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Foredunes constitute a fundamental part of the coastal environment, acting as a buffer against storm erosion and natural coastal defence. Foredune size and volume play a pivotal role in determining coastal vulnerability to marine hazards, and the governing processes driving variations in foredune morphology, particularly over regional, or larger spatial scales, are still relatively poorly understood. This paper presents a regional‐scale investigation into foredune morphology along the New South Wales (NSW) coast (SE Australia), comprising not only a state‐wide inventory of foredune morphology for use in management/hazard assessment, but also testing long‐standing hypotheses and conceptual models of the physical processes that are driving, or influencing, foredune size. We applied a remote sensing protocol to 47 foredune environments, covering the length of the NSW coastline, comparing morphology (including dune height, width, shape, and volume) of established and incipient foredunes both along, and between, sandy embayments. Results, at regional spatial scales, show that the largest foredunes (volumes up to 850 m3 m−1) occur along the central coast as large, steep landforms; intermediate‐sized dunes (550–650 m3 m−1) were found on both the Mid‐north and Far North coast, and the smallest foredunes (334–380 m3 m−1) occur on the south coast as wider dunes with steep stoss slopes. Surfzone–beach state was found to be the most significant factor influencing foredune size and volume. The more energetic and more dissipative/high‐energy intermediate surfzone–beach states were correlated with larger foredunes (i.e. greater dune volume, width and crest elevation), whereas the lower‐energy surfzone–beach states generally had smaller dunes. Changes in vegetation cover, shoreline orientation and associated onshore (and alongshore) wind systems were also demonstrated to be important factors in determining foredune morphology. The largest foredunes in NSW generally occur to the north of embayments, with dune size decreasing southward with decreasing exposure to wind/wave energy. [ABSTRACT FROM AUTHOR]

Barchan dunes do not often coexist with grasslands. However, in Gonghe Basin, north‐eastern part in Qinghai‐Tibetan Plateau (QTP), China, many barchan dunes are distributed on the grassland at high altitude. Identifying celerity and morphodynamics of barchan dunes and exploring the interaction between barchans and grassland landscape can help us better understand aeolian system sand mitigate damages. In this work, we tracked dune celerity and observed three‐dimensional changes of symmetrical and asymmetrical barchan dunes in Ertala based on high‐resolution UAV‐SfM reconstruction in short‐term monitoring and discussed the factors influencing dune celerity and deformation at high altitude. The results revealed that the barchan dunes are highly mobile with an average celerity of 0.85 m/M for the whole study area. Based on observations of dune morphology and dynamics, we found the following: (1) The dune deformation degree in a short time is not large but is widespread, especially in the elongated arm of asymmetric dune. The deformation of symmetric dune is symmetrical, whereas that of dune with extended horn is asymmetrical; (2) the sand supply, vegetation and airflow at low air density all influence the celerity and deformation degree in the development of barchan dunes; (3) the asymmetric airflow and sediment supply are important cause of dune asymmetry. The above results help us understand the deformation of barchan dune from the three‐dimensional, especially the difference reflected by the symmetry of barchan dune at high altitude. [ABSTRACT FROM AUTHOR]

Fire has been suggested to be an initiation mechanism of landscape instability and coastal dune transgression, but modern evidence showing a shift to a transgressive dune phase is lacking. Following the largest wildfire in historical records on Kangaroo Island, South Australia, bimonthly uncrewed aerial vehicle (UAV) surveys were conducted on three coastal dune sites to study their post‐fire responses. The three sites studied here represent the landscape diversity of the temperate dunes of Kangaroo Island with both active coastal and inland relict stabilised dune fields studied. UAV surveys were used to reconstruct landscapes with structure from motion (SfM) photogrammetry and compared over time to illustrate significant changes in the landscape. The geomorphic and vegetation changes are compared in net and intra‐survey comparisons to illustrate the post‐fire dunefield response and trends towards stabilisation. Because of a lack of reliable baseline pre‐fire data, satellite geomedians are used to compute spectral indices to show the trajectory of ground cover in the study sites in the years preceding and following the fire. Satellite indices are used to separate 3D changes according to ground cover types and show their differing post‐fire responses. Local and regional wind, temperature and rainfall records are presented to provide weather patterns of the years preceding and following the fire, illustrating the wet and mild post‐fire weather. The overall results indicate no significant landscape instability across the studied sites and that the ground cover of vegetation is nearing pre‐fire baselines, showing that a severe fire has not caused a transgressive dunefield to develop. [ABSTRACT FROM AUTHOR]

The vast majority of coastal dunes in Europe have been stabilized by increasing vegetation cover since the mid‐20th century. However, some systems may experience a remobilization phase, generally occurring locally and further propagating alongshore, the drivers of which remain poorly documented. This study investigates the evolutionary paths (stabilization/destabilization/remobilization) from 1945 to 2020 of a 2 km‐long modern coastal transgressive dunefield located in southwest France with a holistic approach (GPR profiles, aerial photographs and LiDAR topographic data). Results show a landward migration of the transgressive dune by approximately 233 ± 7.5 m, through two distinct stages of rapid landward migration from 10 to 23 m/yr (Stage I: 1949–1959 and Stage III: 2000–2021) separated by an approximately 40‐year stage of slow to no migration, but with substantial windward slope deflation (Stage II). The onset of Stage II is due to the fixation of vegetation by human action between 1950 and 1959. The onset of Stage III is hypothesized to be driven by long and sustained upper backshore/dune toe erosion beginning in 1968 due to a massive shoal welding that locally disturbed the longshore drift. It induced a destabilization of the dune and erosion of the vegetation cover over some decades. A non‐synchronization is therefore observed between the start of the perturbation (1968), then the migration (2000), in line with the hysteresis concept of Tsoar (2005). This study shows that almost all of the sedimentary volume of the 1945 dune has been remobilized by translation to shape the dune system in its current form. The 2.2 km dunefield has grown by approximately 673 000 ± 190 000 m3 during the 2005–2020 period. Among this volume, there is a new foredune that was built from 2005 between the upper beach and the transgressive dune (volume in 2020 of about 394 000 ± 68 000 m3). [ABSTRACT FROM AUTHOR]

Wind flow and sediment transport across a northern California beach‐foredune system with two adjacent vegetation types are examined for the same incident wind conditions. The invasive Ammophila arenaria was taller (c. 1 m) with denser coverage than the neighbouring Elymus mollis alliance canopy (c. 0.65 m), which consisted of a variety of interspersed native plants. Wind flow was measured with rotating cup and sonic anemometry, while sediment transport was measured using laser particle counters. Wind speed profiles over the two canopies were significantly different because of differing vegetation height, coverage density, and stem stiffness. In both cases, there was a lower zone of semi‐stagnant air (below about 0.3 m) that transitioned upward to a shear zone comprising the upper part of the canopy and immediately above. The shear zone above the Elymus canopy was relatively thin (confined to 0.3–0.5 m above‐ground) whereas the shear zone in the Ammophila canopy was thicker extending from a height of about 0.5h (h is average plant height) to about 1.5h. Vertical profiles of Reynolds shear stress (RSS) and turbulence kinetic energy (TKE) are consistent with the shear layer structure over these two contrasting vegetation canopies. The degree of topographically‐forced and vegetation‐enhanced flow steering was significant, with Ammophila strongly shifting the highly oblique (55°) incident wind to essentially shore‐perpendicular trajectories. In comparison, the shore‐perpendicular steering effect was not as pronounced for the Elymus canopy. Sediment transport intensity on the beach was continuous, but decreased progressively to the dune toe, and then dropped to essentially zero once the vegetation canopy was encountered (on the stoss slope). Overall, the study illustrates the significant differences in wind flow and turbulence conditions that may occur in contrasting plant canopies on foredunes, suggesting that greater attention needs to be placed on vegetation roughness characteristics in models of foredune morphodynamics and sediment transport potential. [ABSTRACT FROM AUTHOR]

The multiple hypotheses which exist to explain the initiation of transgressive aeolian sand sheets and dunefields, are reviewed and discussed. Direct evidence supporting many of these hypotheses is largely lacking. In South Australia, the Younghusband Peninsula coastal barrier extends ~180 km and predominantly comprises transgressive and parabolic dunefields. The 42 Mile Crossing area on the barrier is undergoing significant erosion at variable rates of 0.5 to 5.0 m/yr, and a new transgressive aeolian sand sheet has rapidly developed in ~1 year and is extending landwards at an average rate of 13 m/yr. This research provides unequivocal evidence that large‐scale shoreline and dunefield erosion does lead to the development of a new transgressive aeolian sand sheet (and eventual dunefield) phase thereby demonstrating an initiation mechanism that is likely linked to future sea level rise and climate change. We also show that the initiation process, and, in particular, the subsequent rate of sand sheet transgression occurs at an incredibly rapid rate (+100 m in 8 years). Plain Language Summary: Coastal sand dunes border many of the world's coastlines and are highly adapted to local climate and conditions. How coastal dunes transition from predominantly vegetated and stable systems to wind‐blown sand sheets and dunefields transgressing prior terrain is a research area of pressing relevance due to forecasts of sea level rise and climate change. The factors or triggers that are considered to initiate transgressive aeolian sand sheets and dunefields are reviewed. The formation and evolution of a new transgressive aeolian sand sheet phase triggered by large‐scale shoreline erosion in South Australia is presented. According to the results from historical and satellite images, local shoreline erosion began in the late 1970s and has continued at highly variable rates. We show that once the foredune was removed, the high scarp created by wave erosion of the relict, vegetated transgressive dunefield destabilized and was then eroded by wind processes leading to the rapid development of a transgressive aeolian sand sheet. The initiation and evolution of the sand sheet provides an excellent example of how dunefields might respond to future sea level rise and climate change. [ABSTRACT FROM AUTHOR]

UAVs‐SfM (unmanned aerial vehicles‐structure‐from‐motion) systems can generate high‐resolution three‐dimensional (3D) topographic models of aeolian landforms. To explore the optimization of UAVs‐SfM for use in aeolian landform morphodynamics, this study tested flight parameters for two contrasting aeolian landform areas (free dune and blowout) to assess the 3D reconstruction accuracy of the UAV survey compared with field point measurements using differential RTK‐GPS (real‐time kinematic‐global positioning system). The results reveal the optimum UAVs‐SfM flight set‐up at the free‐dune site was: flying height = 74 m, camera tilt angle = −90°, photograph overlap ratio = 85%/70% (heading/sideways). The horizontal/vertical location error was around 0.028–0.055 m and 0.053–0.069 m, respectively, and a point cloud density of 463/m3 was found to generate a clear texture using these flying parameters. For the < 20 m deep blowout the optimum set‐up with highest accuracy and the lowest cliff texture distortion was: flying height = 74 m combined camera tilt angle = −90° and −60°, photograph overlap ratio = 85%/70% (heading/sideways), and an evenly distributed GCPs (ground control points) density of 42/km2 using these flying parameters. When the depth of the blowouts exceeded 40 m, the optimum flight/survey parameters changed slightly to account for more challenging cliff texture generation: flying height = 80 m (with −90° and −60°combined camera tilt angle), GCPs density = 63/km2 to generate horizontal and vertical location error of 0.024 m and 0.050 m, respectively, and point cloud density of 2597.11/m3. The main external factors that affect the successful 3D reconstruction of aeolian landforms using UAVs‐SfM are the weather conditions, manipulation errors, and instrument system errors. The UAVs‐SfM topographic monitoring results demonstrate that UAVs provide a viable and robust means for aeolian landform morphodynamics monitoring. Importantly, the rapid and high precision 3D reconstruction processes were significantly advanced using the optimal flight parameters reported here. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A number of studies have measured and numerically modelled near surface wind velocity over a range of aeolian landforms and made suppositions about topographic change and landform evolution. However, the precise measurement and correlation of flow dynamics and resulting topographic change have not yet been fully realized. Here, using repeated high‐resolution terrestrial laser scanning and numerical flow modelling within a bowl blowout, we statistically analyse the relationship between wind speed, vertical wind velocity, turbulent kinetic energy and topographic change over a 33‐day period. Topographic results showed that erosion and deposition occurred in distinct regions within the blowout. Deposition occurred in the upwind third of the deflation basin, where wind flow became separated and velocity and turbulent kinetic energy decreased, and erosion occurred in the downwind third of the deflation basin, where wind flow reattached and aligned with incident wind direction. Statistical analysis of wind flow and topographic change indicated that wind speed had a strong correlation with overall topographic change and that vertical wind velocity (including both positive and negative) displayed a strong correlation with negative topographic change (erosion). Only weak or very weak correlations exist for wind flow parameters and positive topographic change (accretion). This study demonstrates that wind flow modelling using average incident wind conditions can be utilized successfully to identify regions of overall change and erosion for a complex aeolian landform, but not to identify and predict regions where solely accretion will occur. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The nature of wind flow over a small, 0.6 m high foredune scarp is investigated on the Sir Richard Peninsula, South Australia during a variety of incident wind directions and speeds. The study provides additional supporting evidence that the presence of the scarp and the dune exerts a strong influence on a landwards trending reduction in wind velocity and an increase in turbulence, with the greatest area of turbulence occurring near and at the foredune scarp base. For an incident oblique wind, an alongshore helicoidal flow is formed within a separation region along the scarp basal region. In this region, the coefficient of variation (CV) of wind speed is high and displays significant fluctuations. The flow at the scarp crest is compressed, streamlined and accelerated, turbulence is suppressed, and local jets may occur depending on the incident wind approach angle. Jets are more likely where the incident flow is perpendicular or nearly so. A flow separation region does not develop downwind of the scarp crest where the morphology of the foredune stoss slope downwind of the scarp is more convex (as in this case) rather than relatively flat, and possibly due to the presence of vegetation at the scarp crest. A tentative model of the flow regions developed across a backshore–scarp–foredune region during oblique incident flow is provided. © 2018 John Wiley & Sons, Ltd. The dynamics of wind flow over a small, 0.6 m high foredune scarp is investigated. For an incident oblique wind, an alongshore helicoidal flow is formed within a separation region along the scarp basal region. The flow at the scarp crest is compressed, streamlined and accelerated, turbulence is suppressed, and local jets may occur. [ABSTRACT FROM AUTHOR]

Studies have shown that the impact of climate change, human and animal actions on coastal vegetation can turn stabilized dunes into active mobile dunes and vice versa. Yet, the driving factors that trigger vegetation changes in coastal dunes are still not fully understood. In the transgressive dunefields of the Younghusband Peninsula (south‐east coast of South Australia) historical aerial photographs show an increase in vegetation cover over the last ~70 years. This study attempts to identify the causes of the changes in vegetation cover (1949 to 2017) observed in a typical section of the coastal dune systems of the Peninsula. Vegetation cover was first estimated for various years using the available historical aerial photography (long‐term changes – 1949 to 2017) and recent satellite imagery (short‐term annual changes – 2010 to 2017) for the area, and then results were discussed against the observed changes in climatic variables and rabbit density, factors that could have played a role in this transformation. Results of long‐term changes show that the vegetation cover has increased significantly from 1949 to 2017, from less than 7% vegetation cover to almost 40%, increasing dune stabilization and forming parabolic dune systems. Periods with the largest growth in vegetation cover (1952‐1956 and 2009‐2013) coincide with a significant decline in rabbit numbers. Rabbit density was found to be the primary factor linked to the rapid vegetation growth and stabilization of the dunefield, for both decadal long‐term (last 68 years) and annual short‐term changes (last 8 years). Other factors such as changes in rainfall, aeolian sediment transport, land use practices, and the introduction of invasive plants have apparently played a limited to negligible role in this stabilization process. © 2018 John Wiley & Sons, Ltd. Historical aerial images show that vegetation cover has increased significantly in one of Australia's largest dune systems, the Younghusband Peninsula dunefield (SA). In the last seven decades, vegetation cover has changed from less than 7% to almost 40% (1949‐2017), increasing dune stabilization and forming parabolic dunes. The reduction of grazing by exotic rabbits was found to be the primary factor linked to the rapid modification of the vegetation cover and indirectly the geomorphology of the dunefield. [ABSTRACT FROM AUTHOR]

Abstract: Geomorphological changes in recent decades in an arid transgressive coastal dune system (Maspalomas, Gran Canaria, Canary Islands) are analyzed. The methodology used is based on the generation of two geomorphological maps (1961 and 2003) by interpretation of digital orthophotos. The overlay of both maps in a geographic information system (GIS) enabled the spatial and surface changes of the landforms to be determined, and the processes that generated these changes. Twelve cultural and geomorphological processes were identified from highest to lowest importance, namely: anthropization by urban occupation (114 ha changed), stabilization (92.5 ha), barchanization (37 ha), salinization/halophytication (15 ha), anthropization (12.4 ha), deflation (11.8 ha), dune loss/beach gain (11.3 ha), dune formation (9.6 ha), progradation (8 ha), retrogradation (7.7 ha), destabilization (2.7 ha) and flooding (0.7 ha). Geomorphological changes are associated with a combination of five main factors, three of anthropogenic origin and two natural ones. The natural factors are: (1) the arid climate, which favors changes occurring at high speed; (2) the existence of a progressive sedimentary deficit. Anthropogenic factors are: (3) construction of tourist urbanizations, infrastructures and facilities; (4) installation of equipment or infrastructure on the beaches; (5) the activities carried out by users. These human factors have altered the aeolian dynamics and reduced the area occupied by vegetation in some areas, causing changes in aeolian sedimentary processes. The geomorphological processes identified can be used as indicators of environmental change, allowing us to synthesize the changes in landforms detected, and group all combinations derived from the analysis by GIS and analyze them spatially. Thus, the environmental changes in the transgressive coastal dune systems could be interpreted more effectively. Copyright © 2018 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The form, height and volume of coastal foredunes reflects the long‐term interaction of a suite of nearshore and aeolian processes that control the amount of sand delivered to the foredune from the beach versus the amount removed or carried inland. In this paper, the morphological evolution of more than six decades is used to inform the development of a simple computer model that simulates foredune growth. The suggestion by others that increased steepness of the seaward slope will retard sediment supply from the beach to the foredune due to development of a flow stagnation zone in front of the foredune, hence limiting foredune growth, was examined. Our long‐term data demonstrate that sediment can be transferred from the beach to the foredune, even with a steep foredune stoss slope, primarily because much of the sediment transfer takes place under oblique rather than onshore winds. During such conditions, the apparent aspect ratio of the dune to the oncoming flow is less steep and conditions are not as favourable for the formation of a stagnation zone. The model shows that the rate of growth in foredune height varies as a function of sediment input from the beach and erosion due to storm events, as expected, but it also demonstrates that the rate of growth in foredune height per unit volume increase will decrease over time, which gives the perception of an equilibrium height having been reached asymptotically. As the foredune grows in size, an increasing volume of sediment is needed to yield a unit increase in height, therefore the apparent growth rate appears to slow. Copyright © 2018 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Jet flows, which are localized flows exhibiting a high speed maxima, are relatively common in nature, and in many devices. They have only been occasionally observed on dunes, and their dynamics are poorly known. This paper examines computational fluid dynamic (CFD) two-dimensional (2D) modelling of jet flow over a foredune topography. Flow was simulated in 10° increments from onshore (0°) to highly oblique alongshore (70°) incident wind approach angles. CFD modelling reveals that the formation of a jet is not dependent on a critical wind speed, and an increase in incident wind velocity does not affect the magnitude of jet flow. A jet is first formed at ~1.0 m seawards of the foredune crest on the Prince Edward Island foredune morphology example examined here. A jet is not developed when the incident wind is from an oblique approach angle greater than ~50° because there is significantly less flow acceleration across a much lower slope at this incident angle. The presence of a scarp does influence the structure of the crest jet, in that the jet is more pronounced where a scarp is present. Surface roughness affects the magnitude of jet expansion and jets are better developed on bare surfaces compared to vegetated ones. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The results from three years of surveying and monitoring a dynamic foredune and dunefield restoration effort on Vancouver Island, Canada is presented. Complete removal of foredune vegetation occurred in three phases spaced a year apart in an effort to control invasive Ammophila spp. The collection of airborne LiDAR, orthophotographs, and bi-monthly topographic surveys provided a means to quantify and examine sediment budgets and geomorphic responses. Three survey swaths, corresponding with each phase of vegetation removal, were established to provide detailed topographic coverage over the impacted beach, foredune, and dunefield landscape units. The swath corresponding with the first phase of removal recorded a positive sediment budget of 1·3 m3 m−2 after three years. A control swath, with data collected for a year prior and two years following removal, exhibited a distinct pulse of sediment delivery into the dunefield unit with a maximum gain of 0·03 m3 m−2 pre-removal compared to 0·11 m3 m−2 post-removal. Vegetation analysis zones, associated with each of the three swaths, demonstrate a range of vegetation responses due to variation in the vegetation removal and subsequent re-invasion or removal methods employed. The first site to be cleared of vegetation, received ongoing invasive re-growth control, and three years following removal vegetation cover dropped from 57% in 2009 to 13% in 2012 (−44%). An adjacent site was cleared of vegetation two years later (only one year of recovery) but experienced rapid Ammophila re-invasion and percent cover changed from 61% in 2009 to 26% in 2012 (−35%). The data presented provides insights for improving the application of sediment budget monitoring in dynamic restorations and discusses the potential for detailed spatial-temporal survey data to improve our understanding of meso-scale landscape morphodynamics following foredune disturbance. Overall, the vegetation removal treatments reduced the extent of invasive grass and increased dunefield mobility and dynamic activity. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT Morphological and vegetation changes on the Moçambique barrier dunefield system are examined for the period 1938-2002 from aerial photography, and a variety of factors are investigated as possible driving factors. Human factors include a decrease in grazing pressure and tree felling from the early 1960s onwards after 200 years of these activities, and fires. In the 1960s tree planting also took place. During the period 1963 to 1970 there was a marked decline in drift potential (DP - potential sand transport), and then a period of very low DPs (1970-1974). This period falls within the time interval when vegetation cover significantly increased by ~70% along the Moçambique barrier (from 1956 to 1978). During the 1960s to present, the rainfall increased. Analyses of other transgressive dunefields in Santa Catarina and Rio Grande do Sul states show similar trends so it is likely that climatic factors such as increasing rainfall and decreasing DPs are responsible for driving dunefield changes and vegetation colonization of the barriers. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article presents the research on the effects of surface moisture on mass flux and aeolian sediment transport threshold on a beach. It discusses the study on the effects of surface moisture on the threshold of movement and sand transport by wind and mass flux. The study involved a five-week observation on the measurements of moisture content, wind speed and wind direction on that was undertaken at Greenwich Dunes, Prince Edward Island, Canada. The study revealed that where there are dry sand, the saltation system responds rapidly to fluctuations in wind speed. It also revealed that transport rate is lower where sand supply from the surface is limited by moisture.

The surface morphology of the transgressive dunefield barrier extending from Itapeva to Tramandai along the northern littoral of Rio Grande do Sul, is examined and an attempt is presented to link morphological changes across the barrier to Holocene sea level changes. The 4-5 km wide Holocene barrier displays two typical morphologies: an inner part dominated by large-scale, continuous alongshore, overlapping dunefield phases comprising sand sheets, dunes, deflation plains and precipitation ridges; and an outer part dominated by discontinuous, medium- to small-scale, triangular to lobate transgressive dunefield phases, cut by both active and relict (palaeo-) creeks or washouts. Holocene sea level in the region rose to c. +1 to +3 m above present reaching a maximum around 5100 years BP and then progressively fell to the present level. We argue that the effect on barrier development was to suppress the development of a drainage system during the rising and maximum stages, and encourage the development of an organized drainage system in the form of regularly spaced washouts during the falling period, and that this change in sea level from rising to falling therefore produced the large-scale differences in barrier morphology. [ABSTRACT FROM AUTHOR]

This paper describes the appearance and maintenance of crescentic dunes in high wind speed conditions on a frozen beach at Schiermonnikoog, The Netherlands. The dunes were cresentic forms with horns. They were barchanoidal in plan view, but had reverse morphologies to typical barchans: the highest and steepest slopes were upwind and led to long low slopes downwind. Slipfaces were absent. It is hypothesized that such crescentic dunes may be a stable aerodynamic form under high to very high (c. 15-20 m s-1) flow conditions. [ABSTRACT FROM AUTHOR]