Spatial Variability in Beach Morphology With Respect to Wave Exposure Along a Zeta-Shaped Coastline

Murray, Thomas; Strauss, Darrell; Silva, Guilherme Vieira da; Wharton, Courtney

doi:10.1142/9789811204487_0056

Cited by 2 publications

(2 citation statements)

References 21 publications

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“…While the topo-bathymetric surveys provide a reliable representation of the bar morphology, capturing such data is time-consuming, resource intensive and weather dependent, thus, regular temporal spacing of these types of surveys are rare in the literature (e.g. de Schipper et al, 2016;Murray et al, 2019;Vidal-Ruiz and Alegria-Arzaburu, 2020). Moreover, conditions that are not captured by the surveys can be analysed with modelling demonstrating that these complementary methods are very useful to understand the sediment pathways around MPARs.…”

Section: Discussionmentioning

confidence: 99%

Sediment pathways and morphodynamic response to a multi-purpose artificial reef – New insights

Silva

Hamilton

Strauss

et al. 2022

Coastal Engineering

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Multi-purpose Artificial Reefs (MPARs) are structures that may provide aesthetically acceptable coastal protection and improve recreational outcomes. Twenty years after construction of the first MPAR, Narrowneck reef on the Gold Coast of Australia, most of the available literature is still focused on the planning, design and construction of such structures and peer-reviewed publications on their post-construction monitoring, interaction with sediment transport and impacts on coastal morphology are lacking. The aim of this paper is to evaluate how does Narrowneck reef influence the sediment transport, and morphological changes around the anthropogenic structure, two decades after construction. To do so, a combination of ten high spatial resolution topo-bathymetric surveys from the top of the dune to the 10 m depth captured over 21 months and a series of 60 simulations using a calibrated numerical model were used. Our results demonstrate that: although not expected during design or reported in similar structures, sand can bypass the MPAR around its offshore end; under oblique waves, the longshore currents are deflected as they pass the reef, resulting in a shadow zone on the downdrift side where sand deposits; the bar crest tends to be higher on the reef's updrift side compared to downdrift, indicating that the MPAR can act as a store for sediments, as initially designed. Furthermore, the MPAR can act to stabilise the bar as it moves onshore with a downdrift offset of the inner bar as a result of low oblique wave incidence. The results presented here demonstrate that the short-term response to the MPAR twenty years after construction is more closely related to the deflection of longshore currents as they encounter the reef than to the dissipation of wave energy. This is because MPARs are designed to dissipate just enough wave energy so that they can achieve their recreational goal (surfing).

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Section: Discussionmentioning

confidence: 99%

Sediment pathways and morphodynamic response to a multi-purpose artificial reef – New insights

Silva

Hamilton

Strauss

et al. 2022

Coastal Engineering

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“…Analogously, the characteristics of forcing variables, such as the prevailing wave and wind directions and intensities, have to be considered, as these are likely to influence the local impacts [24,25]. The importance of wave direction for the variability of coastal morphodynamics has been widely studied and acknowledged, with wave direction affecting sediment transport, beach rotation and morphology [26]. While, on open-coast, non-embayed beaches, morphology is considered to be primarily controlled by wave di-rection and energy, sediment transport will vary locally along a non-straight coastline due to uneven wave attenuation [27].…”

Section: Introductionmentioning

confidence: 99%

Linking Short- to Medium-Term Beach Dune Dynamics to Local Features under Wave and Wind Actions: A Northern Portuguese Case Study

et al. 2022

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Many coasts suffer from prevailing erosion, with them being particularly vulnerable to predicted climate change impacts, threatening coastal ecosystems, their services, infrastructures and populations. Understanding coastal morpho-sedimentary dynamics is thus essential for coastal management. However, coastal vulnerability may differ locally, depending on exposure/protection and local geological and morpho-hydrodynamical features, suggesting that a local approach to erosion risk assessment is needed to identify and understand local patterns. Digital elevation models of a 14 km long coastal stretch in northern Portugal that were extracted from aerial surveys obtained between November 2008 and February 2019 were analysed to quantify changes in shoreline position and sediment budgets, both for the whole study area and for distinct beach segments. The observed dynamics were subsequently analysed by considering prevailing wave and wind intensities and directions. Overall and during the decade analysed, the beach–dune system of the studied stretch slightly increased in volume (0.6%), although the shoreline retreated (by 1.6 m on average). Temporal variability in coastal dynamics was observed at all of the temporal scales considered—from seasons to 5-year periods—with them being related to variability in ocean and wind patterns. There was a trend from accretional to erosional conditions, with the first 5-year period showing a mean increase in the beach–dune system’s volume of 0.6% and a mean shoreline progradation of 1.5 m, followed by 5-years with 0.0% volume change and 3.1 m shoreline retreat. Locally, the dynamics were very variable, with shoreline dynamics ranging from 24.0 m regression to 51.5 m progradation, and sediment budgets from 213.8 m3 loss to 417.0 m3 gain, per segment and for the decade. Stretches with relatively stable morphologies and others with erosional or accretional trends were found, depending on the beach type, shoreline orientation and the presence of defence structures. Rocky beaches were the least dynamic and sandy beaches the most dynamic, with mean shoreline position changes of 0.0 m and −3.4 m, respectively, and mean sediment budgets of −1.1 m3 and −2.9 m3 per linear meter of coastline, respectively, for the studied decade. The observed dynamics showed how local conditions interacted with meteo-ocean conditions in shaping local morpho-sedimentary dynamics, stressing the importance of a local approach to coastal erosion monitoring and risk assessment.

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Spatial Variability in Beach Morphology With Respect to Wave Exposure Along a Zeta-Shaped Coastline

Cited by 2 publications

References 21 publications

Sediment pathways and morphodynamic response to a multi-purpose artificial reef – New insights

Sediment pathways and morphodynamic response to a multi-purpose artificial reef – New insights

Linking Short- to Medium-Term Beach Dune Dynamics to Local Features under Wave and Wind Actions: A Northern Portuguese Case Study

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