Foredune Morphology Research Articles

Foredune morphology: Regional patterns and surfzone–beach–dune interactions along the New South Wales coast, Australia

AbstractForedunes 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.

Signatures of Pleistocene Marine Transgression Preserved in Lithified Coastal Dune Morphology of The Bahamas

The morphology of some lithified wind-blown, carbonate dunes in The Bahamas preserves the signature of erosion from paleo-marine processes: wave-induced swash, scarping, and longshore transport. Digital elevation models were used to distinguish between two dune morphotypes—those disconnected versus connected to beach processes. Dune sinuosity and upwind slope were quantified and used to interpret which dunes remained beach-attached and subject to marine erosion and processes versus dunes that became disconnected from the shoreline via inland migration or shoreline regression. Disconnected dunes possess low slopes over stoss surfaces with sinuous planforms mimicking their crestlines. Beach-connected foredunes preserve steep, kilometers-long linear upwind faces, which are interpreted to be signatures of beach-dune morphodynamics. Foredune morphology serves as a proxy for shoreline position during past sea-level high-stands, while the basal elevations of their stoss dune toes provide an upper limit on the beach and adjacent sea level. A growing library of digital topography will allow for this tool to be used to interpret global paleo-shoreline positions through time and space.

50 years of beach–foredune change on the southeastern coast of Australia: Bengello Beach, Moruya, NSW, 1972–2022

A fifty-year time series of high-resolution field-surveyed beach profiles from a southeast Australian ocean beach was analysed to determine spatial and temporal variability and changes in beach–foredune morphology at annual to decadal time scales. Data from 452 surveys obtained at two to six-weekly intervals was available from four closely spaced (within 422 m) cross-shore profiles in the centre of a 6 km long beach. Each profile extended 110–130 m seaward from a dune datum at ~5 m Australian Height Datum (AHD) to mean sea level (MSL). Morphometric indicators examined included beach–foredune sand volume, four shore position contours at 0 m AHD (MSL) +1 m, +2 m, +3 m AHD, and across-shore topographic changes. Five phases of different beach/foredune conditions were identified, two in the 1970s, and three in the following four decades. After a brief accretion period (phase 1) major storms in May–June 1974 caused the loss of over 100 m3/m from each profile and a 50–60 m landward shift of the MSL shoreline. The substantial sand deficit lasted for the next five years with average beach volumes of 134 m3/m followed by incremental accretion of 120 m3/m from 1979 to 1982 (phase 2). In the next 12 years (phase 3, 1982–1994) the beach maintained high volumes averaging 268 m3/m. This declined by 45–60 m3/m in the mid 1990s (phase 4). Since 2002 (phase 5) sand stored above MSL has averaged 279 m3/m, ~10 m3/m greater than at any time since surveys began although the volume gradually declined in the decade prior to 2022. Morphological changes and shifts in shoreline position have accompanied volumetric changes. An incipient dune developed during the 1980s at the site of the 1970s foreshore later to become an established, vegetated foredune. Comparison of results with other long-term beach profile sites in Europe, Japan and USA showed some differences most notably Bengello exhibits no consistent seasonal summer-winter cycle in beach volume. General similarities include lack of clear beach change evidence of decadal–scale sea level rise, and all locations contend with the impacts of storms. Bengello averages 15 storms per year (H sig ≥3.0 m) and in the fifty-year period there have been 21 major events (H max >10 m) all of which have caused substantial erosion. Recovery times have varied from a few months to over 5 years. The net effect of these erosion-recovery events over 1972–2022 has not resulted in beach recession.

Conceptualizing Aeolian Sediment Transport in a Cellular Automata Model to Simulate the Bio-Geomorphological Evolution of Beach–Dune Systems

Understanding the dynamics of beach–dune systems is crucial for effective coastal management. The cellular automata model DuBeVeg provides a powerful tool for simulating and understanding the bio-geomorphological evolution of these systems, capturing key interactions of aeolian, hydro-, and vegetation dynamics in a simplified manner. In this study, we present an alternative representation of the aeolian transport component in DuBeVeg, aiming to better capture the saltation transport mode that prevails on beaches. This new representation is compared with the original aeolian transport representation in DuBeVeg, which is inspired by ripple migration. For three beach width scenarios, we considered the effects of the different aeolian transport representations on the predicted foredune morphology after 50 years, as well as the spatio-temporal evolution of the beach–dune system leading to that morphologic state. The saltation transport representation resulted in a more realistic simulation of the seaward expansion of the foredune compared with the original representation, particularly in scenarios with wide and prograding beaches. The new representation also more accurately captured the amplitude of aeolian bedforms emerging across the beach. These findings highlight the importance of selecting the representative transport mode when simulating the transient bio-geomorphological evolution of beach–dune systems.

Modified foredune eco-morphology in southeast Australia

Human activities are playing increasingly significant roles in the dynamics and evolution of coastal dunes, one of the most intensively used environments on Earth. Not only do beaches and adjacent foredunes provide tourism and recreational uses but they also form an important buffer between coastal settlements and the ocean. Modified or “urbanised” foredunes often differ from their natural counterparts in terms of characteristics such as location, dimension, orientation, topographic variability, sediment features, mobility, and the degree to which they can initiate and/or develop further through natural processes (e.g. progradation). Much of this research has been focused on dunes found in Europe and the USA, with limited work done elsewhere. The availability of LiDAR-derived topographic data for the entire coast enables a state-wide assessment of foredune morphology in New South Wales (NSW), and a basis for determining the effects of human modification. This study examines the current morphological characteristics of foredunes in NSW, by comparing modified with natural settings, to understand how human activities and uses have impacted foredune morphology. Results show highly modified incipient and established foredunes were significantly narrower and reached lower elevations, consequently with smaller volumes of sand than their more natural counterparts. On average, both highly modified established and incipient dunes were half the size of the unmodified systems, and on average modified dunes had volumes of ∼350 m3 m−1, whereas unmodified dunes contained sand volumes of ∼740 m3 m−1. By lowering dune elevation and sand volumes, human modifications have created environments that are more exposed and potentially vulnerable to erosion, placing coastal properties, infrastructure and communities (especially those found behind modified dune systems) at greater risk of erosion, coastal flooding and inundation, particularly during storm events.

Sand supply and dune grass species density affect foredune shape along the US Central Atlantic Coast

AbstractCoastal foredunes form via biophysical feedbacks between sand accretion and burial‐tolerant vegetation and can protect coastlines from hazards such as extreme storms and sea level rise. Predicting how coastal dunes, and the services they provide, will change in the future requires an understanding of the relative roles of the physical and ecological processes that shape their structure and function. Here we assess the relative roles of sand supply, beach morphology, and vegetation in determining foredune morphology, and its change, along a 300‐km stretch of the US Central Atlantic coast. In particular, we used the spatial variability inherent in beaches and dunes of this region to determine the relative importance of shoreline change rate (SCR; a proxy for sand supply to the beach), beach morphology, and grass density of four widespread dune grasses (Uniola paniculata, Ammophila breviligulata, Panicum amarum, and Spartina patens) to foredune morphology metrics (height, width, and aspect ratio) along the North Carolina Outer Banks barrier islands. Foredune morphology and change metrics are correlated with three main factors: multidecadal SCR (1997–2016), beach slope, and dune grass density and species identity. Multidecadal SCR and beach width explained the most variation in, and were positively correlated with, foredune height and width, and were negatively correlated with foredune aspect ratio (height divided by width). In addition, grass density and changes in grass density contributed significantly to foredune morphology change. We found a positive relationship between change in A. breviligulata density and foredune width, which aligns with previous studies on the US Atlantic and Pacific Northwest coasts. Our results demonstrate the interactive roles of beach sand supply and dune grass functional morphology in dune building processes on highly vulnerable coastlines.

Ammophila Invasion Ecology and Dune Restoration on the West Coast of North America

The invasive ecosystem engineer Ammophila arenaria, native to Europe, was first introduced to California (USA) in 1896. More than a century later, it has come to dominate coastal foredune vegetation on the west coast of North America to the near exclusion of native species. A. arenaria builds a narrow, steep, peaked, and densely vegetated foredune, in contrast to the broad, more sparsely vegetated foredunes built by the native Elymus mollis. As such, it has modified dune processes by fixing the foredune and disrupting exchange of sediment between the beach, foredune, and dunefield. In the 1930s the congener A. breviligulata, native to the east coast and Great Lakes USA, was first introduced to Oregon, and has been displacing A. arenaria in southern Washington. Ammophila spp. have drastically reduced biodiversity, outcompeting native plant species, and displacing both invertebrate and vertebrate species. Restoration of west coast dunes through the removal of Ammophila began in the 1990s. Methods usually consist of one or a combination of manual digging, burning/herbicides, or excavation with heavy equipment. There are benefits and disadvantages to each method. Manual removal has proven most effective at restoring foredune form and process but is expensive. Excavation and herbicides may result in the loss of foredune morphology. Managers must articulate goals carefully before selecting restoration methods.

The relative role of constructive and destructive processes in dune evolution on Cape Lookout National Seashore, North Carolina, USA

AbstractCoastal dunes are dynamic features that are continuously evolving due to constructive (e.g., wind‐ and wave‐driven sediment transport) and destructive (e.g., elevated total water levels during storm events) processes. However, the relative importance of these processes in determining dune evolution is often poorly understood. In this study, ten lidar datasets from 1997 to 2016 are used to determine the relative role of erosion and accretion processes driving foredune change on the coast of Cape Lookout National Seashore, North Carolina, USA. Beach and dune morphometrics reveal that dune toe locations have generally retreated since 1997, while dune crest heights accreted by 0.01–0.02 m/year. We develop three univariate metrics that represent (1) the potential for erosion, i.e., total water level impact hours per year, (2) accretion, i.e., dune building hours per year, and (3) the relative net effect of foredune accretion and erosion processes, i.e., constructive–destructive dune forcing (CDDF) ratio, and test the correlative power of these metrics in explaining changes in foredune morphology. The total water level impact hours per year metric explained as much as 66% and 67% of the variance in dune crest and toe elevations, respectively, across the nearly two decades of dune evolution. The greatest number of dune building hours per year and largest dunes within the study site co‐occurred at locations exposed to the dominant cross‐shore wind direction as a result of varying shoreline orientation. The CDDF ratio was positively correlated to changes in the dune toe elevation in approximately 70% of dunes within the study site, outperforming the impact and dune building hours per year metrics. Our results show that these three metrics can provide first‐order estimates of dune morphometric change across multiple spatial and temporal scales, which may be particularly useful at sites where lidar acquisition is intermittent.

Decadal monitoring of Traganum moquinii's role on foredune morphology of an human impacted arid dunefield

Foredunes in arid zones have been little studied, being significantly different than tropical and temperate foredunes. In the case of the foredune of the arid Canary Islands' dune systems, Traganum moquinii is the predominant plant species, forms nebkhas and nebkhas fields, and acts as a structuring element in the dune field. In this work, the eco-anthropogenic evolution of the foredune surface, and the morphology and distribution of Traganum moquinii species in the Maspalomas dunefield (Gran Canaria, Canary Islands) are analysed, to understand the role that this plant species plays on the foredune's geomorphology and on the biogeomorphological processes altered by human actions. Eight variables were measured in 10 plots at five different times, from the 1960's to the present, through historical aerial photographs and orthophotos, integrated in a GIS. Significant decadal changes in the number and distribution/morphology of Traganum moquinii plants and also in the morphology of the foredune are observed, although not in a spatially homogeneous manner, as three different foredune behaviors are observed. The number of nebkhas/number of T. moquinii plants, has decreased between 1961 and 2012. The largest changes occurred in the north and south of the study area, and the lowest numbers of nebkhas occur where tourist activities and services are intense. In addition, the distance between Traganum moquinii individuals and variables measured in the foredune front (e.g. the diameter of the individuals) have significant relationships. Also, the greater the distance between plant individuals in the foredune front, the greater is the distance of T. moquinii individual plants in the rest of the plot. The alongshore variations in foredune development are due to natural processes (e.g. natural decline or growth of plants), and human impacts (e.g. carpark and kiosk construction, heavy tourist use). This research could be useful for the management of foredunes in arid regions.

Controls on dune scarping

The controls that affect the degree of spatio-temporal change to foredunes following scarping are reviewed herein. As sea-levels rises and climate changes, dune scarping will become more common. Thus, it is critical to understand what factors contribute to the magnitude of scarping, and what effect this has on dune systems to better manage coastal erosion into the future. Scarping occurs when foredunes are partially eroded by waves, generally during periods of high water level. The controls on the degree and magnitude of scarping examined include water level, foredune vegetation cover and species present, plant root mass, height and volume of the foredune, the original foredune morphology, surfzone–beach type, and compaction of sediment. Water-level height and duration of high water is the most significant control as it determines the elevation at which wave action can erode the dune and, therefore, the extent of scarping and dune volumetric loss. Higher plant density, greater rooting depth, high root mass, and greater compaction aid in reducing the degree of scaping. The presence of large woody debris and wrack may also influence the degree of scarping. The effects scarping has on the morphology of a foredune after the initial erosion event can range from small changes (e.g. minor, small scarps and slight slumping), to moderate changes such as the foredune translating landwards, to large change such as the transition of an entire dune system into a new transgressive dunefield phase. A new model summarising the key controls and their relationship/significance to the magnitude and extent of scarping is presented.

Geomorphologic characteristics and evolution of managed dunes on the South West Coast of France

The calibrated foredunes of the Aquitaine coast (SW France) constitute an example of secular extensive application of nature-based solution. Being one of the longest and largest dune systems in Europe, this iconic landscape offers considerable services to coastal societies. Since the mid-half of the 18th century, human work on sediment flows has resulted in the emergence of large sets of foredunes, currently constituting an almost 230 km-long managed barrier against inland sand invasion, coastline erosion, coastal flooding and also a major reserve of biodiversity. Last massive mechanic shaping of the foredunes following a so-called “ideal profile” date back to the 1970s–80s and aimed to limit erosion dynamics and sediment mobility. Since, they have been facing multiples disruptions over the years which have considerably modified their morphology, especially during the last decades. Calibrated foredunes are currently exhibiting impressive dimensions with a mean dune height of about 16.6 m (peaking at >30 m in some locations) and a dune width mean along the coast of 187 m. Today, 55.5% of them meet the “ideal profile” shape standards or surpass the in terms of dimensions whereas 21,5% of the calibrated foredunes are considered “narrowed” and need specific attention. This regional analysis, based on extensive airborne LiDAR datasets from 2011 to 2018, includes (i) a dune morphology classification based on several basic geomorphological indicators (dune width, height, crest position, back dune elevation) compared to a calibrated “idealised” shaped profile, (ii) a quantification of marine beach-dune and aeolian sediments flows (in m/year and m/m2/year) and forms on dunes (scarps, blowouts, depositional lobes), as an indicator of the recent dynamics affecting dune morphology and (iii) a study of management control of calibrated foredunes (4613 interventions) including actions taken after the outstanding winter of 2013–2014. As expected, intensive dune management are mainly focused where assets are directly threatened. The study highlights the importance and the efficiency of human management on dune evolutions (long term dune form stability, control of gullies and incipient frontal blowout after marine erosion, protection of human issues). However, today management actions (wind fence, branch cover, planting and reshaping) are not conditioned by foredune morphology or last decade's beach-dune dynamic (sediment availability, chronic coastline erosion). Considering long-term erosion projections and expected impact of climate change, the analysis shows the need of more global and extensive strategies in order to preserve the protection role of foredunes in the coming decades.

Elucidating Coastal Foredune Ecomorphodynamics in the U.S. Pacific Northwest via Bayesian Networks

AbstractAs sea level rise and possible changes in storminess threaten coastal communities and infrastructure, the capacity for foredunes to provide protection depends on their geomorphology, which is determined by interactions between physical beach processes and vegetation. Here we use descriptive Bayesian network analyses to examine how sediment supply, beach characteristics, and two species of beachgrass (Ammophila arenaria and Ammophila breviligulata) alter foredune morphology and patterns of sand accretion on U.S. Pacific Northwest foredunes. We show that sediment supply and beach type primarily determine foredune morphology. Beachgrass density also influences foredune shape, but its effects differ among species: increasing density of A. arenaria was associated with steeper sloping dunes, whereas increasing density of A. breviligulata was associated with wider, more shallow sloping dunes. An examination of the change in foredune morphology over a 2‐year period found sand accretion was most strongly influenced by species‐specific patterns of vegetation growth and beach type. Specifically, A. breviligulata exhibited more lateral growth, resulting in greater sand accretion at the seaward margin of the foredune. In contrast, A. arenaria exhibited little lateral growth, resulting in comparatively more sand accretion near the foredune crest. Consequently, growth form‐generated sand accretion patterns resulted in steep, narrow A. arenaria‐dominated foredunes and shallow‐sloping, wider A. breviligulata‐dominated foredunes. These results illustrate that vegetation density and patterns of growth influence foredune morphology and its changes over time.

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

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.

Species-Specific Functional Morphology of Four US Atlantic Coast Dune Grasses: Biogeographic Implications for Dune Shape and Coastal Protection

Coastal dunes arise from feedbacks between vegetation and sediment supply. Species-specific differences in plant functional morphology affect sand capture and dune shape. In this study, we build on research showing a relationship between dune grass species and dune geomorphology on the US central Atlantic Coast. This study seeks to determine the ways in which four co-occurring dune grass species (Ammophila breviligulata, Panicum amarum, Spartina patens, Uniola paniculata) differ in their functional morphology and sand accretion. We surveyed the biogeography, functional morphology, and associated change in sand elevation of the four dune grass species along a 320-kilometer distance across the Outer Banks. We found that A. breviligulata had dense and clumped shoots, which correlated with the greatest sand accretion. Coupled with fast lateral spread, it tends to build tall and wide foredunes. Uniola paniculata had fewer but taller shoots and was associated with ~42% lower sand accretion. Coupled with slow lateral spread, it tends to build steeper and narrower dunes. Panicum amarum had similar shoot densities and associated sand accretion to U. paniculata despite its shorter shoots, suggesting that shoot density is more important than morphology. Finally, we hypothesize, given the distributions of the grass species, that foredunes may be taller and wider and have better coastal protection properties in the north where A. breviligulata is dominant. If under a warming climate A. breviligulata experiences a range shift to the north, as appears to be occurring with U. paniculata, changes in grass dominance and foredune morphology could make for more vulnerable coastlines.

Patterns of early-colonising species on eroding to prograding coasts; implications for foredune plant communities on retreating coastlines

Shoreline erosion is predicted to increase as the result of climate change, yet the effects on foredune-building species and associated dune processes remain poorly understood. To predict the response of foredune plant communities to increased erosion we examined the abundance of six early colonising dune-building species across 71 beach-foredune sites in south-east Australia. The assumption being that those species better adapted to shoreline retreat will be more frequent and have increased abundance on erosional coasts than species lacking the capacity to withstand or re-establish following periods of storm-induced erosion. All species were frequently recorded regardless of the rate of shoreline progradation or erosion, which ranged 3.8 to −2.2 m year−1. Species presence was not related to erosion rates; however, there was a significant association between the rate of shoreline change and abundance for some of the studied species. Variation in traits related to tolerance to salinity and burial and the ability to establish following erosion appear to correspond to the observed patterns of species abundance. While this study examined only six species, it appears that species that are restricted to zones closer to the spring-tide level, that have a persistent rather than opportunistic growth-history or that are limited in their ability to recolonise following erosion, are more likely to be negatively impacted by increased rates of coastal erosion. Given the association between vegetation and foredune morphology these findings have important implications for the management of sandy coasts.

The application of LiDAR to investigate foredune morphology and vegetation

LiDAR (Light Detection and Ranging) has been used to investigate coastal landform morphology, evolution, and change for almost a decade. Repeated airborne LiDAR surveys can provide the scientific community with significant observations of how shorelines have evolved, which may then enable forecasts of future patterns of change. However, there have been few studies that have considered the application of this new technology to the specific study of foredune morphology and vegetation. The accuracy and appropriateness of airborne LiDAR needs to be assessed, particularly where the density of vegetation may obscure the underlying topography, prior to interpreting derived geomorphic features. This study: i) tests the vertical accuracy of airborne LiDAR in 37 foredune systems along the coast of south-eastern Australia, and ii) demonstrates that it can be used to describe foredune morphology and vegetation in considerable detail. There was a strong correlation between the remotely-sensed LiDAR-derived elevation and field topographic and vegetation surveys (R2=0.96). A protocol for obtaining foredune geomorphic and botanical parameters is described. It enables widespread biogeomorphic characterisation along coasts for which LiDAR data is available, which can benefit both coastal managers and researchers alike.

Numerical modeling of the morphodynamic response of a low-lying barrier island beach and foredune system inundated during Hurricane Ike using XBeach and CSHORE

Follet's Island (FI) is a sediment-starved barrier island located on the Upper Texas Coast; a stretch of coastline along the Gulf of Mexico that experiences on average four hurricanes and four tropical storms per decade. During Hurricane Ike, water levels and wave heights at FI exceeded the 100-year and 40-year return values, respectively, leading to significant overtopping and morphology changes of this low-lying barrier island. The physical processes governing the real-time morphodynamic response of the beach and dune system during 96h of hurricane impact were modeled using XBeach (2D) and CSHORE (1D). Hydrodynamic boundary conditions were obtained from ADCIRC/SWAN model runs validated with measured buoy and wave gauge data while LiDAR surveys provided pre- and post-storm measured topography.XBeach displayed a decent model skill of 0.34 and provided numerical outputs of the entire 2D domain such as topography, suspended sediment load and bed load which was very useful in visualizing erosion and deposition patterns. CSHORE also displayed a decent model skill of 0.33 and was able to accurately predict the post-storm beach slope and shoreline, but was less effective at simulating the foredune morphology. Modeling results show that the complete morphodynamic response of FI to Hurricane Ike was governed by a sequence of impact regimes, including swash, collision, overwash, inundation, and storm surge ebb.

Jet flow over foredunes

AbstractJet 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.

Evolution of foredune texture following dynamic restoration, Doughboy Bay, Stewart Island, New Zealand

Abstract Growing concern regarding the geomorphic and associated biotic effects of dune management practises has led to an increase in the number of dune restoration projects globally. Most recent projects aim to enhance the efficiency of aeolian sediment dynamics and increase dune mobility by decreasing vegetation cover, but we lack objective measures to evaluate such projects. Here we demonstrate the use of landscape metrics to quantify the evolution of foredune texture following the removal of vegetation. A long-term program of marram grass ( Ammophila arenaria ) eradication in southern New Zealand (Doughboy Bay, Stewart Island) is examined. Four metrics: bare sand area, patch adjacency, complexity, and the range of proximity, are used to classify a series of foredune textures beginning with the pre-restoration state through the phases of marram removal, to the current state. Foredune texture at Doughboy Bay has evolved from a semi-stable to an active state as the consequence of restoration. Two metrics, bare sand and adjacency, appear to be particularly good measures of change following marram removal. Patterns and rates of change for these metrics are consistent with ground observations of increased ‘naturalness’ (native plant communities, sand mobility) over the same period. The set of landscape metrics derived for Doughboy Bay were compared to similar sets measured for a nearby foredune system where marram invasion has not occurred, and where conditions presumably represent equilibrium foredune texture. Since the removal of marram at Doughboy Bay and the consequent remobilization of the sand surface, the foredune texture has increased in similarity to that of the reference site, indicating a favourable shift in plant cover as a result of the restoration program. We conclude that landscape metrics can be used to track changes in foredune morphology following restoration. Second, the planning, management, and monitoring of coastal dune restoration programs will benefit by the routine use of reference sites to evaluate the appropriateness and success of restoration actions.

Preservation potential of foredunes in the stratigraphic record

Barboza, E.G., Rosa, M.L.C.C., Dillenburg, S.R and Tomazelli, L.J., 2013. Preservation potential of foredunes in the stratigraphic record. In: Conley, D.C., Masselink, G., Russell, P.E. and O'Hare, T.J. (eds.)Foredunes occur worldwide on shorelines, especially those which are wave-dominated and with moderate to high sediment supply. Pelotas Basin, located in southern Brazil, has a significant record of foredunes which are present on modern beaches as well as in the geological record. Many locations along the Holocene coastal plain of Pelotas Basin were investigated with a Ground Penetrating Radar (GPR). Foredunes are present in almost all the investigated areas. However some peculiarities were found along these areas. At some places it is still possible to see foredune morphology in the field. At these places GPR profiles show a convex ridge morphology preserved and its separation by concave, sometimes filled swales. At other sites foredunes are covered by transgressive dunes, the morphology is not preserved and erosive surfaces are found on the top of the unit. Along the progradational sectors, dip profiles show that even where foredunes have their morphology preserved, some erosive scarps are found at the seaward face. These patterns indicate that high frequency events lead to the erosion of foredunes. The combination of sedimentary budget with climatic events sets foredune preservation and its pattern. Where sedimentary budget is high, progradation occurs faster and foredunes are preserved. However, where the sedimentary budget is not very expressive, the progradation is slower and part of the foredune is destroyed forming transgressive dunes or sand sheets.