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Knowledge of wind flow over dune scarps and, as scarps fill, their subsequent various slopes, is important for understanding sediment transport pathways from beach to dunes. In this study, flow over scarps (also termed forward-facing steps) is reviewed, and the flow over a vertical scarp (90°) and three slopes of 45°, 24°, and 14°, all 2 m in height, is examined via CFD modelling. The flow over three 90° scarps, with heights of 1 m, 2 m and 4 m, and over a 2-m high vertical (90°) scarp for three oblique incident winds is studied. The extent of wind flow deceleration and separation becomes smaller with decreased slope, with maximum flow separation and reverse vortex development occurring on the vertical scarp. The extent of crest wind flow separation is greatest for the scarp and considerably less for the 45° slope. As scarp height increases, so too does the spatial extent of turbulent wind flow, wind speed, and extent of the flow separation region. As incident wind direction became more oblique over a vertical scarp, less deceleration occurs, and helicoidal vortices replace roller vortices. Our results demonstrate how scarp morphology and wind direction are likely to influence transport pathways. [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]

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]

AbstractThe essence of stories of human–environment interactions can be preserved in oral contexts for millennia, creating novel opportunities for humanizing the past. This study examines stories (knowledge-rich narratives) about the ancestral being Ngurunderi, told by Ngarrindjeri peoples of South Australia. Three elements of the Ngurunderi narrative are considered. The first recalls his journey along a 170-km long coastal barrier (Younghusband Peninsula) when this was continuous. The second discusses Ngurunderi’s encounters with what are now islands off the Fleurieu Peninsula, some of which he created, interpreted as memories of when sea level was lower and “islands” were contiguous with the mainland. The third refers to the crossing of a land connection between modern Kangaroo Island and the Fleurieu Peninsula, later submerged to form Backstairs Passage. Using paleogeographic data, the most recent times at which each narrative element could have taken place and observed by people are estimated. This research suggests that: (1) stories about Younghusband Peninsula may be >6700 years cal BP; (2) islands off the Fleurieu Peninsula were created 6800–10,400 cal BP; and (3) submergence of Backstairs Passage occurred 11,000–10,100 cal BP. Narratives are linked to the period of early Holocene sea-level rise, the rapid 8200-cal BP sea-level rise event, and stabilization of sea level 7000–6000 cal BP. These narratives humanize the past and provide information that can be interpreted as both observed coastal and seascape changes as well as past human responses to rising sea level that can inform our future encounters with coastal-landscape change. [ABSTRACT FROM AUTHOR]

Various studies have detailed the evolution of barchan dunes to parabolic dunes and a very few studies describe the evolution of coastal transgressive dunefields and continental sand seas to parabolic dunefields. This study examines the evolution and transformation of a 12 km long portion of a formerly large (~50 km along-coast), active, transgressive dunefield (coastal sand sea or erg) dominated by transverse dunes to a coastal barrier dominated by parabolic dunes. A GIS study of vegetation cover change from 1950 to 2017 was conducted, and a stereographic analyses of 1945 to 2020 aerial photography was carried out to determine morphological changes across the dune system. Historical rainfall, aeolian drift potentials, and rabbit numbers are examined as possible drivers of change, and rabbit numbers most strongly correlate with vegetation change. The vegetation cover of the greater dunefield increased in the study area from 26 % cover in 1950 to 54 % by 2020. A largely unvegetated transgressive dunefield dominated by transverse dunes evolved into a parabolic dunefield in <70 years. Vegetation colonisation primarily took place from landward slipfaces, by nebkha formation on dune lobe crests, from interdune swales and flats, and within deflation basins and plains. Vegetation colonisation also occurred above the backshore in the same period. Aeolian landform units such as marginal ridges, nebkha fields, deflation basins and plains, dune ridges, remnant knobs, parabolic dunes, and a foredune-blowout complex were formed as the dune field was colonised and stabilised by vegetation growth. The study provides far greater detail on how vegetational and morphological changes take place as a transgressive dunefield evolves into a parabolic dunefield. • A former transgressive dunefield evolves into a parabolic dunefield. • Parabolic dunes form via vegetation colonisation along the margins of transverse dunes and on precipitation ridges/slipfaces. • 1945 to 2020 aerial imagery study of coastal dunefield change and relationships to environmental drivers [ABSTRACT FROM AUTHOR]

This study is the first to simultaneously compare flow and sediment transport through a blowout and over an adjacent foredune, and the first study of flow within a highly sinuous, slot and cauldron blowout. Flow across the foredune transect is similar to that observed in other studies and is primarily modulated by across-dune vegetation density differences. Flow within the blowout is highly complex and exhibits pronounced accelerations and jet flow. It is characterised by marked helicoidal coherent vortices in the mid-regions, and topographically vertically forced flow out of the cauldron portion of the blowout. Instantaneous sediment transport within the blowout is significant compared to transport onto and/or over the adjacent foredune stoss slope and ridge, with the blowout providing a conduit for suspended sediment to reach the downwind foredune upper stoss slope and crest. Medium term (4 months) aeolian sedimentation data indicates sand is accumulating in the blowout entrance while erosion is taking place throughout the majority of the slot, and deposition is occurring downwind of the cauldron on the foredune ridge. The adjacent lower stoss slope of the foredune is accreting while the upper stoss slope is slightly erosional. Longer term (16 months) pot trap data shows that the majority of foredune upper stoss slope and crest accretion occurs via suspended sediment delivery from the blowout, whereas the majority of the suspended sediment arriving to the well-vegetated foredune stoss slope is deposited on the mid-stoss slope. The results of this study indicate one mechanism of how marked alongshore foredune morphological variability evolves due to the role of blowouts in topographically accelerating flow, and delivering significant aeolian sediment downwind to relatively discrete sections of the foredune. [ABSTRACT FROM AUTHOR]

In this study, wind flow is simulated via CFD over five ‘nebkha’ dune forms that range in shape from a cone, to a hemisphere (approximately) and to a dome in order to examine the structure of the wake zone formed downwind and the effect on the leeward flow separation zone and shadow dune formation. Dune height was fixed at 0.5 m while the nebkha diameter increased in 0.25 m increments from 0.5 m to 1.5 m and aspect ratio (h/D) from 1.0 to 0.3. The mean flow comprises an upwind region of reduced velocity which expands as nebkha width increases, high velocity marginal wings, and paired counter-rotating reversing vortices leeward of the nebkha. The point at which flow separation occurs moves further downwind as the nebkha diameter increases. The core regions of the reversing vortices are situated further downwind behind the smaller nebkha than in the case of the larger nebkha. These factors in combination allow for higher velocity perturbations (TKE) and narrower wake behind the smaller nebkha, and the suppression of downwind wake development in the case of the increasingly larger nebkha. Shadow dune length increases as nebkha width increases for lower incident velocity flow and is barely affected by nebkha width at higher flows. The extent of the leeward separation or wake zone, and hence shadow dune length, more strongly varies as a function of wind velocity. [ABSTRACT FROM AUTHOR]

The flow and sediment transport over a reversing ~ 6.9 m-high barchan dune is examined on the Changli Gold Coast in Hebei Province, China. Wind velocity profiles are non-logarithmic, exhibit rapid accelerations up slope, and display near-surface jets at the dune crest and downwind lee slope. From the windward lower slope to dune crest, the wind speed at 5 cm height increased by 55%. The windward slope is a slipface and therefore has a significantly greater gradient than most ‘normal’ windward slopes, and the magnitude of speed-up is significantly greater (speed-up ratio of 5.25). The majority of sediment was transported in the 0–4 cm height above the bed range. Maximum total sediment flux occurred at the dune crest and was greater than the total flux from three other sites combined. The leeward mid-slope sedimentation rate is strongly influenced by the sediment plume streaming upwards and downwind from the actively reversing dune crest. Dunes in the process of reversing display quite different wind flow and sedimentation patterns than when the dune is in ‘normal’ flow conditions. [ABSTRACT FROM AUTHOR]

Hesp, Patrick A. and Smyth, T.A.G., 2016. Surfzone-Beach-Dune interactions: Review; and flow and sediment transport across the intertidal beach and backshore. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp.8-12. Coconut Creek (Florida), ISSN 0749-0208. The original wave-beach-dune model (Hesp, 1982) stated that in the medium to long term, modal dissipative beaches display maximum onshore wave driven sediment transport, maximum aeolian transport off beaches, the largest foredune heights and volumes, and the largest Holocene dunefields. Modal reflective beaches display the opposite, while modal intermediate beaches display a trend in these from relatively high to relatively low sediment transport, foredune volumes, and Holocene barrier volumes with a trend from dissipative to reflective. New Computational Fluid Dynamic (CFD) modelling of flow and calculation of sediment transport over three modal beach types presented here shows that the original conceptual ideas and field data regarding aeolian sediment transport are correct. Dissipative beaches show the greatest long term potential for sediment delivery to the backshore whilst reflective beaches display the least, with a trend from relatively high to low in the intermediate beach state range. [ABSTRACT FROM AUTHOR]

Hesp, Patrick A.; Smyth, Thomas A.G.; Walker, Ian J.; Gares, Paul A., and Wasklewisz, Thad, 2016. Flow within a trough blowout at Cape Cod. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 288-292. Coconut Creek (Florida), ISSN 0749-0208. The Province Lands dunefield at Cape Cod is characterised by large parabolic dunes on which have developed very significant numbers of active saucer and bowl blowouts. Blowouts occur across the entire dune landscape but many are initiated on the high lee margins of large erosional ridges and bowl blowouts within the larger parabolic dune landscape. Evolution of these blowouts is characterised by multiple stages. The first few evolutionary stages are described. In addition, the aerodynamics and flow structure within a trough blowout and former saucer blowout developed within a high ridge crest is elucidated from 2D sonic anemometer data, smoke bombs and videography. The flow is characterised by decreasing then increasing flow up the blowout centreline, and marked, highly turbulent opposed flow separation immediately inside and around the marginal entrance walls of the blowout. [ABSTRACT FROM AUTHOR]

Smyth, T.A.G. and Hesp, Patrick A., 2016. Numerical Modelling of Turbulent Flow Structures in a Blowout. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 328-332. Coconut Creek (Florida), ISSN 0749-0208. Blowouts are erosional landforms often formed on coastal sand dunes by the deflation of sediment by wind flow. Quantitative observations of wind flow within blowouts aided by the deployment of smoke-bombs, have noted that temporal and spatial variations in sediment transport occur with the presence of turbulent flow structures. However because of the discrete nature of anemometry data, the presence of flow structures has been difficult to quantify and our understanding remains largely conceptual. This study presents a detailed investigation of turbulent flow structures within a trough blowout using high resolution, three-dimensional computational fluid dynamic modelling. We show that when incident wind flow was parallel to the blowout axis, only limited flow steering took place but a well-defined near surface jet developed along the deflation basin. Conversely when incident wind flow was oblique to the axis of the blowout wind flow became steered along the axis of the blowout but no near surface jet was produced. During neither incident wind direction were corkscrew or helicoidal vortices produced. Our study concludes that the incident wind flow direction is critical to the effectiveness of a trough blowout as a corridor for wind-blown sediment. While wind from a range of oblique angles may be steered along the axis of blowout, its relative effectiveness of eroding and transporting sediment beyond the deflation basin and erosional walls is much reduced compared to axis parallel wind flows of the same incident wind speed. [ABSTRACT FROM AUTHOR]