Foredune Height Research Articles

Assessing the Coastal Vulnerability by Combining Field Surveys and the Analytical Potential of CoastSat in a Highly Impacted Tourist Destination

Tropical sandy beaches provide essential ecosystem services and support many local economies. In recent times, however, there has been a massive infrastructure expansion in popular tourist destinations worldwide. To investigate the shoreline variability at a popular tourist destination in Mexico, we used the novel semi-automatic CoastSat program (1980 to 2020) and the climate dataset ERA5 (wave energy and direction). We also measured the beach cross-shore distance and the foredune height with topographic surveys. The results indicate that the section of real estate seafront infrastructure in the study site presents a considerable shoreline erosion due to the fragmentation between the foredune ridge and the beach berm, based on the in situ transects. Moreover, foredune corridors with cross-shore distances of up to 70 to 90 m and dune heights of 8 m, can be seen in the short unobstructed passages between buildings. In the south section we found the coastline in a much more stable condition because this area has not had coastal infrastructures, as of yet. For the most part, the remote sensing analysis indicates constant erosion since 1990 in the real estate section (mainly seafront hotels) and an overall accretion pattern at the unobstructed beach-dune locations. This study demonstrates the catastrophic consequences of beach fragmentation due to unplanned real estate developments, by combining in situ surveys and a freely available big-data approach (CoastSat).

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.

Dynamic restoration and the impact of native versus invasive vegetation on coastal foredune morphodynamics, Lanphere Dunes, California, USA

AbstractThe Lanphere Dunes, part of the Humboldt Bay National Wildlife Refuge, has been the focus of foredune restoration efforts since the 1980s. Efforts have centred around removal of an invasive European beach grass species, Ammophila arenaria, introduced in the early 1900s to stabilize the dunes to protect landward communities from coastal flooding and storm surges. Despite effectively stabilizing the foredune, A. arenaria forms monotypic vegetation stands, with highly dense roots, rhizomes, and above‐ground biomass that can lead to pronounced scarping of the seaward slope, alongshore steering of wind and sediment, a lack of landward transfer of sand, and a steeper, more peaked profile.Effective foredune restoration must consider the coupled interactions between dominant plant type and the geomorphic processes that influence dune form. A 5 ha reach of recently restored foredune was monitored biannually with terrestrial laser scanner and uncrewed aerial systems platforms between 2015 and 2021 to characterize the impacts of dynamic restoration on foredune form and resiliency. This reach included two control plots: (1) native, non‐restored and (2) invasive, and three restored plots revegetated with native species: (3) a native grass (Elymus mollis), (4) a low‐lying herb and subshrub assemblage, and (5) a mixture of the native grass, herbs, and subshrubs.After five growing seasons, restored plots exhibited distinct geomorphic and sediment budget differences. Natively vegetated plots recovered from extensive scarping 2 years faster than the invasive plot. Restored plots saw foredune height (0.5–0.7 m) and width increase, landward extension (1 m) while maintaining a similar seaward position, and positive lee‐slope sediment budgets that exceeded both control plots (up to 0.015 m3 m−2 month−1). These results suggest that the native vegetation plots allowed increased landward sand transport across the foredune, and increased the capacity of the foredune to recover more quickly following dune scarping.

Foredune height variations along the western coast of Taiwan Strait

AbstractKnowledge of the morphological characteristics of coastal foredunes, particularly crest height, is of crucial importance in evaluating coastal vulnerability to marine disasters. However, the factors driving variation in foredune height and the corresponding mechanisms remain poorly understood, especially for regional, large‐scale landscapes. In this contribution, an extensive foredune–beach topographic survey and comprehensive data collection, including regional wind regime, wave and tide climate, were conducted along the ~400 km‐long western coast of Taiwan Strait. The results show that the factor with the most significant effect on the spatial variation in foredune height is wave power, followed by aeolian drift potential (shore‐normal component), while beach width and grain size appear to have only marginal impacts for our study sites. Under a relatively high‐energy wave climate, significant volumes of sandy sediments can be delivered to the beach–dune system, and the beach state tends to be more dissipative, thus contributing to a higher/larger foredune. In particular, the in‐phase synchronization of sediment supply (contributed by wave processes) and transport potential (controlled by wind processes) can lead to the greatest potential for foredune growth. Finally, the source (river) to sink (coastal foredune) dispersal of sediments along this ~400 km‐long strait coastal regime is summarized.

The relationships between environmental conditions and parallel ecosystems on the coastal dunes of the Mexican Caribbean

Coastal dunes are very important, for both their ecosystem services and their ecological importance. A quantification of the area occupied by dunes was made for all of the Mexican Caribbean coast, and a qualification was assigned, according to the type of dune, its height and condition. 4981 ha of coastal dunes were identified on the coast, with heights of 1 to more than 10 m above mean sea level. Offshore wave climate was evaluated, showing relatively constant characteristics all along the coast. Aeolian drift potential was calculated and was found to be unrelated to the height of the dunes. The empirical relationship between coastal ecosystems (coral reefs and sea pastures) and the characteristic of the dunes are promising. The interconnectivity of ecosystems adjacent to coastal dunes, such as seagrass, coral reef and mangroves, affects the conditions of incident wave energy and/or the transport and availability of marine sediment. In the Mexican Caribbean, these ecosystems often exist parallel to one another, and their interrelationships could explain the variability of coastal dune height. It was observed that where the coast is protected by a coral barrier reef (less than 1000 m from the shore, with a crest at less than 2 m depth) and seagrasses, the foredunes are lower (under 2 m height) than those in more exposed areas, without coral reef protection (foredune height more than 10 m). A conceptual model was proposed to explain the size of the dunes in the study area, based on the characteristics of adjacent ecosystems (presence, distance from coastline, height of water column above corals and/or seagrasses) and the submerged morphology of the area.

Dune Dynamics Drive Discontinuous Barrier Retreat

AbstractBarrier islands and spits tend to migrate landward in response to sea‐level rise through the storm‐driven process of overwash, but overwash flux depends on the height of the frontal dunes. Here, we explore this fundamental linkage between dune dynamics and barrier migration using the new model Barrier3D. Our experiments demonstrate that discontinuous barrier retreat is a prevalent behavior that can arise directly from the bistability of foredune height, occurring most likely when the storm return period and characteristic time scale of dune growth are of similar magnitudes. Under conditions of greater storm intensity, discontinuous retreat becomes the dominant behavior of barriers that were previously stable. Alternatively, higher rates of sea‐level rise decrease the overall likelihood of discontinuous retreat in favor of continuous transgression. We find that internal dune dynamics, while previously neglected in exploratory barrier modeling, are an essential component of barrier evolution on time scales relevant to coastal management.

Surfzone-beach-dune interactions along a variable low wave energy dissipative beach

The different possible factors that influence or drive the observed volumetric and morphological variation in foredunes located along 16 km of a low wave energy, dissipative southern section of the 190 km long Younghusband Peninsula (South Australia) are examined. Grain size, wind energy, coastline orientation, and vegetation species presence/absence vary only slightly along this coast providing a unique site to study other drivers of coastal change. Results show that foredune height and volume progressively increase towards the north coincident with a gradual increase in wave energy. A significant correlation between foredune volume and wave energy is established, while no apparent relationship with other controlling factors was found, confirming the importance of wave energy in the dune building process on wave-dominated beaches. Results indicate that (1) all other factors being equal, wave energy can drive the morphological evolution of foredunes; (2) minor changes in wave energy can result in differences in the long-term beach and dune sediment budget; and, (3) the surfzone-beach-dune interactions model is applicable to coasts with small scale gradients in wave energy.

Differences in the Morphology of Restored and Invaded Foredunes on the North Spit of Humboldt Bay, California, U.S.A.

McDonald, K.L., 2020. Differences in the morphology of restored and invaded foredunes on the North Spit of Humboldt Bay, California, U.S.A. Journal of Coastal Research, 36(5), 973–980. Coconut Creek (Florida), ISSN 0749-0208.Invasive plants have altered wide-ranging coastal dune vegetation communities worldwide, and the effects of nonnative vegetation and invasive plant management on dune geomorphology are of interest to many coastal land managers, researchers, and coastal communities. This study compared the slopes, elevations, and profiles of invaded and restored foredunes on the North Spit of Humboldt Bay, California, using data from a high-resolution 2010 digital elevation model. Restoration of foredunes by removing invasive European beachgrass (Ammophila arenaria [L.] Link) took place over the last three decades in approximately half of the study area, and the restored areas now primarily support American dunegrass (Elymus mollis Trin.) and other native dune species. Despite recently voiced public concerns that restoration might be permanently lowering the foredune, restored and invaded areas showed no significant difference in height. However, invaded foredunes were significantly steeper with a flatter, plateau-like top, while restored areas were more gently sloping with rounded peaks. Foredune heights increased from the southern end of the study area to the north, regardless of restoration status, suggesting that other factors control foredune height.

The development and stability of beach-dune system on the wave-dominated coast: A case study of the Curonian Spit, Lithuania

Abstract The complexity of the foredune system is responsible for its morphological diversity and different development scenarios. On wave-dominated coasts, wave activity that permanently changes foredune and beach morphometry is the main limiting factor of foredune development. Based on a field data collected on the Curonian Spit in 2002–2017, the dynamic pattern of the cross-shore profile parameters was determined. There is a close correlation between the foredune height and horizontal distance between the shoreline and foredune top. In foredunes with differing morphology and sedimentology, the established ratio between these indices is rather stable and makes 0.14–0.21 (an average of 0.17). During accretion-dominated periods, with minimal storm surge impact on the foredune, the slope flattens and, under ideal conditions the foredune toe approaches the shoreline, and the stoss slope angle reaches 0.17 (i.e. ∼10°).

Do PFOS/PFOA levels in Italian women pose a risk to fetal growth?

The complexity of the foredune system is responsible for its morphological diversity and different development scenarios. On wave-dominated coasts, wave activity that permanently changes foredune and beach morphometry is the main limiting factor of foredune development. Based on a field data collected on the Curonian Spit in 2002–2017, the dynamic pattern of the cross-shore profile parameters was determined. There is a close correlation between the foredune height and horizontal distance between the shoreline and foredune top. In foredunes with differing morphology and sedimentology, the established ratio between these indices is rather stable and makes 0.14–0.21 (an average of 0.17). During accretion-dominated periods, with minimal storm surge impact on the foredune, the slope flattens and, under ideal conditions the foredune toe approaches the shoreline, and the stoss slope angle reaches 0.17 (i.e. ∼10°).

Coupling nearshore and aeolian processes: XBeach and duna process-based models

A new dune profile model, Duna, is developed and coupled with the existing XBeach model, in which some key improvements allow a much better behaviour of the intertidal beach and the inclusion of structural erosion or accretion through a longshore transport gradient. The model is shown to represent typical behaviour of a beach-dune system in Praia de Faro, Portugal and to be able to simulate processes on a decadal timescale. The model captures a balance between longshore gradients and cross-shore processes in the surf zone, competing effects of moderate conditions and storms in the intertidal area and between build-up by storm waves and aeolian transport on the berm. Vegetation behaviour is shown to play a key role in the development of the shape of the foredunes. The relation between progradation or recession rate and foredune height as often reported in literature is reproduced and explained.

The Role of Local Geomorphology Influencing Coastal Response to Sea Level Rise

ABSTRACT Olsen, W.S.; Figueiredo, S.A.; Albuquerque, M.G., and Calliari, L.J., 2018. The Role of Local Geomorphology Influencing Coastal Response to Sea Level Rise. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 311–315. Coconut Creek (Florida), ISSN 0749-0208. Considering projected climate change scenarios with accelerated rates of mean sea level rise, Cassino Beach in Southern Brazil, a wave dominated low-gradient coastal plain, is inherently at a very high risk in relation to its impacts. Additionally, the presence of small-scale creeks (washouts) can increase coastal susceptibility to erosion in two ways: (i) changing substrate morphology by lowering foredune height; (ii) displacing sediments causing a local deficit. In order to compare coastal response under sea level rise in the presence of a washout versus at well-established foredune, two independent ...

Sediment budget controls on foredune height: Comparing simulation model results with field data

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

Stability and bistability in a one‐dimensional model of coastal foredune height

AbstractOn sandy coastlines, foredunes provide protection from coastal storms, potentially sheltering low areas—including human habitat—from elevated water level and wave erosion. In this contribution we develop and explore a one‐dimensional model for coastal dune height based on an impulsive differential equation. In the model, coastal foredunes continuously grow in a logistic manner as the result of a biophysical feedback and they are destroyed by recurrent storm events that are discrete in time. Modeled dunes can be in one of two states: a high “resistant‐dune” state or a low “overwash‐flat” state. The number of stable states (equilibrium dune heights) depends on the value of two parameters, the nondimensional storm frequency (the ratio of storm frequency to the intrinsic growth rate of dunes) and nondimensional storm magnitude (the ratio of total water level during storms to the maximum theoretical dune height). Three regions of phase space exist (1) when nondimensional storm frequency is small, a single high resistant‐dune attracting state exists; (2) when both the nondimensional storm frequency and magnitude are large, there is a single overwash‐flat attracting state; (3) within a defined region of phase space model dunes exhibit bistable behavior—both the resistant‐dune and the low overwash‐flat states are stable. Comparisons to observational studies suggest that there is evidence for each state to exist independently, the coexistence of both states (i.e., segments of barrier islands consisting of overwash‐flats and segments of islands having large dunes that resist erosion by storms), as well as transitions between states.

Stability and bistability in a one-dimensional model of coastal foredune height

Stability and bistability in a one-dimensional model of coastal foredune height

Coastal foredune evolution: the relative influence of vegetation and sand supply in the US Pacific Northwest.

Biophysical feedbacks between vegetation and sediment are important for forming and modifying landscape features and their ecosystem services. These feedbacks are especially important where landscape features differ in their provision of ecosystem services. For example, the shape of coastal foredunes, a product of both physical and biological forces, determines their ability to protect communities from rising seas and changing patterns of storminess. Here we assessed how sand supply and changes in vegetation over interannual (3 year) and decadal (21 year) scales influenced foredune shape along 100 km of coastline in the US Pacific Northwest. Across 21 years, vegetation switched from one congeneric non-native beachgrass to another (Ammophila arenaria to A. breviligulata) while sand supply rates were positive. At interannual timescales, sand supply rates explained the majority of change in foredune height (64-69%) and width (56-80%). However, at decadal scales, change in vegetation explained the majority of the change in foredune width (62-68%), whereas sand supply rates explained most of the change in foredune height (88-90%). In areas with lower shoreline change rates (±2 m yr(-1)), the change in vegetation explained the majority of decadal changes in foredune width (56-57%) and height (59-76%). Foredune shape directly impacts coastal protection, thus our findings are pertinent to coastal management given pressures of development and climate change.

Vegetation controls on the maximum size of coastal dunes

Coastal dunes, in particular foredunes, support a resilient ecosystem and reduce coastal vulnerability to storms. In contrast to dry desert dunes, coastal dunes arise from interactions between biological and physical processes. Ecologists have traditionally addressed coastal ecosystems by assuming that they adapt to preexisting dune topography, whereas geomorphologists have studied the properties of foredunes primarily in connection to physical, not biological, factors. Here, we study foredune development using an ecomorphodynamic model that resolves the coevolution of topography and vegetation in response to both physical and ecological factors. We find that foredune growth is eventually limited by a negative feedback between wind flow and topography. As a consequence, steady-state foredunes are scale invariant, which allows us to derive scaling relations for maximum foredune height and formation time. These relations suggest that plant zonation (in particular for strand "dune-building" species) is the primary factor controlling the maximum size of foredunes and therefore the amount of sand stored in a coastal dune system. We also find that aeolian sand supply to the dunes determines the timescale of foredune formation. These results offer a potential explanation for the empirical relation between beach type and foredune size, in which large (small) foredunes are found on dissipative (reflective) beaches. Higher waves associated with dissipative beaches increase the disturbance of strand species, which shifts foredune formation landward and thus leads to larger foredunes. In this scenario, plants play a much more active role in modifying their habitat and altering coastal vulnerability than previously thought.

Vegetation dynamics on eroding to accreting beach‐foredune systems, Florida panhandle

ABSTRACTVegetation surveys were conducted on a variety of coastal foredunes in a largely natural region along the Gulf County region of the Florida panhandle. Species presence, absence and percentage cover were surveyed on 12 foredune profiles during different seasons. The vegetation data were analyzed using the Shannon–Wiener Diversity Index and Sørensen Index. Uniola sp. and Andropgon sp. were the dominant species on foredunes. Uniola sp. was found predominantly on the gulfward facing or stoss slopes, and Andropgon sp. was found to be dominant on the inland or lee slopes of foredunes. While they are present on all foredunes, their presence and percentage cover are dominant on rapidly prograding coasts. Prograding/accretional beaches had higher Sørensen Index values (i.e. higher similarities) than did the foredune‐vegetation profiles on eroding beaches. Diversity as indicated by the Shannon–Wiener analysis (H’) is greatest on the highest, and generally eroding dunes. Foredune diversity increased with foredune height, and the tallest foredunes were found on shorelines with relatively low erosion rates, where dunes were slowly translating landwards, cannibalizing older dunes, and moving into areas colonized by late successional species, such as Quercus sp. These observations of foredune species richness, diversity, profile similarities, and the use of ecological indices can provide excellent proxy evidence of shoreline dynamics, and in particular the degree of beach erosion and accretion, in the absence of historical erosion/accretion data. Copyright © 2013 John Wiley & Sons, Ltd.

Alongshore variation in foredune height in response to transport potential and sediment supply: South Padre Island, Texas

The height and extent of coastal dune development can exhibit considerable variability over short distances, leading to variable storm impact alongshore. The source of this variation is not well understood in general, and in many cases is not easily explained by models that ascribe dune height and development to regional variations in sediment availability and foreshore slope. In this paper, LiDAR data collected in 2000 and 2005 from South Padre Island, Texas are used to characterize the alongshore variation in dune morphology, and to identify how the variation is related to foreshore morphology and nearshore state. Results of cross-wavelet analysis suggest that foredune height exhibits a statistically significant coherence with the surf similarity parameter at length scales of ~ 1300 of 2300 m. The resulting variation in beach state alongshore, from intermediate to dissipative, is the consequence of wave refraction and focusing by transverse ridges on the inner shelf. Dune height reaches a local maximum approximately halfway between the more intermediate and dissipative sections of the coast, where the volume of sediment in the backshore and in the foreshore bars are also at a maximum. The greater elevation of the foreshore and backshore also provides a wider fetch and potential for aeolian transport during the storm surge that tends to accompany storm winds. It is argued that the variation in dune morphology is not strictly the result of transport limitations as suggested by the fetch model, but rather depends on the alongshore coincidence of transport potential with an available supply of sediment in the backshore and on the foreshore.

Relação da morfodinâmica praial e da vegetação da duna frontal da Praia do Santinho, SC, Brasil

A Praia do Santinho é uma praia de enseada localizada na costa leste da Ilha de Santa Catarina, Brasil. Neste trabalho, três perfis de praia foram dispostos nos setores sul, central e norte, cada um com extensão do reverso da duna frontal até a face da praia. A Praia do Santinho apresentou estágio morfodinâmico intermediário, com variabilidade entre os três setores, com o norte mostrando tendência ao estágio dissipativo. A altura de onda, largura e altura das dunas frontais aumentaram do setor sul para o norte. O tamanho de grão foi homogêneo com areia fina. Um total de 14 famílias e 28 espécies foi amostrado na análise de cobertura vegetal dos setores. O setor central teve maior riqueza de espécies, o maior índice de diversidade (H = 0,95), e também a maior cobertura de vegetação. Os setores norte e sul tiveram H = 0,80 e H = 0,73, respectivamente. O balanço de sedimentos afetou a cobertura vegetal total e a riqueza de espécies. A maior riqueza ocorreu no setor central, de estágio intermediário, enquanto a menor riqueza ocorreu no setor norte, em uma fase dissipativa. O setor sul mostra uma etapa intermediária, mas com menor riqueza de espécies, possivelmente associada a uma duna incipiente e uma grande dominância de uma espécie arbustiva.