Incipient Dunes Research Articles

Topographic–Vegetation Interactions on an Incipient Foredune Field Post-Tropical Storm

Sand dunes protect the most important economic and ecologically critical landscapes from coastal hazards (storms and high-tide flooding). The characteristics of the dune affect their protective ability. This paper qualitatively and quantitatively assesses the relationships between pre- and post-storm conditions for vegetation and the morphology of an incipient dune system along the South Carolina coast. Field-based dune vegetation and morphology measurements were obtained before and after tropical storm Dorian (2019). Vegetation is assessed with respect to distribution and functional type, and subgroups are introduced to categorize land cover transitions. At the quadrat scale (0.2 m2) following the storm, there was a shift from stabilizer to builder, a decrease of sand (2%), and the vegetation remained consistent at around 61% of the land cover. Transect-level analysis (0.2 m × 1.0 m) revealed distinct variability concerning post-storm morphology change in the extreme study site extents. Dorian resulted in approximately 10% volumetric loss over the entire study site (101 m2). This study demonstrated changes to a dune system following a tropical storm with wind as the dominant forcing factor. This study revealed that vegetation presence is not broadly correlated with reduced levels of post-storm erosion.

A multi-scale assessment of shoreline changes at an undeveloped beach in southern Brazil

This research aims to investigate shoreline variability at an undeveloped beach in southern Brazil on interannual and millennial scales. The long-term coastal evolution was investigated by GPR, whereas the interannual scale shoreline changes were analyzed by the Digital Shoreline Analysis System (DSAS). Simultaneously, a supervised Maximum Likelihood image classification was applied to the dune systems to differentiate vegetation from sand. The results show that the coastline in the Praia das Cabras region is retreating at different scales. The stratigraphic record in GPR shows that the coast has a retrogradational stacking pattern behavior in geological time. At the same time, the results obtained from the digital shoreline analysis revealed that the coast has suffered short-term erosion in the analyzed period, and this is attributed to natural causes. Another point is the higher values of erosion in the extreme parts of the study area, which are related to the presence of washouts. There is also a differentiation in the stage of the dunes and vegetation between the northern and southern parts of the stretch. The northern area is more densely vegetated and has a continuous foredune ridge with incipient dunes forming a ramp, whereas in the southern part, the vegetation is more dispersed, with interrupted dunes forming nebkhas. Between 2019 and 2023 there was a recovery of the dune field, by filling in the blowouts and minimizing the indentations, forming a more homogeneous foredune line.

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.

Dune toe dynamics along the urbanised macro‐tidal coast of Belgium

AbstractThe dynamics of the dune toe along the urbanised 65 km macro‐tidal coast of Belgium has been examined based on (bi‐)annual cross‐shore profiles derived from airborne LiDAR surveys conducted between 2000 and 2019. Results indicate that the average dune toe level is located at +5.9 m Tweede Algemene Waterpassing (TAW, Belgian Ordnance Datum), which is 1 m lower than the conventional dune toe level. However, this level is not static but rather increasing over time with an average rate of 2.3 cm/year, making it comparable with coastal areas along western Europe. Both landward retreat and seaward progradation of the dune toes are observed, with rates up to 2 m/year. The analysis revealed that dune growth is primarily facilitated by the development of incipient or embryonic dunes, new foredunes and modifications to the stoss slope of the original dune profile. Half of the sea‐fronting dunes were observed to be developed by brushwood fences, which had a positive effect on dune growth. At some locations, incipient dune development and shoreline progradation were observed seaward of old foredunes. Other dune regions were characterised by natural dune blowouts and management activities for recreational purposes. Dune toe reinforcements were implemented in the west to stabilise the dune toe and prevent erosion by waves. However, it was noted that if the adjacent beach accreted because of natural growth or periodic nourishment, incipient dunes could form in front of the reinforcement.

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.

Late Weichselian and Holocene climatic and local controls on aeolian deposition inferred from decomposing grain size-shape distributions

Aeolian deposits form rich archives of climatic and environmental changes, which have not been fully explored. In this study, results from end-member modelling of grain size-shape distributions were combined with palynological records to reconstruct sedimentary environments and transport mechanisms, and to distinguish climatically-caused from local or system-intrinsic variabilities. We compare results from Weichselian aeolian type locality Lutterzand in the Eastern Netherlands to those of a aeolian site in the Central Netherlands. Four grain size-shape end-members were determined. These represent coarse fluvial or aeolian bedload, fine aeolian bedload, aeolian modified saltation and aeolian suspension (loess) transport mechanisms. We assume that synchronous changes in end-member composition at the two sites are effects of climate change; non-synchronous changes are the result of local or system-intrinsic variability, which are attributed to the influence of the paleo-topographic position on local humidity of the sediment bed. Our results show that during the final stage of the Late Pleniglacial, a change from polar desert to wet sand-sheet paleo-environment occurred, which implies increased humidity and decreased wind speed that may be linked to a northward shift of the polar front preceding warming during the Bølling time interval. The deposition of loess during the Bølling implies further climate amelioration and a concomitant increase in vegetation density. The landscape re-opens during the Older Dryas. The high degree of sediment sorting and near absence of modified saltation and suspension transport mechanisms/end members during this phase are indicative of an undulating aeolian topography and the formation of incipient dunes, for which sparse vegetation forms growth nuclei. A high loess content reveals that the Betula phase of the Allerød was humid. The subsequent Allerød Pinus phase was drier, potentially due to Pinus-induced drought and wildfires. The deposits of the Younger Dryas reflect a paleo-environment similar to that of the Older Dryas. Land use-induced sand-drifting in the Middle Ages is differentiated from the Late-Weichselian aeolian depositional phases by a higher proportion of suspension and modified saltation end members, reflecting wetter climate and denser vegetation during the Holocene.

The Role of Vegetation in Incipient Dune and Foredune Development and Morphology: A Review

McGuirk, M.T.; Kennedy, D.M., and Konlechner, T., 2022. The role of vegetation in incipient dune and foredune development and morphology: A review. Journal of Coastal Research, 38(2), 414–428. Coconut Creek (Florida), ISSN 0749-0208. Vegetation is the principal boundary condition on the coast for foredune development, both by trapping sand and protecting it from erosion. Plants that colonise beaches and dunes grow in a variety of forms and have different life cycles. Plant characteristics (e.g., leaf length, width) are important in the initiation of a dune, and their interaction with sand being transported inland from the beach is highly variable. This review aimed to identify gaps in knowledge regarding the influence of specific plant species on dune morphological processes. Many studies that relate the influence of vegetation on dune morphology are of a descriptive and qualitative nature. These studies record elements of plant architecture and species presence on the dune. Quantitative studies have primarily focused on exotic species growing on the U.S. Pacific Northwest coast, whilst numerical modelling of dune growth incorporating vegetation has parameterised the plant drag coefficients. In these highly numeric investigations, the parameters used are derived from desert vegetation or artificial proxies such as rigid cylinders. Direct measurements derived from dune vegetation are often lacking. Biogeomorphologists and ecological engineers have placed coastal vegetation into a variety of categories related to their growth form and response to abiotic factors. A consensus on the categories for plant functional and engineering groups used for research and planning purposes is necessary, for example, sand stabilisers and sand accumulators. There is an urgent requirement for quantitative data on the growth and sand-capture ability of coastal plants. This is necessary because dune responses to climate change will be a function of their floral communities. In many instances, these floral communities are undergoing rapid change due to exotic invasions, which means that the resilience of the dunes may change faster than climate-driven change.

New Beach Landscapes to Promote Social Distancing and Coastal Conservation during and after the COVID-19 Pandemic

The Coronavirus disease 2019 (COVID-19) is a pandemic that has altered practically all human activities worldwide. Since the pandemic started at the beginning of 2020, infections have fluctuated drastically over time. It is difficult to predict how this situation will evolve in the coming months/years or when a return to some semblance of ’normal’ activity might occur. Because of global lock-up and distancing measures, the beaches, otherwise filled with tourists, first emptied and then had a reduced density of visitors owing to a wide variety of social-distancing measures. Therefore, new safety protocols need to include a wide range of aspects, such as epidemiological conditions, socioeconomic realities, and ecological contexts in which the pandemic occurs. Here, we propose new nature-based landscapes for sandy beaches to help maintain the social distancing of beach visitors while beaches and dunes are restored. When sufficient sediment is available, the maintenance and restoration of healthy beaches with incipient dunes and vegetation will help reduce contagion, promote human health, and recover natural ecosystems.

Direct validation of dune instability theory

Modern dune fields are valuable sources of information for the large-scale analysis of terrestrial and planetary environments and atmospheres, but their study relies on understanding the small-scale dynamics that constantly generate new dunes and reshape older ones. Here, we designed a landscape-scale experiment at the edge of the Gobi desert, China, to quantify the development of incipient dunes under the natural action of winds. High-resolution topographic data documenting 42 mo of bedform dynamics are examined to provide a spectral analysis of dune pattern formation. We identified two successive phases in the process of dune growth, from the initial flat sand bed to a meter-high periodic pattern. We focus on the initial phase, when the linear regime of dune instability applies, and measure the growth rate of dunes of different wavelengths. We identify the existence of a maximum growth rate, which readily explains the mechanism by which dunes select their size, leading to the prevalence of a 15-m wavelength pattern. We quantitatively compare our experimental results with the prediction of the dune instability theory using transport and flow parameters independently measured in the field. The remarkable agreement between theory and observations demonstrates that the linear regime of dune growth is permanently expressed on low-amplitude bed topography, before larger regular patterns and slip faces eventually emerge. Our experiment underpins existing theoretical models for the early development of eolian dunes, which can now be used to provide reliable insights into atmospheric and surface processes on Earth and other planetary bodies.

Different tolerance to salinity of two populations of Oenothera drummondii with contrasted biogeographical origin

Oenothera drummondii is a native species from the coastal dunes of the Gulf of Mexico that has nowadays extended to coastal areas in temperate zones all over the world, its invasion becoming a significant problem locally.The species grows on back beach and incipient dunes, where it can suffer flooding by seawater, and sea spray. We were interested in knowing how salinity affects this species and if invasive populations present morphological or functional traits that would provide greater tolerance to salinity than native ones. To this end, we conducted a greenhouse experiment where plants from one native and from one invading population were irrigated with five salinity treatments. We measured functional traits on photosynthetic, photochemical efficiency, water content, flowering, Na+ content, pigment content, and biomass.Although O. drummondii showed high resistance to salinity, the highest levels recorded high mortality, especially in the invasive population. Plants exhibited differences not only in response to time under salinity conditions, but also according to their biogeographic origin, the native population being more resistant to long exposure and high salt concentration than the invasive one. Native and invasive populations showed different response to salt stress in photosynthesis and transpiration rates, stomatal conductance, water use efficiency, carboxylation efficiency, electron transport rate, electron transport efficiency, energy used in photochemistry, among others. The increasing salinity levels resulted in a progressive reduction of photosynthesis rate due to both stomatal and biochemical limitations, and also in a reduction of biomass and number and size of flowers, compromising the reproductive capacity.

Quantifying Changes in Surface Elevation in Conjunction with Growth Characteristics of Incipient and Foredune Vegetation

McGuirk, M.T.; Kennedy, D.M.; Konlechner, T., and Chiaradia, A., 2021. Quantifying changes in surface elevation in conjunction with growth characteristics of incipient and foredune vegetation. Journal of Coastal Research, 37(1), 216-224. Coconut Creek (Florida), ISSN 0749-0208. Vegetation is critical for the initiation and growth of incipient dunes and foredunes by providing structure to entrap and store sand. Vegetation characteristics (leaf length, width, height, and quantity) directly influence the rate and volume of sand deposition and therefore the final dune morphology. This paper describes a low-cost and highly portable method to quantify changes in sand surface elevation in relation to plant growth character. A sediment elevation platform was constructed from steel and Perspex, from which surface elevation and plant character can be measured with a movable wooden dowel. This was used in conjunction with a point intercept pin frame to quantify leaf height and number of touches, from which leaf density and frequency were calculated. The system is collapsible, lightweight, and costs AUD 360. It may be operated by a single person. It was tested in a pilot study conducted at Phillip Island, Australia. Plant attributes of two dominant coastal grasses (Spinifex sericeus and Thinopyrum junceiforme) were quantified in December 2018 and January 2019, and sand elevation changes were quantified in January and February 2019. Data collected during the measurement period displayed the influence of plant growth on sand accumulation on a monthly scale. Measurements showed an increase in sand surface elevation from January to February. The average vertical sand accretion for the quadrant with T. junceiforme in January was 29 mm and in February was 89 mm, whereas S. sericeus had an average vertical sand accretion for January of 95 mm and for February of 162 mm. The number of leaves of S. sericeus increased from December (48) to January (169). This new method enables tracking of changes in sand morphology, along with the specific plant growth characteristics. This knowledge may enable the planning of specific dune morphologies using specific plant species and assist in dune recovery after erosion.

Spatial and Temporal Development of Incipient Dunes

AbstractIn zones of loose sand, wind‐blown sand dunes emerge due the linear instability of a flat sedimentary bed. This instability has been studied in experiments and numerical models but rarely in the field, due to the large time and length scales involved. We examine dune formation at the upwind margin of the White Sands Dune Field in New Mexico (USA), using 4 years of lidar topographic data to follow the spatial and temporal development of incipient dunes. Data quantify dune wavelength, growth rate, and propagation velocity and also the characteristic length scale associated with the growth process. We show that all these measurements are in quantitative agreement with predictions from linear stability analysis. This validation makes it possible to use the theory to reliably interpret dune‐pattern characteristics and provide quantitative constraints on associated wind regimes and sediment properties, where direct local measurements are not available or feasible.

Investigating the Impact of Hurricane Harvey and Driving on Beach-Dune Morphology

Beach and dune morphology are spatially and temporally variable, changing over a broad range of scales simultaneously. Strong wind, waves, and storm surge from Hurricane Harvey substantially eroded the beach and dunes along the Texas coast, causing significant scarps and berms. This paper presents information about how anthropogenic activity, such as driving on the beach, affected the response and recover of a barrier island with regard to the post-storm resiliency along the Texas-Gulf of Mexico coast by comparing two adjacent 7 km stretches of coast: a driving section and a limited-access section. A collection of field photos, aerial imagery, and a September 2016 LiDAR-derived digital elevation model (DEM) dataset provide information on pre-storm morphology, while field photos, taken only 3 days after Hurricane Harvey made landfall, and a structure-from-motion (SfM)-derived DEM and imagery provide qualitative and quantitative information about the post-storm morphology. While beach and dune erosion in the non-driving section was restricted entirely to the beach and incipient dune system, the driving section exhibited complex patterns of erosion and deposition along the beach and the entire foredune profile was altered. Despite the hurricane making landfall north of the study site and closer to the non-driving section, beach-dune erosion and scarping was greatest in the southern section which is accessible to public vehicles. Results demonstrate that human activity affects the response and recovery of the beach-dune system along the Gulf side of the island by decreasing alongshore variability in erosion-deposition and limiting vegetative and geomorphic recovery.

Terrestrial LiDAR monitoring of coastal foredune evolution in managed and unmanaged systems

AbstractCoastal dunes provide essential protection for infrastructure in developed regions, acting as the first line of defence against ocean‐side flooding. Quantifying dune erosion, growth and recovery from storms is critical from management, resiliency and engineering with nature perspectives. This study utilizes 22 months of high‐resolution terrestrial LiDAR (Riegl VZ‐2000) observations to investigate the impact of management, anthropogenic modifications and four named storms on dune morphological evolution along ~100 m of an open‐coast, recently nourished beach in Nags Head, NC. The influences of specific management strategies – such as fencing and plantings – were evaluated by comparing these to the morphologic response at an unmanaged control site at the USACE Field Research Facility (FRF) in Duck, NC (33 km to the north), which experienced similar environmental forcings. Various beach‐dune morphological parameters were extracted (e.g. backshore‐dune volume) and compared with aeolian and hydrodynamic forcing metrics between each survey interval.The results show that LiDAR is a useful tool for quantifying complex dune evolution over fine spatial and temporal scales. Under similar forcings, the managed dune grew 1.7 times faster than the unmanaged dune, due to a larger sediment supply and enhanced capture through fencing, plantings and walkovers. These factors at the managed site contributed to the welding of the incipient dune to the primary foredune over a short period of less than a year, which has been observed to take up to decades in natural systems. Storm events caused alongshore variable dune erosion primarily to the incipient dune, yet also caused significant accretion, particularly along the crest at the managed site, resulting in net dune growth. Traditional empirical Bagnold equations correlated with observed trends of backshore‐dune growth but overpredicted magnitudes. This is likely because these formulations do not encompass supply‐limiting factors and erosional processes. © 2019 John Wiley & Sons, Ltd.

Set of indices to assess dune development and dune restoration potential in beach-dune systems on Mediterranean developed coasts

The purpose of this paper is to contribute with a tool to guide decision makers with some level of understanding of coastal dynamics as to the most appropriate management measures to adopt. A set of indices for assessing beach-dune systems and their potential for dune restoration are presented. The systems analysed are described using variables related to physical and anthropic factors, and the sites are classified according to the intervention actions required. Fifty beach-dune systems representing the range of types of beaches, the degree of urbanisation, and the dune morphologies found on the Catalan coastline (NE Iberian Peninsula) are sampled. The results show that beaches with the most developed dunes usually have high scores for management and low scores for urbanisation, while the less developed dunes are found on beaches with very low scores for management. Regarding the potential for dune restoration, the beaches are classified into four groups according to the management measures recommended: dune conservation, dune restoration, dune recovery, and renaturalisation of beaches where only incipient dunes can be developed.

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.

Wind flow and sedimentation in artificial vegetation: Field and wind tunnel experiments

The flow dynamics within and immediately above an artificial plastic vegetation canopy are measured in the field and wind tunnel. Artificial plants created from wooden dowels and cable (zip) ties were arranged in a variety of arrays on pegboards where plant cover (or lateral cover) could be accurately controlled. Plant covers examined ranged from ~12% to 60%. Wind velocity profiles and the bedforms (incipient dunes) that developed within and beyond the vegetation in a few hours were measured. The results indicate that flow deceleration and drag increases within the canopy as plant density increases. In general, there is a marked reduction and inflection in velocity at the canopy top, and a second major inflection in the velocity profiles occurs immediately below the base of the four arrays equal or >23% density. Tall vegetation allows flow to sweep under the canopy and local high speed maxima flows may develop leading to minimal sedimentation in those canopies, but deposition downwind beyond the canopies. Short vegetation, where the leaves fill the canopy close to the ground, display significantly greater drag and rapid rates of sand deposition. Flow velocities above the canopy increase as plant cover or density increases due to flow compression and acceleration. Bedform development is strongly correlated with plant cover, density or lateral cover and short plants such that shorter length, higher bedforms develop in higher density and/or shorter plants. The relationship between plant cover, density or lateral cover and within canopy velocity is non-linear, and a new tentative flow regime is proposed, canopy flow, which may occur between wake interference flow and skimming flow. This study further confirms that plant density plays a defining role in determining bedform and dune morphology. The results also apply to flow in semi-arid grasslands.

Accommodation space indicates dune development potential along an urbanized and frequently nourished coastline

Abstract. With densely populated areas well below mean sea level, the Netherlands relies heavily on its dunes to ensure coastal safety. About half of the sandy coastline, however, is subject to structural marine erosion and requires frequent sand nourishment as a counteractive measure. A key component of present-day coastal safety policy is creating favorable conditions for natural dune development. These conditions essentially involve (1) a steady supply of wind-blown sand towards (2) a wide accommodation space where sand can accumulate and dunes are sheltered from frequent storm surge impacts. This paper examines to what extent an experimental mega-scale beach nourishment (termed Zandmotor in Dutch) has contributed to creating accommodation space favorable for dune development. Using publicly available airborne lidar data and Sentinel-2 satellite imagery, favorable accommodation space is identified by comparing recent changes in coastal morphology against dune vegetation-cover dynamics. With a focus on European marram grass (Ammophila arenaria) as the most prominent dune-building species, this paper demonstrates that the Zandmotor supports an especially high potential for incipient (embryo) dunes to develop as most of its favorable accommodation space is located on the beach. However, considering the conditions required for successful marram grass establishment as well as persistent anthropogenic disturbances arising from recreation and nature management practices, it is not likely that dune development along this urbanized coastline reaches its full potential.

Parabolic dune development modes according to shape at the southern fringes of the Hobq Desert, Inner Mongolia, China

Since the 1970s, parabolic dunes at the southern fringe of the Hobq Desert, Inner Mongolia, China have exhibited many different shapes (V-shaped, U-shaped, and palmate) each with a unique mode of development. In the study area, parabolic dunes are mainly distributed in Regions A, B, and C with an intermittent river running from the south to the north. We used high-resolution remote-sensing images from 1970 to 2014 and RTK-GPS measurements to study the development modes of different dune shapes; the modes are characterized by the relationship between the intermittent river and dunes, formation of the incipient dune patterns, the predominant source supply of dunes, and the primary formation of different shapes (V-shaped, U-shaped, and palmate). Most parabolic dunes in Region A are V-shaped and closer to the bank of the river. The original barchans in this region exhibit “disconnected arms” behavior. With the sand blown out of the riverbed through gullies, the nebkhas on the disconnected arms acquire the external sand source through the “fertile island effect”, thereby developing into triangular sand patches and further developing into V-shaped parabolic dunes. Most parabolic dunes in Regions B and C are palmate. The residual dunes cut by the re-channelization of river from transverse dune fields on the west bank are the main sand source of Region B. The parabolic dunes in Region C are the original barchans having then been transformed. The stoss slopes of V-shaped parabolic dunes along the riverbank are gradual and the dunes are flat in shape. The dune crest of V-shaped parabolic dune is the deposition area, which forms the “arc-shaped sand ridge”. Their two arms are non-parallel; the lateral airflow of the arms jointly transport sand to the middle part of dunes, resulting in a narrower triangle that gradually becomes V-shaped. Palmate parabolic dunes have a steeper stoss slope and height. The dune crest of the palmate parabolic dune is the erosion area, which forms a long and narrow trough between nebkhas by the “funnelling effect”. This process forces sand towards lee slopes, which transform from concave (original barchans) into convex, ultimately resulting in the formation of palmate parabolic dunes.

Aeolian sand transport and aeolian deposits on Venus: A review

Abstract We review the current state of knowledge about aeolian sand transport and aeolian bedforms on planet Venus. This knowledge is limited by lack of observational data. Among the four planetary bodies of the Solar System with sufficient atmospheres in contact with solid surfaces, Venus has the densest atmosphere; the conditions there are transitional between those for terrestrial subaerial and subaqueous transport. The dense atmosphere causes low saltation threshold and short characteristic saltation length, and short scale length of the incipient dunes. A few lines of evidence indicate that the typical wind speeds exceed the saltation threshold; therefore, sand transport would be pervasive, if sand capable of saltation is available. Sand production on Venus is probably much slower than on the Earth; the major terrestrial sand sinks are also absent, however, lithification of sand through sintering is expected to be effective under Venus’ conditions. Active transport is not detectable with the data available. Aeolian bedforms (transverse dunes) resolved in the currently available radar images occupy a tiny area on the planet; however, indirect observations suggest that small-scale unresolved aeolian bedforms are ubiquitous. Aeolian transport is probably limited by sand lithification causing shortage of saltation-capable material. Large impact events likely cause regional short-term spikes in aeolian transport by supplying a large amount of sand-size particles, as well as disintegration and activation of older indurated sand deposits. The data available are insufficient to understand whether the global aeolian sand transport occurs or not. More robust knowledge about aeolian transport on Venus is essential for future scientific exploration of the planet, in particular, for implementation and interpretation of geochemical studies of surface materials. High-resolution orbital radar imaging with local to regional coverage and desirable interferometric capabilities is the most effective way to obtain essential new knowledge about aeolian transport on Venus.