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Recent studies along the southern Baltic Sea coast have revealed sedimentary records of catastrophic storm surges that significantly exceed the magnitude of storms documented by instrumental measurements. The present study aimed to apply heavy mineral analysis for storm surge deposits along coasts of Gulf of Gdansk (southern Baltic), as well as for contemporary marine, beach, dune and coastal plain sediments, to test the applicability of the method and to provide new insights into the depositional processes and sediment sources of the storm deposits. The transparent, 0.125–0.25 mm heavy mineral fraction (>2.85 g/cm3) in 118 sediment samples was investigated, and the results were subjected to multivariate statistical analyses (cluster, PCA, LDA). Storm deposits showed higher concentrations of heavy minerals comprising enrichment in garnet, zircon, and rutile. General heavy mineral assemblage depended on regional provenance and primary sediment sources. However, flooding regime (overwash or inundation) played a key role in selective hydrodynamic sorting of grains and mineralogical composition of storm deposits. Interpretation of deposits formed in inundation regime was more certain than deposits formed in overwash regime. In the latter case, deposits showed more similarities to adjacent mineral provinces. Statistical analyses proofed that heavy minerals together with other sedimentological descriptors may be a promising proxy for recognition of deposits related to defined sedimentary environment or identification of particular sedimentological process, e.g. event layers resulted from storm surges.

Chicago’s lakefront beaches experienced inundation and coastal erosion when Lake Michigan’s mean annual water level rose by >1.5 m between 2013 and 2019. Understanding beach geomorphic response to this type of lake-level event is important, as future climate predictions call for a continuation of decadal oscillatory patterns. A GIS-based study of beach change was conducted along the city’s urban lakefront, where sand is embayed by groins, jetties, and revetments. Morphologic changes associated with the most recent decadal lake-level rise were evaluated in context of the surrounding infrastructure. Beach morphometrics, derived from historical aerial images and available LiDAR products, were compared against the characteristics of the fixed urban infrastructure. Overwash volumes associated with an ∼1 m-rise in lake level scaled well with beach size (R2 = 0.88), suggesting that the creation of new sediment accommodation and its spatial distribution along the urban lakefront during lake-level rise is an important control on beach morphodynamic behavior. Overwash patterns were influenced by embayment orientation and groin characteristics. Counterclockwise beach rotation of up to 21° occurred in places where shorelines were exposed to the open lake. More tightly enclosed beaches retreated more uniformly along strike due to passive inundation of terrain with lake-level rise. Our insights provide managers with useful information on key beach behavioral patterns and how they are influenced by infrastructure design, allowing for the possibility of mitigation strategies to be emplaced in anticipation of future lake-level oscillations.

The Great Lakes are non-tidal, but experience significant water level fluctuations at hourly, seasonal, and decadal scales. A rise of 0.83 m was observed between 2013 and 2020 on Lake Erie with the annual water level near the previous record high of 174.89 m set in 1986. In response to elevated water levels, barrier beach-ridges located on the eastern shore of the Point Pelee foreland, in the Lake Erie’s central basin, experienced accelerated erosion including overwash and breaching, removal or burial of vegetation, and damage to infrastructure and sensitive habitat. Historical aerial imagery between 1931 and 2020 and annual average lake levels between 1920 and 2020 were examined to characterize barrier retreat and breach initiation, expansion, and closure. Results indicate that the barriers have transgressed at a rate of >1 m y−1, but the rate of transgression and progradation, overwash, and breaching are dependent on decadal-scale variations in water level. Ephemeral breaches and delta deposits were found to be a significant source of landward sediment transport if breaches remained open for multiple years. This may represent a self-reinforcing cycle that promotes breach fill-in processes, even during high lake levels, and increases the barrier width and resiliency in response to further lake level fluctuations. While common patterns of barrier dynamics were found throughout the time series, human impacts may modify historic barrier transgression rates and breach and recovery processes.

Few paleotempestological studies have focused on coastal sinkholes, a common feature in Florida, which can receive and preserve storm overwash sediments. The major goal of this research is to improve our understanding of the characteristic signatures of storm sediments in sinkholes thereby determining reliability of these environments as proxies for hurricanes. Hurricane Irma as a category 5 storm provides an excellent case study for characterizing storm deposits in sinkholes on Big Pine Key. We cored at four sinkholes along a 350 m transect normal to the shoreline. Core sediments were characterized using physical description, short-lived radioisotope dating, sediment grain size analysis, loss-on-ignition, microfossil analysis, and x-ray fluorescence elemental analysis. We found that Irma deposits had higher abundances of marine foraminifera, less total organic matter and elevated Si/Al and Ca/Ti ratios, compared to pre- or post-Irma sediments. In addition, there was a thinning of the storm sediments along the inland transect. Consequently, we propose that sinkholes, particularly those that are closer to the shoreline, can provide reliable sites for paleotempestology studies.

Subsidence, changes in sediment supply and environments, sea storms, current sedimentary deficit and recent anthropic action are factors determining coastal geomorphological processes and evolution of a transgressive Mediterranean coastal barrier. At a longer timescale, the barrier landward migration is partially due to local subsidence of tectonic origin. Peatmarsh remains under seawater at around 100 m from the present-day coastline (4821–4566 and 4874‒4820 cal BP) show evidence of the more advanced position towards the sea of the late Holocene coastal barrier, which has not been preserved. Furthermore, behind the present gravel barrier, wide sandy washover fans dating about 665 cal BP and 503 cal BP were deposited in the early Little Ice Age (LIA) and during the Sporer Minimum, in periods when sea storms were highly frequent in the Western Mediterranean. The source of the washover fine sands was an ancient deltaic lobe of the Sant Miquel river southern palaeochannel. The avulsion towards the current northern mouth (ca. 1790) produced important sedimentary coastal changes, from fine to gravelly sands. More recently, gravelly washover fans indicating rollover processes were found in the 1945 barrier. Nevertheless, progradational sets of gravelly beach ridges were identified in the central sector between 1977 and 1997. Since 2003, overtop and overwash processes during storms have formed a steep beach ridge nearly 3 m high. Finally, recent direct anthropic action has favoured rapid landward migration of the barrier, with processes of fast rollover, cannibalization and dissolution phases.

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.

Williams, H.F.L. and Liu, K.-b., 2021. Testing XRF discrimination of marine and terrestrial flood deposits in southeastern Texas coastal marshes. Journal of Coastal Research, 37(6), 1081–1087. Coconut Creek (Florida), ISSN 0749-0208. This study tests the ability of X-ray fluorescence (XRF) analysis to discriminate between storm-generated marine and terrestrial sediment beds in coastal wetlands. Cluster analysis was applied to the elemental compositions of a sediment core and a monolith collected from McFaddin National Wildlife Refuge in southeastern Texas. The core contains washover sediment beds previously attributed to hurricanes Ike, Rita, Carla, and Audrey. The monolith contains a terrestrial flood deposit attributed to Hurricane Harvey and a washover sediment bed attributed to Hurricane Ike. Clustering correctly distinguished between washover, flood, and marsh deposits. This level of discrimination was not achieved by previous studies based on loss-on-ignition and microfossil analyses because sediment from these different sources can have similar moisture, organic, carbonate, texture, and microfossil characteristics. Cluster analysis places every centimeter of a sediment core into a cluster, providing a more precise means of evaluating the relative contributions of marine and terrestrial sources. In the study area, for example, cluster analysis suggests that 50.5% of coastal marsh sediment was derived from marine sources. The XRF technique used in this study is a promising tool for discrimination of marine and terrestrial sediment sources. Further research is warranted to apply this technique in other coastal environments subject to marine and terrestrial sediment inputs.

Napatree Point, an isolated barrier in southern Rhode Island, provides a case study of barrier spit migration via storm driven overwash and washover fan migration. Documented shoreline changes using historical surveys and vertical aerial photographs show that the barrier had little in the way of net change in position between 1883 and 1939, including the impact of the 1938 hurricane. The barrier retreated rapidly between 1945 and 1975, driven by both tropical and extra-tropical storms. The shoreline position has been largely static since 1975. The removal of the foredune during the 1938 hurricane facilitated landward shoreline migration in subsequent lower intensity storms. Dune recovery following the 1962 Ash Wednesday storm has been allowed due to limited overwash and barrier migration over the last several decades. Shoreline change rates during the period from 1945–1975 were more than double the rate of shoreline change between 1939 and 2014 and triple the rate between 1883 and 2014, exceeding the positional uncertainty of these shoreline pairs. The long-term shoreline change rates used to calculate coastal setbacks in Rhode Island likely underestimate the potential for rapid shoreline retreat over shorter time periods, particularly in a cluster of storm activity. While sea-level rise has increased since 1975, the barrier has not migrated, highlighting the importance of storms in barrier migration.

Beachrock may be considered a reliable indicator of sea level, in addition to a reliable and recognizable source for onshore movement of beachrock clasts by overwash processes associated with extreme events. Key to this is its geomorphology and preservation potential, both of which are poorly understood. Here we examine the processes and deposits associated with beachrock breakdown from Camurupim, NE Brazil and compare its preservation to beachrocks found on continental shelves in South Africa. We study a prominent and continuous 50–60 m-wide beachrock complex that crops out along a 10 km stretch of coastline, and which mostly comprises 1.5 to 2 m-thick trough-crossbedded sandstones. These have generated large joint-bounded blocks that have been transported landwards under extreme energy conditions (based on numerical modelling and comparisons to the contemporary wave climate). Tabular clasts have accumulated as isolated, very coarse boulders on the seaward margin, small clasts in various topographic traps, boulder ridges with large landward- and seaward-dipping clasts on the uppermost part of the outcrop, and subaqueous and subaerial washover fans. Isolated fine meso-boulders emplaced during extreme waves (Hs = ca. 12 m) exhibit fitted textures and pressure-solution contacts, pointing to subsequent rocking and shaking. Smaller clasts in boulder ridges and overwash settings are initially liberated and transported by waves within the annual-decadal frequency spectrum, deposited on the high points of the outcrop. Subsequent movement during less extreme wave action progressively transports the clasts across the surface, where they are often trapped in the fitted fabric on top of the platform. Our breakdown model and overall beachrock preservation scheme is consistent with reported seismic signatures of submerged Holocene beachrock shorelines. Beachrock preservation during transgression is strongly influenced by the original sedimentary facies; thick, trough-crossbedded joint-bound clasts preserve the former shoreline. Clasts from the planar units accumulate as washover fans to landwards of the ridge.

In the afternoon of October 2, 2015, Hurricane Joaquin made landfall on San Salvador Island, the easternmost island in the Bahamian Archipelago. In this study, post-storm surveys that estimated storm surge height and assessed structural damage on the island were evaluated within the context of Joaquin’s meteorological characteristics. The findings from Hurricane Joaquin were then compared to impacts from other notable storms that affected San Salvador in recent decades, namely Hurricane Lili (1996), Hurricane Floyd (1999), and Hurricane Frances (2004). Hurricane Joaquin’s trajectory likely contributed to the extent and distribution of storm surge and damage on San Salvador. Near its peak strength, Joaquin approached the island from the south, which is a climatologically unusual track. Lili also approached San Salvador from the south and exhibited similar patterns of storm surge, overwash, and vegetation disturbance, particularly along the southern end of the island. During Joaquin’s passage, winds of at least tropical storm-force likely impacted San Salvador for 48 consecutive hours, which is twice the duration of such winds associated with the other three hurricanes. Storm surge recorded from Joaquin was more evenly distributed across the island, whereas surge recorded from Floyd and Frances was more concentrated on the western and eastern sides of the island, respectively. While the average surge height on the island was highest from Frances, the percentage of structures with heavy damage was much higher from Joaquin, which may be due to the extended duration of strong winds.

With global warming, the ice-covered areas in the Arctic are being transformed into open water. This provides increased impetus for extensive maritime activities and attracts research interests in sea ice modelling. In the polar region, ice sheets can be several kilometres long and subjected to the effects of ocean waves. As its thickness to length ratio is very small, the wave response of such a large ice sheet, known as its hydroelastic response, is dominated by an elastic deformation rather than rigid body motions. In the past 25 years, sea ice hydroelasticity has been widely studied by theoretical models; however, recent experiments indicate that the ideal assumptions used for these theoretical models can cause considerable inaccuracies. This work proposes a numerical approach based on OpenFOAM to simulate the hydroelastic wave-ice interaction, with the Navier-Stokes equations describing the fluid domain, the St. Venant Kirchhoff solid model governing the ice deformation and a coupling scheme to achieve the fluid-structure interaction. Following validation against experiments, the proposed model has been shown capable of capturing phenomena that have not been included in current theoretical models. In particular, the developed model shows the capability to predict overwash, which is a ubiquitous polar phenomenon reported to be a key gap. The present model has the potential to be used to study wave-ice behaviours and the coupled wave-ice effect on marine structures., Comment: 23 pages 9 figures, submitted journal paper

Storm surge is a critical component in the evolution of barrier island systems, eroding the shoreface and depositing sediment landward as overwash deposits; this “rollover” process enables barrier islands to migrate landward during periods of rising sea level. However, cyclonic storms may also generate seaward-directed flow and sediment transport, which is not typically accounted for in barrier island modeling. A strong outflow occurred at Port Aransas, Texas during Hurricane Harvey in 2017, as evidenced from field observations, satellite photos, and tide data; modeling indicates that outflow was forced by offshore winds to the left of landfall. To investigate the impact of this event on the barrier system, we collected post-storm multibeam bathymetry data and sediment samples within Aransas Pass and Lydia Ann Channel, important conduits linking the bays to the Gulf of Mexico, and where such data were previously collected in 2009 and 2012. The 2009–2012 comparison provides a baseline against which to ascertain the storm impact contained in the 2012–2017 comparison. Both land- and marine-based evidence indicate that significant erosion accompanied the outflow event, focused at the edges of the Corpus Christi ship channel and Lydia Ann Channel. Large quantities of sand, up to 6.5 m thick, also accumulate in deeps of Aransas Pass and Lydia Ann Channel, presumably as the outflow event waned in strength. We infer that the outflow event transported a large amount of barrier system sands offshore, but do not have sufficient constraints at this time to quantify it.

Due to their position at the land-sea interface, barrier islands are vulnerable to both oceanic and atmospheric climate change-related drivers. In response to relative sea-level rise, barrier islands tend to migrate landward via overwash processes which deposit sediment onto the backbarrier marsh, thus maintaining elevation above sea level. In this paper, we assess the importance of interior upland vegetation and sediment transport (from upland to marsh) on the movement of the marsh-upland boundary in a transgressive barrier system along the mid-Atlantic Coast. We hypothesize that recent woody expansion is altering the rate of marsh to upland conversion. Using Landsat imagery over a 32 year time period (1984-2016), we quantify transitions between land cover (bare, grassland, woody vegetation, and marsh) and the marsh-upland boundary. We find that the Virginia Barrier Islands have both gains and losses in backbarrier marsh and upland, with 19% net loss from the system during the timeframe of the study and increased variance in marsh to upland conversion. This is consistent with recent work indicating a shift toward increasing rates of landward barrier island migration. Despite a net loss of upland area, macroclimatic winter warming resulted in 41% increase in woody vegetation in protected, low-elevation areas, introducing new ecological scenarios that increase resistance to sediment movement from upland to marsh. Our analysis demonstrates how the interplay between elevation and interior island vegetative cover influences landward migration of the boundary between upland and marsh (a previously underappreciated indicator that an island is migrating), and thus, the importance of including ecological processes in the island interior into coastal modeling of barrier island migration and sediment movement across the barrier landscape.

This paper investigates the response of a mixed sand and gravel (MSG) barrier coastline to storms and sudden relative sea-level change using the numerical model XBeach-G. The barrier beaches of southern Hawke's Bay, New Zealand provide a natural laboratory for the work owing to spatial variability in instantaneous land deformation that occurred during the 1931 Hawke's Bay earthquake. Historic (1931) and contemporary (2017) morphodynamics of one tectonically uplifted (+1.5 m) and one subsided (−0.78 m) barrier were modelled under energetic waves (Hs 1–6 m). XBeach-G was designed to simulate pure gravel beach morphodynamics, but despite this, the model demonstrated high quantitative skill when calibrated for the MSG coast. Results reveal the storm impact regimes of each profile and potential linkages to decadal-scale barrier development observed in historical beach profile data. Storm-swash processes at the uplifted profile indicate long-term barrier stability due to a lack of change at the barrier crest, and ridge building observed in model simulations provides a potential formative mechanism for decadal-scale beach progradation. At the subsided barrier, modelled historic crest build-up (up to 0.3 m) and narrowing (over 5 m) indicate an overtopping mode of response to sudden relative sea-level rise. Simulation results are consistent with historical beach profile observations that also show chronic narrowing of the subsided barrier through time. Simulations of the modern barrier draw attention to the possibility that it may be on a trajectory toward catastrophic breakdown under extreme conditions, but further work is needed to distinguish the relative importance of historical sudden sea-level rise versus deficits in sediment supply to this shoreline.

Shoreline erosion can transition freshwater coastal wetlands from carbon sinks to carbon sources. No studies have explored the impacts of coastal geomorphic processes on freshwater wetland carbon budgets. To do so, we modified a saltmarsh carbon budget model for application in freshwater coastal wetlands. We validated the model with data from a shoreline wetland in the Laurentian Great Lakes. The model generates the carbon budget by differencing carbon export and carbon storage. The inputs for carbon storage are the carbon inventory and maximum wetland age. Inputs for carbon export include erosion rates and overwash extent. The model demonstrates that the wetland examined in this study transitioned to a source of carbon during periods of erosion. In fact, the net carbon export between 2015 and 2018 was 8.1% of the wetland’s original carbon stock. This study indicates that geomorphic change can dictate whether and how freshwater coastal wetlands serve as sources or sinks for terrestrial carbon, and that carbon stocks can fluctuate on a geologically rapid timescale. We recommend that such geomorphic processes be considered when developing carbon budgets for these marginal environments. Furthermore, the carbon budget model refined in this study can be used to prioritize wetlands in land management and conservation efforts.

Waves and water level setup during storms can create overwashing flows across barrier islands. Overwashing flows can cause erosion, barrier breaching, and inlet formation, but their sediments can also be deposited and form washover fans. These widely different outcomes remain difficult to predict. Here we suggest that a breach develops when the sediment volume transported by overwashing flows exceeds the barrier subaerial volume. We form a simple analytical theory that estimates overwashing flows from storm characteristics, barrier morphology, and dune vegetation, and which can be used to assess washover deposition and breaching likelihood. Our theory suggests that barrier width and storm surge height are two important controls on barrier breaching. We test our theory with the hydrodynamic and morphodynamic model Delft3D as well as with field observations of 21 washover fans and 6 breaches that formed during Hurricane Sandy. There is reasonable correspondence for natural but not for developed barrier coasts, where traditional sediment transport equations do not readily apply. Our analytical formulations for breach formation and overwash deposition can be used to improve long-term barrier island models.

Beaches responses to storms, as well as their potential adaptation to the foreseeable sea level rise (SLR), were investigated along three beaches in a coastal tract in western Sardinia (Western Mediterranean Sea). The grain size of the sediments, the beach profile variability and the wave climate were analyzed in order to relate morphological changes, geological inheritances and waves forcing. Multibeam, single-beam and lidar data were used to characterize the inner shelf morphologies and to reproduce the flooding due to the SLR. The studied beaches experienced major changes when consecutive storms, rather than singles ones, occurred along the coastline. The sediment availability, the grain size and the geomorphological structure of the beaches were the most important factors influencing the beach response. On the sediment-deprived coarse beaches the headlands favor the beach rotation, and the gravel barrier morphology can increase the resistance against storms. On the sediment-abundant beaches, the cross-shore sediment transport towards a submerged area leads to a lowering in the subaerial beach level and a contemporaneous shoreline retreat in response to storms. A very limited ingression of the sea is related to the SLR. This process may affect (i) the gravel barrier, promoting a roll over due to the increase in overwash, (ii) the embayed beach increasing its degree of embayment as headlands become more prominent, and (iii) the sediment-abundant beach with an erosion of the whole subaerial beach during storms, which can also involve the foredune area.

Castagno, K.A.; Donnelly, J.P., and Woodruff, J.D., 2021. Grain-size analysis of hurricane-induced event beds in a New England salt marsh, Massachusetts, USA. Journal of Coastal Research, 37(2), 326–335. Coconut Creek (Florida), ISSN 0749-0208.Tropical cyclones pose a growing threat to coastal infrastructure and livelihood. Because instrumental and historic records are too short to help us understand interactions between tropical cyclones and climate on a longer scale, proxy records are the only means for reconstructing millennia of tropical cyclone impacts. This study determines grain-size trends in storm-induced overwash deposits along a transect of sediment cores from a salt marsh in Mattapoisett, Massachusetts, to characterize sorting trends and compare deposits associated with individual storms. The overwash deposits preserved within the high-marsh peat provide a record spanning the last two millennia. Building on a 2010 study, a different approach was used to accurately determine the grain-size distribution of overwash deposits from cores in a transect running perpendicular to the adjacent sandy/gravely barrier. Although maximum grain-size values are expected to decrease as distance from the barrier increases, not all event deposits that were studied follow this trend within uncertainty. Analysis of the storm event beds reveal a significant difference in settling trends between historic and prehistoric deposits, with historic deposits largely displaying landward-fining trends and prehistoric deposits largely displaying landward-coarsening trends. This suggests changes in the hydrodynamic or that geomorphic regime may have altered the way in which storm beds were deposited at this site. This new in-depth, transect-based approach has utility for improving the accuracy of future storm reconstructions, particularly for events for which no historic record exists.

Small, low-lying islands are particularly vulnerable to global climate change and sea level rise with the principal impacts falling into three main categories: shoreline erosion, inundation and flooding, and saline water intrusion into surficial freshwater aquifers. Fresh groundwater on small islands occurs primarily as freshwater lenses, floating atop saline groundwater, whose natural size depends on island area, shape, and topography, aquifer properties (transmissivity), and rainfall. Freshwater lenses are limited resources that are vulnerable to salinization from over exploitation and from storm overwash. The sustainability of freshwater lenses depends on maintaining a balance between recharge, captured discharge, and pumping. Decreases in recharge during drought periods can result is a profound shrinkage of freshwater lenses. Anthropogenic activities can impact freshwater lenses through induced changes in recharge rates caused by increased impervious covers. Management of freshwater lenses can be improved through improved well and wellfield design, monitoring of aquifer water levels and salinity, controls on groundwater pumping, implementation of land use practices to reduce the risk of anthropogenic contamination, and managed aquifer recharge.

Rising sea levels pose a direct threat to coastal communities through permanent inundation of low-elevation areas and greater and more widespread temporary inundation from possibly more intense storms and king tides atop a higher sea level baseline. Sea level rise will also cause higher groundwater levels in coastal areas causing inundation of low-lying areas and impacts to shallowly buried infrastructure. The risks posed by rising sea levels are compounded by the large and growing populations of coastal urban areas. Areas vulnerable to direct marine inundation and groundwater inundation sea level are most commonly screened using the hydrostatic or “bathtub” approach, which assumes that sea level and the water table rises at the same rate everywhere in a coastal study area, or more accurate dynamic and groundwater modeling. Sea level rise will contribute to the salinization of coastal aquifers through more frequent and greater extent overwash events and saline water intrusion, with the later evaluated through density-dependent numerical groundwater modeling.

Gravel beaches and barriers form a valuable natural protection for many shorelines. The paper presents a numerical modelling study of gravel barrier beach response to storm wave conditions. The XBeach non-hydrostatic model was set up in 1D mode to investigate barrier volume change and overwash under a wide range of unimodal and bimodal storm conditions and barrier cross sections. The numerical model was validated against conditions at Hurst Castle Spit, UK. The validated model is used to simulate the response of a range of gravel barrier cross sections under a wide selection of statistically significant storm wave and water level scenarios thus simulating an ensemble of barrier volume change and overwash. This ensemble of results was used to develop a simple parametric model for estimating barrier volume change during a given storm and water level condition under unimodal storm conditions. Numerical simulations of barrier response to bimodal storm conditions, which are a common occurrence in many parts of the UK were also investigated. It was found that barrier volume change and overwash from bimodal storms will be higher than that from unimodal storms if the swell percentage in the bimodal spectrum is greater than 40%. The model is demonstrated as providing a useful tool for estimating barrier volume change, a commonly used measure used in gravel barrier beach management.

Barrier islands are ubiquitous coastal features that create low-energy environments where salt marshes, oyster reefs, and mangroves can develop and survive external stresses. Barrier systems also protect interior coastal communities from storm surges and wave-driven erosion. These functions depend on the existence of a slowly migrating, vertically stable barrier, a condition tied to the frequency of storm-driven overwashes and thus barrier elevation during the storm impact. The balance between erosional and accretional processes behind barrier dynamics is stochastic in nature and cannot be properly understood with traditional continuous models. Here we develop a master equation describing the stochastic dynamics of the probability density function (PDF) of barrier elevation at a point. The dynamics are controlled by two dimensionless numbers relating the average intensity and frequency of high-water events (HWEs) to the maximum dune height and dune formation time, which are in turn a function of the rate of sea level rise, sand availability, and stress of the plant ecosystem anchoring dune formation. Depending on the control parameters, the transient solution converges toward a high-elevation barrier, a low-elevation barrier, or a mixed, bimodal, state. We find the average after-storm recovery time—a relaxation time characterizing barrier’s resiliency to storm impacts—changes rapidly with the control parameters, suggesting a tipping point in barrier response to external drivers. We finally derive explicit expressions for the overwash probability and average overwash frequency and transport rate characterizing the landward migration of barriers.

The effect of waves on ice sheet is critical in the marginal ice zone (MIZ). Waves break large sea ice into small pieces and cause them to collide with each other. Simultaneously, the interaction between sea ice and waves attenuates these waves. In this study, a numerical research is conducted based on a computational fluid dynamics (CFD) method to investigate the response of single ice floe to wave action. The obtained results demonstrate that the sea ice has a violent six degree of freedom (6DoF) motion in waves. Ice floes with different sizes, thicknesses, and shapes exhibit different 6DoF motions under the action of waves. The heave and surge response amplitude operator (RAO) of the sea ice are related to wavelength. Furthermore, the overwash phenomenon can be observed in the simulation. The obtained results are compared with the model test in the towing tank based on artificial ice, and they agree well with test results.

The aim of the collaborative project PADO (“Processes and implication of dune breaching at the German Baltic Sea Coast”) is the investigation of dune breaching and the resulting flooding of the hinterland based on a large-scale research dune. During the physical model test, which was located at the beach of Rostock-Warnemuende, the dune was destroyed by a storm surge in November 2018. The measured data served as basis for the set-up of a numerical coastal erosion model with XBeach. The application of the latest XBeach-X release with the default settings results in an underestimation of the mean wave height at the model entrance. Moving closer to the shore, the underestimation decreases leading to a good agreement with observed wave heights in the nearshore zone, especially after the first third of the simulation. Furthermore, the model computes dune erosion due to collision and overwash which is in line with the observation. The predicted final dune erosion is in good agreement with the post-storm measurements of the dune topography and, hence, only minor calibration is needed.

The character and energetics of infragravity (“IG,” 25 s < period < 250 s) and very-low frequency (“VLF,” period > 250 s) waves over coral reef flats can enhance shoreline erosion or accretion, and also govern extreme shoreline events such as runup, overwash, and flooding on coral reef-lined coasts. Here we use in situ wave measurements collected along cross-reef transects at 7 sites on Pacific islands with varying reef geomorphologies to examine under what conditions IG waves occur and what factors enhance their irregularity. In general, a greater fraction of total wave energy was transferred to the IG band on reefs with steeper fore reef slopes and shallower reef flats. The IG wave amplitudes scaled with increasing water levels, but it was primarily at lower water levels when these waves became pitched onshore (negatively asymmetrical) and peaked (positively skewed). However, our results also highlight the importance of reef-flat width and slope as important morphological controls on IG waves, as the most asymmetric, bore-like, IG waves occurred on the wider reef flats, and the most skewed IG waves at the site with the steepest reef-flat. On the wider reef flats, IG wave-wave capture was observed during periods of large offshore wave forcing and enhanced VLF wave energy. Because similar IG wave motions over plane beaches enhance sea-swell (“SS,” period < 25 s) bore-merging in the surf zone, we posit that VLF waves over reef flats may facilitate IG bore merging, and this may lead to larger, more pitched-onshore bores at the shoreline. In addition, greater IG wave heights appear to support the transmission of larger secondary short-period waves over the reef flat, independent of overall water levels. As irregular IG waves may be strong drivers of cross-reef sediment transport as well as runup, understanding the conditions and reef geomorphologies that lead to low-frequency, energetic bores on reef flats is critical to forecasting how coral reef-lined coasts will respond to sea-level rise and climate change.

This entry broadly addresses the causes of and responses to coastal erosion and shoreline change. Three major causes of shoreline change are examined in detail: sea level change, storms and waves, and sediment supply and transport. The history of both postglacial and recent global sea level change is discussed, and factors that influence relative sea level change are also fully considered. Short- and long-term impacts of storms, including dune recession, cliff and bluff erosion, and overwash are described. Finally, sediment transport related to longshore drift and tidal dynamics is included. Three major responses to coastal erosion and their impacts are then described: hard stabilization, soft stabilization, and relocation. Sea walls, jetties, and groins are described as the most common forms of hard coastal stabilization. Beach nourishment is covered as the major form of soft stabilization. Finally, examples of structural and community-scale relocation efforts are included. The entry concludes with a projection of what shoreline change may look like in the future, specifically in the context of climate change.

The Outer Banks of North Carolina extend from the Virginia-North Carolina border south to Cape Lookout, a distance of 240 km. These islands were originally one continuous biophysical system, but the upper section has experienced three decades of dune and beach stabilization, coupled with extensive public and private development. In 1957 the stabilized islands became the Cape Hatteras National Seashore. The southern segment, which includes Core Banks, remains in a natural state and is authorized to become the new Cape Lookout National Seashore. The responses of these two different systems to the inshore processes are of special interest for both preservation and management reasons. Natural barrier islands are much better adapted to steady-state processes and extreme events than are the man-manipulated islands. Since there is little resistance to the storm surge movement across the natural barriers, wave energy is dissipated across the wide berm, among the low dunes, and finally in the grasslands and marshes behind. These islands actually gain material from the beach as the surge moves across the islands, and such deposits serve as sources of supply for new dune growth. Within the stabilized segment of the Outer Banks, the massive and unbroken man-made dunes act as an impenetrable obstruction to a storm surge, so the energy dissipation and sediment transfer processes are significantly different. The most important differences are associated with the restrictions of the run-up profile and the elimination of oceanic overwash. Overwash is the major means by which low barrier islands retreat before the rising sea. It is the only way massive quantities of coarse sediment can be moved inland from the beach.

Marine litter pollution on coastal dunes has received limited scientific attention when compared with sandy shores. This paper proposes a new framework based on the combined use of Unmanned Aerial Systems (UAS) and a mobile application to map and quantify marine macro-litter (>2.5 cm) accumulation on coastal dunes. The first application on a dune area of 200 m × 80 m at the north-east Atlantic Portuguese coast is shown. Nine different marine litter categories were found, with styrofoam fragments (23% of the total amount) and plastic bottles (20%) being the most abundant items. Plastic was the most common material (76%). The highest number of items (272) was found on the backdune, mostly related with fishing activities (octopus pots and Styrofoam fragments). In contrast, the highest density (0.031 items/m2) was found on the foredune, with the most abundant items associated with human recreational activities (for example, plastic bottles, bags, papers and napkins). Three major marine litter hotspots (~0.1 items/m2) were identified in correspondence of dune blowouts. The recognition of the primary marine litter pathways highlighted the main role that wind and overwash events play on dune contamination, and suggests that the dune ridge restoration can act as a mitigation measure for preventing marine litter accumulation on the backdune. This study shows how UAS offer the possibility of a detailed non-intrusive survey, and gives a new impulse to coastal dune litter monitoring, where the long residence time of marine debris may threaten the bio-ecological equilibrium of these ecosystems.

Human encroachment and development on coastlines have led to greater amounts of armoring of shorelines. Breakwaters are a common feature along coastlines, which are used to dampen wave energy and protect shorelines from flash floods or overwash events. Although common, their effects on sediment transport and marsh geomorphology are poorly understood. To address this gap, our study quantifies the effects of breakwaters on sediment transport and marsh evolution under different wave regimes using Delft3D-SWAN, a dynamic geomorphodynamic numerical model. Model configurations used the same numerical domain, but scenarios had different sediments, waves, tides, basin slopes and breakwater distances from the shoreline to explore how waves and tidal currents shape coastal margins. Model results suggested breakwaters were responsible for an average wave damping between 10&ndash, 50%, proportional to the significant wave height across all modeled scenarios. Shear stress at the beginning of the marsh and the volume of sediment deposited at the end of the simulation (into the marsh behind the breakwater) increased on average between 20&ndash, 40%, proportional to the slope and distance of the breakwater from the shoreline. Sediment trapping, defined as the ratio between the volume of sediment housed into the salt marsh behind and away from the breakwater, was found to be less than 1 from most model runs. Study results indicated that breakwaters are advantageous for wave breaking to protect shorelines from the wave&rsquo, s energy, however, they might also be an obstacle for sediment transport, negatively affecting nourishment processes, and, consequently, impeded long-term salt marsh survival. Identifying a balance between waves dampening and shoreline nourishment should be considered in the design and implementation of these structures.

Tsunami and other extreme-wave deposits are often searched for along sandy, wave-dominated coastlines that are characterized by ridge-and-swale topography. Understanding the morphodynamics of beach-ridge formation and the evolution of ridge-and-swale topographies on short and long timescales is essential to identify sites where tsunami and storm deposits are most likely preserved. In addition, the geomorphic expression of individual ridges and beach-ridge sets provides an important proxy for overwash events, related modifications to sediment supply, and seismically induced land-level changes. Using a combination of remote-sensing techniques, field surveys, and sediment analysis, large-scale impacts on coastal morphologies can be detected and chronologies of extreme-wave events developed. This chapter introduces the characteristics of beach-ridge plains, summarizes the signature of tsunami- and storm-induced erosion and reorganization of such coastal settings, and describes approaches on how to best detect these imprints.

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.

Author(s): Gernant, Cameron Michael | Advisor(s): Simms, Alexander R | Abstract: Raised beach ridges in polar environments are recorders of relative sea-level (RSL) change. The South Shetland Islands (SSI) contain large areas of ice-free raised beaches used to resolve paleo-sea-level change. The largest of these ice-free areas is Byers Peninsula (60 km2) on Livingston Island, SSI. This peninsula and other ice-free coasts within the SSI contain series of raised beach ridges correlated by age and elevation. The internal architecture of these beach ridges is critical to understanding paleo-RSL. The non-destructive method of ground penetrating radar (GPR) was used to investigate the internal architecture of the South Beaches of Livingston Island where a flight of nine beach ridges (five of which were the focus of in this study) have been glacio-isostatically raised since the last glacial maximum (LGM). Recalibrated radiocarbon ages collected from these and other beach ridges in previous studies are used to relate beach morphology and stratigraphy to the glacial history of the region. Over 10 km of 200 MHz GPR transects and synchronous GPS were collected over a two-week period in the spring of 2019. Sediment pits l1 m in depth were dug to search for dateable material and described for ground truthing of GPR reflections. Six key radar facies and three radar surfaces were identified: a seaward dipping progradational facies, a landward dipping overwash facies, a flat and concave down aggradational facies, a discontinuous hyperbola rich cobble facies, a flat lying lagoon facies, and a channelized fluvial facies. Erosional and toplapping surfaces were identified in addition to the top of the bedrock. Within this flight of raised beach ridges evidence was found of transgressive depositional patterns marked by progradational seaward dipping facies deposited during periods of RSL fall followed by erosion and overlying deposition of landward dipping overwash and aggrading beds. This succession is routinely located over a notch in the bedrock interpreted to represent a wave-cut feature. An apparent correlation between the ages of beach ridges and wave-cut notches with known neoglacial advances at ~5.5 ka, ~3-1 ka, and ~0.4 ka suggests that the influence of glacial-isostatic adjustment (GIA) on RSL is responsible for the origin of the beach ridges and the underlying wave-cut scarps. This GIA hypothesis further supports recent assertions of a much more dynamic RSL history for Antarctic coastlines, which may “contaminate” the LGM RSL signal across Antarctica.

A laboratory experiment was conducted in a wave flume to compare sand beach profile evolution and wave overtopping of a sand berm for the three cases of (1) no structure, (2) a stone revetm...

Due to the impact of global warming on sea ice cover, experimental research is required to better understand the interactions between sea ice and waves. In this study, an experiment was conducted on waves propagating through a solitary floe model, at Shanghai Jiao Tong University. The front (reflected) and rear (transmitted) wave fields and the overwash waves around the floe model with regular incident waves were investigated within a range of incident periods and steepness values. The floe model exhibited loose mooring in the wave flume. This paper proposed a novel material to model an ice floe, which is composed of three layers of elastic plates. By conducting bending tests, the Young's modulus and density of the composite plate were found to be within the range of field-measured ice parameters after scaling. Two materials, namely, a novel material and polypropylene, were used to model the ice floe in this experiment. The results of the experiment conducted on a polypropylene plate are presented in this paper for verification and comparison with the results for the novel material. The results revealed that the proportion of incident waves transmitted through a solitary ice floe decreases with an increase wave steepness for both plates. The lowest of transmission coefficient and highest reflection coefficient are achieved when the incident wavelength is equal to the floe length. With an increases in the steepness of the incident wave, the overwash height continues and the higher-order harmonic of wave energy increases.

The Barrier-Lagoon System III is the better preserved Pleistocene depositional system in the southern Coastal Plain of the state of Rio Grande do Sul, Brazil. The origin of this unit is correlated to the sea-level highstand of the last interglacial stage, but so far very little is known about the evolution and stratigraphy of this unit due to the scarcity of outcrops. A fossil assemblage consisting of thousands of bivalve and gastropod shells were recovered from drilling holes and SPT (Standard Penetration Test) surveys performed at depths up to 17 m on that unit. The characterization of these fossils in addition to the analysis of the sediments and SPT data allowed to interpret the depositional setting of the fossil-bearing sediment as backbarrier deposits representing a retrogradational sequence characterized by lagoon bottom and margin facies superposed by sandy aeolian facies, covered by loess deposits. The fossil assemblage found in the lagoon bottom and margin deposits is dominated by bivalve and gastropod molluscs, mostly characteristic of open marine, shallow (≤30 m) environment, but including some Erodona mactroides and Anomalocardia brasiliana, bivalves typical of lagoon environments. The presence of species that do not currently live in the region suggests the influence of warmer coastal waters during the last interglacial stage. The good degree of preservation of a large part of the molluscan assemblage, with no signs of abrasion, bioerosion or incrustation, indicates short residence time at the sediment-water interface after death and disarticulation, followed by rapid burial below the Taphonomically Active Zone (TAZ). The presence of marine species together with species from low energy mixohaline environments indicates the transport of sediments and marine fauna to the backbarrier, which would have occurred during the transgressive phase of System III evolution. This process could have been related to increased storminess during the last interglacial, which promoted the transportation of large amounts of sediments and shells from the shoreface to the backbarrier through overwash and opening of ephemeral inlet channels.

A large body of chronologically well-constrained and detailed Quaternary data accumulated in the last decades from the coastal-shelf region of the northern Gulf of Mexico. Consequently, a preliminary synthesis of major aspects of the late Quaternary barrier and mainland coastal development on the northern Gulf of Mexico is timely. Several major factors account for the striking differences between barrier size and development styles in the three northern Gulf coast regions. Barriers are nearly continuous in the NW where they dominate by the greatest dimensions and continuity. Sand supply from shelf and mainland sources, continued at variable rates throughout six stages of the Last Eustatic Cycle (LEC). Differences in antecedent topography, in fluvial runoff volumes and relative sea level rise, including rapid overstepping-flooding events were critical in the regional distinctions. Leaving fewer and smaller relict fluvial delta behind, drowned shore and nearshore landforms on the shelf, only two large fluvial systems impacted the NE. The NW shelf and nearshore received abundant sediment supply from the Mississippi and lesser streams; indirectly by ravinement erosion of relict landforms and landward-directed cross-shelf sediment transfer. Sands originated mainly in relict deltas, fluvial, tidal channel, and inlet fill, as well as from submerged shore ridge remnants on the continental shelf. Shelf-margin deltas represented major secondary sources. Barrier formation categories and their respective importance in specific areas represent critical aspects of coastal development. The authorship of various formation concepts (e.g., Penck, Gilbert, McGee, Haage, Ganong, and Keilhack) often is still miscredited or remains unrecognized in the literature. Recognition of the stratigraphic and sedimentological diagnostic characteristics of the basic genetic barrier categories plays a key role in testing the validity of barrier evolution models. Closely-knit process-form relationships prevail between hydrodynamic (sea level change, storm, tidal current, overwash), sedimentary (shoal and island aggradation, rollover, and eolian accumulation) processes, and the resulting landform morphology. The most detailed accounts that deal with the development of the Alabama-Louisiana and Apalachicola barrier chains are particularly instructive. Almost all modern Gulf barriers with identifiable genetic background formed by shoal aggradation between 5.5 and 2.0 ka, during a marked deceleration in sea level rise. Concurrently, a sizable mainland strand plain complex extended the NE coastal plain. Tide- and storm-driven sediment transport to the large Mobile Bay ebb-delta, the focal role of composite east Dauphin Island in establishing the MS-LA island chain and the island-blocking role of Mississippi Delta advance were prime factors in a complex barrier history. Migration, paradoxically, may also occur by transgressive rollover concurrently with regressive landward progradation of island strand plains. Stream discharge and sand reworked from relict lithosomes on the shelf were insufficient in compensating for wave- and tide-related sediment loss. Gulf levels stayed below the present throughout the mid- and late Holocene.

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.

Rising sea levels are expected to cause widespread coastal recession over the course of the next century. In this work, new insight into the response of sandy beaches to sea level rise is obtained through a series of comprehensive experiments using monochromatic and random waves in medium scale laboratory wave flumes. Beach profile development from initially planar profiles, and a 2/3 power law profile, exposed to wave conditions that formed barred or bermed profiles and subsequent profile evolution following rises in water level and the same wave conditions are presented. Experiments assess profile response to a step-change in water level as well as the influence of sediment deposition above the still water level (e.g. overwash). A continuity based profile translation model (PTM) is applied to both idealised and measured shoreface profiles, and is used to predict overwash and deposition volumes above the shoreline. Quantitative agreement with the Bruun Rule (and variants of it) is found for measured shoreline recession for both barred and bermed beach profiles. There is some variability between the profiles at equilibrium at the two different water levels. Under these idealised conditions, deviations between the original Bruun Rule, the modification by Rosati et al. (2013) and the PTM model predictions are of the order of 15% and all these model predictions are within ±30% of the observed shoreline recession. Measurements of the recession of individual contour responses, such as the shoreline, may be subject to local profile variability; therefore, a measure of the mean recession of the profile is also obtained by averaging the recession of discrete contours throughout the active profile. The mean recession only requires conservation of volume, not conservation of profile shape, to be consistent with the Bruun Rule concept, and is found to be in better agreement with all three model predictions than the recession measured at the shoreline.

Comprehensive onshore-offshore surficial and sub-surface mapping of a composite barrier (combination of prograded, aggraded, and/or transgressive segments) have provided a better understanding of the (i) mechanisms responsible for the formation and development of coastal barrier systems, (ii) relationships and interactions among individual parts of those systems, and (ii) the overall stratigraphic framework of subaerial and subaqueous segments of the barriers. Here, we investigate these facets of barrier evolution through integration of stratigraphic data from subaqueous high-resolution seismic and subaerial ground-penetrating radar, sedimentology (terrestrial cores and seafloor surface samples), and merged topographic and bathymetric mapping of the Miquelon-Langlade Barrier (northwest Atlantic Ocean, south of Newfoundland). This barrier system has two open coasts and evolved in a paraglacial setting, influenced by the reworking of glaciogenic sediment (glacial moraines) in a regime of complex sea-level changes. The barrier stratigraphic sequence is placed within the context of a shifting period from shoreline transgression to one of regression; the resulting sedimentary units reflect the isolated position of the Saint-Pierre-and-Miquelon Archipelago distal from continental influence. Seismic profiles reveal the position of the lowstand shoreline, located 20–25 m below modern sea level, further refining the existing lowstand model of southern Newfoundland. Continuous onshore-offshore subsurface geophysical mapping of the barrier allows for the identification of the relative positioning of distinct sedimentary units interpreted as subaerial barrier (beaches, dunes, spit), shoals, and shoreface deposits, and allows for estimation of the total barrier sediment volume (235 × 106 m3) and its relative subaqueous (90%) and subaerial (10%) components. Moreover, it reveals the three distinct morphological units comprising the Holocene barrier: (i) central, regressive, swash-aligned beach-ridge plains developed atop both thin (westward-prograding) and thick (eastward-prograding) shoreface deposits, (ii) drift-aligned, elongating spits located in the northwest and northeast of the island, and (iii) a transgressive barrier located adjacent to the northwest spit, pinned on its landward side to parabolic sand dunes, and currently experiencing erosion and limited overwash. Finally, this study places evolution of this system in the framework of paraglacial barrier evolutionary typology.

A series of large storms attributed to Atmospheric River conditions struck the California coast in the winter of 1861-2. Although historical accounts document inland flooding, little is known about how the 1861-2 storms impacted the now heavily-developed California coast. Here we show that the 1861-2 storms emplaced a deposit of beach sand up to 50 cm thick over 450 m inland within a southern California salt marsh. This deposit is unprecedented in the post-European sediments of the marsh and more extensive than that derived from any other historical event. It is comparable in scale to hurricane and tsunami washover fans in back-barrier environments along other coastlines. The presence of overwash deposits in Carpinteria suggests that the 1861-2 storm season was erosive enough to remove coastal barriers, allowing for inundation of parts of the coastline currently developed. Efforts to prepare for a recurrence of an 1861-2-like storm season should address potential coastal impacts; likewise, interpretations of past washover deposits should consider these unusually prolonged stormy periods in addition to hurricane and tsunami inundation.

Hurricane Sandy was a large and intense storm with high winds that caused total water levels from combined tides and storm surge to reach 4.0 m in the Atlantic Ocean and 2.5 m in Great South Bay (GSB), a back-barrier bay between Fire Island and Long Island, New York. In this study the impact of the hurricane winds and waves are examined in order to understand the flow of ocean water into the back-barrier bay and water level variations within the bay. To accomplish this goal, a high resolution hurricane wind field is used to drive the coupled Delft3D-SWAN hydrodynamic and wave models over a series of grids with the finest resolution in GSB. The processes that control water levels in the back-barrier bay are investigated by comparing the results of four cases that include: (i) tides only; (ii) tides, winds and waves with no overwash over Fire Island allowed; (iii) tides, winds, waves and limited overwash at the east end of the island; (iv) tides, winds, waves and extensive overwash along the island. The results indicate that strong local wind-driven storm surge along the bay axis had the largest influence on the total water level fluctuations during the hurricane. However, the simulations allowing for overwash have higher correlation with water level observations in GSB and suggest that island overwash provided a significant contribution of ocean water to eastern GSB during the storm. The computations indicate that overwash of 7500–10,000 m 3 s − 1 was approximately the same as the inflow from the ocean through the major existing inlet. Overall, the model results indicate the complex variability in total water levels driven by tides, ocean storm surge, surge from local winds, and overwash that had a significant impact on the circulation in Great South Bay during Hurricane Sandy.

Numerous studies have been carried out to identify storm deposits and decipher storm-induced sedimentary processes in coastal and shallow-marine areas. This study aims to provide an in-depth review on the study of coastal storm deposits from the following five aspects. 1) The formation of storm deposits is a function of hydrodynamic and sedimentary processes under the constraints of local geological and ecological factors. Many questions remain to demonstrate the genetic links between storm-related processes and a variety of resulting deposits such as overwash deposits, underwater deposits and hummocky cross-stratification (HCS). Future research into the formation of storm deposits should combine flume experiments, field observations and numerical simulations, and make full use of sediment source tracing methods. 2) Recently there has been rapid growth in the number of studies utilizing sediment provenance analysis to investigate the source of storm deposits. The development of source tracing techniques, such as mineral composition, magnetic susceptibility, microfossil and geochemical property, has allowed for better understanding of the depositional processes and environmental changes associated with coastal storms. 3) The role of extreme storms in the sedimentation of low-lying coastal wetlands with diverse ecosystem services has also drawn a great deal of attention. Many investigations have attempted to quantify widespread land loss, vertical marsh sediment accumulation and wetland elevation change induced by major hurricanes. 4) Paleostorm reconstructions based on storm sedimentary proxies have shown many advantages over the instrumental records and historic documents as they allow for the reconstruction of storm activities on millennial or longer time scales. Storm deposits having been used to establish proxies mainly include beach ridges and shelly cheniers, coral reefs, estuary-deltaic storm sequences and overwash deposits. Particularly over the past few decades, the proxies developed from overwash deposits have successfully retrieved many records of storm activities during the mid to late Holocene worldwide. 5) Distinguishing sediments deposited by storms and tsunamis is one of the most difficult issues among the many aspects of storm deposit studies. Comparative studies have investigated numerous diagnostic evidences including hydrodynamic condition, landward extent, grain property, texture and grading, thickness, microfossil assemblage and landscape conformity. Perhaps integrating physical, biological and geochemical evidences will, in the future, allow unambiguous identification of tsunami deposits and storm deposits.

Paleomagnetic sampling and measurement of a boulder accumulation on Little Beecroft Head on the Illawarra coastline of New South Wales was undertaken to evaluate potential emplacement mechanisms. This deposit is of central importance in the Australian Megatsunami Hypothesis (AMH) debate, but to date, there has been no unequivocal determination of its provenance. The most likely emplacement mechanisms are by slow collapse during denudation of overlying strata, storm wave overwash or a combination of these. Characteristic Remanent Magnetisation (ChRM) directions were obtained from 15 individual boulders and the in situ bedrock platform on which they currently rest. The in situ Permian bedrock has a normal polarity mean ChRM direction of D/I = 1.6°/–66.7° (α95 = 5.2°; k = 33.9) that is statistically indistinguishable from the Present Earth Field direction at the site. The magnetisation is most likely due to Cenozoic/recent weathering, which is common in surficial rocks throughout the Sydney Basin. Ch...

This paper presents a software platform to compute the total water level, one of the key variables for the environmental management of coastal zones. The platform integrates six modules: (1) simulation of deep-water wave variables, storm surge and river flow; (2) wave downscaling; (3) wave propagation; (4) contribution of the river discharge; (5) astronomical tide; and (6) total water level. It was applied to three case studies in southern Spain. The first case study consisted of designing the extension of a fluvial marina in a highly dynamic area (Guadalete estuary, Cadiz), and the maximum number of floating docks to avoid flooding events was obtained. The second case study involved calculating the operation conditions for navigation purposes in an inlet with sedimentation problems (Punta Umbria, Huelva), and a relationship between the percentage of operation hours and the dredged volume was obtained. The third case study consisted of estimating the number of overwash events as a function of the height of the berm on a deltaic beach with erosion issues (Guadalfeo, Granada), and a simple design curve to help managers during the decision-making process of artificial nourishment projects was provided. These results highlight the potential of the developed software, whose methodology is feasibly extensible to other coastal areas worldwide, to help managers handle a wide range of environmental problems related to the total water level. This is especially relevant due to the expected sea level rise in the coming years.

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).

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%.

Tropical cyclone inundation is a major threat to the highly exposed islands of the South Pacific. This vulnerability was highlighted in March 2015 when Tropical Cyclone (TC) Pam made landfall on Vanuatu as a Category 5 storm, impacting coastlines with storm surges that produced high water marks up to 7 m above mean sea level (MSL) and deposited overwash sediments up to 400 m inland. We examined the foraminiferal assemblages contained within TC Pam sediments at two locations in Vanuatu: a mixed-carbonate embayment at Manuro on Efate Island and a volcaniclastic beach at Port Resolution Bay on Tanna Island. At Manuro, the TC Pam sediments were up to 10 cm thick and composed of coarse to medium sand that contained abundant foraminifera (955 to 2015 individuals per 5 cm3) and fragments of corals and mollusks. At Port Resolution Bay, TC Pam sediments were up to 44 cm thick and composed of medium sand-sized volcaniclastics with low to moderate abundances of foraminifera (27 to 206 individuals per 5 cm3). TC Pam sediments could be discriminated from underlying units by a sharp basal contact, an abrupt decrease in organic matter, and an increase in the concentration of foraminifera. Foraminiferal assemblages between the two sites varied in terms of taxonomy and taphonomy. At both sites, the TC Pam assemblage was generally dominated by intertidal (e.g., Amphistegina spp., Baculogypsina sphaerulata, Calcarina mayori, Elphidium spp., Pararotalia spp.) and subtidal (e.g., Peneroplis pertusus, Quinqueloculina spp.) foraminifera that are characteristic of beach, reef flat, and reef crest environments. The TC Pam assemblage at Manuro was characterized by individuals that were dominantly unaltered (i.e., pristine), but also those that showed signs of abrasion (including edge rounded fragments). By contrast, TC Pam sediments at Port Resolution Bay contained fewer unaltered and more corraded (i.e., combined influence of corrosion and abrasion) foraminifera. We compared modern surface foraminiferal distributions with those from TC Pam sediments to assess provenance. Partitioning Around a Medoid (PAM) cluster analysis discriminated six subenvironments within the modern coastal zone: open bay, forereef, reef crest, reef flat, mangrove, and beach. Discrete intervals sampled from TC Pam sediments at Manuro were individually clustered with the surface samples and revealed a shallow nearshore to supratidal (reef crest to beach; − 4.9 to 1.3 m above MSL) source for the sand.