The links between entrance geometry, hypsometry and hydrodynamics in shallow tidally dominated basins

Ruiter, Peter J. de; Mullarney, Julia C.; Bryan, Karin R.

doi:10.1002/esp.4622

Cited by 10 publications

(12 citation statements)

References 64 publications

(155 reference statements)

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“…We define velocity asymmetry ratios greater and smaller than one as flood‐ and ebb‐dominant, respectively, recognizing that these VA ratios represent not only asymmetries in tidal velocities (previously defined as TVA; e.g. de Ruiter et al, 2019), but also include the effects of wind‐induced currents. The horizontal velocity asymmetry ratios provide an indication of potential sediment transport directions inside the tidal basins (e.g.…”

Section: Resultsmentioning

confidence: 99%

“…Modelled tidal velocity asymmetry patterns inside the idealized infilled divergent (a) and less infilled convergent (b) tidal basin geometries, calculated using the depth‐averaged velocity with tidal forcing only, from de Ruiter et al (2019). The dashed black lines represent TVA = 1.…”

Section: Resultsmentioning

confidence: 99%

“…Conversely, convergent and less infilled basins with concave profiles may display greater ebb dominance and hence be preferable in coastal regions where navigability is of prime importance (e.g. de Ruiter et al, 2019; Meerman et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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The effects of wind‐generated currents on velocity asymmetry in tidal basins with varying geometries

Ruiter

Mullarney

Bryan

2021

Earth Surf Processes Landf

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Geomorphologic characteristics of tidal basins have been shown to control tidal asymmetry and associated sediment transport potential in coastal regions. In this study, we examine how winds modulate horizontal velocity asymmetry patterns in shallow tidal basins. Numerical modelling experiments for a series of idealized basins in which planform shape and bathymetry were varied, reveal that an increase in wind speed promotes more extreme horizontal velocity asymmetry (larger velocity asymmetry values) without substantially altering the overall spatial pattern of velocity asymmetry throughout the domains. The wind forcing primarily influences mean and peak flow velocities, with a limited effect on tidal harmonics. Changes to the velocity asymmetry patterns are most evident for wind speeds of 6 m/s and greater, and for wind directions parallel to the main axes of the basins’ tidal channels. However, the velocity asymmetry is strongly depth‐dependent. Shallow intertidal basin regions are characterized by a downwind‐directed increase in velocity asymmetry, whereas deeper subtidal channels display asymmetry changes in the opposite direction. Additionally, the timing and duration of a wind event are found to influence the velocity asymmetry patterns. Wind events coinciding with flooding tides result in the most noteworthy differences between the relative size of the peak flood‐ and ebb‐directed currents inside the shallow basins, for wind event durations of both 3 and 6 h.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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The effects of wind‐generated currents on velocity asymmetry in tidal basins with varying geometries

Ruiter

Mullarney

Bryan

2021

Earth Surf Processes Landf

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“…The estuary axis is oriented northwestward, and the entrance is ~10 km from the southern mouth of Tauranga Harbor. The prevailing wind direction is from the southwest with typical wind speeds <3 m/s (de Ruiter et al, 2019). In Tauranga Harbor, wind waves are limited by short fetch, and ocean swell propagation is limited by the barrier island and tombolos at each entrance.…”

Section: Study Area Observational Methods and Numerical Modelingmentioning

confidence: 99%

Decadal‐scale impacts of changing mangrove extent on hydrodynamics and sediment transport in a quiescent, mesotidal estuary

Glover

Stokes

Ogston

et al. 2022

Earth Surf Processes Landf

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Mangroves are often considered integral engineers of morphologic evolution, but mangroves can also opportunistically respond to morphologic change created by abiotic sedimentary processes. Consequently, predicting the response of individual estuarine environments to changes in mangrove extent is challenging. Here, the impact of mangrove extent was explored using in‐situ observations and numerical modeling of the quiescent Waikaraka Estuary in Tauranga Harbor, Aotearoa, New Zealand. Mangrove coverage expanded in the estuary from 1940 until a removal program began in 2005 with the goal of reducing fine sediment and restoring bivalve habitat. In June 2019 water velocity, turbidity, wave height, and bed‐sediment grain size were measured at multiple sites to identify how sediment dynamics in the estuary were responding to removal. Flow in the predominantly sandy lower estuary was ebb dominant, resulting in net sediment export, while flow in the muddy upper estuary was weakly flood dominant, resulting in sediment import and retention. Therefore, fine sediment is unlikely to be flushed out of quiescent estuaries after mangrove removal. A Delft3D numerical model calibrated with in‐situ data showed that tidal asymmetry, velocity skew, and peak ebb‐tide shear stress were not significantly altered by varying the mangrove extent between the 2005 maximum coverage and complete removal. Mangroves did not significantly impact flow in this system; instead, the hydrodynamics and net sediment transport were controlled by tidal interactions with bathymetry. In model runs with mangroves covering all tidal flats, the water velocity on the intertidal flats decreased while the peak ebb‐tide velocity in the main channel increased, indicating that the potential for fine‐sediment export may actually decrease with mangrove removal. These results emphasize the role of mangroves as opportunistic colonizers, not engineers, and highlight the importance of considering site specific parameters when planning mangrove removals.

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“…The model domain consists of a 4 km by 2 km flood-tidal basin enclosed by two non-erodible barriers, connected to the open coast with a 2 km by 2 km rectangle offshore area (Figure 4.6). The grid resolution is set to 15 m by 15 m to allow evolution of channel networks and changes of mangrove forests following previous research (Horstman et al, 2013;van Maanen et al, 2015;Brückner et al, 2019;de Ruiter et al, 2019). The initial bed elevation in the basin is set to 1.5 m below mean sea level, while the offshore area is set to a sharp slope from -1.5 in the inlet to -100 m on the most eastern seaward edge (Figure 4.6b).…”

Section: Idealized Landscape Settingsmentioning

confidence: 99%

Bio-morphodynamics of coastal wetlands with mangrove vegetation

Xie¹

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Mangroves, occupying the transition between land and sea, provide valuable ecosystem services for hundreds of millions of people across the tropics and subtropics. What would happen in a world without mangroves? Large amounts of carbon dioxide would be released into the atmosphere, contributing to global warming and accelerating global climate change, affecting humans, animals, plants and almost all other organisms on the planet. Dismal scenarios would be seen in almost every (sub)tropical coastal city, for example, a barren coast with unprotected shorelines periodically inundated by polluted water, driving away coastal inhabitants from the shore. Although this extreme situation is predicted not to occur within this century, global loss of mangrove coverage is currently occurring under the pressure from sea-level rise and human interventions. While the appeal to the conservation of mangrove forests has become globally recognized, limited knowledge on the complex interactions between ecosystems and coastal morphology hampers coastal zone management and the safeguarding of mangroves. External forcings, such as sea-level rise, tidal currents, wind waves, river flows, sediment supply, and human activity vary with mangrove systems influencing profile changes and vegetation dynamics. It is often thought that mangroves can keep up with sea-level rise and withstand natural and human-induced pressures, but to what extent is this true and which non-linear relations with the external forcings and internal dynamics are most important? Sustainable coastal management needs to be based on a better understanding of the underlying mechanisms controlling the development of mangrove ecosystems, especially in the face of predicted sea-level rise and intensifying human interventions.Mangroves are often characterized by numerous pneumatophores, which are their special aerial root systems growing upward out of the mud and water so that mangroves can stand in seawater without asphyxiation. These root systems add flow resistance when water flushes through mangrove-covered areas. As a result, currents slow down, which promotes sedimentation and increasing bed surface elevation. Locally, flow between vegetated flats, such as in tidal channels, becomes more concentrated due to convergence of water flow, leading to a larger flow velocity and sediment erosion and thus lowering channel bed elevation.These hydro-morphodynamic interactions in turn affect vegetation biological processes, such as seedling establishment, mangrove growth and mortality, which then further change the impacts of vegetation on the above physical processes. Such non-linear interactions between vegetation dynamics, water movement, sediment transport and morphological changes are called bio-morphodynamic feedbacks. Sea-level rise and increasing human interventions have increasingly affected mangrove ecosystems and caused more uncertainty about future system evolution. Rising sea levels disturb hydro-morphodynamic processes through modulating water levels, which directly an...

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The links between entrance geometry, hypsometry and hydrodynamics in shallow tidally dominated basins

Cited by 10 publications

References 64 publications

The effects of wind‐generated currents on velocity asymmetry in tidal basins with varying geometries

The effects of wind‐generated currents on velocity asymmetry in tidal basins with varying geometries

Decadal‐scale impacts of changing mangrove extent on hydrodynamics and sediment transport in a quiescent, mesotidal estuary

Bio-morphodynamics of coastal wetlands with mangrove vegetation

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