The response of vegetated dunes to wave attack

Bryant, Duncan B.; Bryant, Mary; Sharp, Jeremy A.; Bell, Gary; Moore, Christine

doi:10.1016/j.coastaleng.2019.103506

Cited by 32 publications

(41 citation statements)

References 27 publications

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“…Dune vegetation helps to trap dune directed aeolian sediment supply [15,16] and also stabilizes the dune from erosion by wind [17] and waves [18]. Waves are typically considered from an erosive perspective in relation to dune systems e.g., [19][20][21][22][23][24][25]; however, there is a recognition that wave-driven onshore transport can provide sediment reservoirs that subsequently can nourish dunes through aeolian transport [26][27][28]. Spatial variation in foredune evolution has been noted over a range of scales [29][30][31][32].…”

Section: Introductionmentioning

confidence: 99%

Spatial Variation in Coastal Dune Evolution in a High Tidal Range Environment

et al. 2020

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Coastal dunes have global importance as ecological habitats, recreational areas, and vital natural coastal protection. Dunes evolve due to variations in the supply and removal of sediment via both wind and waves, and on stabilization through vegetation colonization and growth. One aspect of dune evolution that is poorly understood is the longshore variation in dune response to morphodynamic forcing, which can occur over small spatial scales. In this paper, a fixed wing unmanned aerial vehicle (UAV), is used to measure the longshore variation in evolution of a dune system in a megatidal environment. Dune sections to the east and west of the study site are prograding whereas the central portion is static or eroding. The measured variation in dune response is compared to mesoscale intertidal bar migration and short-term measurements of longshore variation in wave characteristics during two storms. Intertidal sand bar migration is measured using satellite imagery: crescentic intertidal bars are present in front of the accreting portion of the beach to the west and migrate onshore at a rate of 0.1–0.2 m/day; episodically the eastern end of the bar detaches from the main bar and migrates eastward to attach near the eastern end of the study area; bypassing the central eroding section. Statistically significant longshore variation in intertidal wave heights were measured using beachface mounted pressure transducers: the largest significant wave heights are found in front of the dune section suffering erosion. Spectral differences were noted with more narrow-banded spectra in this area but differences are not statistically significant. These observations demonstrate the importance of three-dimensionality in intertidal beach morphology on longshore variation in dune evolution; both through longshore variation in onshore sediment supply and through causing longshore variation in near-dune significant wave heights.

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Section: Introductionmentioning

confidence: 99%

Spatial Variation in Coastal Dune Evolution in a High Tidal Range Environment

et al. 2020

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“…To date, there is little research on this factor or control, as noted by Feagin et al (2015) in their review on the role of vegetation in coastal dune erosion protection. Bryant et al (2019) conducted experiments to investigate the effect of aboveand below-ground biomass (using wooden dowels and coir fibres as proxies for vegetation) in a model dune under wave attack. Erosion was reduced under both collision and overwash conditions, with the greatest reduction occurring where both above-and below-ground biomass were present.…”

Section: Levels Of Vegetation Cover Density and Root Massmentioning

confidence: 99%

“…It is paramount that we understand the mechanisms and processes involved in how dunes respond to scarping if we are to successfully manage our coasts into the future. Foredunes (and other dune types that exist behind the backshore) offer a natural buffer for mitigating sea-level rise to various extents, but we do not yet fully understand or appreciate the degree of control that various factors including water-level height (Guisado-Pintado and Jackson, 2018), tidal state (Guisado-Pintado and Jackson, 2019), height and volume of the foredune (Splinter et al, 2018), vegetation density and distribution (Silva et al, 2016), root mass (Bryant et al, 2019), compaction of sediment (Hanley et al, 2014;Van de Graaff, 1994), the original foredune morphology (Christiansen and Davidson-Arnott, 2004;Hanley et al, 2014), and surfzone-beach type (Hesp, 1988b;Masselink and Short, 1993) play in increasing, decreasing, or mitigating dune erosion. This review attempts to provide a first pass at assessing these various controlling factors and their importance.…”

Section: Introductionmentioning

confidence: 99%

Controls on dune scarping

Davidson

Hesp

Silva

2020

Progress in Physical Geography: Earth and Environment

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The controls that affect the degree of spatio-temporal change to foredunes following scarping are reviewed herein. As sea-levels rises and climate changes, dune scarping will become more common. Thus, it is critical to understand what factors contribute to the magnitude of scarping, and what effect this has on dune systems to better manage coastal erosion into the future. Scarping occurs when foredunes are partially eroded by waves, generally during periods of high water level. The controls on the degree and magnitude of scarping examined include water level, foredune vegetation cover and species present, plant root mass, height and volume of the foredune, the original foredune morphology, surfzone–beach type, and compaction of sediment. Water-level height and duration of high water is the most significant control as it determines the elevation at which wave action can erode the dune and, therefore, the extent of scarping and dune volumetric loss. Higher plant density, greater rooting depth, high root mass, and greater compaction aid in reducing the degree of scaping. The presence of large woody debris and wrack may also influence the degree of scarping. The effects scarping has on the morphology of a foredune after the initial erosion event can range from small changes (e.g. minor, small scarps and slight slumping), to moderate changes such as the foredune translating landwards, to large change such as the transition of an entire dune system into a new transgressive dunefield phase. A new model summarising the key controls and their relationship/significance to the magnitude and extent of scarping is presented.

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“…More recently, Schweiger and Schuettrumpf [32] extended XBeach's code with a literature-derived root model to account for the reducing effect of belowground (landbased) biomass on dune erosion volumes that is acknowledged in the literature [10,33,34]. The basic idea is to locally increase the critical velocity for erosion due to additional root cohesion until the cumulative erosion exceeds a user-defined constant rooting depth.…”

Section: Introductionmentioning

confidence: 99%

“…The basic idea is to locally increase the critical velocity for erosion due to additional root cohesion until the cumulative erosion exceeds a user-defined constant rooting depth. Applying the root model to the small-scale wave flume experiment of Bryant et al [34], where the presence of belowground biomass (BGB) reduced the observed dune erosion in comparison to a control dune (no vegetation), resulted in higher agreement with the BGB measurements. However, a general model-data mismatch was observed since there was no dune overwash in the simulations.…”

Section: Introductionmentioning

confidence: 99%

Considering the Effect of Land-Based Biomass on Dune Erosion Volumes in Large-Scale Numerical Modeling

Schweiger

Schuettrumpf

2021

JMSE

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This paper presents and validates a novel root model which accounts for the effect of belowground biomass on dune erosion volumes in XBeach, based on a small-scale wave flume experiment that was translated to a larger scale. A 1D-XBeach model was calibrated by using control runs considering a dune without vegetation. Despite calibration, a general model–data mismatch was observed in terms of overestimated erosion volumes around the waterline. Furthermore, the prediction of overwash had to be induced by increasing the maximum nearshore wave height within the XBeach simulation. Subsequently, applying the root model resulted in a good agreement with the belowground biomass cases, and the consideration of spatially varying rooting depths further improved the results. Predictions of the root model while using locally increased friction coefficients were in line with the aboveground and belowground biomass cases. However, the effect of the root model on the erosion predictions varied among the hydrodynamic conditions, so further improvements are required. Therefore, future research should focus on quantifying the effects of land-based biomass and individual plant characteristics, such as root density, on dune erodibility at large scales, along with their influences on the temporal evolution of dune scarping and avalanching.

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The response of vegetated dunes to wave attack

Cited by 32 publications

References 27 publications

Spatial Variation in Coastal Dune Evolution in a High Tidal Range Environment

Spatial Variation in Coastal Dune Evolution in a High Tidal Range Environment

Controls on dune scarping

Considering the Effect of Land-Based Biomass on Dune Erosion Volumes in Large-Scale Numerical Modeling

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