This study aims to understand the spatial distribution, formative conditions and preservation of mud deposits in the intertidal zone of bars in high‐energy sand‐dominated estuaries, and to elucidate the effects of mud on morphology, ecology and stratigraphic architecture. To meet these objectives, field data (historic bathymetry, bio‐morphological maps and sediment cores of the shoal of Walsoorden, Western Scheldt estuary, the Netherlands) were combined with complementary hydro‐morphodynamic numerical modelling (Delft3D). Based on the field observations, two types of mud deposits were distinguished: (1) mudflat deposits, which are thick (>10 cm) mud beds at the surface associated with high elevations and low accumulation rates; and (2) mud drapes, which are thin (millimetre to centimetre) buried laminae that form and preserve at a wide range of elevations and energy conditions. Model results show that deposition on mudflats occurs just after high‐tide slack water in areas shielded from high flood velocities, suggesting that mud accumulation is mostly controlled by elevation, flow velocity and flow direction. Mud accumulation increases shoal elevation, sometimes to supratidal levels. This reduces flow over the shoal, which in turn reduces chute channel formation, stabilises bar morphology and decreases local tidal prism. These effects further promote mud deposition and vegetation settling. Although observations show that mud cover at the surface is relatively high (20%–40% of the intertidal area), mud constitutes only a small percentage of the total estuary volume (ca 5%) revealing that only a small fraction is preserved in the stratigraphy. Due to this mismatch between surface and subsurface expression of mud, interpretations of estuarine stratigraphy risk underestimating the influence of mud at the surface on morphodynamics and habitats.

show abstract

Morphodynamic Feedback Loops Control Stable Fringing Flats

Cited by 14 publications

References 45 publications

Morphodynamic Evolution of a Fringing Sandy Shoal: From Tidal Levees to Sea Level Rise

Morphodynamic Evolution of a Fringing Sandy Shoal: From Tidal Levees to Sea Level Rise

Morphodynamic Resilience of Intertidal Mudflats on a Seasonal Time Scale

Observed and modelled tidal bar sedimentology reveals preservation bias against mud in estuarine stratigraphy

Contact Info

Product

Resources

About