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Flow dynamics and sediment transport responses over a large, vegetated foredune at Prince Edward Island, Canada, during an offshore wind event are examined. Data were collected along an instrumented transect that extended from the dune crest, down the lee-side (seaward) slope of the dune, across a wave-cut scarp, and on to the back-beach. When the wind direction at the dune crest was approximately crest-normal (less than about 15° deviation), the mean near-surface flow directions along the dune slope and on the back beach were generally onshore, indicating reversed (onshore) flow relative to the regional (offshore) wind direction. Although flow patterns were consistent with a lee-side recirculation eddy, large excursions in flow direction were also prevalent, suggesting that the eddy was unstable and alternated with highly turbulent wake flow. As wind direction at the crest veered to greater than 20° from crest-normal, lee-side winds shifted toward strongly alongshore flow with minimal directionally variability. On the dune slope, the wind vectors were slightly offshore whereas on the back-beach they were slightly onshore. Wind speeds and sediment transport were greatest at the foredune crest and declined rapidly downslope due to flow expansion and deceleration in the wake zone as well as to the influence of a sparse vegetation layer. Mean particle counts (averaged over a 15-min interval) derived from laser sensors positioned at the crest were large (7.76 per second) in comparison to those measured in the immediate lee of the crest (0.52 per second) and farther down the dune slope (< 0.13 per second). In contrast, the values were as large as 25.62 per second on the middle of the back-beach, declining rapidly to a value of only 0.24 per second at the dune toe. Transport intensity was highly variable with the largest Activity Parameter (AP = 0.5) values at the dune crest and on the back-beach, and with the smallest values (AP < 0.1) on the lee-side dune slope down to the top of the scarp. Calculations of sediment (particle) flux divergence between instrument stations show that deposition was significant immediately downwind of the dune crest but negligible across most of the lower dune slope. Deposition was also prevalent on the dune ramp below the scarp. These results demonstrate that sediment transport across the beach–dune system was spatially discontinuous during this offshore wind event. Rebuilding of the dune ramp at the toe of the scarp occurred quite independently of, and with a different sediment source than, the broadening of the dune crest, which was fed with sediment from the landward side of the foredune. Such process ‘decoupling’ is an example of the complexity by which foredunes evolve or are maintained, and as with previous research reinforces the importance of offshore and alongshore wind events to beach–dune morphodynamics. [ABSTRACT FROM AUTHOR]

Where urban areas are situated close to a beach, sand dunes act as protection from flooding and erosion. When a dune has been removed or damaged by erosion, dune, ridge or dyke re-building using heavy machinery, a process known as beach scraping, is a common method of restoration. Following construction, natural accretion of sediment on the backshore is preferable as it facilitates sustained natural dune building, growth of vegetation, and habitat creation and reduces the need for further beach scraping. This study investigates the near surface flow and transport potential for three artificial structure designs: a single ridge, a double ridge and a dyke. The three shapes contained an identical volume of sand and were preceded by 50 m of beach at an angle of 3°. A computational fluid dynamic model (CFD) was created for each scenario to calculate wind flow and shear velocity from 4 different wind directions at 22.5° intervals from 0° (onshore) to 67.5°. From this data sediment flux was predicted along a two dimensional transect for each of the scenarios. For all structures, shear velocity on the beach and stoss slope decreased as incident wind direction became more oblique; conversely shear velocity in the lee of the crest increased. A reduction in shear velocity at the foot of each structure also occurred and appears related to stoss slope, with the greatest reduction at the toe of the dyke structure (stoss slope 34°) and the least before the single ridge (stoss slope 17°). Specifically the results suggest that the double ridge structure is the most resilient to aeolian erosion. Shear velocity reduction on the back beach is comparable to the dyke and sediment flux from the stoss slope of the double ridge structure may become trapped in the swale between the two ridges encouraging sediment deposition, thus reducing sediment transport beyond the dunes and backshore. Although the dyke structure underwent the greatest reduction in shear velocity on the back beach it experienced substantial sediment flux at the crest and along the top of the structure, making it susceptible to erosion during a strong wind event. The highest sediment transport rate was calculated at the crest of the single ridge, and the single ridge structure also created the smallest reduction of shear velocity on the back beach, thus making it less desirable than the double ridge. [ABSTRACT FROM AUTHOR]

Silva, R.; Martínez, M.L.; Hesp, P.; Catalan, P.; Osorio, A. F.; Martell, R.; Fossati, M.; Miot da Silva, G.; Mariño-Tapia, I.; Pereira, P.; Cienfuegos, R.; Klein, A., and Govaere, G., 2014. Present and future challenges of coastal erosion in Latin America. The coastal zones of Latin America have many landforms and environments, including sedimentary cliffs, deeply incised estuaries, headlands, barrier coasts and low lying, muddy coastal plains. These forms will respond differently to the expected changes in climate and associated sea level rise, which may produce coastal erosion in the future. Considering the coasts of Latin America overall, erosion is not yet a serious threat, although it is widespread and it is severe in some parts. Major erosion problems are frequently associated with human intervention in sediment supply, with poor planning or with the morphodynamic nature of the coast. Permanent erosional processes, locally or regionally, are caused by tectonic subsidence, deforestation and the fragmentation of coastal ecosystems, land use changes and sediment deficits because of infrastructure built along the coast. In this article we analyse coastal erosion in Latin America and the challenges it presents to the region. We first highlight the relevance of Latin America in terms of its biodiversity; then we describe the population at risk, demographic trends and economic growth throughout the low lying coastal zones. We also examine the vulnerability of the region by analyzing the resilience of key coastal ecosystems after exposure to the most frequent hazards that affect coastal zones in Latin America, namely tropical cyclones, sea level rise, ocean acidification, earthquakes and tsunamis. Finally, we discuss seven case studies of coastal erosion across Latin America. We close the study by pinpointing the main areas of concern in Latin America and explore possible strategies to overcome erosion and thus sustain economic growth, minimize population risk and maintain biodiversity. [ABSTRACT FROM AUTHOR]

Flow dynamics over a high, unvegetated, and steep scarp slope that fronts a severely eroded relict transgressive dunefield were investigated at Salmon Hole (also known as Post Office Rock), a small headland-bay beach located near Beachport, south east South Australia. The ~15-metre-high steep dune at Salmon Hole provided the opportunity to conduct a wind flow experiment on a larger, higher and longer stoss slope than previously studied. The scarp slope is comprised of segments of varying slope that have a significant impact on flow dynamics over the dune. Percentage speed up and a decrease in turbulence were recorded up the stoss slope due to streamline convergence and flow compression. However, flow expansion at a change in gradient on the upper stoss slope caused a significant drop in wind speed and an increase in turbulence, contrary to what has previously been found in the literature where maximum percentage speed up is primarily recorded at the crest. Topographic steering typically seen in wind flow over scarps and foredunes was observed at Salmon Hole along with flow separation and the formation of a reversing vortex on the lee slope. This study also demonstrates how a lack of sediment delivery back to the beach and thence to the dune between storm events results in the inability for dune recovery or translation. However, the Salmon Hole study shows that blowouts can still develop and grow through dune cannibalization regardless of the lack of sediment supply from the beach and the recession of the shoreline. General model of the flow dynamics over the dune slope. (A) Topographic compression and flow expansion, flow expansion, and flow separation. (B) Flow dynamics over the scarp responsible for changes in wind speed, direction and turbulence over the scarp. Inset: Fig. 8 showing percentage speed up the scarp. [Display omitted] • Wind flow experiment on higher, steeper, and longer slope than previously studied in scarp or transverse dune literature. • Flow expansion at change in slope gradient caused a drop in wind speed and an increase in turbulence at the crest. • Lack of sediment delivery to the dune results in the inability for dune recovery/translation, and therefore net erosion. [ABSTRACT FROM AUTHOR]

Hesp, P.A., 2013. A 34 year record of foredune morphodynamics at Dark Point, NSW, Australia In: Conley, D.C., Masselink, G., Russell, P.E. and O'Hare, T.J. (eds.) Incipient foredunes are formed by æolian deposition in plants on the backshore. They commonly evolve into established foredunes, and are present on many of the world's coasts, yet there are very few medium to long term studies on how they evolve and change over time. An incipient foredune suite has been monitored at Dark Point, NSW, Australia since 1978, providing a 34 year record of dune evolution and dynamics, and therefore representing one of the very few medium term foredune monitoring sites in the world. The foredune was initiated by the growth of a zone of discrete pioneer plant species (principally Spinifex) on the backshore following the destructive 1974-75 storms. Over a period of 24 years, 5 separate incipient foredunes developed as sediment was gradually returned to the surfzone and beach, and the beach prograded 70m. Sometime after 1998, storms cut back the seawardmost foredune and former foredunes were reactivated landwards of the 1998 foredune. This study demonstrates (i) how incipient foredunes form by both discrete seedling development, and seawards rhizome extension over time, (ii) how ramp and terrace morphologies eventually evolve into ridges, (iii) rates of beach accretion following storm erosion and backshore response, (iv) how wave erosion drives morphological changes and evolutionary sequences on foredunes, (v) the relationships between backshore height, foredune development and sea levels, and (vi) indications for the initiation and evolution of so-called 'beach ridges'. [ABSTRACT FROM AUTHOR]

Miot da Silva, G., Hesp, P., Keim, B., Martinho, C.T. and Ferligoj, Y., 2013. Changes in dunefield geomorphology and vegetation cover as a response to local and regional climate variations. In: Conley, D.C., Masselink, G., Russell, P.E. and O'Hare, T.J. (eds.) Published analyses of aerial photographs show a marked increase in vegetation cover of coastal transgressive dunefields along the Southern Brazilian Holocene Barrier around the late 1970s. This phenomenon is reflecting an increase in precipitation and a decrease in aeolian sediment transport. These climatic changes are associated with recurring high intensity El Niño events related to the 1976/1977 regime shift of the Pacific Decadal Oscillation (PDO). [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]

A palynological analysis of sediments sampled from core HI-178, offshore High Island, Texas, provided a diverse and well-preserved palynoflora. The main objective was to analyze the environmental conditions at time of deposition. A secondary objective was to evaluate whether or not this site might have been occupied by Native Americans by looking for signs of human-driven changes in vegetation. Here we focus on the abundance of hornwort spores recovered from these samples, review their diversity, compare the fossil spores to modern analogues and discuss the paleoenvironmental implications of hornwort abundance. Although no direct evidence of human occupation was found, the pollen and spore assemblage recovered, marked by high abundance and diversity in spores of hornworts belonging to the families Anthocerotaceae and Notothyladaceae, indicate that this site was most likely not submerged at the time of deposition; human occupation was therefore possible. This site represents a coastal low-lying area with ponds or slow-moving waters that provided the humid environment needed for hornworts to reproduce and thrive under warm climatic conditions. [ABSTRACT FROM PUBLISHER]

Abstract: This paper examines the æolian dynamics of a deep bowl blowout within the foredune of the Greenwich Dunes, on the northeastern shore or Prince Edward Island, Canada. Masts of cup anemometers and sonic anemometers were utilized to measure flow velocities and directions during a strong regional ESE (offshore) wind event. The flow across the blowout immediately separated at the upwind rim crest, and within the blowout was strongly reversed. High, negative vertical flows occurred down the downwind (but seaward) vertical scarp which projected into the separation envelope and topographically forced flow back into the blowout. A pronounced, accelerated jet flow existed near the surface across the blowout basin, and the flow exhibited a complex, anti-clockwise structure with the near-surface flow following the contours around the blowout basin and lower slopes. Significant æolian sediment transport occurred across the whole bowl basin and sediment was delivered by saltation and suspension out the blowout to the east. This study demonstrates that strong offshore winds produce pronounced topographically forced flow steering, separation, reversal, and more complex three-dimensional motions within a bowl blowout, and that such winds within a bowl blowout play a notable role in transporting sediment within and beyond deep topographic hollows in the foredune. [Copyright &y& Elsevier]

This paper aims to verify how wave energy and longshore sediment transport rates could have influenced the evolution of the Rio Grande do Sul Holocene barriers in the last 5000 y, assuming that wave climate conditions did not change much during the Middle and Late Holocene. Calculations of wave energy based on visual observations and longshore sediment transport show that both wave energy and sediment transport decrease as the coastline becomes concave (embayed) and increase as the coastline becomes convex (projected). These variations alongshore create a positive and negative imbalance, respectively, in the sediment budget. The long-term operation of these processes has produced progradational barriers in embayments and retrogradational barriers along projections. In the transition zones between embayed to convex coastlines, neither depositional nor erosional processes predominate, creating a sediment balance and producing aggradational barriers. [ABSTRACT FROM AUTHOR]