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The interaction between regular waves and ice floes under certain wave conditions involves overwash which is characterized by waves running up over the surface of an ice floe with large deformed free surfaces. An in-house moving particle semi-implicit (IMPS) method is employed to simulate the wave-ice floe interaction, especially for the specific behavior namely overwash due to a small freeboard of sea ice and a large body motion. In this work, a series of regular waves are generated using the Lagrangian particle method based on the Stokes wave theory. Models of the floating sea ice are simplified as circular disks without and with an edge barrier and a circular disk with a central hole, which can be used to study the influences of overwash. Hydrodynamic responses of the ice floe in regular wave conditions with different wave lengths and a constant wave height are analyzed. Compared with the mesh-based methods, the Lagrangian particle-based methods have advantages in treating highly deformed free surfaces during wave overwash processes. A piston-type wave maker and a sponge layer are applied for generating waves and avoiding the wave reflection from wall boundaries, respectively. Validations are presented including the circular ice floe with a diameter of 400 mm and a thickness of 15 mm interacting with regular waves with the wave length λ/D from 1.5 to 3.5. RAOs of the original circular disk are compared with those of the circular disks with an edge barrier and with a central hole. Overwash on the ice floe can be prevented by using an edge barrier. A new type of overwash which waves flow over the upper surface and then into the hole was proposed and simulated. The present results of numerical predictions are in good agreement with the experimental data and the published numerical results using the CFD code Flow-3D. • An in-house Moving Particle Semi-implicit method is employed to study the interactions between waves and ice floes. • The coupled surge, heave and pitch motions and their effects on overwash are analyzed. • Overwash was found over the disks in short waves. • New overwash indicates that waves can flow over disks and interact with the waves inside the ice hole. [ABSTRACT FROM AUTHOR]

Infragravity (IG) waves are expected to contribute significantly to coastal flooding and sediment transport during hurricane overwash, yet the dynamics of these low-frequency waves during hurricane impact remain poorly documented and understood. This paper utilizes hydrodynamic measurements collected during Hurricane Harvey (2017) across a low-lying barrier-island cut (Texas, U.S.A.) during sea-to-bay directed flow (i.e., overwash). IG waves were observed to propagate across the island for a period of five hours, superimposed on and depth modulated by very-low frequency storm-driven variability in water level (5.6 min to 2.8 h periods). These sea-level anomalies are hypothesized to be meteotsunami initiated by tropical cyclone rainbands. Estimates of IG energy flux show that IG energy was largely reduced across the island (79–86%) and the magnitude of energy loss was greatest for the lowest-frequency IG waves (0.01 Hz). Assuming this pattern of nonlinear energy exchange persists across the wide and downward sloping barrier-island cut, it likely contributes to the observed frequency-dependence of cross-barrier IG energy losses during this relatively low surge event (

This research presents a study on the morphodynamic evolution of the Rossbeigh coastal barrier and its dune system, located in Dingle Bay, County Kerry, Ireland. The study examines the evolution of the system over a 19-year period (2001–2019) through remote sensing, geographic information system (GIS) analysis, and field-based surveys. This research provides an ideal opportunity to examine a natural erosion event, referred to as cannibalization on a coastal barrier and its dune system. Since the beginning of this century, significant erosion has been visible on the coastal barrier, with the erosion eventually leading to a breaching event in the winter of 2008/2009. Over the study period, analysis has shown that the vegetated dunes decreased by more than 60 percent, the width of the breached area reached a maximum width of over 1 km and a change in orientation and appearance on the coastal barrier has been quantified. The analysis identifies a growing drift-aligned zone, contrasted with a reduction in the stable swash-aligned zone. Significantly, the point between these zones (i.e., the hinge point) has been shown to have moved by more than 1 km also. The migration of this hinge point and cannibalization of the dunes are illustrated. Finally, the potential mechanism for beach healing is identified, utilizing the rich datasets collected during the study, thus providing an insight into the long-term behavior of a dynamic coastal barrier system undergoing naturally driven cannibalization.

Our study analyses the long-term development of a tidal backbarrier salt marsh in the northern German Wadden Sea. The focus lies on the development of the high-lying, inner, mature part of the salt marsh, which shows a striking history of changing sediment dynamics. The analysis of high-resolution old aerial photographs and sampled sediment cores suggests that the mature part of the marsh was shielded by a sand barrier from the open sea for decades. The supply with fine-grained sediments occurred from the marsh inlet through the tidal channels to the inner salt marsh. Radiometric dating (210Pb and 137Cs) reveals that the sedimentation pattern changed fundamentally around the early-mid 1980s when the sedimentation rates increased sharply. By analyzing the photographic evidence, we found that the sand barrier was breached during storm events in the early 1980s. As a result, coarse-grained sediments were brought directly through this overwash from the sea to the mature part of the salt marsh and increased the sedimentation rates. We show that the overwash and the channels created by these storm events built a direct connection to the sea and reduced the distance to the sediment source which promoted salt marsh growth and a supply with coarse-grained sediments. Consequently, the original sediment input from the tidal channels is found to play a minor role in the years following the breach event. The presented study showcases the morphological development of a mature marsh, which contradicts the commonly accepted paradigm of decreasing sedimentation rates with increasing age of the marsh. We argue that similar trends are likely to be observed in other backbarrier marshes, developing in the shelter of unstabilized sand barriers. It further highlights the question of how resilient these salt marshes are toward sea level rise and how extreme storm events interfere in determining the resilience of a mature salt marsh.

Mattheus, C.R. and Yovichin, R.D., III, 2018. Hurricane trajectory and irregular bedrock topography as drivers of washover fan geomorphology on an isolated carbonate platform. Although washover fan geomorphology is widely studied along sandy passive continental margins, little is known about rocky carbonate platform analogs. This paper addresses the multidecadal evolution of a compound washover fan complex on San Salvador Island, an isolated and hurricane impact–prone Bahamian carbonate platform. Its geomorphic development is assessed from pre– and post–Hurricane Joaquin topographic measurements, historic aerial photographs, ground-penetrating radar imagery, and sediment cores. Survey information provides insight into event-based surficial processes, while subsurface mapping and aerial photography offers a window into past events. Hurricane Frances left the fan largely unmodified in 2004, whereas the comparably strong Hurricane Joaquin was affiliated with heavy scouring of the fan apex and extensive accretion across the distal fan in 2015. Mimicking the surficial geomorphic changes affiliated with Joaquin, a superposition of five distinct event-based depositional units is elucidated from subsurface architectures. Cores from the distal, subaqueous fan sample interbedded lagoon muds and overwash sands, while truncated subsurface radar units near the fan apex map erosional events. The susceptibility of this particular island locale to repeated modification relates to the irregularity of the carbonate bedrock terrain, which funnels surge waters inland through low topography under favorable hydrodynamic conditions. These were met during the NE-trending Hurricane Joaquin, but not the NW-trending Frances. Storm characteristics, particularly trajectory, appear to play a significant role in determining overwash potentials along highly irregular bedrock-dominated coastlines. These implications for overwash dynamics must be considered and reconciled when attempting to reconstruct regional storm histories from coastal sedimentary archives. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

ABSTRACT Youn, D. and Park, Y.H., 2018. The Application of Mathematical Analysis to Examine the Beach Erosion along the Upper Texas Coast. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 846–850. Coconut Creek (Florida), ISSN 0749-0208. The upper Texas coast has been severely damaged by repeated beach erosion without any landfall of tropical storm. Since the average wave height was lower than 1.5 m and the mean tide range was smaller than 0.5 m there, they were not enough to explain the extreme erosion along the coast. Many studies had been conducted to find the causes of continuous erosion and then overwash was suspected by morphological analysis. The past studies, through the analysis of the observation data, concluded that the impact of remote storm might be a major cause of coastal erosion. The Texas Land Office has developed a master plan for coastal resilience and they switched to recovery from investigation. However, beach erosion is still a complicated process and continuous erosion has not been studied until now. For that reason, we here propose an alternative way for the further examination. A mathematical approach called as Empirical Orthogonal Function (EOF) is chosen to analyze spatiotemporal variations. We here applied the EOF method to the observed beach profile data to examine the spatiotemporal characteristics of waves related to the erosion problem. During the observation, the landfall of hurricane was made in the study area and it would be an interesting analysis of affected or unaffected beach change by storm. The short and long-term variations by landfall of storm or impact of remote storm were also studied by EOF method respectively. The dominance of cross-shore process such as overwash was also analyzed in this study. [ABSTRACT FROM AUTHOR]

ABSTRACT Talavera, L.; Del Río, L.; Benavente, J.; Barbero, L., and López-Ramírez, J.A., 2018. UAS & SfM-based approach to Monitor Overwash Dynamics and Beach Evolution in a Sandy Spit. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 221–225. Coconut Creek (Florida), ISSN 0749-0208. The role of overwash processes is of great relevance in the long-term evolution of sandy barriers, and it can also affect coastal infrastructures in the short term. In this work, a 10-month monitoring program based on the use of Unmanned Aerial Systems (UAS) in combination with Structure from Motion (SfM) algorithms was performed in order to monitor morphological changes and ulterior evolution at Camposoto beach, an overwash-prone coastal spit located in SW Spain. This UAS&SfM approach allowed the reconstruction of 6 Digital Elevation Models (DEMs) of the area with high temporal and spatial resolutions (RMS vertical errors spanning from 5 to 8 cm). The morphological changes occurred were detected using Geomorphic Change Detection Software in ArcGIS, and they were correlated with the oceanographic conditions that prevailed during the analysed period. The results obtained provided insight into the response of the system against storm-induced overwash, which caused significant erosion/accretion patterns over a pre-existing washover fan, as well as the landward migration of the system. In addition, this methodology captured the progressive partial recovery of the system, which included onshore transport of sand, fore-beach accretion, and berm reconstruction. Despite the partial recovery observed, spring tides also triggered non-storm overwash in the area during fair-weather conditions, allowing to rethink the actual vulnerability state of the spit against rollover processes. [ABSTRACT FROM AUTHOR]

This study tests the effectiveness of physical barriers in blocking or reducing washover sedimentation in coastal marshes. It is widely assumed that natural and artificial physical barriers, such as foredunes and roads, block or reduce storm overwash. However, there appears to be little documented assessment of this effect. This topic has gained significance recently because of concerns over sea-level rise induced by global warming creating a larger potential threat from storm overwash. Nearshore physical barriers act to protect populations and infrastructure farther inland from storm surge, but they may also reduce sediment delivery to coastal marshlands, slowing their vertical accretion and contributing to their submergence by rising sea level. Consequently, there is a critical need for more information on the effect of physical barriers on marsh sedimentation. Washover sediment beds were examined along two transects across marshes in McFaddin National Wildlife Refuge in southeastern Texas, one in the lee of a higher and wider foredune barrier and one where foredunes are lower and narrower. Washover sediment beds deposited by Hurricanes Rita (2005) and Ike (2008) were found on both transects. Comparison of washover sedimentation along the two transects showed an average 40% reduction in sediment volume and an average reduction in inland extent of deposits of 505 m in the lee of the higher and wider barrier. These results show that even relatively subtle increases in barrier dimensions can cause substantial reductions in the magnitude of washover sedimentation in marshes. These findings have implications for paleotempestology studies that use the magnitude of washover sedimentation in the lee of dynamic coastal barriers as geologic proxies of storm intensity. Coastal management agencies contemplating the use of physical barriers to block storm surge should take into consideration the impact of such barriers on the sustainability of coastal marshes faced with rising sea level. [ABSTRACT FROM AUTHOR]

Abstract: Marine overwash events are among the most serious short‐term threats to groundwater supply of small coral islands. During such events, seawater can inundate small islands partially or completely, causing salinization of the aquifer. A comprehensive knowledge of freshwater lens recovery is essential for water planners on these islands. In this study, a numerical modelling approach is used to quantify recovery of the freshwater lens on 4 islands of the Maldives after a tsunami‐induced overwash event similar to that experienced from the Indian Ocean earthquake in December 2004. The islands vary in size (0.2 to 10.1 km2) and span the climatic regions of the Maldives. A tested 3‐dimensional SEAWAT groundwater model for each island is used to simulate the recovery process. Recharge rates from historical rainfall data and from global climate models are imposed on each island during the post‐overwash recovery period. The effect of groundwater pumping on lens recovery also is examined. Results show abrupt decrease in fresh groundwater volumes for each island, followed by recovery that is significantly influenced by island size and recharge patterns. Overall, salinization is more widespread on small islands (<1 km2), but recovery is more rapid than for large islands. Between 50% and 90% of lens recovery occurs after 2 years for small islands (<1 km2) whereas only 35% and 55% for large islands. Imposing pumping rates required to sustain the local population lengthened the recovery time between 5% and 15%, with smaller islands having the higher percentage. However, the governing factor on recovery time is the spatial extent of land surface inundation by the overwash event, with wave height and duration of the event having a negligible impact. A strong relationship exists between required recovery time and island surface area, thereby providing a method to determine recovery time for other atoll islands not investigated in this study with similar geologic structure. Our results can be used to aid in managing water resources during the post‐overwash period. [ABSTRACT FROM AUTHOR]

Coastal communities are threatened by the impact of severe storms that may cause significant loss or damage of property and life. The main processes causing such impacts at sandy coastlines and nearby coastal communities are storm erosion, overwash and inundation. Coastal response under present conditions and under predicted climate change has been frequently assessed on the basis of numerical models, which in turn can be also used to evaluate the effectiveness of Disaster Risk Reduction (DRR) measures to mitigate the response of the coast to the imposed conditions. However, detailed morphodynamic models are computationally expensive and not commonly used by coastal managers. The present work proposes the construction of a probabilistic Bayesian Network (BN) as a surrogate for the numerical simulations. This BN is trained with a large number of morphodynamic simulations, under a variety of storm conditions and DRR measures, in order to serve as a front-end platform for visualising, analysing and evaluating combined results of the numerical modelling. The BN introduced in an early warning system will be able to serve both, as a predictive and as a working tool to determine impacts and evaluate risk reduction after measures implementation. Here, an example of the implementation and results of such a BN system is presented. The BN system was built for a coastal sector of the Ria Formosa barrier island system (South Portugal) to inform the degree of impact derived from overwash and erosion over the study area. The BN boundary conditions include variable wave height, water level, and wave period. The impact on receptors, including houses and infrastructure, was assessed. In addition, this tool can inform about the effectiveness of a particular DRR measure. The evaluated DRR measures were two primary measures (partial house removal and beach replenishment) and a non-primary measure (improve channels of communication), all measures proposed by local stakeholders. Results show that for a storm with wave characteristics of the 1 in 50 year return period and spring tide conditions, the house removal DRR reduces the overwash impact by 15% and erosion impact by 58%. The implementation of beach replenishment could reduce the erosion impact of the same event by 96% while it would have a smaller effect on the overwash impact (16%). The implementation of non-primary measures would have a much smaller effect on risk reduction. The combined effect of the above DRR measures (mainly house removal and beach nourishment) reduces storm impacts at the study area to a value near zero. The BN surrogates the model simulated onshore hazards and translates them into impacts for the current conditions, which give a high degree of confidence in the potential application of the BN as a management tool. [ABSTRACT FROM AUTHOR]

Coastal communities are threatened by the impact of severe storms that may cause significant loss of life and damage to properties. Among the main processes behind such impacts on coastal barriers are the occurrence of overwash and breaching during storm events. In order to estimate potential losses associated with a particular event, the above processes must be properly parameterized. Here, we propose a novel methodology to estimate overwash and breaching hazards suitable for a regional scale analysis (Ø 100 km). For the overwash hazard assessment, the method is based on the application of the approach developed by Donnelly (2008) that allows the parametrisation of the overwash hazard considering both flow velocity and flow depth. Moreover, the inland extension of the associated hazard, which is critical to assess subsequent vulnerability, can also be estimated following this methodology. The proposed method requires the selection of a runup formula validated for the study area, a storm beach profile, a runup lens angle, and a percolation constant for infiltration. To assess the breaching, hazard, a new multivariable evaluation is proposed that allows ranking the potential of breaching. The multivariable evaluation combines overwash and erosion hazards as well as their extensions with the main morphological characteristics of the barrier, resulting in the breaching hazard index, that ranks from 0 to 5 (no breaching to inlet formation). Inland breaching extension is also relevant for the vulnerability assessment. The breaching extension can be estimated using historical or contemporary analogues of the nearest flood deltas. The developed approaches were applied to Ancão Peninsula (Algarve, Portugal) as a demonstration example. The advantages of the present approach are: adaptability to various environments where overwash and/or breaching processes are important, time efficiency on evaluating overwash and breaching hazards, and the assessment of hotspot areas at a regional scale. [ABSTRACT FROM AUTHOR]

Wave run-up and dune overwash are typically assessed using empirical models developed for a specific range of often-simplistic conditions. Field experiments are essential in extending these formulae; yet obtaining comprehensive field data under extreme conditions is often challenging. Here, we use XBeach Surfbeat (XB-SB)—a shortwave-averaged but wave-group resolving numerical model—to complement a field campaign, with two main objectives: i) to assess the contribution of infragravity (IG) waves to washover development in a partially-sheltered area, with a highly complex bathymetry; and ii) to evaluate the unconventional nested-modeling approach that was applied. The analysis shows that gravity waves rapidly decrease across the embayment while IG waves are enhanced. Despite its exclusion of gravity-band swash, XB-SB is able to accurately reproduce both the large-scale hydrodynamics—wave heights and mean water levels across the 30 × 10 km embayment; and the local morphodynamics—steep post-storm dune profile and washover deposit. These findings show that the contribution of IG waves to dune overwash along the bay is significant and highlight the need for any method or model to consider IG waves when applied to similar environments. As many phase-averaged numerical models that are typically used for large-scale coastal applications exclude IG waves, XB-SB may prove to be a suitable alternative.

Storms are responsible for several hazards (e.g. overwash, erosion, inundation) in coastal areas, leading to the destruction of property and loss of life in populated areas. Various indicators are used to express potential storm impact and describe the associated hazards. The most commonly used indicators include either forcing parameters (e.g. wave height, sea level) or coastal morphologies (e.g. dune height or berm width). Whereas they do not represent the processes associated with storm induced hazards in coastal areas. Alternatively, a hazard could be better characterised if process-based indicators are used instead. Process-based indicators express the result of the forcing mechanisms acting over the coastal morphology and reflect both hydrodynamic and morphological characteristics. This work discusses and synthesizes the most relevant process-based indicators for sandy shores subject to overwash, erosion and inundation promoted by storms. Those include: overwash depth, potential and extent; shoreline, berm or dune retreat; vertical erosion; and inundation depth and extent. The selection of a reduced set of process-based indicators to identify coastal hazards induced by storms in sandy coasts will facilitate comparison of different coastal behaviours for distinct storm return periods, and help to optimise coastal management plans, thereby contributing to the reduction of coastal risks. [ABSTRACT FROM AUTHOR]

Tropical cyclones (hurricanes in the northern hemisphere) are amongst the most devastating of the world's natural disasters and cause billions of dollars in damage every year. Data on the likelihood of a coastal site being struck by a major hurricane strike can potentially aid in planning and mitigation efforts that could save money and lives. However, forecasting requires data that are currently insufficient for the Georgia Bight. This study provides information to enhance the paleohurricane record by analysis of a 467 cm thick vibracore raised from St. Catherines Island, GA. Sediment geochemistry and foraminiferal assemblages indicate deposits attributable to seven paleohurricane events, five of which were likely major hurricanes when they made landfall on St. Catherines. Magnitudes were estimated by comparison to the overwash deposit left by “The Sea Islands hurricane of 1893”, a major hurricane recorded by the recent sediment of St. Catherines Island. The St. Catherines record also shows a change in the activity levels on the Georgia coast with two distinct activity regimes over the past 3000 years. [ABSTRACT FROM AUTHOR]

Quantitative recruitment of ichthyofauna into a South African temporarily open/closed estuary (TOCE) was investigated during three distinct hydrological phases: closed overwash, open outflow and tidal mouth conditions. Maximum recruitment densities occurred during outflow conditions and declined when the system became tidally inundated. Recruitment densities were lowest during overwash events. Selective diel variation was evident, with higher night-time densities for each phase. This study highlights the importance of seasonal timing and duration of open conditions and overwash events for structuring ichthyofaunal community composition of southern African TOCEs. [ABSTRACT FROM PUBLISHER]

Washover deposits are among the most remarkable sedimentary signatures of dune breaching and coastal inundation. Overwash of the barrier leading to washover development can be related either to storms or tsunamis but the distinction between these two processes based on the depositional record is still a matter of debate. Hence, studying recent well-documented washover deposits, combining sedimentological and hydrodynamic investigations is a key approach to identify the processes governing the washover deposition and to analyze their sediment record within the washover. During the winter of 2013–2014, the coasts of the Bay of Biscay experienced an exceptional wave climate, leading to dune breaching and washover deposition at many locations, including the Gatseau Spit (South of Oléron Island, France). Field observations, aerial photographs, topographic measurements, GPR investigations, trenches and cores, grain size analysis and magnetic fabric measurements were carried out and complemented with hydrodynamic modeling of tides, storm surges, short waves and infra gravity waves in order to compute maximum runup during the winter of 2013–2014. Such an interdisciplinary approach led to propose that: (1) large overwash events occurring during the winter of 2013–2014 were mainly driven by infra gravity (IG) waves combined with high tides; (2) the washover elongated outer shape was strongly controlled by the antecedent morphology of the back-barrier area; (3) one overwash flow driven by one IG wave is recorded by one normally graded lamina composed of quartz sand at base and heavy minerals enriched sand at top; (4) dominant settling of the particles from a suspension during sedimentation occurred in the end of each overwash flow in response to flow velocity decrease; (5) laminae can be grouped in laminasets generally composed of thinning upward laminae, related to overwash flow depth decrease during falling tide and to erosion of basal laminae by highest overwash flows occurring more likely around the high tide; (6) the number of laminasets in a proximal position is in the same order of magnitude as the number of modeled highest runup events, offering an almost complete record of overwash events that occurred during the winter 2013–2014. [ABSTRACT FROM AUTHOR]

Backbarrier saltmarshes are considered carbon sinks; however, barrier island transgression and the associated processes of erosion and overwash are typically not included in coastal carbon budgets. Here, we present a carbon-budget model for transgressive barrier islands that includes a dynamic carbon-storage term, driven by backbarrier-marsh width, and a carbon-export term, driven by ocean and backbarrier shoreline erosion. To examine the impacts of storms, human disturbances and the backbarrier setting of a transgressive barrier island on carbon budgets and reservoirs, the model was applied to sites at Core Banks and Onslow Beach, NC, USA. Results show that shoreline erosion and burial of backbarrier marsh from washover deposition and dredge-spoil disposal temporarily transitioned each site into a net exporter (source) of carbon. The magnitude of the carbon reservoir was linked to the backbarrier setting of an island. Carbon reservoirs of study sites separated from the mainland by only backbarrier marsh (no lagoon) decreased for over a decade because carbon storage could not keep pace with erosion. With progressive narrowing of the backbarrier marsh, these barriers will begin to function more persistently as carbon sources until the reservoir is depleted at the point where the barrier welds with the mainland. Undeveloped barrier islands with wide lagoons are carbon sources briefly during erosive periods; however, at century time scales are net carbon importers (sinks) because new marsh habitat can form during barrier rollover. Human development on backbarrier saltmarsh serves to reduce the carbon storage capacity and can hasten the transition of an island from a sink to a source. [ABSTRACT FROM AUTHOR]

Gravel barriers provide a natural form of coastal protection and flood defence for many sites around the UK and worldwide. Predicting their vulnerability to different storm impact regimes that cause overtopping and overwash is crucial as these processes can lead to hazardous consequences such as inundation of the back of the barrier or breaching. This paper presents the first field measurements of storm overwash events on a gravel beach (Loe Bar, Cornwall, England). High frequency in-situ observations (2 Hz) were performed using a 2D laser-scanner and allowed a complete characterization of the overwash flows (velocity and depth) and morphological response along a cross-shore section of the barrier. These novel measurements are used to validate the numerical model XBeach-G, to forecast overwash discharge. Several simulations were performed with XBeach-G to investigate the thresholds for the different storm impact regimes, given a variety of water levels and wave heights. Wave period and wave spectral shape are found to significantly affect these thresholds. While short period waves dissipate most of their energy by breaking before reaching the swash zone and produce short runup excursions, long period waves due to their low steepness arrive at the swash zone unbroken with enhanced heights (due to shoaling) thus promoting large runup excursions. When the offshore wave spectrum has a bimodal shape, wave transformation in shallow water causes the long period peak to dominate the swash giving large runup excursions. Long period waves or strongly bimodal waves result in enhanced runup thereby reducing the thresholds for barrier overtopping or overwashing. [ABSTRACT FROM AUTHOR]

Since the Belize coast was repeatedly affected by hurricanes and the paleohurricane record for this region is poor, sediment cores from coastal lagoon environments along the central Belize coast have been examined in order to identify storm deposits. The paleohurricane record presented in this study spans the past 8000 years and exhibits three periods with increased evidences of hurricane strikes occurring at 6000-4900, 4200-3600 and 2200-1500 cal yr BP. Two earlier events around 7100 and 7900 cal yr BP and more recent events around 180 cal yr BP and during modern times have been detected. Sand layers, redeposited corals and lagoon shell concentrations have been used as proxies for storm deposition. Additionally, hiatuses and reversed ages may indicate storm influence. While sand layers and corals represent overwash deposits, the lagoon shell concentrations, which mainly comprise the bivalve Anomalocardia cuneimeris and cerithid gastropods, have been deposited due to changes in lagoon salinity during and after storm landfalls. Comparison with other studies reveals similarities with one record from Belize, but hardly any matches with other published records. The potential for paleotempestology reconstructions of the barrier-lagoon complexes along the central Belize coast differs depending on geomorphology, and deposition of washovers in the lagoon basins is limited, probably due to the interplay of biological, geological and geomorphological processes. [ABSTRACT FROM AUTHOR]

Evolutionary adaptations in the morphology and physiology of cactus species have been associated to their mechanisms of dispersal and colonization. The dispersal mechanisms and modes of Opuntia monacantha (Willd.) Haw. (Cactaceae) were characterized in two beaches in Florianopolis, SC, Brazil. A marsupial from the genus Didelphis (Mammalia: Didelphidae) was the only frugivorous and, thus, disperser of fruits, presenting specific eating places. The maritime hydrochory was due to the overwash on restinga vegetation, it is characterized by the dispersal of cladodes and fruits at various times of the year. It is here firstly described the sea action as a potential disperser for a cactus species.

Beach responses to sea level rise are investigated experimentally in laboratory wave flume by detecting the beach profile continuously using video cameras in high space and time resolution. Experiments are conducted to discuss the profile response in three scenarios of water level rise: a step-change in water level, continuous water level rise as well as extremely high water levels to find out the intensification and dissipation of swash motion waves in overwash and inundation hydrodynamic and the retreat of the shoreline due to water level rise. The sediment transport rates are estimated from the detailed monitoring of the beach profiles, from which the responses of the shoreline to the water level rise are examined. The morphological characteristics of the dunes caused by sea-level rise are discussed and it is noted that sea-level rise leads to an increase of more than 40% in sediment loss from sand dunes, while extreme solitary wave conditions are less affected by water level changes. The characteristics of shoreline retreat for different sea levels and wave conditions are analyzed from the experiment data. The developments of shoreline and beach response prediction model using the laboratory experiment data to the sea level rise are discussed for better estimation of the shoreline change to the sea level rise. Meanwhile, the trend of wave energy is consistent with the frequency of profile change as the water level continues to rise. When the water level is high enough close to the dune crest, partially broken waves in nearshore areas transmitted landward with large wave energy quickly destroy the dunes, which is a great threat to the beach ecosystem. There is an inhibitory effect on the morphological changes of the dunes as the water level is high in the back of the dunes. • A systematic discussion of water level rise effects based on image technology. • A new method is proposed to predict coastal dune erosion after sea level rise. • The change in absolute mass M a b s corresponds to the wave energy flux P. • The dunes will be destroyed in a short time due to the extremely high water level. [ABSTRACT FROM AUTHOR]

The identification of tsunami deposits in the geological record remains a challenge because the proxies availabilities are subject to the environment. The proxies may degrade over time and inherently inhibit the robustness of event interpretations. Multi-proxy methods, which leverage on each other's advantage/s and limitation/s, are employed to improve the identification of tsunami deposits from the geological record. Here, we assess the utility of environmental DNA (eDNA) for tsunami research by comparing and contrasting the eDNA collected from a sequence of well-documented palaeotsunami deposits spanning the past three millennia. We study swales in a coastal beach ridge sequences on Phra Thong Island, Thailand and test if eDNA can robustly discriminate the tsunami-deposited sand sheets that intercalate between the non-tsunami derived organic mud layers. Our results indicate that the 2004 Indian Ocean tsunami deposit and preceding tsunami deposits (approximately 550 to 700 years ago) contain microbial communities that differ significantly from the overlying and underlying organic mud layers (p -value = 0.0269) but the signal becomes restricted in the older sediment layers up to 2800-year-old that are constantly submerged in groundwater. This work demonstrates the potential for applying eDNA to study tsunami deposits over centennial time frames and perhaps longer. • eDNA can discriminate the tsunami-deposited sand sheet from non-tsunami derived layers within a well-documented geological record. • The eDNA analysis shows clear differences between sediment layers up to 700-year-old but limited in older sediment layers beyond 2800-year-old. • eDNA tsunami indicators are site-specific and source-dependent. [ABSTRACT FROM AUTHOR]

This study uses storm surge sediment beds deposited by Hurricanes Audrey (1957), Carla (1961), Rita (2005) and Ike (2008) to investigate spatial and temporal changes in marsh sedimentation on the McFaddin National Wildlife Refuge in Southeastern Texas. Fourteen sediment cores were collected along a transect extending 1230 m inland from the Gulf coast. Storm-surge-deposited sediment beds were identified by texture, organic content, carbonate content, the presence of marine microfossils and 137 Cs dating. The hurricane-derived sediment beds facilitate assessment of changes in marsh sedimentation from nearshore to inland locations and over decadal to annual timescales. Spatial variation along the transect reflects varying contributions from three prevailing sediment sources: flooding, overwash and organic sedimentation from marsh plants. Over about the last decade, hurricane overwash has been the predominant sediment source for nearshore locations because of large sediment inputs from Hurricanes Rita and Ike. Farther inland, hurricane inputs diminish and sedimentation is dominated by deposition from flood waters and a larger organic component. Temporal variations in sedimentation reflect hurricane activity, changes in marsh surface elevation and degree of compaction of marsh sediments, which is time-dependent. There was little to no marsh sedimentation in the period 2008–2014, firstly because no hurricanes impacted the study area and secondly because overwash sedimentation prior to 2008 had increased nearshore marsh surface elevations by up to 0.68 m, reducing subsequent inputs from flooding. Marsh sedimentation rates were relatively high in the period 2005–2008, averaging 2.13 cm/year and possibly reflecting sediment contributions from Hurricanes Humberto and Gustav. However, these marsh sediments are highly organic and largely uncompacted. Older, deeper marsh deposits formed between 1961 and 2005 are less organic-rich, more compacted and have an average annual sedimentation rate of 0.38 cm/year, which is closely comparable to long-term sedimentation rates in similar marsh settings nearby. These results demonstrate the utility of using hurricane storm surge marker beds to investigate marsh sedimentation, provide insights into the sedimentary response of coastal marshes to hurricanes and provide useful guidance to public policy aimed at combating the effects of sea-level rise on coastal marshes along the northern Gulf of Mexico. [ABSTRACT FROM AUTHOR]

Barrier island dunes are postulated to exhibit two states, or stability domains. In this model, transitions between domains can exhibit irreversibility. However, these transitions may also be bistable, whereby the topography of either domain can develop at a location. To infer evidence for these dynamical properties and link them to dune topography, statistical mapping of dune topographic state space was undertaken for six barrier islands of the southeastern U.S. Atlantic coast. Topographies for three to four plots per island were constructed from airborne LiDAR data. Elevation in each was quantified in terms of descriptive statistics, spatial autocorrelation and landscape patch structure. The state space derived from ordination of these data was not primarily structured by the domain model. Instead, positive and negative relief defined the major axis of topographic variability. Only the plot topographies intermediate of these extremes in relief and contained within a smaller window of elevations resembled those of the two-state model. Their emergence along the second axis of variability was correlated with the spatial autocorrelation of elevation and geographic factors related to wave and tidal energy. Topographies suggestive of irreversibility and bistability were distinguishable based on their position in state space relative to these two domains regions. [ABSTRACT FROM PUBLISHER]

A model developed to describe long-term cross-shore (CS) exchange of sand and resulting profile evolution at regional scale was employed to simulate the evolution at three different sites. The model consists of modules for calculating dune erosion and overwash, bar-berm material exchange, and dune build-up by wind-blown sand transport, as described in detail in a companion paper (Larson et al., 2016). Selected study sites represent coastal stretches influenced by beach nourishment (Barra in Portugal), overwash and breaching (Macaneta spit in Mozambique), and dune development (Ängelholm in Sweden). The model applications showed overall good performance and the results of the simulations are promising. Due to limitations in data availability in Ängelholm and Macaneta, values on calibration parameters were mainly determined based on previous studies. For Barra, where more field measurements were available, the application showed good agreement between the simulated results and observations. The CS-model proved to be a useful tool to predict long-term evolution of beach-dune systems in a time perspective from years to decades. However, additional efforts should be directed towards improving the schematized model profile so that it can better represent other beach shapes such as a sloping berm or a barrier shape. [ABSTRACT FROM AUTHOR]

A model is developed to simulate the cross-shore (CS) exchange of sand and the resulting profile response at decadal scale to be used in regional coastal evolution models. The CS model consists of modules for calculating dune erosion and overwash, wind-blown sand transport, and bar-berm material exchange. The sand transport equations included in these modules are formulated based on relevant physics in combination with empirical observations and then validated towards laboratory and field data. In order to couple the transport equations to the evolution of key morphological features describing the profile a set of sand volume conservation equations are employed and solved together with the transport equations. The features that are modeled include dune height (from dune foot to crest), the locations of the landward dune foot, seaward dune foot, berm crest, and shoreline as well as the longshore bar volume. The CS model is employed and tested at three different field sites in a companion paper (Palalane et al., 2016), whereas in the present paper the properties of the model are demonstrated by simulating the evolution of the dune, berm, and shoreline in connection with accretion and erosion of sand in a groin compartment. This case derives from a study at Westhampton Beach that focused on shortening the length of a number of groins in order to release accumulated sand in the groin field to eroding downdrift beaches. [ABSTRACT FROM AUTHOR]

Large-scale laboratory experiments focusing on the main physical processes driving dune erosion have been performed in a wave flume with a sandy dune exposed to a combination of water levels and wave conditions (Tomasicchio et al., 2011b) providing observations of different interaction regimes: collapsing, overwash and breaching (Sallenger et al., 2003). The large set of data has been considered to obtain measurements of beach–dune cross-shore profile evolution, hydrodynamic properties and suspended sediment concentration. Results show that erosion develops faster during the first hundred waves, there is a clear influence of wave period (van Gent et al., 2008) and water depth on the resilience of the beach–dune system, and that sediment concentration at a given transect depends on the bar position. Furthermore, the observed data have been adopted to verify the predictive accuracy of two open source process-based profile numerical models. [ABSTRACT FROM AUTHOR]

Overwash is an important process that controls short-term barrier dynamics, as well as long-term barrier migration, but this process is difficult to study in the field due to its rare occurrence and the challenging conditions under which it occurs. This paper uses data collected during the BARDEX II experiment in the Delta Flume, the Netherlands, where a proto-type barrier was subjected to a range of wave and water level conditions. The objectives of this research are to: (1) compare the morphologic response to overwash on a gravel barrier (BARDEX 2008 experiment) with that on a sandy barrier (BARDEX II); (2) understand the influence of wave period on overwash characteristics and sediment transport; and (3) improve current knowledge of overwash hydrodynamics. The comparative analysis shows that barrier overwash can be affected by negative feedback that stabilises the barrier through barrier crest accretion on gravel barriers, and by submerged bar development on sandy barriers. An increase in the wave period induced a reduction in overwash frequency over the crest, but no significant relation was found between wave peak period and overwash discharge. Nevertheless, overall water discharge during an overwash episode significantly correlates with overall overwash sediment transport rate. Overwash flow depths during the experiment were relatively shallow and velocities were similar compared to those measured during previous studies and reported in the literature. Despite the controlled laboratory conditions, collection of reliable and accurate measurements of overwash velocities remains challenging. [ABSTRACT FROM AUTHOR]

Despite the increased sophistication of numerical models and field techniques for investigating wave-induced nearshore sediment transport and ensuing beach morphological response, there remains a significant demand for large-scale laboratory experiments to address this research topic. Here, we describe the Barrier Dynamics II Experiment ( BARDEX II ), which involved placing a near prototype-scale sandy barrier in the middle of the Delta Flume in the Netherlands and subjecting the structure to a range of wave, tide, and water level conditions. A unique aspect of the experiment was the presence of a lagoon behind the barrier, as often occurs in natural barrier settings, providing a convenient means to experimentally manipulate the groundwater hydrology within the barrier. The overall aim of the BARDEX II was to collect a large-scale data set of energetic waves acting on a sandy beach/barrier system to improve our quantitative understanding and modeling capability of shallow water sediment transport processes in the inner surf, swash, and overwash zone. In this paper, we introduce BARDEX II and provide a detailed description of the experiment, including the experimental design, instrumentation, test program, and data set, as well as presenting some examples of the morphological and hydrodynamic data set. We also reflect objectively on the strengths and weaknesses of the data set. This paper serves as an introduction to a special issue of Coastal Engineering , solely devoted to the results of BARDEX II . [ABSTRACT FROM AUTHOR]