Morphological coupling in multiple sandbar systems – a review

Price, Timothy; Ruessink, Gerben; Castelle, Bruno

doi:10.5194/esurf-2-309-2014

Cited by 37 publications

(42 citation statements)

References 60 publications

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“…Regarding the morphological coupling discussed by other authors (Castelle et al, 2010a;Price et al, 2014), our results derived from linear stability analysis can distinguish between modes that develop in one of the bars and that force an instability over the other sandbar. At the same time, we obtain modes that develop simultaneously over the two sandbars.…”

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confidence: 67%

“…It should be pointed out that while remote sensing provides increasing evidence of coupling between sandbars, bathymetric surveys providing details about the geometry of the system remain scarce and sparse. More observations are available to describe the coupling between shoreline and sandbar patterns (e.g., Coco et al, 2005;Ruessink et al, 2007;Price et al, 2014). 40 The conditions leading to transitions from alongshore uniform to variable have been ascribed to wave height (or wave power) and/or to parameters combining hydro-and sedimentological characteristics (e.g., sediment fall velocity or Iribarren number).…”

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confidence: 99%

“…In this contribution we aim to systematically address the role of initial bathymetry on the coupling between sandbars, an area that so far has received only limited attention (see also Price et al, 2014). Calvete et al (2007) used linear stability analysis to show that the initial cross-shore beach profile can be as important as wave height in determining the growth rate 65 and alongshore spacing of crescentic bars.…”

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Emerging crescentic patterns in modeled double sandbar systems

Coco

Calvete

Ribas

et al. 2019

Preprint

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The morphodynamic stability of double-barred beaches is explored using a numerical model based on linear stability analysis. Surfzone hydrodynamics is described by coupling depth and wave averaged conservation of mass and momentum with the wave-energy and phase equations, including roller dynamics. A simplified sediment transport formulation relates flow to seabed changes. Under normal wave incidence an alongshore uniform coast with a cross-shore profile characterized by the presence of two sandbars, can be unstable, thereby resulting in the development of crescentic/rip channel patterns. Our 5 study demonstrates that sandbar coupling can be either in-phase (highs and lows of both sandbars are at the same alongshore position) or out-of-phase (highs and lows of one sandbar correspond to lows and highs of the other sandbar). In line with observations, results of numerical simulations show a large variability in the possible emerging bottom patterns. Our analysis indicates that the inner bar-modes are dominant for large height/depth differences between the two sandbars crests and small offshore wave heights, while patterns related to the outer sandbar dominate for small values of the difference in sandbar depth. 10 For intermediate differences between the two sandbars depths, patterns on both longshore bars appear to be fully coupled. For relatively larger waves and large depth over the outer sandbar, patterns develop close to the shoreline/inner surfzone. 1 Introduction Multiple sandbar systems have been observed in a variety of settings worldwide. We specifically focus on the dynamics of double sandbar systems in the surfzone where the sandbars almost constantly affect (and are affected by) wave transformation and 15 onshore/offshore exchanges of sediment. Alongshore changes in double sandbar configurations sometimes result in rhythmic patterns, usually called crescentic bars or rip channels (Figure 1).The development of alongshore patterns in multiple sandbar settings has been studied through both observations (e.g. Castelle et al., 2007Castelle et al., , 2015 and numerical studies (e.g. Klein and Schuttelaars, 2006;, and has also been considered in the wider framework of a conceptual model of sequential beach changes by Short and Aagaard (1993). 20This conceptual model as well as field data (e.g. Castelle et al., 2007) indicate that the inner and outer sandbars are likely to be characterized by different spatial and temporal scales. In a double-barred system like the one considered in this study, the inner sandbar usually displays crescentic features with an alongshore spacing (distance between consecutive sandbar horns) smaller than the one characterizing the outer sandbar. Moreover, in the case of accretionary conditions, Short and Aagaard (1993) assume that the inner sandbar responds faster than the outer one. The Short and Aagaard (1993) model also indicates that 25 1 https://doi.

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Emerging crescentic patterns in modeled double sandbar systems

Coco

Calvete

Ribas

et al. 2019

Preprint

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“…Observing natural processes is one of the best ways to develop engineering. The large amount of temporal and spatial coastal diversity around the world makes coasts potential natural laboratories for beach dynamic studies [1][2][3][4][5][6][7][8], helping to improve the knowledge of shoreline adjustment for different coastal features [9][10][11]. Climate change makes it increasingly urgent to find coastal engineering solutions that could help control the coastal dynamics, thereby solving or reducing erosion problems [12].…”

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confidence: 99%

“…New strategies must also be developed, especially in coastal urban centers where the highest population density on the planet is found [13,14], requiring social amenities and safety. Conventional beach protection structures such as groins, shore-parallel rubble mounds, seawalls, and emergent breakwaters are becoming increasingly unpopular, mostly due to their adverse impact on beach amenities and aesthetic considerations of modern civil conceits [7,10,12]).…”

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confidence: 99%

Beach Morphodynamic Response to a Submerged Reef

Nemes

Criado-Sudau

Gallo

2019

Water

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To develop beach engineering, the submerged structure’s primary physical functions have to be understood. This study focuses on submerged structures in order to understand the strategy of reduced wave energy, stabilizing the shoreline and not generating erosion or adversely modifying coastal processes. Important developments have been made since the 1990s, taking into account the functions of recreational amenity. However, non-dimensional models cannot explain the physical mechanisms that generate accretion or erosion morphological features in the lee of the submerged structure. The present study aims to collaborate with the understanding of the mechanism of beach response to a submerged structure. For this, 26 surveys were made using topographic, Lagrangian, and Eulerian hydrodynamic measures during one seasonal cycle of a beach system from Rio de Janeiro (Brazil) with a natural submerged reef or rocky bank V-shape in the plan. This beach system is energetic and intermediate when referring to wave energy conditions and beach states, respectively. The wave breaking vector system on the rocky bank’s geometry was examined in the intermediate and dissipative beach morphodynamic organization. The variability of the wave breaking vector system determines the establishment, deformation, and erosion features in the lee of the structure. During high-energy waves, the submerged structure’s hydrodynamic and morphodynamic processes are transparent. When the submerged structure combines with the dissipative beach state, the surfing wave conditions are improved. These results provide the dimensional and positional references for an engineering proposal for a beach system.

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Observations on decadal sandbar behaviour along a large‐scale curved shoreline

Gijsman

Ruessink

Visscher

et al. 2021

Earth Surf Processes Landf

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Nearshore sandbars are characteristic features of sandy surf zones and have been observed with a variety of geometries in cross‐shore (e.g. location) and longshore direction (e.g. planform). Although the behaviour of sandbars has been studied extensively on spatial scales up to kilometres and timescales up to years, it remains challenging to observe and explain their behaviour on larger spatial and temporal scales, especially in locations where coastline curvature can be prominent. In this paper, we study a data set with 38 years of coastal profiles, collected with alongshore intervals of 50 m, along the 34 km‐long curved sandy shoreline of Sylt island, Germany. Sylt's shoreline has an orientation difference of ~20° between the northern and southern half of the island. We found that the decadal coastal profiles on the southern half show features of a low‐tide terrace and a sandbar located further from the shoreline (~441 m). On the nothern half, the sandbar was located closer to the shoreline (~267 m) and was less pronounced, while the profiles show transverse bar and rip features. The alongshore planform also differed systematically and significantly along the two island sides. The sandbar on the southern island half, with alongshore periodicity on a larger length scale (~2240 m), was coupled out‐of‐phase to the shoreline, while no phase coupling was observed for the sandbar with periodicity on a shorter length scale (~670 m) on the northern half. We related the observed geometric differences of the sandbars to the difference in the local wave climate along Sylt, imposed by the shoreline shape. Our observations imply that small alongshore variations in wave climate, due to the increasing shoreline curvature on larger spatial scales, can lead to significant alongshore differences in the decadal evolution of coastal profiles, sandbars and shorelines. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

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Morphological coupling in multiple sandbar systems – a review

Cited by 37 publications

References 60 publications

Emerging crescentic patterns in modeled double sandbar systems

Emerging crescentic patterns in modeled double sandbar systems

Beach Morphodynamic Response to a Submerged Reef

Observations on decadal sandbar behaviour along a large‐scale curved shoreline

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