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Unoccupied aerial systems can collect aerial imagery that can be used to develop structure-from-motion products with a temporal resolution well-suited to monitoring dynamic barrier island environments. However, topographic data created using photogrammetric techniques such as structure-from-motion represent the surface elevation including the vegetation canopy. Additional processing is required for estimating bare-earth elevation, which is critical for understanding the underlying geomorphology of these islands. In this study, we used a vegetation and elevation survey to produce bare-earth digital elevation models from structure-from-motion-derived elevation products for two sites on Dauphin Island, Alabama (USA). One site was exposed to high wave energy and included a mix of beach, dune, and barrier flat habitats that were dominated by supratidal/upland herbaceous vegetation. The second site was exposed to low wave energy and was dominated by intertidal marsh. Aerial imagery was collected in late fall of 2018 and spring of 2019. We tested several machine learning algorithms for predicting and removing elevation bias for vegetated areas using predictors that included spectral indices from unoccupied aerial systems-based multispectral imagery and landscape position information (e.g., relative topography and distance from shore). Models were developed for each site and season. We also explored how well the model from one season generalized to data from a different season for the same site. For developing initial digital surface models, we found that utilizing a minimum bin algorithm, as opposed to interpolation, led to lower elevation bias. For bias removal, Gaussian process regression performed the best and led to a root mean square error for the bare-earth digital elevation models of around 0.10 m for the high energy site and 0.15 m for the low energy site. Compared to the digital surface models, the root mean square error for the bare-earth digital elevation models was reduced by at least 29 percent for the high energy site and 69 percent for the low energy site. For all models, common predictors included surface elevation, vegetation greenness, and distance from the shoreline. The models produced comparable results when trained using data from a different season. The error estimates for all analyses were within published elevation standards for lidar data for vegetated areas. With calibration, this approach could be portable to other areas or data, such as aerial lidar (conventional or unoccupied), to provide an efficient and repeatable framework for monitoring geomorphology or provide baseline elevations for predicting changes to these environments under future conditions.

The coastal zone, a highly dynamic and complex environment, has important ecological and jurisdictional implications for governments and coastal managers. Based on the CORINE Land Cover classificat...

Barrier coasts, including barrier islands, beach-ridge plains, and associated landforms, can assume a broad spectrum of morphologies over multi-decadal scales that reflect conditions of sediment availability, accommodation, and relative sea-level rise. However, the quantitative thresholds of these controls on barrier-system behavior remain largely unexplored, even as modern sea-level rise and anthropogenic modification of sediment availability increasingly reshape the world's sandy coastlines. In this study, we conceptualize barrier coasts as sediment-partitioning frameworks, distributing sand delivered from the shoreface to the subaqueous and subaerial components of the coastal system. Using an idealized morphodynamic model, we explore thresholds of behavioral and morphologic change over decadal to centennial timescales, simulating barrier evolution within quasi-stratigraphic morphological cross sections. Our results indicate a wide diversity of barrier behaviors can be explained by the balance of fluxes delivered to the beach vs. the dune or backbarrier, including previously understudied forms of transgression that allow the subaerial system to continue accumulating sediment during landward migration. Most importantly, our results show that barrier state transitions between progradation, cross-shore amalgamation, aggradation, and transgression are controlled largely through balances within a narrow range of relative sea-level rise and sediment flux. This suggests that, in the face of rising sea levels, subtle changes in sediment fluxes could result in significant changes in barrier morphology. We also demonstrate that modeled barriers with reduced vertical sediment accommodation are highly sensitive to the magnitude and direction of shoreface fluxes. Therefore, natural barriers with limited sediment accommodation could allow for exploration of the future effects of sea-level rise and changing flux magnitudes over a period of years as opposed to the decades required for similar responses in sediment-rich barrier systems. Finally, because our model creates stratigraphy generated under different input parameters, we propose that it could be used in combination with stratigraphic data to hindcast the sensitivity of existing barriers and infer changes in prehistoric morphology, which we anticipate will provide a baseline to assess the reliability of forward modeling predictions.

Beach nourishment is a common strategy for erosion mitigation that also increases coastal resilience to storm impacts, provides habitat, and supports the economy. Regulations often require that placed sediment closely match the native grain size distribution and composition, however characteristics can vary based on the borrow site. Certain sediment properties will also influence beach slope and other critical beach functions. This study evaluates the 3-dimensional sediment properties and beach morphology of nourished and non-nourished barrier island beaches in northern Palm Beach County, Florida, USA. Surveyed beach profiles were compared with predicted slope based on median grain size. The inlet-adjacent beach managed with annual placement of beneficial use of dredged materials consisted of poorly sorted coarse sand and the steepest measured slope. Sediment was progressively finer and better sorted downdrift with decreasing foreshore slopes. Although sediment near the shoreline is typically the coarsest, clasts were finer than the mid-beach location suggesting that the sampling period coincided with beach recovery and onshore sediment transport of finer material. Sediment at the surface differed from sediment at depth, likely due to the frequent introduction of sediment from various borrow areas compared to the dominance of weathered coquina at depth. The non-carbonate, siliciclastic fraction was primary quartz with few other minerals. The estimated beach slope at the location with the coarsest sediment matched the measured slope. A lower beach slope was predicted for the other locations with finer grain sizes at the shoreline that was attributed to slightly steeper slopes associated with beach accretion. Therefore, complicated spatio-temporal morphodynamics of beaches should be considered when using median grain size from only one sampling event.

Oceans are warming, sea level is rising, storms are intensifying, sunny-day floods are increasing, and coastal development is increasingly threatened. There are two long-term response choices: Move back from the threatened shoreline or hold the shoreline in place. For major low-lying cities, extensive hard structures (seawalls) could be justified to stem flooding. In suburban communities such as those on many barrier islands and floodplains, purposeful, coordinated, and planned managed retreat can be the answer to the threat of inundation. This will include physically moving buildings and infrastructure to higher ground, or abandonment and destruction of threatened buildings, leaving behind space designated for public use as natural space. This may even become a solution in large cities. In this chapter, a variety of policy mechanisms for such moves of people and buildings are discussed from examples around the world.

Barrier islands and their backbarrier saltmarshes have a reciprocal relationship: aeolian and storm processes transport sediment from the beaches and dunes to create and build marshes along the landward fringe of the island. In turn, these marshes exert a stabilizing influence on the barrier by widening the barrier system and forming a platform onto which the island migrates, consequently slowing landward barrier migration and inhibiting storm breaching. Here, we present a novel framework for applying these natural interdependencies to managing coastal systems and enhancing barrier-island resilience. Further, we detail application of these principles through a case study of the design of a marsh creation project that showcases the interdisciplinary engagement of scientists, engineers, stakeholders, and policymakers. Specifically, we describe: (1) the ecologic, sedimentologic, stratigraphic, and morphologic data obtained from the southern 4 km of Cedar Island (Virginia, United States) and nearby backbarrier tidal channels, tidal flats, and flood-tidal deltas, and (2) the use of those data to develop an engineering and design plan for the construction of a high (46 ha) and low (42 ha) fringing marsh platform located behind the island, proximal to a former ephemeral inlet. Additionally, we chronicle the process used to narrow five initial alternative designs to the optimal final plan. This process involved balancing best-available existing science and models, considering design and financial constraints, identifying stakeholder preferences, and maximizing restoration benefits of habitat provision and shoreline protection. Construction of this marsh would: (1) provide additional habitat and ecosystem benefits, (2) slow the rapid migration (up to 15 m/yr at present) of the barrier island, and (3) hinder island breaching. Ultimately, this project – presently at the final design and permitting stage – may enhance the storm and sea-level rise resilience of the island, backbarrier marshes and lagoons, and the mainland town community; and provide an example of a novel science-based approach to coastal resilience that could be applied to other global barrier settings.

Shallow coastal ecosystems have high ecological value and contribute to flood protection. Their stability is, however, sensitive to the amount and rate of future sea level rise (SLR), their ability to trap sediment which allows them to grow with rising sea level, and human response to SLR. So far, studies have focused on assessing SLR impacts using resource-intensive tools. Here, we present an approach for a first-order assessment and easily accessible ‘barcode’ visualization to rapidly assess potential impacts of both SLR and adaptation strategies on coastal ecosystems in a spatially explicit way. Our approach relates habitat types (ecotopes) to water level, morphology and salinity, allowing users to determine shifts in spatial arrangements of ecological zones under different SLR rates and strategies. We illustrate this approach for a transect in the Dutch Wadden Sea. We find that beyond a critical rate of SLR, major changes in ecotope distribution are projected to occur as this part of the Wadden Sea starts to drown due to insufficient sediment import. Even larger impacts arise from adaptation strategies. Closing the barrier islands will turn the Wadden Sea into a freshwater lake-system with the absence of intertidal areas, infilling of channels and bank erosion. A strategy that allows for inland migration of the shoreline, results in a deep tidal basin with large subtidal habitats, and a shifted intertidal zone. Our case study shows that the barcoding approach provides a rapid, quantitative and spatially explicit overview of the potential implications for coastal ecosystems under different SLR scenarios, adaptation strategies and time horizons. This can then be used to screen adaptation strategies before going into a more comprehensive analysis. The barcode visualization allows for easy dissemination of potential ecological impacts to a broad community.

Quantifying and characterizing groundwater flow and discharge from barrier islands to coastal waters is crucial for assessing freshwater resources and contaminant transport to the ocean. In this study, we examined the groundwater hydrological response, discharge, and associated nutrient fluxes in Dauphin Island, a barrier island located in the northeastern Gulf of Mexico. We employed radon (222Rn) and radium (Ra) isotopes as tracers to evaluate the temporal and spatial variability of fresh and recirculated submarine groundwater discharge (SGD) in the nearshore waters. The results from a 40-day continuous 222Rn time series conducted during a rainy season suggest that the coastal area surrounding Dauphin Island was river-dominated in the days after storm events. Groundwater response was detected about 1 week after the precipitation and peak river discharge. During the period when SGD was a factor in the nutrient budget of the coastal area, the total SGD rates were as high as 1.36 m day–1, or almost three times higher than detected fluxes during the river-dominated period. We found from a three-endmember Ra mixing model that most of the SGD from the barrier island was composed of fresh groundwater. SGD was driven by marine and terrestrial forces, and focused on the southeastern part of the island. We observed spatial variability of nutrients in the subterranean estuary across this part of the island. Reduced nitrogen (i.e., NH4+ and dissolved organic nitrogen) fluxes dominated the eastern shore with average rates of 4.88 and 5.20 mmol m–2 day–1, respectively. In contrast, NO3– was prevalent along the south-central shore, which has significant tourism developments. The contrasting nutrient dynamics resulted in N- and P-limited coastal water in the different parts of the island. This study emphasizes the importance of understanding groundwater flow and dynamics in barrier islands, particularly those urbanized, prone to storm events, or located near large estuaries.

Low‐lying, wave‐dominated, sandy coastlines can exhibit high rates of shoreline change that may impact coastal infrastructure, habitation, recreation, and economy. Efforts to understand and quantify controls on shoreline change typically examine factors such as sea‐level rise; anthropogenic modifications; geologic substrate, nearshore bathymetry, and regional geography; and sediment grain size. The role of shoreline planform curvature, however, tends to be overlooked. Theoretical and numerical‐model considerations indicate that incident offshore waves interacting with even subtle shoreline curvature can drive gradients in net alongshore sediment flux that can cause significant erosion or accretion. However, these predictions or assumptions have not often been tested against observations, especially over large spatial and temporal scales. Here, we examined the correlation between shoreline curvature and shoreline‐change rates for spatially extended segments of the U.S. Atlantic and Gulf Coasts (~1700 km total). Where shoreline stabilization (nourishment or hard structures) does not dominate the shoreline‐change signal, we find a significant negative correlation between shoreline curvature and shoreline‐change rates (i.e. convex‐seaward curvature (promontories) is associated with shoreline erosion, and concave‐seaward curvature (embayments) with accretion) at spatial scales of 1–5 km alongshore and time scales of decades to centuries. This indicates that shoreline changes observed in these reaches can be explained in part by gradients in alongshore sediment flux acting to smooth spatial variations in shoreline curvature. Our results suggest that shoreline curvature should be included as a key variable in modelling and risk assessment of coastal change on wave‐dominated, sandy coastlines.

This study aimed to quantify the morphological variations of the tropical mesotidal barrier-spit systems (MBs) in Northeast Brazil to understand their evolution. Therefore, Landsat 5 TM and Landsat 8 OLI images were used to construct two multitemporal analyses: one in 4-year intervals (low frequency) and another in 1-year intervals (high frequency). The results revealed that the coastal dynamic was so intense that only high-frequency analysis could represent its evolutionary behavior. Low-frequency analysis, on the other hand, could lead to the misinterpretation of the data. Despite the strong coastal dynamic, there was a long-term equilibrium in the areas occupied by the MBs. Furthermore, regarding evolutionary behavior, there were two different types of MBs: migrant and stationary. Migrant MB movement resulted from the joint actions of the meteo-oceanographic forcings that generally push the whole barrier westward, conserving its shape. The migration rate can reach 100 m per year. This process represents the visible and massive movement of sediment along the shore. The changes observed in most MBs, whether migrant or stationary, reflect their ephemeral nature and must serve as a warning for human interventions.

Inlet Barrier Islands (IBIs) are infrequently studied, and are often poorly represented in coastal lidar records. The fetch limited barrier island (FLBI) model was introduced to describe geomorphic changes of IBIs over time. The FLBI model predicts that the morphology of IBIs should remain largely static during predominate weather conditions due to sheltering from oceanic wave energy but undergo significant erosion when local and non-local waves magnify during storms, subsequently failing to recover volume and elevation losses. Using three years of high-frequency small unoccupied aircraft systems (sUAS, aka drone) surveys and existing lidar records, we document geomorphic changes on Bird Shoal (a protective IBI near the town of Beaufort, NC) resulting from storms and predominate conditions, testing the FLBI model and documenting island evolution. Our results indicate that Bird Shoal exhibits different spatial trends in erosion, accretion, and shoreline migration across its 4 km length, likely driven by varying shoreline orientation to the Beaufort Inlet and back barrier bathymetry in Back Sound. Our data indicate that the geomorphic behavior of Bird Shoal currently does not adhere to the classic FLBI model. Foreshore storm recovery and growth on Western Bird Shoal and shoreline retreat on Central Bird Shoal occurred during predominate conditions, and beach morphology was not an artifact of past storm events. The Western Bird Shoal shoreline consistently retreated landward in decades of historic imagery, but transitioned to seaward expansion sometime between 2011 and 2014. This shift is likely driven by erosion of the western end of Shackleford Banks and concurrent widening of the Beaufort Inlet, allowing increased wave energy to enter the back-barrier sound and push flood deltas onto Bird Shoal during predominate conditions. Our results suggest that open ocean inlet width and location interact with back-barrier deltas to control sediment supply and wave energy for IBIs, and that IBIs may fall into and out of conformance with the FLBI archetype over time. This study demonstrates sUAS deploying frequently over a municipal scale to fill spatial and temporal gaps in traditional coastal remote sensing datasets.

Dune spits of the island of Sylt (North Sea) persisted through millennia by mobile dunes transferring sand from exposed to sheltered shores. However, 150 years of systematic planting on washovers, blowouts and migrant dunes have almost completely stopped this sand conveyor belt. Spits lost sand until sand replenishments to the exposed side compensated for losses during the last three decades. Based on maps since 1878, aerial images from the 1930s onward as well as botanical ground surveys, we document a long-term shift from loose grass cover to dense heather dominated vegetation. Bare sand areas almost vanished and high shrubs proliferated. Only three dunes continue migrating with about 3 m a-1 since 1936. Mainly artificial dune stabilizations and introduced plants have facilitated succession to an almost complete plant cover. Thus, revitalization of aeolian dynamics would be desirable, and pilot projects may acquire the appropriate knowledge. For a 1.7 × 2.5-km corridor across the island spit, we therefor discuss two suggested experiments: (1) intensify sand nourishments to the eroding beach and stop stabilization measures to allow excess sand blown inland and washovers entering deflation plains, and (2) examine the potential of tunnels for roads to let mobile dunes passing over. Such experiments may not only contribute to dune biodiversity but also to long-ranging adaptations of crowded barrier islands to accelerating sea level rise.

The sand dunes found on coastal shores and barrier islands along the Northern Gulf of Mexico are important for protecting inland areas from wind and wave action, especially from tropical storms and hurricanes. The geomorphology of the dunes interacts with the plant community to create this dynamic coastal ecosystem. This study explored the processes that shape the foredunes, the youngest set of dunes where sediments are deposited by winds blowing up from the beach. These sands are thought to be slowed or trapped by early successional vegetation, leading to dune creation and growth. Our results suggest that the vegetative community is strongly associated with distance from the shore, where abiotic conditions are harshest closest to the ocean and gradually reduced moving toward the interior of the island. This deterministic community pattern appears to be maintained by the vegetation’s ability to regenerate through time, especially in response to disturbances after heavy wind and wave action. A multifactorial germination experiment revealed strong differences among the germination rates of different species and the effects of salinity on species-specific germination rates. High rates of germination might be beneficial in colonizing open habitats following storms, where high salinity conditions are especially present. Understanding the patterns that shape vegetative community diversity should help guide restoration management in coastal dune systems and shed light on the importance of individual species and their function within the coastal ecosystem.

In this research it is given the Classifying Coasts, Primary Coasts and Land Erosion Coasts, Coasts Built Out by Land Processes, Coast, Coasts Shaped by Earth Movements, Secondary Coasts,Some Features of Secondary Coasts, Shore Straightening, The Accumulation of Beaches, Beaches, The Composition and Slope of Beaches, Beach Shape,Minor Beach Features, Coastal Cells, Large-Scale Features of Secondary Coasts, Sand Spits and Bay Mouth Bars, Barrier Islands and Sea Islands, Coasts Formed by Biological Activity, Estuaries, Classification of Estuaries, Characteristics of Estuaries, The Value of Estuaries, Lagoons and Wetlands with useful data.

Marine debris is an economic, environmental, human health, and aesthetic problem posing a complex challenge to communities around the globe. To better document this problem in the Gulf of Mexico we monitored the occurrence and accumulation rate of marine debris at twelve sites on nine barrier islands from North Padre Island, Texas to Santa Rosa, Florida. With this information we are investigating three specific questions: (1) what are the major types/sources of marine debris; (2) does debris deposition have seasonal oscillations; and (3) how does debris deposition change spatially? Several trends emerged; plastic composed 69-95% of debris; there was a significant increase in debris accumulation during the spring and summer seasons; accumulation rates were ten times greater in Texas than the other Gulf States throughout the year; and the amount of debris accumulating along the shoreline could be predicted with high confidence in areas with high freshwater influx.

Stranded sea turtles provide valuable information about causes of mortality that threatens these imperiled species. Many potential factors determine whether drifting sea turtles are deposited on shore, discovered by people, and reported to stranding networks resulting in successful documentation. We deployed 182 sea turtle cadavers and 115 wooden effigy drifters with affixed GPS-satellite tags to study stranding probability in the northern Gulf of Mexico (nGOM) in an effort to better understand seasonal stranding variations in this region. Public reports of beached carcasses were recorded to determine reporting rates. Season and distance from shore greatly influenced beaching results. During winter months when strandings are infrequent and sea turtle abundance is likely low in cold nearshore waters, carcasses had an 80–90% probability of beaching. Beaching probability was reduced to 37–50% during the spring, which is the period of greatest strandings in this region. During summer months when relatively few strandings are documented, the probability of a carcass beaching dropped to only 4–8%. Low summer stranding rates were coincident with higher rates of decomposition (7%) attributed to warmer water temperatures, more frequent scavenging (69% of carcasses), and shifting wind and current patterns which drive carcasses offshore or to remote locations. As waters cooled in the fall, probability of carcasses beaching increased to 40–48%, coincident with a small pulse in strandings that often occurs during this period. Only 28% of carcasses and effigies came ashore on mainland beaches and were easily available for discovery by the public, 49% were on barrier islands that are publicly accessible and 23% beached in dense salt marshes where discovery would be unlikely. The 47% of objects that did not beach included those lost at sea and carcasses that were likely scavenged or decomposed. Only 22% of beached carcasses were reported due to infrequent (11%) reporting on barrier islands. Notably, only 50% of carcasses deposited on mainland beaches were reported, which was lower than anticipated. We recommend additional efforts to increase reporting rates of carcasses by the public and use of dedicated surveys to detect stranded sea turtles, especially on barrier islands in this region.

Barrier sandspits are biodiverse natural features that regulate the development of lagoon systems and are popular areas for human settlement. Despite many studies on barrier island dynamics, few have investigated the impacts of sea-level rise (SLR) on sandspits. In peri-urban settings, we hypothesised that shoreline environment change would be strongly dependent on contemporary land use decisions, whilst modern engineering capabilities also present new opportunities for working with nature. Our study site in Christchurch, New Zealand, included a unique example of SLR caused by tectonic subsidence and an associated managed retreat initiative. We used a novel scenario modelling approach to evaluate both shorelines simultaneously for 0.25m SLR increments and incorporating open coast sediment supply in 25-year periods. Our key questions addressed the potential impacts of shoreline change on open coast dune and estuarine-coast saltmarsh ecosystems and implications for the role of ‘nature-based’ climate change solutions. The results identify challenges for dune conservation, with a third of the dune system eliminated in the ‘1-m SLR in 100-year’ scenario. The associated exposure of urban areas to natural hazards such as extreme storms and tsunami will likely fuel demand for seawalls unless natural alternatives can be enabled. In contrast, the managed retreat initiative on the backshore presents an opportunity to restart saltmarsh accretion processes seaward of coastal defences with the potential to reverse decades of degradation. Considering both shorelines simultaneously highlights the existence of pinch-points from opposing forces that result in small land volumes above the tidal range. Societal adaptation is delicately poised between the paradigms of resisting or accommodating nature and challenged by the long perimeter and confined nature of the sandspit feature. The use of innovative policy measures in disaster recovery contexts, as highlighted here, may offer a beneficial framework for enabling nature-based solutions to climate change and natural hazards.

Rodil, I.F.; Long, Z.T.; Fegley, S.R.; Rodriguez, A.B., and Peterson, C.H., 2021. Benthic community responses to the filling of a hurricane-induced barrier island inlet. Journal of Coastal Research, 37(3), 601–610. Coconut Creek (Florida), ISSN 0749-0208.In September 2003, Hurricane Isabel created a new tidal inlet through Hatteras Island, a barrier island of North Carolina (U.S.A.). Within two months, the breach was filled with sand dredged from nearby areas. Subsequent ecological response of the benthic macroinvertebrate communities to the filling differed on shores on opposite sides of the island. Thus, the filled area on the high-energy sandy beach exhibited convergence in community composition and abundance with a nearby reference area within 30 months, whereas the filled area on the lower-energy sound shoreline still possessed a depauperate benthos. The high volume of long-shore sediment transport documented along the ocean beaches of Hatteras Island probably acted quickly to transport benthic macrofauna to the fill along with natural beach sediments, and thereby activating a rapid ecological response of the beach community. The beach community was dominated by annual macroinvertebrate species, which could account for mixing from nearby areas in the rapid macrofauna community response. In contrast, the Pamlico Sound shoreline experiences only local wind-driven waves and modest long-shore currents likely insufficient to import macrobenthos readily. Infrequent passive transport of macrobenthos and persistence of defaunated sediment habitats nearby probably slowed the macrofauna community response on the sound-shore side. Management intervention through habitat restoration would be recommended in the less dynamic sound shore environment compared to the high-energy ocean beach where ecological responses of the invertebrate community occurred rapidly.

Coastal roadways are vulnerable to changes in landscape that occur at variable spatiotemporal scales. In particular, highways on barrier islands suffer the consequences of the combined acti...

Accelerated coastal erosion and elevated risks of flooding due to global warming put enormous burden on the ecosystems and economic health of coastal communities. Optimal policies to lessen these negative impacts require an estimation of their costs and benefits. The aim of this paper is to calculate the costs of beach erosion and flood risk through the valuation of property prices in Hilton Head Island, a barrier island located in South Carolina, USA. Spatial lag hedonic pricing was introduced in order to account for spatial autocorrelation in the dataset. The results show that properties that are located within the zone of high, or very high, flood risk experience a 15.6% reduction in value. The implicit price of being located close to an eroded beach is approximately 26% of the price of an oceanfront property. However, this negative impact on property value diminishes with distance from the shoreline.

Barrier islands are indicators of coastal resilience. Previous studies have proven that barrier islands are surprisingly resilient to extreme storm events. At present, little is known about barrier systems&rsquo, resilience to seismic events triggering tsunamis, co-seismic subsidence, and liquefaction. The objective of this study is, therefore, to investigate the morphological resilience of the barrier islands in responding to those secondary effects of seismic activity of the Sumatra&ndash, Andaman subduction zone and the Great Sumatran Fault system. Spatial analysis in Geographical Information Systems (GIS) was utilized to detect shoreline changes from the multi-source datasets of centennial time scale, including old topographic maps and satellite images from 1898 until 2017. Additionally, the earthquake and tsunami records and established conceptual models of storm effects to barrier systems, are corroborated to support possible forcing factors analysis. Two selected coastal sections possess different geomorphic settings are investigated: (1) Lambadeuk, the coast overlying the Sumatran Fault system, (2) Kuala Gigieng, located in between two segments of the Sumatran Fault System. Seven consecutive pairs of comparable old topographic maps and satellite images reveal remarkable morphological changes in the form of breaching, landward migrating, sinking, and complete disappearing in different periods of observation. While semi-protected embayed Lambadeuk is not resilient to repeated co-seismic land subsidence, the wave-dominated Kuala Gigieng coast is not resilient to the combination of tsunami and liquefaction events. The mega-tsunami triggered by the 2004 earthquake led to irreversible changes in the barrier islands on both coasts.

Sea-level is expected to continue to rise in the next century, and as society prepares to deal with this hazard it is critically important to understand how coastal systems will respond, especially in regions with rapid rates of coastal erosion and relative sea-level rise like the Gulf of Mexico Texas coast. Tide gauge records in Galveston Bay, Texas, indicate that local sea level rise rates are more than twice the global average, raising important questions about the long-term stability of the barrier islands protecting the bay and how the estuary and coastline will respond to sea-level rise. However, tide gauge records only go back to the beginning of the last century, and longer records are needed to provide insight into dynamic coastal response to sea-level fluctuations. Here, we combine geophysical (chirp sub-bottom profiler) surveys and sediment cores (providing sedimentological and micropaleontological data constrained by radiocarbon dating) to characterize paleoenvironmental change in the Holocene estuary system offshore modern Galveston Bay over the last ~10 kyr; with the first 4 kyr of this time span undergoing a period of rapid sea level rise more than twice the modern rate. Our foraminiferal analysis provides ecological context on the stability of these paleoenvironments and the timing of coastal change over the last ~10 kyr. We provide a model of Holocene shoreline change differing from existing interpretations of rapid landward shifts with asymmetric coastal geometry to one composed of more gradual transitions matching modern coastal geometry and argue for an overall stable paleoestuarine environment throughout the middle Holocene (~6.9 ka – 8.8 ka). Subsequent shoreline shifts occurred after global sea level rise slowed below modern rates, indicating hydroclimate impacts on sediment flux likely had a greater influence on the earlier stability of the estuarine system and later shoreline retreat than rates of sea-level rise.

Inlet-driven processes are capable of modifying the adjacent shoreline. However, few studies have attempted to understand how these changes affect coastal dunes. The present study aims to understand how shoreline changes induced by shoal attachment affect coastal dunes. A barrier island in the Netherlands is used as a case study. Both bathymetric and topographic annual data were analysed, together with the application of a cellular automata model for dune development. The objective of the model is to explore idealised scenarios of inlet-driven shoreline movements. With the model, ten different scenarios were examined regarding beach width increase and rate of alongshore spreading of the shoal. Field data showed that, for the case study, dune volume and shoal attachments could not be directly linked. Instead, rates of dune volume change differed significantly only due to long-term ebb-tidal delta evolution. Such morphological evolution oriented the beach towards the main wind direction, increasing overall aeolian transport potential. Modelling results showed that shoals significantly increased dune volumes only on three out of ten scenarios. This suggests that beach width increase, and rate of alongshore sediment spreading, determine whether the shoal will influence dune growth. Therefore, within the studied time-scale, local rates of dune growth are only increased if shoals are capable of increasing the beach width significantly and persistently.

Studies of the transgressive barrier elements of the mid-Atlantic Delmarva Peninsula show four major types of morphologic and vertical sedimentary sequence models. Each model shows a response to present wave and current conditions as well as to the paleotopography inundated by the ongoing transgression. The geomorphic features of the shoreline areas of a transgressive barrier coast, as studied in the Delmarva Peninsula area, include numerous discreet geomorphic features that are in fact single sedimentary environment lithosomes. These sedimentary environment lithosomes are part of a dynamic condition in which geomorphic environment-sedimentary lithosomes are moving landwards and upwards in space and time with the presently continuing coastal transgression. As the present coastal transgression is in part a product of late Holocene relative sea level rise and in part the product of coastal erosion, vertical sequences and the sedimentary environment lithosomes of the late Holocene stratigraphic record at the edge of the transgression are in part truncated by erosion and, accordingly, are incomplete. However, detailed geomorphic and subsurface studies of the various elements of the estuarine and Atlantic Ocean barrier coast have shown that the linking of studies of coastal processes, surface geomorphic features, and subsurface stratigraphic sections make possible a relatively complete understanding of the sequence of geomorphic events that have occurred in the coastal zone during late Holocene time. Four major geomorphic-sedimentary environment sequence models established are as follows: Barrier Systems: barrier islands, baymouth barriers, and, barrier island chains vary in amount of separation from the mainland by lagoons, distance from other islands, and number of inlets. All are characterized by a vertical transgressive sequence of sedimentary lithosomes identical to the horizontal sequence in the direction of the transgression. 322 Beach against highland: beach system impinges on low lying (20–30 ft) pre-Holocene highlands formed of Pleistocene sediments which erode and provide a partial source of sands, gravels, and mud to the system. Estuarine barriers: long, arcuate barriers, small in width (150 ft) and thickness (10 ft) but of extreme length (up to 50–75 mi), occur along shorelines of large and small estuaries. Internal structures of these sand and gravel barriers are variable and complex; mainly composed of washover features. Four variants are identified. Spit complex: extends into open marine and bay areas. All expected coastal transgressive environments of the barrier systems are seen in addition to regressive spit accretion sands and gravels. Consequently, vertical sequences may be disrupted and out of order. Model studies of the variants of coastal morphologic units of the Delmarva Peninsula may be used to summarize the geologic history of the edge of the ongoing Holocene transgression. In addition, these models may be used to predict continuing changes in coastal morphology, assuming present and past processes will continue into the future. These predictions are useful to man in understanding and developing a more effective use of the coastal zone as man’s intensity of involvement with coastal geomorphic environments continues to increase.

At the coast, risk arises where, and when, static human developments are situated within dynamic surroundings. Barrier islands are often sites of heightened coastal risk since they frequently support substantial human populations and undergo extensive morphological change owing to their low-lying form and persistence in energetic hydrodynamic and meteorological conditions. Using the mixed sand-gravel barrier of Blakeney Point, this study argues that to avoid an only partial understanding of coastal zone processes, it is necessary to make use of multiple shoreline proxies, capturing processes operating both at different timescales and different cross-shore positions. Here, five shoreline proxies were extracted from three data sources. Shoreline error was quantified and compared to observed shoreline change rates to establish proxy-specific, appropriate timescales for shoreline change analysis. The map derived Mean High Water Line at Blakeney Point revealed landward retreat of −0.61 m a−1 over the past 130 years with a shift from drift- towards swash-alignment of the barrier since 1981. Over the past 24 years, the High Water Line, Ridge Line and Vegetation Line reveal proxy-specific response to management regime change. The termination of barrier reprofiling of the eastern section of the barrier has resulted in increased sediment release to the downdrift barrier terminus, buffering retreat there at the expense of the updrift section. The Vegetation Line represents an effective proxy for storm-driven overwash with maximum shoreline retreat during surge events of 172 m, illustrating a strong event-driven component to barrier morphodynamics. By comparison to the other proxies, the LiDAR (Light Detection and Ranging) derived Mean High Water Line offers relatively limited insights into barrier dynamics, emphasising the importance of multi-proxy approaches. In the face of technological advance, we demonstrate the continued importance of critical attention towards the dependencies that exist between shoreline proxy selection and the processes that can be observed as a result.

The large-scale littoral sediment drift along barrier island coasts involves alongshore sand transport at the islands’ surf zone and across tidal inlets. Mechanisms of sediment bypassing at non-migrating, mixed-energy tidal inlets are discussed based on process-based numerical modeling of sediment dynamics at an exemplary barrier island system in the southern North Sea. Residual transport pathways of distinct sediment grain-size fractions and morphological changes reveal the complexity of processes at tidal inlets driven by the non-linear interaction of competing tidal and wave forces. Sediment bypassing from the updrift to the downdrift shoreline of a tidal inlet is evaluated and the ratio of bypassed to recirculated sand volumes is estimated. Common inlet bypassing schemes are discussed and verified. It is shown that the different bypassing mechanisms can happen simultaneously and are related to the transport behavior of particular sediment grain-size fractions: Very fine to fine sand bypasses the inlet along the entire ebb-tidal delta periphery by wave-induced transport processes. Fine to medium sand is transported by the ebb-directed tidal currents in the inlet throat to the ebb-tidal delta where wave-driven transport processes and bar welding bypasses the sediments to the downdrift shore. For fine to medium and medium sands, a sediment recirculation cell at the downdrift ebb-tidal delta and reversal to the main inlet throat is identified.

Arctic sea-ice is declining in extent, leaving coastlines exposed to more storm-wave events. There is an urgent need to understand how these changes affect geomorphic processes along Arctic coasts. Here we describe spatial and temporal patterns of shoreline changes along two geomorphologically distinct, storm-wave dominated reaches of the Chukchi Sea coastline over the last 64 years. One study area encompasses the west- to southwest-facing, coarse-clastic shoreline and ice-rich bluffs of Cape Krusenstern (CAKR). The other covers the north-facing, sandy shorelines on barrier islands, ice-rich bluffs, and the Cape Espenberg spit in the Bering Land Bridge National Park (BELA). Both study areas lie within the zone of continuous permafrost, which exists both on and offshore and outcrops as ice-rich bluffs along the BELA coast. We mapped changes in coastal geomorphology over three observation periods: 1950–1980, 1980–2003, and 2003–2014 using aerial and satellite imagery. We then compared these geomorphic changes to changes in sea-ice coverage, which declined ~10 days per decade between 1979 and 2016 in the southern Chukchi Sea. Changes in coastal geomorphology in both BELA and CAKR exhibited high spatial variability over the study period. Between 2003 and 2014, shorelines of barrier islands in BELA exhibited the highest mean rates of change, −1.5 m yr−1, while coarse, clastic barrier beaches in CAKR showed only minimal change. Overall, shorelines in both BELA and CAKR became more dynamic (increasing erosion or increasing accumulation) after ca. 2003, with spatial variability in shoreline changes roughly doubling between the first period of observation (1950–1980) and the last (2003–2014). This increase in coastal dynamism may signal a transitional period leading to new state of geomorphic equilibria along these ice-affected coastlines.

Barrier islands and their associated backbarrier ecosystems front much of the U.S. Atlantic and Gulf coasts, yet threshold conditions associated with their relative stability (i.e., state changes between progradation, erosion, and landward migration) in the face of sea-level rise remain poorly understood. The barrier islands along Virginia's Eastern Shore are among the largest undeveloped barrier systems in the U.S., providing an ideal natural laboratory to explore the sensitivity of barrier islands to environmental change. Details about the developmental history of Parramore Island, one of the longest (12 km) and widest (1.0–1.9 km) of these islands, provide insight into the timescales and processes of barrier-island formation and evolution along this mixed-energy coast. Synthesis of new stratigraphic (vibra-, auger, and direct-push cores), geospatial (historical maps, aerial imagery, t-sheets, LiDAR), and chronologic (optically stimulated luminescence, radiocarbon) analyses reveals that Parramore has alternated between periods of landward migration/erosion and seaward progradation during the past several thousand years. New chronology from backbarrier and barrier-island facies reveals that Parramore Island has existed in some form for nearly 5000 years. Following a period of rapid overwash-driven retrogradation, and coinciding with a period of slow relative sea-level rise (~1 mm/ yr), Parramore stabilized ~1000 years ago in partial response to pinning by and sediment delivery from erosion of a Pleistocene-aged antecedent high. Following pinning, Parramore built seaward through development of successive progradational beach and dune ridges. Morphological and historical evidence suggests that these processes were interrupted by inlet formation—possibly associated with an interval of enhanced storminess—at least three times during this period. Following inlet closure in the early 1800s, island progradation was rapid, with Parramore Island reaching its maximum width ca. 150 years ago. It has since switched states again, undergoing accelerating erosion (~12 m/ yr since 1980). The relative youth of Parramore Island is in contrast to many East Coast barrier islands, which generally reached their present positions about 3500–2000 years ago. Moreover, these results demonstrate that the apparent robustness and stability of Parramore are ephemeral features of an island that has undergone multiple state changes within the last 1000 years. Finally, they refine current knowledge of the roles of antecedent topography, sediment delivery rates, storms, and sea-level rise in barrier-island stability and resilience to future climate change.

Recent projections of global climate change necessitate improved methodologies that quantify shoreline variability. Updated analyses of shoreline movement provide important information that can aid and inform likely intervention policies. This paper uses the Analyzing Moving Boundaries Using R (AMBUR) technique to evaluate shoreline change trends over the time period 1856 to 2015. Special emphasis was placed on recent rates of change, during the 1994 to 2015 period of active storm conditions. Small segments, on the order of tens of kilometers, along two sandy barrier island regions on Florida’s Gulf and Atlantic coasts were chosen for this study. The overall average rate of change over the 159-year period along Little St. George Island was − 0.62 ± 0.12 m/year, with approximately 65% of shoreline segments eroding and 35% advancing. During periods of storm clustering (1994–2015), retreat rates along portions of this Gulf coast barrier accelerated to − 5.49 ± 1.4 m/year. Along the northern portion of Merritt Island on Florida’s Atlantic coast, the overall mean rate of change was 0.22 ± 0.08 m/year, indicative of a shoreline in a state of relative dynamic equilibrium. In direct contrast with the Gulf coast shoreline segment, the majority of transects (65%) evaluated along the oceanfront of Merritt Island over the long term displayed a seaward advance. Results indicate that episodes of clustered storm activity with fairly quick return intervals generally produce dramatic morphological alteration of the coast and can delay natural beach recovery. Additionally, the data show that tidal inlet dynamics, shoreline orientation, along with engineering projects, act over a variety of spatial and temporal scales to influence shoreline evolution. Further, the trends of shoreline movement observed in this study indicate that nearshore bathymetry—the presence of shoals—wields some influence on the behavior of local segments of the shoreline.

Under rising sea level conditions, barrier islands are largely ephemeral features, eroded on the seaward side by the transgressing shoreline and reformed by overwash to a more landward position. Locally, however, and over shorter time scales, shorelines can either advance or retreat, even in an overall transgressive environment, and the stratigraphy and morphology of the shoreface can be significantly impacted by the evolution of shoreface-attached bedforms. Fire Island, New York, is a well-studied example of such variability, with a stable-to-accreting shoreline at the western end and a retreating shoreline on the eastern end. In this study, we seek to better understand these differences by investigating the lower-shoreface stratigraphy at both stable/accreting (Fire Island West, or FIW) and retreating (Fire Island East, or FIE) shorefaces, using ultra-high resolution chirp seismic reflection data. Within the barrier/marine sands (the seismic unit between seafloor and shoreface ravinement), we identify six seismic units (WSUs 1–6 from bottom to top) in the FIW survey and two units (ESU1 and ESU2 from bottom to top) in the FIE survey; these units constitute the modern lower shoreface wedge. The barrier shoreface in the FIW survey is dominated by discrete and spatially-confined lobes. Isopach maps indicate that the lobe shifting was an episodic process with westward-migrating depocenters. The prograding shoreface was constructed by this lobate deposition; we speculate that these are related to ebb deposition from ephemeral barrier breaches/inlets. In the FIE survey, ESU2 accounts for the majority accumulation of the barrier shoreface and it is more linear than the lobate structure observed within the FIW survey, possibly derived from eroded shoreface sediments. Portions of this unit are absent however, exposing lower Pleistocene units to the erosive forces.

Shoreline changes affect functionality of a sandy beach as a wildlife habitat and coastal erosion is among the primary causes of the changes. We examined temporal shifts in locations where loggerheads placed nests in relation to coastal erosion along a barrier island beach in the northern Gulf of Mexico. We first confirmed consistency in long-term (1855–2001), short-term (1976–2001), and more recent (2002–2012) shoreline change rates in two adjacent beach sections, one historically eroding (west beach) and the other accreting (east beach). The mean annual shoreline change rate in the two sections was significantly different in all time periods. The recent (1998–2012) mean change rate was −10.9 ± 9.9 m/year in the west beach and −2.8 ± 4.9 m/year in the east beach, which resulted in the loss of about 70% and 30% of area in the west and east beaches, respectively. Loggerheads nested significantly closer to the vegetation line in 2012 than in 2002 in the west beach but the difference between the two time periods was not significant in the east beach. However, the distance from nests to the vegetation line from 2002 to 2014 was significantly reduced annually in both beaches; on average, loggerheads nested closer to the vegetation line by 9 m/year in the west beach and 5.8 m/year in the east beach. The observed shoreline change rate and corresponding shift of nest placement sites, combined with the forecasted future beach loss, highlighted the importance of addressing the issue of beach erosion to conserve sandy beach habitats.

Barrier islands are found around the world and are important environmentally and economically. With accelerated sea level rise and relentless storms, their evolution is complex but important to understand, especially from a coastal planning and managing perspective. In this study, shoreline change estimates from aerial photography (1949, 1974, 2006), sedimentological and stratigraphic investigation, and analysis of geomorphic character were used to evaluate the hurricane response and decadal evolution of Ocracoke Island, NC. Between 1949 and 2006, the majority (> 65% of transects) of the entire island eroded at an average rate of − 0.54 m/year. Cross-island width decreased by as much as 40% (180 m) over the period. Hurricane Isabel (2003) represented up to 23% of the long-term net change in some regions of the island. The rate of narrowing of Ocracoke Island appears to have increased in the last half century and is due to a combination of natural and anthropogenic factors. Isabel overwashed a total of 9% of the island based on aerial photographic analysis with an average deposit thickness of 0.24 m based on trench investigation. Assessment with the Storm Impact Scale showed a direct relationship between overwash and the pre-existing dune conditions, which had been affected by long-term erosion. Sedimentological signatures interpreted from cores show up to four distinct stacked overwash deposits, potentially dating back as far as 1944. This multi-pronged analysis shows the complexity of barrier island evolution and highlights the necessity to examine and model a system response in four dimensions (i.e., spatially and with time).

Amos, C.L.; Brylinsky, M.; Forbes, D.L.; Robertson, A.; Thompson, C.E.L., and Kassem, H., 2018. Stability of seabed sediments in the embayments of North Rustico, Prince Edward Island, Canada. This paper describes a series of 15 deployments of the annular benthic flume Sea Carousel made along the two estuaries of North Rustico, Prince Edward Island (PEI), Canada: The Hunter River estuary and the Wheatley River estuary. The study was part of a wider study on the environmental impact of coastal changes and aquaculture (Mytilus edulis) development in the region. The study site was situated on the dynamic north shore of PEI that is characterised by sandy barrier islands, inlets and beaches, and muddy lagoons. The lagoons are dominated by the seagrass Zostera marina in the muddy outer parts and by Ulva lactuca in the eutrophic inner parts. The thresholds for surface erosion of cohesive sediments (0.10 < τcrit,o < 0.75) derived from trends of suspended sediment concentration (C) increased with distance ...

This study investigates differences in geomorphology between two barrier island systems, one considered to be in a pristine or natural geomorphic state, and another in some way geomorphically altered by humans. Alteration here is defined by the presence of a continuous, protective dune wall designed and installed alongshore to arrest island erosion and protect interior infrastructure. In contrasting the two environments we focus on a single question: how does the presence of such a dune wall alter the physical response of an island system to forces that compel change (e.g. storms, sea level rise)? Island widths, and ocean and sound shoreline positions are measured along a series of shore-normal transects on Core Banks and Ocracoke Island, both members of North Carolina’s Outer Banks. Surveys date from the mid-nineteenth century through 2012. Four surveys were retained for Core Banks, five for Ocracoke Island. Findings point to differences in the geomorphic character along both islands. More of Core Banks is narrow with evidence of current overwash and inlet activity. Ocracoke presents more stability, width, limited overwash, and no inlets. Evidence uncovered points to three fundamental conclusions. First: there appears to exist a minimum threshold width about which an island tends to oscillate. Second, differential shoreline retreat along Ocracoke Island has resulted in a counterclockwise (CCW) rotation along the island’s northern half. Finally, the protective dunes along Ocracoke appear to have slowed the rate of shoreline retreat, and the observed CCW rotation, by more than 40%.

The impact of storm surge on a barrier island tends to be considered from a single cross-shore dimension, dependent on the relative elevations of the storm surge and dune crest. However, the foredune is rarely uniform and can exhibit considerable variation in height and width at a range of length scales. In this study, LiDAR data from barrier islands in Texas and Florida are used to explore how shoreline position and dune morphology vary alongshore, and to determine how this variability is altered or reinforced by storms and post-storm recovery. Wavelet analysis reveals that a power law can approximate historical shoreline change across all scales, but that stormscale shoreline change (~10 years) and dune height exhibit similar scale-dependent variations at swash and surf zone scales (

Hurricane Sandy at Fire Island, New York presented unique challenges in the quantification of storm impacts using traditional metrics of coastal change, wherein measured changes (shoreline, dune crest, and volume change) did not fully reflect the substantial changes in sediment redistribution following the storm. We used a time series of beach profile data at Fire Island, New York to define a new contour-based morphologic change metric, the Beach Change Envelope (BCE). The BCE quantifies changes to the upper portion of the beach likely to sustain measurable impacts from storm waves and capture a variety of storm and post-storm beach states. We evaluated the ability of the BCE to characterize cycles of beach change by relating it to a conceptual beach recovery regime, and demonstrated that BCE width and BCE height from the profile time series correlate well with established stages of recovery. We also investigated additional applications of this metric to capture impacts from storms and human modification by applying it to several post-storm historical datasets in which impacts varied considerably; Nor'Ida (2009), Hurricane Irene (2011), Hurricane Sandy (2012), and a 2009 community replenishment. In each case, the BCE captured distinctive upper beach morphologic change characteristic of these different beach building and erosional events. Analysis of the beach state at multiple profile locations showed spatial trends in recovery consistent with recent morphologic island evolution, which other studies have linked with sediment availability and the geologic framework. Ultimately we demonstrate a new way of more effectively characterizing beach response and recovery cycles to evaluate change along sandy coasts.

Three years of observations of groundwater elevations, ocean tides, surge, and waves, and rainfall are used to study coastal groundwater-driven flooding along the ocean side of a barrier island. Increases in surge and wave-driven water levels (setup) during 26 ocean storms with little rainfall, including the passage of 3 hurricanes, caused O(1 m) increases in groundwater heads under the dunes on the ocean side of the island, nearly double previously reported magnitudes. The inland propagation of the resulting pulses in groundwater levels is consistent with an analytical model (without recharge) based on shallow aquifer theory (Nash Sutcliffe model efficiencies of >0.7, maximum water-table level estimates within 0.1 m of observations). Infiltration of precipitation results in approximately a threefold increase in the groundwater level relative to the amount of rainfall. The analytical model (with recharge) driven with estimated ocean shoreline water levels (based on the 36-hr-averaged offshore tide, surge, and wave height) and measured precipitation predicts the maximum water-table height within 0.15 m of that observed across the barrier island during Hurricane Matthew, which was the only wave event during the 3-yr data set with more than 0.1 m rainfall. Citizen-science reports from a smartphone app (iFlood) are used to evaluate the regional application of the model. Twenty-five ocean-side reports associated with 7 ocean storms (6 of which had minimal rainfall) between Sept 2019 and Feb 2020 showed flooding on natural (permeable) land surfaces along 70 km of the northern Outer Banks barrier island, from Corolla to Rodanthe, NC. The analytical model (with recharge) predicts flooding that is consistent with the timing and location for 19 of the 25 reports. Applying the model regionally suggests that more than 10% of the land area on the ocean side of the northern Outer Banks would be inundated by coastal groundwater even in the absence of rainfall for an ocean storm that generates a 2.25 m increase in the shoreline water level.

Ship wakes generated by vessels moving through ecologically sensitive areas, or near poorly-protected infrastructure, can negatively impact these systems. This is especially true in regions hosting large seaports. Ship wakes in Tampa Bay, Florida, were calculated during two time periods using vessel movement data reported through the Automatic Identification System (AIS). The first period was for the years 2015–2017 using data from a government database. The second was during part of 2018 obtained by local monitoring. Only vessels operating at low Froude numbers were examined. Wake heights were estimated from each AIS record using an empirical equation and partitioned by functional vessel class. The largest estimated wakes were produced by the Passenger class. Cargo class vessels had the largest number of ships estimated to produce high wakes. Egmont Key, a long-eroding barrier island at the mouth of the Bay, was potentially subjected to the highest number of ship wakes and the highest cumulative wake energy. Differences in vessel representation in the two sets of AIS data yielded different distributions of wake energy by vessel class. Some strategies for managing wake energy are discussed.

This study investigates the mechanisms of dune formation and growth on a micro-tidal beach. The study area, located on a barrier island on the northern Yucatan peninsula, is characterized by persistent sea breeze conditions and a wide and shallow continental shelf. Beach topography data was collected over 5 years, on a prograding beach (0.5–7 m y-1), using a Real-Time Kinematic Differential Global Positioning System. The beach surveys (>100) cover from the subaerial beach (seaward from the existing foredune in 2015) to a 1.5 m water depth with a high spatial (0.2 m–0.5 m) and temporal (weekly to bi-weekly) resolution. Thus, shoreline evolution, offshore/onshore inner sandbar migration, and foredune initiation and growth can be analyzed from this data set. Moreover, environmental conditions, obtained from in situ observations and numerical model simulations, allow us to investigate the role of marine and aeolian processes on foredune morphodynamics. A net shoreline advance is observed, induced by the presence of a port's jetty, allowing the formation of a new foredune during the period of study. Field observations suggest that seasonal beach variability is explained by the onshore (offshore) sediment transport during fall-winter (spring-summer). The dune growth rate is well correlated with the monthly mean wind speed that reaches a maximum during spring months, when sea-breezes are more persistent and intense (W > 12 m s-1), the effective fetch length is larger, and the moisture content is lower. Empirical Orthogonal Function (EOF) analysis of beach profiles in the fast progradation area (>1 m y-1) shows that the variability is dominated by sustained beach width increase throughout the study period. On the other hand, at the slow progradation area the first and second EOF modes explain the seasonal beach and foredune variability, respectively. Thus, it is suggested that beach sand supply (during fall-winter) followed by aeolian transport (during spring) control the natural foredune growth in this region.

The behavior of siliciclastic coastal systems is largely controlled by the interplay between accommodation creation and infilling. Factors responsible for altering sediment fluxes to and along open-ocean coasts include cross-shore mobilization of sediment primarily from tidal currents and storms as well as changes in alongshore transport rates moderated by changing wave conditions, river sediment inputs, artificial shoreline hardening and modification, and natural sediment trapping in updrift coastal landforms. This paper focuses on the latter relationships. To address understudied interactions between updrift coastal landforms and downdrift coastal behavior, we quantify the volume and fluxes of sediment trapped in the Assateague-Chincoteague-Wallops barrier-island complex along the Virginia, USA coast and relate these volumes to downdrift coastal-system behavior. During the last ca. 2250 years, these barriers trapped 216 million m3 of sand through the growth of complex beach- and foredune-ridge systems. A period (ca. 400 to 190 years ago) of reduced/no progradation on Chincoteague and Assateague islands corresponds with sediment sequestration in updrift flood-tidal deltas. This finding emphasizes the important control of tidal inlets on alongshore sediment fluxes on barrier-island coasts. Rapid historical spit elongation during the last 190 years has trapped an average of 681,000 m3 yr−1 of sand; this occurred coincident with downdrift barrier-island erosion/migration at long-term rates of >3 m yr−1. Historical sand fluxes to the elongating spit on southern Assateague Island and progradational beach ridges on northernmost Wallops Islands are equivalent to at least 60% of estimated regional longshore transport rates. We therefore propose that sediment trapping and associated wave refraction are the primary drivers of downdrift barrier erosion, while storminess and sea-level rise are secondary forcings of change affecting equally the entire barrier-island chain. Global context is provided by a compilation of sediment trapping through growth of similar longshore sand sinks, which indicates the volume of sediment incorporated into the elongating spit end of Assateague Island is similar to sandy beach- and foredune-ridge plains (108 m3), but average annual trapping at the spit is at least six times greater than those at most mainland-attached, progradational systems. However, Chincoteague and Wallops, two progradational barrier islands, incorporate sand at rates broadly similar to large strandplains. Our findings emphasize the need to account for natural longshore sediment trapping in multi-decadal coastal management efforts on sandy, siliciclastic coasts.

Mechanisms relating offshore geologic framework to shoreline evolution are determined through geologic investigations, oceanographic deployments and numerical modeling. Analysis of shoreline positions from the past 50 years along Fire Island, New York, a 50 km long barrier island, demonstrates a persistent undulating shape along the western half of the island. The shelf offshore of these persistent undulations is characterized with shoreface-connected sand ridges (SFCR) of a similar alongshore length scale, leading to a hypothesis that the ridges control the shoreline shape through the modification of flow. To evaluate this, a hydrodynamic model was configured to start with the US East Coast and scale down to resolve the Fire Island nearshore. The model was validated using observations along western Fire Island and buoy data, and used to compute waves, currents and sediment fluxes. To isolate the influence of the SFCR on the generation of the persistent shoreline shape, simulations were performed with a linearized nearshore bathymetry to remove alongshore transport gradients associated with shoreline shape. The model accurately predicts the scale and variation of the alongshore transport that would generate the persistent shoreline undulations. In one location, however, the ridge crest connects to the nearshore and leads to an offshore-directed transport that produces a difference in the shoreline shape. This qualitatively supports the hypothesized effect of cross-shore fluxes on coastal evolution. Alongshore flows in the nearshore during a representative storm are driven by wave breaking, vortex force, advection and pressure gradient, all of which are affected by the SFCR.

The ability to accurately quantify shoreline variability is essential in order to establish aggressive mitigation strategies, based on recent global climate change projections. This investigation e...

Paine, J.G.; Caudle, T.L., and Andrews, J.R., 2017. Shoreline and sand storage dynamics from annual airborne LIDAR surveys, Texas Gulf Coast. Annual airborne LIDAR surveys were conducted along the Texas Gulf of Mexico shoreline between 2010 and 2012 to map shoreline position, determine shoreline movement and its historical context, and quantify beach and dune morphology by determining elevation threshold area (ETA) relationships for Holocene barrier islands, strandplains, and fluvial and deltaic headlands and marshes. Historical (1800s to 2007) movement is erosional for all major Texas shoreline segments, averaging 1.3 m/y of retreat. Shorelines retreated between 2007 and 2010 at a higher average rate of 2.8 m/y because of erosion and partial recovery from Hurricanes Ike (2008), Humberto (2007), and Dolly (2008). Despite the erosional context, airborne LIDAR surveys show that the shoreline advanced at 75% of 11,783 monitoring sites between 2010 and 2011 and moved an average of 6.5 m seaward durin...

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 96 h 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.

Human interventions on sandy barriers disturb natural barrier dynamics, to the extent of having become key forces in modifying geomorphological evolution. This work identifies natural and human-induced drivers and analyses their importance to the multi-decadal evolution of the Ria Formosa barrier island system, in South Portugal. Aerial photographs from the last six decades and historical maps are used to assess changes in cross-shore rates, morphological characteristics (barrier and dune widths, inlet morphology and migration) and barrier areas, through systematic methods that can be easily transferred to other barrier systems. Interventions, and especially hard engineering ones (jetties, inlet stabilisations), affected barrier evolution trends. Shore-perpendicular works increased shoreline progradation updrift and initiated coastal retreat downdrift, with strongest erosive impacts along the edges of the system. Inlet stabilisations changed tidal inlet hydrodynamics and initiated ebb-shoal attachment to the barriers on either side of a non-migrating inlet that experienced loss of tidal prism. This shoal attachment was the main factor for the increase in total barrier area of Ria Formosa during the 60 years of analysis. Barrier growth after 2005 was slower, which could indicate that the system is reaching morphodynamic stability. The work was implemented in the framework of the EVREST project (PTDC/MAR-EST/1031/2014), funded by FCT (Fundação para a Ciência e a Tecnologia), the Portuguese national funding agency for science, research and technology. Ana Matias was supported by the contract IF/00354/2012, Susana Costas by the contract IF/01047/2014 and A.-Rita Carrasco by the grant SFRH/BPD/88485/2012, all funded by FCT. info:eu-repo/semantics/publishedVersion

The southern Gulf of Carpentaria coast is a relatively straight coast trending southeast for 900 km and forming the southern shore of the large Gulf. It has a monsoonal climate with the trade winds generally flowing off to alongshore. The coast occupies part of the Carpentaria Basin and has a low to very low gradient coastal zone, with supratidal flats extending in places tens of kilometre inland. A series of small- to moderate-sized rivers delivered terrigenous sediment to the coast and have built deltas and extensive tidal flats, though beach sediments remain 40% carbonate. Tides are meso and wave energy low decreasing to the south as the tide-dominated beaches are replaced by tidal flats and mangroves. Regressive Pleistocene and Holocene barrier islands back the high energy sections, the islands now stranded by a mid-Holocene fall in sea level. To the south the barrier grades into wide chenier-capped tidal flats, usually fringed by mangroves. This chapter examines the coastal processes, beaches, barriers and sediment transport and compartments.

Inundation of barrier islands can cause severe morphological changes, from the break-up of islands to sediment accretion. The response will depend on island geometry and hydrodynamic forcing. To explore this dependence, the non-hydrostatic wave model SWASH was used to investigate the relative importance of bedload transport processes, such as transport by mean flow, short- (0.05&ndash, 1 Hz) and infragravity (0.005&ndash, 0.05 Hz) waves during barrier island inundation for different island configurations and hydrodynamic conditions. The boundary conditions for the model are based on field observations on a Dutch barrier island. Model results indicate that waves dominate the sediment transport processes from outer surfzone until landwards of the island crest, either by transporting sediment directly or by providing sediment stirring for the mean flow transport. Transport by short waves was continuously landwards directed, while infragravity wave and mean flow transport was seaward or landward directed. Landward of the crest, sediment transport was mostly dominated by the mean flow. It was forced by the water level gradient, which determined the mean flow transport direction and magnitude in the inner surfzone and on the island top. Simulations suggest that short wave and mean flow transport are generally larger on steeper slopes, since wave energy dissipation is less and mean flow velocities are higher. The slope of the island top and the width of the island foremost affect the mean flow transport, while variations in inundation depth will additionally affect transport by short-wave acceleration skewness.