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37 pages, 9196 KiB

Open AccessArticle

Interdecadal Foredune Changes along the Southeast Australian Coastline: 1942–2014

by Thomas B. Doyle, Andrew D. Short, Peter Ruggiero and Colin D. Woodroffe

J. Mar. Sci. Eng. 2019, 7(6), 177; https://doi.org/10.3390/jmse7060177 - 04 Jun 2019

Cited by 14 | Viewed by 5234

Foredunes are important features within coastal landscapes, yet there are relatively few medium to long-term studies on how they evolve and change over time. This study of Australia’s New South Wales (NSW) foredunes has used 70 years of aerial photographs (or photogrammetry) and [...] Read more.

Foredunes are important features within coastal landscapes, yet there are relatively few medium to long-term studies on how they evolve and change over time. This study of Australia’s New South Wales (NSW) foredunes has used 70 years of aerial photographs (or photogrammetry) and recent Light Detection and Ranging (LiDAR) datasets to assess multi-decadal fluctuations in foredune morphology. It was shown that over the past 70 years NSW foredunes have exhibited considerable spatial variation, ranging from accretion/aggradation to recession. Those sites that accreted predominantly extended seaward as new incipient dunes, gaining a maximum of 235 m³ m⁻¹ in sand volume over the study period (for the entire dune system). These sites were commonly found in the north of the state, within closed sediment compartments, and with strong onshore (and alongshore) wind climates present (increasing the potential for aeolian sand transport). Stable foredunes were those that remained within +/− 50 m³ m⁻¹ of their initial volume and managed to recover from the various storm impacts over the study period. The majority of these sites were found within the central to southern half of the state, behind embayed beaches, and within leaky sediment compartments, or those that have estuarine sinks. Finally, those foredunes in recession have retreated landwards and/or have reduced in height or width, and lost up to 437 m³ m⁻¹ of sand volume over the study period. There was no clear spatial trend for these sites; however, generally they were found in compartments that had unusual orientations, had disruptions in longshore drift/cross shore sand delivery (i.e., rocky reefs), or were being impacted by humans (i.e., the installation of river training walls, sand bypassing systems, or coastal management programs). This study has shown that NSW foredunes have undergone substantial recent changes and, by understanding their past history, will provide better insight into how they can be managed into the future. Full article

(This article belongs to the Special Issue Coastal Dune Dynamics and Management)

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15 pages, 3919 KiB

Open AccessArticle

Assessing Natural and Mechanical Dune Performance in a Post-Hurricane Environment

by Jean T. Ellis and Mayra A. Román-Rivera

J. Mar. Sci. Eng. 2019, 7(5), 126; https://doi.org/10.3390/jmse7050126 - 02 May 2019

Cited by 10 | Viewed by 2922

Abstract

The purpose of this study is to document the geomorphic evolution of a mechanical dune over approximately one year following its installation and compare it to the recovery of a natural dune following the impact of Hurricane Matthew (2016). During the study period, [...] Read more.

The purpose of this study is to document the geomorphic evolution of a mechanical dune over approximately one year following its installation and compare it to the recovery of a natural dune following the impact of Hurricane Matthew (2016). During the study period, the dunes’ integrity was tested by wave and wind events, including king tides, and a second hurricane (Irma, 2017), at the end of the study period. Prior to the impact of the second hurricane, the volumetric increase of the mechanical and natural dune was 32% and 75%, respectively, suggesting that scraping alone is not the optimal protection method. If scraping is employed, we advocate that the dune should be augmented by planting. Ideally, the storm-impacted dune should naturally recover. Post-storm vegetation regrowth was lower around the mechanical dune, which encouraged aeolian transport and dune deflation. Hurricane Irma, an extreme forcing event, substantially impacted the dunes. The natural dune was scarped and the mechanical dune was overtopped; the system was essentially left homogeneous following the hurricane. The results from this study question the current practice of sand scraping along the South Carolina coast, which occurs post-storm, emplacement along the former primary dune line, and does not include the planting of vegetation. Full article

(This article belongs to the Special Issue Coastal Dune Dynamics and Management)

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28 pages, 15930 KiB

Open AccessFeature PaperArticle

Spatial Variability of Coastal Foredune Evolution, Part A: Timescales of Months to Years

by Katherine Brodie, Ian Conery, Nicholas Cohn, Nicholas Spore and Margaret Palmsten

J. Mar. Sci. Eng. 2019, 7(5), 124; https://doi.org/10.3390/jmse7050124 - 29 Apr 2019

Cited by 31 | Viewed by 4825

Abstract

Coastal foredunes are topographically high features that can reduce vulnerability to storm-related flooding hazards. While the dominant aeolian, hydrodynamic, and ecological processes leading to dune growth and erosion are fairly well-understood, predictive capabilities of spatial variations in dune evolution on management and engineering [...] Read more.

Coastal foredunes are topographically high features that can reduce vulnerability to storm-related flooding hazards. While the dominant aeolian, hydrodynamic, and ecological processes leading to dune growth and erosion are fairly well-understood, predictive capabilities of spatial variations in dune evolution on management and engineering timescales (days to years) remain relatively poor. In this work, monthly high-resolution terrestrial lidar scans were used to quantify topographic and vegetation changes over a 2.5 year period along a micro-tidal intermediate beach and dune. Three-dimensional topographic changes to the coastal landscape were used to investigate the relative importance of environmental, ecological, and morphological factors in controlling spatial and temporal variability in foredune growth patterns at two 50 m alongshore stretches of coast. Despite being separated by only 700 m in the alongshore, the two sites evolved differently over the study period. The northern dune retreated landward and lost volume, whereas the southern dune prograded and vertically accreted. At the start of and throughout the study, the erosive site had steeper foredune faces with less overall vegetation coverage, and dune growth varied spatially and temporally within the site. Deposition occurred mainly at or behind the vegetated dune crest and primarily during periods with strong, oblique winds (>∼45

^{\circ}

from shore normal). Minimal deposition was observed on the mostly bare-sand dune face, except where patchy vegetation was present. In contrast, the response of the accretive site was more spatially uniform, with growth focused on the heavily vegetated foredune face. The largest differences in dune response between the two sections of dunes occurred during the fall storm season, when each of the systems’ geomorphic and ecological properties modulated dune growth patterns. These findings highlight the complex eco-morphodynamic feedback controlling dune dynamics across a range of spatial scales. Full article

(This article belongs to the Special Issue Coastal Dune Dynamics and Management)

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25 pages, 14992 KiB

Open AccessArticle

Exploring Marine and Aeolian Controls on Coastal Foredune Growth Using a Coupled Numerical Model

by Nicholas Cohn, Bas M. Hoonhout, Evan B. Goldstein, Sierd De Vries, Laura J. Moore, Orencio Durán Vinent and Peter Ruggiero

J. Mar. Sci. Eng. 2019, 7(1), 13; https://doi.org/10.3390/jmse7010013 - 11 Jan 2019

Cited by 58 | Viewed by 8693

Abstract

Coastal landscape change represents aggregated sediment transport gradients from spatially and temporally variable marine and aeolian forces. Numerous tools exist that independently simulate subaqueous and subaerial coastal profile change in response to these physical forces on a range of time scales. In this [...] Read more.

Coastal landscape change represents aggregated sediment transport gradients from spatially and temporally variable marine and aeolian forces. Numerous tools exist that independently simulate subaqueous and subaerial coastal profile change in response to these physical forces on a range of time scales. In this capacity, coastal foredunes have been treated primarily as wind-driven features. However, there are several marine controls on coastal foredune growth, such as sediment supply and moisture effects on aeolian processes. To improve understanding of interactions across the land-sea interface, here the development of the new Windsurf-coupled numerical modeling framework is presented. Windsurf couples standalone subaqueous and subaerial coastal change models to simulate the co-evolution of the coastal zone in response to both marine and aeolian processes. Windsurf is applied to a progradational, dissipative coastal system in Washington, USA, demonstrating the ability of the model framework to simulate sediment exchanges between the nearshore, beach, and dune for a one-year period. Windsurf simulations generally reproduce observed cycles of seasonal beach progradation and retreat, as well as dune growth, with reasonable skill. Exploratory model simulations are used to further explore the implications of environmental forcing variability on annual-scale coastal profile evolution. The findings of this work support the hypothesis that there are both direct and indirect oceanographic and meteorological controls on coastal foredune progradation, with this new modeling tool providing a new means of exploring complex morphodynamic feedback mechanisms. Full article

(This article belongs to the Special Issue Coastal Dune Dynamics and Management)

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17 pages, 21415 KiB

Open AccessArticle

Using Argus Video Monitoring to Determine Limiting Factors of Aeolian Sand Transport on a Narrow Beach

by Pam Hage, Gerben Ruessink and Jasper Donker

J. Mar. Sci. Eng. 2018, 6(4), 138; https://doi.org/10.3390/jmse6040138 - 13 Nov 2018

Cited by 9 | Viewed by 3303

Abstract

Aeolian sediment transport on beaches is responsible for dune growth and/or recovery. Models predicting potential aeolian sediment transport rates often overpredict the amount of deposition on the foredune when applied to narrow (<100 m) beaches, pointing to supply limitations. Our goal is to [...] Read more.

Aeolian sediment transport on beaches is responsible for dune growth and/or recovery. Models predicting potential aeolian sediment transport rates often overpredict the amount of deposition on the foredune when applied to narrow (<100 m) beaches, pointing to supply limitations. Our goal is to better understand these limitations, especially in the long-term (>years) in order to improve predicted transport volumes and the timing of transport. Here, we used 8 years of Argus video images at Egmond aan Zee, The Netherlands, in combination with routine weather data to delineate 241 limited from 467 unlimited sand transport events to explore supply-limiting factors. Our research shows that the wind is more oriented to the west (shore normal) and is generally stronger for limited transport events. This indicates that the available fetch distance is often less than the critical fetch needed for unlimited transport. This is further confirmed by the timing of the transport events, as limited events often became unlimited during low tide when the beach was the widest and fetch potentially the longest. Our results help understanding the nature of aeolian sediment transport on narrow beaches, which will hopefully lead to better predictions of annual aeolian sediment transport rates. Full article

(This article belongs to the Special Issue Coastal Dune Dynamics and Management)

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22 pages, 66727 KiB

Open AccessFeature PaperArticle

Estimating Annual Onshore Aeolian Sand Supply from the Intertidal Beach Using an Aggregated-Scale Transport Formula

by Leonardo Duarte-Campos, Kathelijne M. Wijnberg and Suzanne J. M. H. Hulscher

J. Mar. Sci. Eng. 2018, 6(4), 127; https://doi.org/10.3390/jmse6040127 - 30 Oct 2018

Cited by 8 | Viewed by 3883

Abstract

In this paper, we explore an approach for annual-scale transport prediction from the intertidal beach, in which we aggregate the surface conditions of the intertidal beach, in particular moisture content and roughness, and use hourly monitoring data of wind speed and wind direction. [...] Read more.

In this paper, we explore an approach for annual-scale transport prediction from the intertidal beach, in which we aggregate the surface conditions of the intertidal beach, in particular moisture content and roughness, and use hourly monitoring data of wind speed and wind direction. For our case study area (Egmond Beach, The Netherlands), we include Argus video imagery in our analysis to assess the occurrence of aeolian sand transport. With the approach described to determine a characteristic moisture content value for aeolian transport, we obtained surface moisture values of 1.2% to 3.2% for wind average and wind gust respectively, implying that we need a quite dry beach. This indicates that the main area for aeolian transport corresponds to the upper part of the intertidal source, most likely the region between mean high tide line and spring high tide line. Full article

(This article belongs to the Special Issue Coastal Dune Dynamics and Management)

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20 pages, 5061 KiB

Open AccessArticle

Spatio-Temporal Variations in Foredune Dynamics Determined with Mobile Laser Scanning

by Jasper Donker, Marcel Van Maarseveen and Gerben Ruessink

J. Mar. Sci. Eng. 2018, 6(4), 126; https://doi.org/10.3390/jmse6040126 - 30 Oct 2018

Cited by 23 | Viewed by 3271

Abstract

Coastal foredunes are highly dynamic landforms because of rapid erosion by waves and currents during storm surges in combination with gradual accretion by aeolian transport during more quiescent conditions. While our knowledge into the mechanisms behind foredune erosion have reached considerable maturity, this [...] Read more.

Coastal foredunes are highly dynamic landforms because of rapid erosion by waves and currents during storm surges in combination with gradual accretion by aeolian transport during more quiescent conditions. While our knowledge into the mechanisms behind foredune erosion have reached considerable maturity, this is not the case for foredune growth. High resolution spatio-temporal data sets of beach and foredune topography, which are needed to increase our understanding of mechanisms behind aeolian transport in coastal environments and to develop predictive dune-accretion models, are scarce. Here we aim to illustrate that repeated Mobile Laser Scanning (MLS) surveys provide an accurate and robust method to study detailed changes in dune volume on the timescales of months to years. An MLS system attached to an inertial navigation system with RTK-GPS (INS-GPS) was used to carry out 13 surveys along a 3.5-km Dutch beach over a 2.5-year period. The height observations were post-processed and averaged into 1 × 1 m Digital Elevation Models (DEMs). Comparison with airborne LiDAR and RTK-GPS data revealed that the obtained DEMs were accurate and robust up to a height of 15 m in the foredune above which dense vegetation hampers the MLS to see the sand surface. Estimates of dune volume change of the lower 13 m of the foredune have an uncertainty of about 0.25 m

^{3}

/m. Time series of dune volume change show that at our study site the foredune accretes throughout the year at similar rates (10 m

^{3}

/m/year), while marine erosion is obviously confined to storm surges. Foredune accretion and erosion vary spatially, which can, in part, be related to variations in beach width. Full article

(This article belongs to the Special Issue Coastal Dune Dynamics and Management)

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Review

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20 pages, 3503 KiB

Open AccessReview

Feedbacks between Biotic and Abiotic Processes Governing the Development of Foredune Blowouts: A Review

by Christian Schwarz, Joost Brinkkemper and Gerben Ruessink

J. Mar. Sci. Eng. 2019, 7(1), 2; https://doi.org/10.3390/jmse7010002 - 28 Dec 2018

Cited by 18 | Viewed by 5193

Abstract

This paper reviews the initiation, development, and closure of foredune blowouts with focus on biotic-abiotic interactions. There is a rich body of literature describing field measurements and model simulations in and around foredune blowouts. Despite this abundance of data there is no conceptual [...] Read more.

This paper reviews the initiation, development, and closure of foredune blowouts with focus on biotic-abiotic interactions. There is a rich body of literature describing field measurements and model simulations in and around foredune blowouts. Despite this abundance of data there is no conceptual framework available linking biotic and abiotic observations to pathways of blowout development (e.g., erosional blowout growth or vegetation induced blowout closure). This review identifies morphological and ecological processes facilitating the transition between blowout development stages and sets them in the context of existing conceptual frameworks describing biotic-abiotic systems. By doing so we are able to develop a new conceptual model linking blowout development to the dominance of its governing processes. More specifically we link blowout initiation to the dominance of abiotic (physical) processes, blowout development to the dominance of biotic-abiotic (bio-geomorphological) processes and blowout closure to the dominance of biotic (ecological) processes. Subsequently we identify further steps to test the proposed conceptual model against existing observations and show possibilities to include it in numerical models able to predict blowout development for various abiotic and biotic conditions. Full article

(This article belongs to the Special Issue Coastal Dune Dynamics and Management)

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