Coastal Sediments 2019

The following sections are included:

• FOREWORD
• CONTENTS

This paper develops a generalized and observational perspective on the short and developing history of the profession of Coastal Engineering. Although the rudiments of engineering activities along the coast extend to the ancients, modern coastal engineering based on analytical procedures is founded in the early twentieth century. This paper also explores the current state of the practice and attempts to foretell future challenges and possible actions. As a keynote paper its content is largely based on the opinions and experiences of the author. The intention of the paper is to promote discussions that might influence future individual and organizational decisions.

Extreme storms have significant impacts on the nearshore water- land system (where ocean and estuarine waves and surge interact with land processes) that pose high risk to society. Disciplinary advances have led to improved understanding and modeling of storm processes, and recent work has highlighted the importance of one-way interactions and two-way feedbacks among sediment transport, wind, rain, waves, surge, groundwater, vegetation, soils, and the built environment that determine the response of the nearshore water-land system to major storms. Here, recent research results are reviewed, and future challenges are discussed.

We analyzed grain-size distributions (GSDs) from a time-series of sediment samples to evaluate sediment transport following anthropogenic sand-berm emplacement at the northern Chandeleur Islands, Louisiana. End-member analysis (EMA) was applied to compare the end-member (EM) GSD of a known sediment source to GSDs from surrounding environments and characterize the physical redistribution of source sediment over time. Although we successfully modeled a proxy borrow-source EM using pre-emplacement (2007-2008) datasets, this EM is not easily distinguishable from the modeled emergent-island EM, possibly because the baseline dataset did not provide the necessary sample distribution to distinguish the range of depositional environments. Comparison of post-emplacement (2012) samples from the berm and natural island with the proxy borrow-source EM suggests that this application of EMA can be a valuable tool for understanding sediment redistribution subsequent to restoration efforts, especially if the GSDs of the emplaced and naturally-occurring sediments are dissimilar and adequately sampled.

A critical piece in the restoration of Louisiana’s barrier shoreline involves identifying suitable sand sediments for use in creating beach and dune habitat. Historically, barrier island restoration projects utilized nearshore borrow areas adjacent to the restoration area. However, as these sand resources become exhausted, project teams have begun using borrow areas further offshore or in the Mississippi River. Increasing the distance between the borrow source and the restoration site typically leads to an increase in project cost yet varying funding sources have aided in offsetting the additional costs.

Drowned barrier deposits exist on passive margins around the world, their origins usually ascribed to allogenic forcing from antecedent topography and changes in the rate of sea level rise. Here, we use a cross-shore morphodynamic model to explore a novel transgressive barrier behavior, ‘deflation drowning’, which occurs during a transition to autogenic periodic retreat. We demonstrate that autogenic sequences of increasingly amplified quasi-periodic deposits can occur in conjunction with deflation drowning during an incomplete changeover to periodicity. Our model results indicate this behavior may arise most readily for large, voluminous barriers.

Aerial photographic data and historical maps were used to identify trends, growth patterns and responses to anthropogenic disturbances in the barriers of the Ria Formosa system (South Portugal). Hard (inlet stabilizations, jetties) and soft (nourishments, inlet relocations) coastal works have influenced, to different extents, the recent (1952–2014) barrier morphodynamics of the system. Shore-perpendicular works had a profound impact on barrier evolution, with direct (progradation updrift, sediment starvation downdrift) and indirect (shoal attachment due to loss of tidal prism) influences that, in many cases, dominated over natural trends. Overall, barrier area in the system grew by 17% during the study period, mainly due to shoal incorporation and to a much lower extent by sediments transported by longshore drift. Four evolution regimes were identified: a) artificially triggered growth, b) stability, promoted by natural or natural and artificial factors, c) artificially triggered decay that can lead to inland migration and d) natural growth.

Satellite derived shorelines are extracted using the Google Earth Engine API for Landsat and Sentinel satellites from 1984 through 2018. These shorelines are evaluated against existing surveys and show satellite-derived breach shorelines are in good agreement with directly-observed shorelines and capture the trend of the Fire Island wilderness breach evolution. Results of this study show the wilderness breach resulted in down drift shoreline erosion at a rate greater than the historical average within 4 km of the breach. This study demonstrates the benefits of utilizing satellite observations for monitoring the full extent of breach development and resulting shoreline changes.

Barrier islands are dynamic environments threatened by sea-level rise. Humans alter barrier island morphodynamics with potentially important but unknown long-term consequences. Here we use a new barrier island model to study how tidal inlet stabilization (jetties, dredging) affect barrier islands. We find that stabalization reduces the capacity of inlets to build flood-tidal delta deposits: jetties limit inlet bypassing and can increase downdrift barrier overwashing. In scenarios where flood-tidal delta deposition is required for barrier rollover during sea-level rise, inlet stabilization increases the risk of barrier drowning.

Barrier islands are dynamic and ephemeral, facing uncertain changes from climate change and anthropogenic redistribution of sediment. Here, we couple a cross-shore, morphodynamic barrier evolution model (LTA model) with an alongshore shoreline evolution model to better understand the internal dynamics of barrier evolution. Under constant sea level rise and waves, we numerically evolve a barrier that is initially narrow in the middle. Rapid overwash over the narrow middle portion of the barrier sets up gradients in alongshore sediment transport, which attempt to straighten the bending shoreline, translating the overwashing region laterally. Comparison of cross shore (overwash) and alongshore transport provides a novel tool to evaluate barrier stability, the Washover Ratio. Using this ratio, we find that decreases in overwash flux within this narrow middle section, possibly representing the effects of development, lead to diminished barrier response to sea-level rise across the entire barrier, and therefore a more vulnerable barrier overall.

The rising demand for marine resources has motivated the study of inner shelf transport processes, especially in locations with highly-developed coastlines and valuable ecosystemic resources. These characteristics are found at Cape Canaveral shoals, on the Florida Atlantic coast, where transport dynamics and morphological evolution are not well understood. To study morphological changes at these shoals, 22 deployments of downward-pointing acoustic Doppler current profilers were conducted between summer 2015 and fall 2016. Shoals were active during summer and winter, with bed elevation changes between –0.9 and 0.8 m. Patterns in bed changes indicate that inactivity (negligible change), erosion and deposition alternated at ridges and swales, therefore ridges and swales did not accreted or eroded in conjunction. Although a mechanistic explanation is not yet clear, we provide suggestive evidence that the morphodynamic behavior of Canaveral shoals depends upon re-suspension by waves, which is consistent with previous observations at similar locations.

‘Barrier island’ refers to a diverse collection of coastal landforms that often support substantial human populations, critical infrastructures, and ecosystems. Globally, many coastal barriers are experiencing climatically altered environmental forcing coupled with increasing anthropogenic pressures. This paper undertakes high resolution shoreline change analysis to reveal how Blakeney Point, a mixed sandy-gravel barrier located on the UK’s East Coast, has evolved over centennial, decadal and event timescales. We seek to establish the implications of barrier evolution, under contrasting management regimes, for present erosion and flooding hazards. Interrogating a series of alternative shoreline proxies reveals a series of interdependent behaviors. Over the 130-year period of study, Blakeney Point is shown to be rolling landward at a mean rate of 0.60 m a^-1. Assuming continued landward retreat over the coming decades, future flood-generating storm events will encounter more landward shoreline positions than today. Superimposed on this trend, we observe the presence of alongshore migrating erosional hotspots which give rise to unpredictable morphologies at any given location on the spit. Finally, we find that instances of barrier setback are driven by individual storm events, which makes barrier retreat both highly variable and discontinuous in time and space. This is illustrated by the presence of overwash, particularly along stretches of the barrier that have experienced a recent shift in management regime towards a non-interventionist approach.

Surge and wave forcing from Hurricane Matthew caused a breach south of Matanzas Inlet (FL, USA) on a complex barrier island, including sandy dunes, hard structures (residential buildings and a highway), wetlands, and the US Intracoastal Waterway. In this paper, the skill of the XBeach model to predict hurricane-induced barrier island overwash, dune erosion, and breaching is demonstrated. The location of the breach is predicted correctly if bottom roughness based on land cover is used to calculate bed shear stresses. While the dunes are initially lowered by wave attack and surge from the ocean side, the main driver for breach formation is the water level difference between the back-barrier and nearshore, causing an ocean-directed outflow of water after the peak of the storm.

Storms can have a devastating impact on barrier coasts and provide a mechanism for inlet creation. We found that if a storm-induced breach is opened in a barrier coast that is in equilibrium; the other pre-storm inlets will become smaller due to interaction between the inlets and the total cross-sectional area remaining approximately the same. To study the morphodynamic effects of storm induced breaches on the long-term evolution of barrier coasts, we built a stochastic shell around an existing barrier coast model, allowing us to perform a Monte Carlo simulation.

The representation of swash zone processes in coastal morphology models such as XBeach does not cover the full complexity of wave breaking, turbulence and sediment transports near the water line. As a result, simulated beach slopes are often too mild which on intermediate and steep beaches can lead to severe overestimation of beach and dune erosion and loss of accuracy in predicting the resulting profile shape. A simple, heuristic ‘bermslope’ transport term to correct for this is shown to have a beneficial effect on profile evolution during storms and recovery periods and allows XBeach, originally focused on dune erosion and overwashing, to be used in longer-term simulations.

The processes driving barrier-island state changes between erosion/migration and growth/progradation are poorly understood. Stratigraphic and chronologic data are used to infer past state changes of Cedar Island, VA, USA. These data indicate that Cedar Island formed seaward of its present position approximately 5000–6000 years ago. Following a period of net landward migration, the north-central section of the island was breached prior to ca. 450 years ago. During this time, an extensive flood tidal delta was deposited in the backbarrier. After inlet closure, the island migrated landward atop these flood delta deposits, and aggraded, eventually entering a phase of net progradation. From 1852 to present the island has eroded and migrated landward ∼1 km. The modern barrier is located stratigraphically above a shallow antecedent high (-5.5 m MSL). The state changes and antecedent geology observed here are discussed and used to infer potential future sediment sources to the island.

In Louisiana, barrier islands are undergoing rapid morphological change due to shoreface retreat and increasing bay tidal prism driven by high rates of relative sea-level rise, storm impacts, and interior wetland loss. Using bathymetric and shoreline data for 1880s, 1930s, 1980s, 2006, and 2015, 100-m spaced shore-normal transects were created to track meter-scale elevation change. An automated framework was used to quantify and track shoreline movement and bathymetric isobath migration. These results were compared with historical storm data to assess the influence of storm magnitude and frequency on barrier island shoreface dynamics.

Post construction performance of barrier island restoration projects on the Louisiana southeast coast were evaluated. The restored barrier islands were suffering from severe gulf shoreline erosion prior to restoration. Post-construction erosion rates of the restored barrier islands were drastically reduced when compared to pre-construction conditions. The substantial reduction in erosion rates due to the large-scale restoration projects supports earlier theories of Campbell (2004) and Rosati (2005), who suggested that that processes resultant from degraded barrier island conditions such as exposure of fine sediments to gulf waves, overwash, breaching, and localized substrate consolidation are the main drivers of erosion along the Louisiana coast. These processes are largely inhibited once large-scale restoration projects are in place and consequently lower erosion rates occur post-construction. The data also suggests that other factors such as large scale subsidence due to extraction of fluids in the Gulf, eustatic sea level rise and lack of modern sediment input are of secondary importance.

A new evaluation of regional geomorphic change was completed for a degrading barrier island system in south Louisiana using original shoreline and bathymetry data from the 1930s, 1980s, and 2015/16. Based on identified geomorphic changes, the once-continuous Isles Dernieres sand transport system has been degraded by inlet enlargement and chronic island/shoreface erosion. Consequently, the modern barrier island chain no longer operates as the contiguous system largely present in the 1930s. A refined understanding of net littoral transport processes and their impact on barrier system evolution provides for integrated decision-making regarding restoration strategies, design, and project evaluation.

Barrier Islands in Louisiana provide the first line of defense against storm events and provide protection to the fragile back-bay estuary systems. The barrier system is experiencing land loss at an alarming rate and, as a result, is one of the top restoration priorities as identified in the Louisiana Coastal Master Plan. The breaching of East Timbalier Island during the design process emphasizes the need for CPRA to have a Barrier Island Renourishment Plan to actively monitor, quickly react to storm events, and apply available funds in the most effective manner.

Grand Isle, located in Jefferson Parish, Louisiana, is the only inhabited barrier island in Louisiana. Recently, erosion has accelerated at the southwest end of the island, requiring continual maintenance to mitigate damages to the existing dune and island. An analysis was conducted to identify the causes of the erosion at this hot spot. Numerical modeling of longshore transport indicates the dominant direction is towards the northeast along the island except at the western end of the island where transport is bi-directional, with localized accretion along the west jetty. Numerical modeling of the nearshore waves indicates that the Caminada Pass ebb shoal modifies the wave transformation near the west end of the Island. Previous studies (List et al, 1991) have identified that the pass’s tidal prism is increasing which results in growth of the ebb shoals. A morphologic analysis of historical ebb shoal bathymetry indicated a progradation of the ebb shoal and a shift of the ebb shoal attachment point. Wave modeling showed that as the ebb shoal grows, the attachment point on Grand Isle has shifted toward the West Jetty, and the wave transformation associated with evolving bathymetric contours resulted in creation of a divergent node in the longshore transport and therefore, an erosional hot spot. The identification of these processes allows for development of solutions to mitigate the hotspot erosion.

Barrier island restoration and nourishment is necessary for sustaining coastal systems worldwide. In the Mississippi River Delta Plain, the lack of sediment supply, relative sea level rise, and reworking of abandoned delta lobes promote rapid disintegration of barriers, which can contribute to mainland storm impacts. Barrier island restorations that utilize higher quality sediments (Outer Continental Shelf-OCS) are expected to exhibit higher resiliency, withstanding coastal erosion, event-induced erosion, and ongoing transgression when compared to barriers nourished using lower quality nearshore (NS) sands. Additionally, use of OCS sediments increases sediment supply by adding material to the system supporting increased barrier longevity by maintaining a subaerial footprint longer compared to NS sediments. We used the Delft3D modeling suite to study barrier geomorphic trajectories nourished using OCS/NS sands, compared with control simulations with no nourishment. Resulting morphologies from 18 simulations with forcing that included annualized forcing, storms, and SLR were evaluated are compared.

As part of the Louisiana Coastal Protection Restoration Authority’s (CPRA) mandate, the CPRA has oversight over all matters relating to the study, planning, engineering, design, and construction of integrated coastal protection and restoration projects within the Louisiana Coastal Zone (LCZ). For decades, the state of Louisiana has successfully designed and implemented marsh creation and back barrier marsh creation projects to restore degrading coastal marsh habitat. Typically, the design of marsh creation projects relied on past project information with limited written guidance for the designer. The CPRA Marsh Creation Design Guidelines (MCDG1.0) were developed by the CPRA Engineering Division based on past project implementation experience to serve as the minimum design standard consistent with sound engineering practices for those engaged in designing and constructing marsh creation projects within the LCZ, and to support the implementation of Louisiana’s Comprehensive Master Plan for a Sustainable Coast (Master Plan).

Restoration efforts to mitigate the ecocatastrophe facing coastal Louisiana, especially the Mississippi River Deltaic Plain (MRDP), have been ongoing for more than two and half decades. However, the spatial scale for restoration has historically been of project level, creating marsh platforms and restoring individual barrier islands. Understanding the severity as well as the scale and magnitude of the landloss and consequential degradation of coastal Louisiana, the approach has tilted towards a more holistic and sustainable ecosystem restoration. The 2017 Coastal Master Plan recommended a programmatic approach for barrier island restoration in place of project specific one. A Barrier Island Re-nourishment Program (BIRP) has been proposed detailing a programmatic approach to categorize, prioritize, select, and fund projects, in coordination with existing restoration plans. It is understood that managing and designing a complex and highly degrading barrier ecosystem in which the natural and socio-economic systems are integrated is challenging. A programmatic approach is recommended and presented here as a solution.

The West Grand Terre Island Beach Nourishment and Restoration project is a critical component of the State’s efforts to restore its barrier island. Through the Engineering and Design Phase a recommended plan has been identified to implement restoration features on the island. Once implemented, this project will restore and enhance the dune and back barrier marsh habitat to provide storm surge and wave attenuation, thereby addressing the issues of gulf shoreline erosion, diminished storm surge protection, and subsidence of back barrier marshes. These restoration measures will result in an increase in the island’s longevity and sustainability of this valuable ecosystem.

Although barrier island projects in Louisiana have been implemented for the last couple of decades, the construction plans, specifications, equipment, and methods have become increasingly complex with each project. For example, as more potential projects are conceived and constructed, the proximity to utilities and infrastructure becomes more common and must be considered as a design parameter. Sediment sources are becoming increasingly complex with respect to sediment type and accessibility. As the restored acreage increases, the manpower, equipment, and coordination required to transform these projects from concept to reality also increase. The Shell Island restoration project (BA-110/111) is located in Plaquemines Parish in the heart of Louisiana’s working coast. Sediment was dredged from the Mississippi River as well as from the Gulf of Mexico to construct different sections of the project. Lessons learned from design and construction of this project, as well as construction challenges associated with utilizing different sediment sources and types are discussed in this paper.

All of the developed beaches from Clearwater Beach to Pass-a-Grille are authorized for periodic nourishment as part of the Federal Pinellas County Shore Protection Project. Segments currently constructed as part of the Federal Shore protection project include Sand Key, Treasure Island, and Long Key. In total these projects have placed 11 million m³ of sand on the beach. This sand is important because of its storm damage reduction and environmental benefits as well as the $2.3 million spent by visiting tourists that has supported 47,000 jobs. Pinellas County also has a robust monitoring program. Beach profiles collected pre- and post-storm were used to verify sand losses that resulted in the obtaining $21 million in Federal storm damage emergency funds. This has allowed Sand Key to receive 1.2 million m3 of sand at a record cost of $45 million.

The present study investigates the evolution of a nourishment experiment carried out at Mariakerke (Belgium) coast. For two neighboring beach sectors beach nourishment was carried out, Raversijde and Mariakerke, while for the later one a shoreface nourishment was added. For a better understating of the local coastal dynamics two adjacent beach sectors were considered, Middelkerke and Oostende. Four years of topographic and bathymetric surveys were used to build digital elevation models in order to investigate the evolution of the nourishments. Results show a rather slow evolution with majority of the sand still in the local coastal system. As expected areas such as the intertidal beach or the shoreface at Mariakerke show an intense erosive trend initially, but the rates decrease after two years. At Mariakerke shoreface nourishment a local reorganization of the sand is observed with formation of submerged sand bar. The active beach profile extension seaward is larger than previously estimated. The human interventions such as extension of the Oostende harbor, frequent nourishments and local redistribution on the dry and intertidal beach have a major impact in the retention of the nourished sand in the local coastal system.

The Coastal Resilience Index (CRI) is introduced to quantify the resiliency of beach and dune systems in Gulf of Mexico coastal areas. The CRI follows the American Shore and Beach Preservation Association (ASBPA) assumption that higher dunes and wider berms provide more resilience. The CRI considers beach and dune morphologic metrics as well as disturbance factors such as storm surge and wave run-up. The combination of these variables leads to five non-dimensional factors: Protective Elevation (PE), Volume Density (VD), Protective Width (PW), Crest Freeboard (CF) and wave run-up (WR). The CRI is the summation of these five non-dimensional factors. This study analyzes the historic beach profiles and profiles extracted from LiDAR data and calculates the CRI for two sites: Anna Maria Island, FL and South Padre Island, TX. The CRI of historic beach and dune conditions was evaluated and compared. Both study areas indicate beach nourishment projects increase coastal resiliency.

The main objective of this work is to analyze the artificial nourishment impact and efficiency under the influence of a coastal structure, a groin. A movable bed reduced scale physical model was prepared and tested at the wave basin of the Hydraulics, Hydraulic Resources and Environment Section (SHRHA) of Porto University, in Portugal. The developed work consisted in modelling two main scenarios: a beach with a linear shoreline, and regular and parallel bathymetric contours, without the presence of hard coastal structures; and the same beach in the presence of a groin at its downdrift limit. In each scenario, an artificial nourishment was placed after subjecting each modelled beach to a random wave climate. It was observed a slower shoreline retreat along the tests for the scenario of the beach influenced by a groin, with and without the presence of an artificial beach nourishment. In both scenarios, adding the artificial nourishment lead to initially higher sediment transport rates and more intense morphological dynamics. The groin scenario proved to be the most efficient scenario by reducing the spreading of the introduced nourishment sediments.

The Caminada Headlands is a beach and dune system that provides natural protection to inland bays against storm surges and wave overtopping. Due to significant shoreline erosion and regional subsidence, a nourishment project was initiated in 2012 to replenish the beach and dune system. This system will be impacted by coastal processes and experience enhanced levels of settlement due to the increased stresses applied by the nourishment. To develop a better understanding of the degree consolidation and overwash affect the beach and dune system and each other, integrated settlement and sediment transport analyses were performed on the site. This information is critical to understand the efficacy of the beach and dune and will serve as a benchmark case study for future nourishment projects.

Tuvalu is a Pacific island nation with a low-wave energy environment which suffers from coastal erosion. When erosion occurs, sand beaches cannot maintain sufficient sand width, and foreshore slopes become steeper from frequent erosion effects. As a result, beaches are trapped in a vicious circle of becoming vulnerable due to incident waves. In order to repair or protect erosive beaches, beach nourishment can be used as a countermeasure which also minimizes environmental impacts. However, this is not a permanent solution and requires periodic renourishment after several years. Thus, to alleviate such problems, minimizing the period of renourishment is a necessary economical alternative. To discover the characteristics of the Tuvaluan coast and the effectiveness of nourishment, field surveys, numerical simulations and hydraulic model experiments were conducted. The effectiveness of both sand and gravel nourishments were analyzed through experiments.

The increasingly popular Building with Nature (BwN) design philosophy, uses natural dynamics to meet structural demands. Allowing for these natural dynamics requires a different method of predicting the uncertain temporal evolution. In translating the variability in natural forcing to the predicted behavior of BwN solutions, the influence of model uncertainty should be explicitly addressed and accounted for. We do this using the GLUE method and a simple morphological model by quantifying model uncertainties on the basis of field data. To that end, we compare predicted volume losses at the Sand Engine and with observations. We show that model uncertainty is strongly dependent on the model time scale and possibly correlated to the incoming wave energy. The derived distribution of model uncertainty can be used to make an accurate prediction of the variability in the volume losses for a forecast period. The estimation of model uncertainty in the presented approach is a key step towards improved predictions of future BwN designs.

Artificial sandbar or shoreface nourishment plays an important role in coastal protection. While the lee effect of an artificial sandbar has been extensively investigated and its physical mechanism is relatively clear, the morphological response of artificial sandbar itself subject to large waves has not been fully understood. Physical experiments were conducted in a wave flume, considering different initial equilibrium profiles and different designs of artificial sandbar. Under large wave conditions, we observed onshore net sediment transport as well as onshore migration of the sandbar with its seaward slope becoming milder and its height decreasing. Experimental results suggest that the artificial sandbar could significantly affect the overall behavior of beach response to storms, and this effect is dynamic as sandbar evolves.

Environmental and anthropogenic sources often negatively impact coastal areas and commonly sandy shorelines. These challenges have to be met by developing new engineering solutions and advancing existing practices to achieve a balance within the confines of law and environmental practice. One of the most common approaches that is employed to achieve this balance is beach nourishment. However, beach quality sediment is a finite resource and in many regions of the world is becoming extremely scarce. The composition of sediment is altered during the dredging and beach placement process, typically improving in sediment beach compatibility. Since there is not an accepted methodology to predict these changes to the sediment, regulators typically take the conservative approach of regulating nourishment and beneficial use projects sediment based on the borrow source characteristics. This paper utilized data collected at various projects in Florida and Texas to generate an empirical formula to estimate the loss of fine sediments during dredging and ultimately through the beach placement process. The formula estimates losses due to dredging equipment operations, slope of the effluent return channel at the beach, sediment settling velocity, and sorting parameter.

An innovative sediment management technology, designated the Sediment Bedload Collector, has been developed that achieves sand harvesting by relying on natural physical processes to capture sediments by gravity as they are transported over the collector’s embedded hopper. Given existing economic and environmental constraints associated with dredging projects, this technology can serve as a cost-effective option for sediment management within riverine and coastal systems. The Sediment Bedload Collector is a stainless-steel hopper set into the waterbody bottom that collects coarse-grained sediment as it is moved by hydrodynamic forces. A urethane manifold system then pumps sediment slurry via a pipeline to a placement area or re-handling station. This paper describes how the Sediment Bedload Collector system works, how it has been applied in riverine environments, and how it has been field-scale modeled along the shorelines of Galveston Island, Texas.

A beach nourishment project was conducted in Weifang coast, China. However, the field observation showed a large amount of filled sands were lost only half a year after the nourishment. In this study, we used XBeach model to simulate the evolution of the nourished beach during the first half year. The surf beat mode and the stationary mode in XBeach model, were switched according to different wave climates. The simulated results were in reasonable agreements with the field measurement. The model was then used to investigate the causes and dominant factors for the erosion. It is demonstrated that two storm events during the first half year and the associated offshore-directed sediment transport are the main causes for the erosion. The existing breakwaters are not effective to protect the beach from storm impacts. During the storm periods, the infragravity waves could play an important role by enhancing beach erosion.

In the light of challenges raised by a changing climate and increasing population pressure in coastal regions, it has become clear that theoretical models and scattered experiments do not provide the data we urgently need to understand coastal conditions and processes. We propose a Dutch coastline observatory named ICON.NL, based at the Delfland Coast with core observations focused on the internationally well-known Sand Engine experiment, as part of an International Coastline Observatories Network (ICON). ICON.NL will cover the physics and ecology from deep water to the dunes. Data will be collected continuously by novel remote sensing and in-situ sensors, coupled to numerical models to yield unsurpassed long-term coastline measurements. The combination of the unique site and ambitious monitoring design enables new avenues in coastal science and a leap in interdisciplinary research.

Critically eroding beaches threaten their function as a major economic driver, of providing storm protection, and serving as habitat, often requiring management or maintenance to ensure their integrity. In Florida, storms and beach nourishment projects are common occurrences that temporarily alter the dynamics of the coastal system, and provide an opportunity to evaluate short-term beach morphology change. The ability to rapidly and accurately map and evaluate coastal change is important for future management and preservation. As technology advances, it is equally important to have a clear understanding of the capabilities and limitations of various methods. This study assessed the event-driven beach morphology change, including nourishments and storm events, on a Southeast Florida beach, with a comparative analysis of measurements using an Unmanned Aerial System (UAS) and traditional topographic surveys.

A 27-day field study was conducted to explore Retrogressive Breach Failures (RBF) at Amity Point, Queensland. Two events were documented over the course of the study, and videos and photographs were obtained of one event in progress. Beach profiles and recovering shoreline position were measured along with deployments of a simple penetrometer to obtain a proxy for surficial sand density. The sand appeared to be in a loose state prior to the second event, being controversial to theory of RBF. The recovering shoreline showed rapid accretion in the first 24-48 hours along with tidal erosion of the beach face. Wind speeds reached ∼35 kilometers/hour out of the NNW on the day of each event, representing the only time these conditions were observed.

While a lot of studies have focused on the hydrodynamics and sediment transport under regular waves, the sediment transport processes beneath irregular waves have not been well understood. In particular, the history effects of irregular wave forcing on sediment transport need to be quantitatively examined. In this study, a numerical model for wave boundary layer was used to simulate the flow velocity, turbulent energy, sediment concentration and sediment flux driven by irregular waves. The sediment transport process associated with each individual wave within a wave group was compared to that of a regular wave with the same wave shape. The history effects related to irregular waves were then investigated based on several dimensionless parameters.

The west coast of Europe is exposed to high-energy winter waves generated in the North Atlantic Ocean by low pressure systems traveling eastward. The present study builds on recent research on atmospheric and ocean wave climate in the North East Atlantic over the last 70 years using numerical weather and wave hindcast, in-situ sea-level pressure measurements, and beach response from a unique dataset of decadal beach morphological changes along the west coast of Europe. Interannual to decadal variability of winter wave activity in the North East Atlantic is strongly affected by the North Atlantic Oscillation (NAO) and the West Europe Pressure Anomaly (WEPA). It is found that extreme winter-mean wave heights become more frequent and variability increases, resulting in extreme winters such as that of 2013/14. We show that the recovery signature is site-specific and multi-annual, and that interannual variability of both erosion and recovery is well correlated with WEPA and NAO.

Nearshore sandbars play an essential role in dissipating incident wave energy and protecting the beach landward. This study examines the sandbar equilibration in terms of bar height and cross-shore bar location with monthly to bimonthly beach profile data from October 2006 to February 2019 along a 12-km stretch of beach in west-central Florida. For the studied coast, alongshore variation in equilibrium bar position measured from the shoreline ranges from 55 to 90 m and equilibrium bar height from 0.20 to 0.50 m. Greater equilibrium sandbar height and farther offshore located equilibrium sandbar position tend to occur around a headland, where incident waves are higher. A representative wave heights were computed as the 90th percentile height in between two consecutive beach surveys over the 13 years study period. This representative wave heights were clustered with respect to the three different scenarios of alongshore variation of sandbar movement along the studied beach, including onshore only, offshore only, and mixture of onshore and offshore sandbar movement. The results indicate that high wave with a median value of 1.5 m typically caused offshore bar movement. Low waves with median value of 0.8 m usually induced onshore bar movement. Moderate wave with median wave height of 1.2 m tended to result in longshore variations of sandbar movement, with opposite sandbar movement direction between northern and southern Sand Key. Although with certain ranges and uncertainty, the threshold value of incident wave height for longshore variations in sandbar movement would provide insight on predicting sandbar movement based on forecast wave conditions.

Numerical models are widely used to manage the beach from coastal erosion. To perform numerical modelling, many researchers have calibrated in an empirical method. XBeach, 2DH hydrodynamics and morphodynamics model, is one of the most popular models, and contains many free parameters. Particularly, six free parameters of XBeach are known to be considered for storm-induced beach evolution modelling: gamma, gammax, smax, facua, eps, and wetslp. In this paper, we performed numerical simulations for the sensitivity and uncertainty analysis of six free parameters for several simplified beach conditions. This information is important for more systematic parameter calibration than empirical calibration.

This paper investigates the hydrodynamic mechanisms that govern the headland bypassing between Forte – Pontal do Capri beach system (FPBS) and Enseada - Ubatuba beach system (EUBS) on north shore of São Francisco do Sul Island – SC. The Delft 3D suite was used to numerically simulate currents, waves and sediment transport in combination with tide and wave climate schematizations. The results shown waves dominate the magnitude and direction of transport at both beaches systems, however, tide interaction has a significant influence in the sediment transport (up to 1 order magnitude higher than tides alone). On FPBS, the main driver of transport is the most frequent wave conditions from east and east-northeast, while the extreme wave cases from the southern quadrant govern the sediment carriage on EUBS. In conclusion, extreme events are responsible for both northward transport in EUBS and its headland bypassing to FPBS, where average waves distribute these sediments alongshore.

The formation of beach cusps were observed during a field experiment at Nha Trang beach, Vietnam, during an accretive event. Simulations of this event were attempted using XBeach, and the model was able to simulate cusp formations similar to those measured. This allowed the model to be further used to investigate the effect of systematically varying wave forcing conditions (wave height, period, direction, and spreading) on the spatial dimensions of the cusps. The wave period was found to primarily influence long-shore length scales, the wave height cross-shore length scales, and directional variability enhances these dimensions, particularly under narrow-banded conditions. Cusps are not prominent if the wave energy is too low to effect significant onshore transport, or if the wave direction and spreading are too large, effectively smoothening out swash perturbations. The model can be further applied to study the effect of changes in sediment composition, or to investigate processes influencing cusp formation.

The dispersal of sand from submerged mounds in the nearshore is driven by the interplay of processes such as converging and recirculating flows, changing roughness, bed slope effects and wave focusing/refraction. This morphological diffusivity is key to understanding sand bars in shallow seas, tidal inlets, estuaries, and the nearshore response to human interventions such as nourishments and dredging. Most of the work on the evolution of submerged mounds has been based on fluvial studies, focusing on flow without waves. In these cases, circular mounds tend to deform to crescentic (barchan) shapes. In contrast, observations of sandbars and berms in the nearshore subjected to waves show much more complex translation and deformation behavior. This contribution introduces the laboratory MOrphological Diffusivity Experiment (MODEX) aimed at examining morphological diffusivity under different forcing conditions. The experiment particularly addresses the linkages between small scale (local) effects (e.g. bed slope, bedforms) on the adjustment of sandy mounds.

An encapsulated sediment budget model was developed that incorporates the balance between beach building and beach eroding parameters on a multi-decadal scale to assess the impact of sea level rise on beaches in Barbados. The model predicts that under the IPCC (2013) RCP8.5 sea level rise scenario and with the current alongshore and onshore sand supply rates, most beaches would lose between 20% and 50% of their existing sand volumes by 2100 if no mitigation measures are implemented. The results emphasize the importance of carbonate sand production along Bajan coasts as the main source of sediment to combat sea level rise. Improvement of nearshore underwater habitat conditions is therefore critical to the resiliency of beaches in Barbados.

We investigate the sediment transport dynamics along a 15-km stretch of embayed coastline in north Cornwall, SW England. Numerically-modelled wave-driven and tidal currents are used to support interpretation of sediment flux pathways inferred from morphological observations. Results for the main embayment (Perranporth) indicate that for an extreme erosive event, sediment ejection beyond the morphological depth of closure (c. -15 m) can exceed 150 m³ m^-1, related to ‘megarip’ formation where an alongshore current is deflected offshore (0.7 m s^-1 at > 20 m depth). Accretionary phases are characterized by entrainment of sediment from adjacent bays and sub-tidal alongshore redistribution (35 m³ m^-1 year^-1). Our study suggests that major mechanisms for redistributing material to and along the lower shoreface for embayed coastlines are longshore residual flow (induced by waves and tide) and headland rip cell circulation, with the latter a function of wave obliquity, embayment length and headland configuration.

Predicting the evolution of mound formations in the nearshore, both natural (e.g. bars) and man-made (e.g. nourishments) requires an understanding of mixed wave-current flow on sediment transport. MODEX (Morphological Diffusivity EXperiment) used a wave-current-sediment flume to observe in detail the evolution of a sand mound in shallow water. Imposed flow included waves-alone, currents-alone, and combined wave-currents. MODEX observations show the impact of currents on waves around the mound and the feedback with morphology. Here, a wave-resolving model SWASH is used to simulate flow patterns around the mound as it diffuses, showing the impact of wave-current interaction on mound evolution. Further, simulations initialized with a diffused mound show the feedback between 3D bed deformation and wave-current flow structures. The results provide a framework for understanding and implementing intra-wave sediment transport in wave-resolving models. Extensions of the results to field conditions with mixed wave-current energy will be explored.

Prediction of sediment suspension in the surf zone remains elusive. We explore how suspended sediment concentration at 19 cm above the bed in the mid-surf zone during a storm is influenced by flow acceleration and deceleration. There is a tendency for higher suspended sediment concentrations during onshore flow, with decelerating onshore flows having higher concentrations than steady, accelerating, or reversing flows. The development of models that exploit information on flow acceleration, deceleration, and flow reversal may lead to improved ability to predict suspended sediment transport in the surf zone and resulting geomorphic changes.

This paper describes a new morpho-dynamic 3D surf-zone model. The hydrodynamic model used for this purpose is the MIKE 3 Wave FM Model. This model solves the 3D Navier-Stokes equations on a 2D horizontal unstructured mesh with a sigma transformation describing the vertical coordinate. A recent solution to the well-known over-production of turbulence outside the surf-zone in RANS models has been applied and is shown to improve the predicted undertow profiles. The sediment transport is modelled using an advection-diffusion equation for the suspended load, together with a bed-load formulation. In the present paper the predicted surf zone hydrodynamics and sea bed evolutions are compared against experimental laboratory data.

Transport by asymmetrical wave motions plays a key role in cross-shore movement of sand, which is important for bar migration, exchange through tidal inlets, and beach recovery after storms. We have implemented a modified version of the SANTOSS formulation in the three-dimensional open-source Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling framework. The calculation of bedload transport requires inputs that include: water depth, bulk wave statistics (significant wave height, wave period, wave orbital velocity), current velocity at the edge of the wave boundary layer, and sediment density and grain size. While the coupled ocean-wave model computes water density, depth, and bulk wave statistics, we implement a method to calculate current velocity assuming a log profile and using the Madsen formulations for wave-current bottom boundary layer flows. We investigate the sensitivity of the calculation of near-bottom current velocity to model choices and its influence on cross-shore bedload transport. Results are compared to available numerical experiments using coupled fluid and discrete element model (CFDEM) simulations.

On the base of field experiment data, it was shown that the wave breaking type differently effects on the evolution of the underwater profile. The plunging breaking waves contribute to the formation of underwater bars, but spilling breaking waves smooth them out. The main reason is the different asymmetry of breaking waves due to different amplitude-phase composition in the process of their nonlinear transformation.

Sand ripple lateral and downslope spreading was observed over a Gaussian-shape sand mound at the MOrphological Diffusivity EXperiment (MODEX). Morphologic change was observed using an underwater GoPro camera, a LIDAR, and sonar imaging. Three dimensional images of the mound evolution were created every thirty seconds by using the LIDAR and sonar images of the mount to rectify the GoPro Images. The mound erosion was observed to occur nonlinearly under wave forcing, with lateral and downslope ripple migration.

Predictions of shoreline change are of great societal importance, but models tend to be tested and tuned for the specific site of interest. To overcome this issue and test the ability of numerical models to simulate shoreline change over the medium scale (order of years) we have organized a non-competitive competition where participants were given data to train their model (1999–2014) and data to predict seasonal to inter-annual future changes (2014–2017). Participants were shown the observed shoreline changes only after submission of their modelling results. Overall, 19 numerical models were tested, the vast majority falling in the broad categories of “hybrid models” or “machine learning”. Models were able to reproduce the mean characteristics of shoreline change but often failed to reproduce the observed rapid changes induced by storms.

Regular, high spatial resolution survey datasets from dune to depth of closure are rare in the literature. These type of datasets have the ability to provide critical information about changing beach morphodynamics in both the two and three-dimensional space. A regional experiment was established for the open ocean beaches of the Gold Coast, Australia. Two years of high spatial frequency survey at five sites within the Gold Coast embayment are presented here. This paper details the usefulness of the unique dataset and its ability to further inform previously poorly understood coastal morphodynamic questions, such as bar migration and spatial variability in beach state energy with respect to wave direction. By comparing the spatial variability in beach morphology between the survey sites, under two different wave directions, it is shown that the wave direction and attenuation play an important a role in shaping bar morphology along the coast.

The nearshore environment can experience extreme changes during storms, and waves in the surf zone are a complex function of the evolving storm energy and bed morphology. In this study, large waves that induced bathymetric changes during storms including Hurricane Joaquin (2015) are investigated. The storm conditions were observed by in-situ directional wave sensors and remote sensing with digital images at the US Army Corps of Engineers (USACE) Field Research Facility (FRF) in Duck, North Carolina (NC). The observations are used to characterize changes in surface waves and morphological change. The non-hydrostatic phase-resolving model (SWASH) is applied on a cross-shore profile grid to simulate waves at selected times during the storm. Model results are compared to wave celerity observations from the application of the cBathy algorithm to optical time series from the Argus video imagery. Model-data comparisons will lead to further understanding of the non-linear effects leading to changes in wave speed due to transformation and breaking over bathymetric features.

This study assesses four beach cusp events through a spectral analysis of alongshore elevation contours. The analysis was conducted using Digital Elevation Models (DEMs) derived from three-dimensional lidar scans of subaerial beach topography collected from a fixed lidar system in Duck, NC, USA. Time periods of rapid cusp evolution were selected, and each event was defined as a 24-hour period starting at low tide. Contours were extracted from the DEMs at an elevation 30 cm above an estimated mean water line for each low tide during the event period. Fourier analysis was applied to each contour to generate spatial cusp spectra, and a mean cusp wavelength was determined. Forcing conditions during cusp events were determined from an array of pressure sensors located in approximately 8m water depth (which provided nearshore wave conditions) as well as cross-shore lidar linescan time series (which provided swash conditions). Data show that beach cusp formation and evolution can occur on the scale of tidal cycles, with cusp morphology rapidly responding to changing forcing conditions.

Observations of lagoon water level, river discharge, and offshore wave heights in conjunction with five bathymetric/topographic surveys show a seasonal adjustment of the Carmel River State Beach in response to both mechanical and natural breaching events. Results indicate an onshore migration of the beach that is not directly influenced by the breach, as well as and offshore flux of sediment at the breach site. The initial mechanical breach of the system succeeded in lowering the water level, but closed immediately resulting in pre-breach water levels.

Ripples are generated on the seafloor when shear stresses exceed the critical threshold for sediment motion but do not exceed the critical threshold for sheet flow. While the full implications for the effect of ripples on sediment transport are still being understood, ripples are important in shaping the seafloor boundary layer and resuspending sediment. Here, we propose a new type of ripple model developed using a Bayesian Network (BN). BNs are a machine learning tool able to handle non-linear systems, missing data, and data from different sources. BNs explicitly model uncertainties, have a simple and intuitive graphical structure, and low computational cost. We developed our BN using an existing database, and performed a cross-validation test to assess quality of the results. Ripple geometry estimates have a Nash-Sutcliffe metric of 0.64 for height and 0.60 for wavelength. The root-mean-square-error is 0.006 m for ripple height and 0.070 m for ripple wavelength.

The East Sea coastline has simple features that are affected by incident high waves. In this study, the coastline changes, which are caused by coast structures, were predicted by modeling the actual site using the developed DCOM (Depth Contours Model). Yeongnang beach in Sokcho, Gangwon Province, Wonpyeong beach in Samcheok, and Bongpyeong beach in Uljin, North Gyeongsang Province, are sites where high waves result in coastline changes after construction of structures nearby. In order to control the coastline erosion in the area, specific measures have taken place such as the installation of headland, and submerged breakwater. Using the developed DCOM, excellent reproducibility has been confirmed by comparing the current coastline, which has changed after the installation of the structures, with the previous coastline. The DCOM developed through this study has proven to be superior to other asymmetric models with no turning parameters and it can be used as a useful tool for predicting the change of coastal environment due to future construction.

Surfzone sandbars contain large amount of sediment that is usually transferred to the subaerial beach during low-energy wave conditions. This study investigates the relation between shorelines and sandbar positions and volumes on a single-barred beach in NW Baja California (Mexico). Four years (August 2014 to September 2018) of monthly topographic and bathymetric measurements and hourly wave data were used for this purpose. Shorelines and sandbar volumes were inversely correlated and evolved in phase. Maximum shoreline progradation occurred when the beach was unbarred. Largest sandbar volumes were associated with major shoreline retreats that took place during high-energy wave conditions. The magnitude of shoreline progradation during the low-energy wave period depended on the offshore sandbar location at the end of the preceding high-energy wave period.

Understanding multi-annual to decadal atmospheric climate controls on winter-wave climate is critical for coastal vulnerability assessment and future development of ‘season ahead’ forecasting of coastal risk. We examine the relationships between winter-average climate indices (NAO and WEPA) and directional wave power at 63 inshore locations throughout the United Kingdom and Ireland (UK&I). Analysis of hindcast wave data between 1980–2017 illustrate the extent of directional bi-modality, with 67% of inshore sites displaying directionally multimodal wave climates. Analysis of directional modes as a function of climatic indices illustrated the control exerted by NAO/WEPA on directional balance of inshore winter wave climate. Along Channel and southern North Sea coasts +WEPA significantly explains winter-averaged wave power for southwesterly wave directional modes (r = 0.58–0.77) and –NAO significantly explains variability in all easterly wave modes (r = −0.6– –0.76), providing a mechanism for which ‘season ahead’ inshore wave climate forecasting and rotational beach response can be based.

Here we present topographic surveys collected during 90 consecutive months at a monthly to bi-monthly frequency. The 7 summer seasons covered here allowed investigating the seasonal recovery of the beach by analyzing the volume variations of the berm and the dynamic of the alongshore averaged cross-shore position of the berm crest. Despite contrasting winter conditions (seasonal cumulated wave energy power varying by a factor 2), the seasonal recovery of the volume of the berm was on average 65m³/m/season and reached up to 100m³/m/season. However a single winter storm occurring even at the beginning of the usual ‘recovery’ season can significantly impact the seasonal recovery capacity of the beach. The disequilibrium between the winter cumulated wave energy power and the summer cumulated wave energy seems not to play a crucial role in the total sediment gain, however it might have an impact on the recovery rate (complete, incomplete or in excess).

Over recent years, data-driven modelling approaches have continued to grow in popularity in environmental modelling fields. In this study a data-driven approach utilising a neural network has been applied to predict shoreline change over daily to decadal timescales at two embayed beaches at which 10 years of daily shoreline position observations exist, Narrabeen Beach in Australia and Tairua Beach in New Zealand. The model shows good cross-validation performance, predicting the shoreline position with 4.75 m RMSE at Tairua and 7.98 m RMSE at Narrabeen on average across approximately 2-year validation periods. At both sites the predictive performance was most dependent on the input variable representing hysteresis in the model.

Detailed morphological sequences of formation, landward migration, and onshore welding of a slip-faced ridge-runnel (RR) system are simulated numerically during two spring-to-spring tidal cycles. The RR system is a morphological feature that often forms in the intermittently wet and dry zone of the beach immediately after a storm event. RR system dynamics can play a significant role in natural beach recovery but our capability to model their formation and onshore migration using process-based numerical models remains limited due to the complex feedback mechanisms between hydrodynamics and morphodynamics contributing to their evolution. The beach recovery process occurs over a long duration during less intense wave conditions after storms and the small incremental changes it entails make this process difficult to model numerically. Here, the process-based cross-shore morphodynamic model (CSHORE) was implemented to simulate the RR evolution measured during an extensive field campaign on an engineered, meso-tidal, semi-diurnal sandy beach.

The knowledge of physical processes and their role in shaping morphology in low-energy microtidal environments lags behind that of exposed coasts. A characteristic morphological feature found in such environments is a distinct platform beneath the water surface. By combining existing data from low-energy microtidal beaches around the world and new bathymetric surveys, relations between hydrodynamic and sedimentary characteristics and geometric parameters of the foreshore platforms have been found. The dimensionless fall velocity describes the wave climate and sediment conditions and is found to be correlated to the cross-shore width and elevation of the platform. Platform development appears to be driven by erosion. This finding follows from a positive correlation between the dimensionless fall velocity and platform width and a negative correlation between dimensionless fall velocity and platform elevation. Wider and deeper platforms are induced by higher wave energy and associated sediment mobility.

The formation of a comet-tail spit was predicted using the BG model. A triangular island was placed on a mud flat of 1 m depth, and waves with a significant wave height of 0.25 m and a period of 2 s were assumed to be incident to the island. Calculations were carried out for two cases: an island composed of sand in Case 1, and an island surrounded by a solid wall with a sand source offshore of the island in Case 2. A pair of sand spits obliquely extended from two corners of the island in Case 1, whereas a slender comet-tail spit extended behind the island in Case 2. The formation of a comet-tail spit is strongly related to the volume of sand available for its formation, and a comet-tail spit can develop only if sand is slowly supplied from upcoast without rapid deformation of the island itself.

The coastal sandy beach is maintenance-free green infrastructure with self-restoring capability and it is expected to reduce high wave damages with the coastal forest. A number of valuable sand beaches are distributed as a conservation of ecosystems and sightseeing and landscape resources along the Kii Channel. However, depending on the scale of liquefaction caused by the Nankai Trough Earthquake, these functions may not be sufficiently appeared. In this study, we studied Eco-DRR (Ecosystem-based Disaster Risk Reduction) function of sandy beaches in this area through simple liquefaction experiments. The correlation with the ease of liquefaction was high in the order of water content, uniformity coefficient and the coefficient of form unevenness and it was considered that the state of void has impact on the onset of Eco-DRR function.

This paper presents new net transport data from the STENCIL full-scale wave flume experiments with a sediment mix of a fine (0.21 mm) and a coarse (0.58 mm) sand fraction. These and existing mixed sand transport data from full-scale oscillatory flow tunnel experiments were used to validate the SANTOSS practical sand transport formula, which includes size-selective transport mechanisms and hiding and exposure effects. The STENCIL data show a strong effect of the sediment mix on the bed form regime and net transport rates. The SANTOSS formula predicts the flow tunnel net sand transport data well, and does a reasonable job in reproducing the net sand transport per fraction in the mix. The new STENCIL net transport data are generally underpredicted. In further research the SANTOSS formula will be further tested and improved using more detailed STENCIL data of flow and sand transport processes.

Bi-directional wave climates often drive beach rotation at embayed locations, increasing erosional risk to shorelines. Decadal records of beach rotation, wave forcing, and atmospheric controls were investigated at 18 sites along the south coast of England, UK. Rotation was identified at 12 of the studied sites, leading to the creation of a rotation index. Beach rotation was attributed to shoreline angle, and obliquity to dominant south westerly waves. Beach rotation was well correlated with the normalized balance of wave power from opposing south westerly and easterly directions, calculated from 14 offshore model nodes. Dominant south westerly waves were well correlated to positive phases of the West Europe Pressure Anomaly (WEPA), whilst easterly waves were well correlated with negative phases of the North Atlantic Oscillation (NAO). Direct comparisons of beach rotation and WEPA at some locations, show future forecasts of atmospheric indices may directly predict rotational beach state, at seasonal scales.

In previous studies addressing coastal erosion hotspots, evidence is presented to demonstrate that geology and nearshore seabed features can exert control on local beach dynamics. In this study, an episodic coastal erosion hotspot at Thorpeness, UK is examined. Antecedent wave conditions and changes in incident wave characteristics resulting from interaction with the seabed geology and/or temporal changes in nearshore bathymetry are measured and modelled. Observations of changing sea bed features derived from radar measurements and results from numerical modelling demonstrate links between nearshore bathymetry and beach erosion events. The study examines also the conditions frequently experienced at the study site whereby persistent waves from a narrow sector reduce beach levels and modify the nearshore bathymetry in such a way that the impacts from storms from an opposing direction are larger than would normally be the case.

In the effort to evaluate movement of nearshore placed material, improve the effectiveness of nearshore placement activities for beach nourishment, and protect eroding shoreline at Ogden Dunes, hydrodynamic, wave, and sediment transport modeling simulations are conducted under various physical conditions. The results of the study indicate that storm-/wave-driven currents are dominant in surf zone area. Stronger longshore currents are responsible for sediment movement and morphology changes in the nearshore area. Through the analysis of driving forcing and the validation to morphology changes, the model’s capability is demonstrated in calculating currents, water surface elevation, waves, bed volumetric changes, and sand migration in coastal lake environment.

The analysis of sediment availability (past and present) on the dredging cycles in the Gulf Intracoastal Waterway (GIWW) and the assessment of capacity and conditions of the dredged material placement areas (DMPAs) were conducted using different approaches in each of the three studies conducted for the State of Texas. The data show how frequent sediments are dredged in different reaches of the GIWW, the general volumes generated by those events, as well as the location of dredging hot spots. The data show which DMPAs have the capacity to receive future dredging cycles that are losing placement capacity due to shoreline erosion and other factors, and which DMPAs have enough material for potential opportunities related to restoration projects through the beneficial use of dredged material. The compilation of results of these different studies can help in the planning of regional sediment management opportunities throughout the Texas coast.

Periodic dredging is a common method for maintaining inlets and navigation channels. The dredged material is often unfit for beach fill, and therefore was historically removed from the littoral system. In 2009 and 2016 the Army Corps of Engineers placed dredged sediment in a nearshore berm off the coast of Fort Myers Beach, Florida to better utilize this sediment.

Samples were collected and processed on the nearshore berm and control areas to determine the change in grain size distribution and sediment composition associated with placement of the berm. Low longshore transport rates within this area made it possible to use statistical analysis to determine changes around the berm. Mixing due to a hurricane event was detected, as well as re-equalization of sediment after the event.

The Spanish Pass Marsh and Ridge Creation Project involves the restoration of 1,134 acres of marsh and 120 acres of ridge habitat. The project will require between 11.5 M m³ and 23 M m³ of sediment to construct the project. Numerous borrow areas have been located within the Mississippi River and within the Gulf of Mexico. The Mississippi River provides a source of sandy sediment, which is advantageous as containment dikes are not required to facilitate construction. While several borrow areas have been previously delineated within the lower confines of the Mississippi River, additional investigations were performed to locate borrow sources closer to the project and thus save on construction costs. Development of the borrow areas required geophysical investigations and bank stability analyses. Due to extended high water levels within the Mississippi River, geotechnical borings have been delayed at time of writing this paper while morphological modeling is underway.

Achieving an appropriate elevation is critical to the success of thin layer placement projects using dredged material to restore degrading marshes. Because the consolidation of hydraulically placed dredged material is large, modeling the elevation change over time is necessary to determine the target construction elevation required to achieve the desired post-consolidation elevation. Processes such as water level fluctuations and vegetative factors can affect consolidation behavior. Laboratory experiments were conducted to evaluate the impacts of these processes on consolidation so that they can be accounted for within the consolidation model. Qualitative evaluation shows that patterns of water level fluctuation do impact consolidation rates, and application of an average annual water table elevation may not be representative. Vegetation appears to impact the rate of consolidation through evapotranspiration, but does not appear to impact the overall consolidation.

Observational records of tropical cyclones can be extended over the past few thousand years using sediment proxies of transport and overwash by large waves. However, in high-energy carbonate environments, conventional methods of identifying large wave events in sediment proxy records can fail due to homogeneous, coarse grain size and homogeneous chemical makeup. We investigated the relative weathering of foraminifera tests as an alternative proxy for large wave events in a blue hole sediment core retrieved from Jaluit Atoll, Republic of the Marshall Islands. We found clear evidence of gradients in weathering under ambient hydrodynamic conditions across the fringing and back reef flats bracketing the blue hole. However, despite the existence of these gradients, event layers in the sediment core were not clearly distinguishable from non-event layers using weathering as a proxy.

Guánica Bay in southwest Puerto Rico is highly turbid and has some of the highest PCB concentrations in the USA. To investigate how and to what extent the bay waters influence coral reef ecosystem health along the coastline, 6 months of hydrodynamic data were collected at 8 sites on the insular shelf. Bed shear stresses were primarily driven by waves and were weakest at the site closest to La Parguera, located downcoast to the west. Due to the prevailing westward shelf currents, suspended particulate material (SPM) exiting the bay likely settles out at these lower energy sites. We postulate the ecosystem in this area was adversely affected immediately after the hurricane because (1) the source concentration of SPM and PCBs in the bay was greatly increased, and (2) regional waves in the months after the hurricane season were less energetic and, thus, less frequently mobilized and flushed the material.

Coral reef islands are unconsolidated deposits of reef-derived sand and gravel that are considered vulnerable to the impacts of global sea-level rise because of their low elevation (< 3 m) and exposure oceanic wave energy. Previous research has shown that sea-level rise will drive an increase in wave overtopping on reef island shorelines, which will be an increasing hazard for atoll island communities. Here, we show that wave overtopping on reef islands is a geomorphically important process that facilitates sediment deposition on the island surface and vertical building. Field evidence from 26 overwash deposits show that vertical island accretion can be driven by king tides, long-period swell, local storms, tropical cyclones and tsunami. Deposit depths ranged between 0.06–1.93 m and increased island elevations by between 4–400%. Recognition that overwash processes can contribute to vertical island building is instructive in considering the potential for islands to adjust to future increases in sea-level and to incorporate this critical morphodynamic response in future flood risk modelling for low islands.

Process-based numerical modeling of reef island morphodynamics has significant potential to enhance our understanding atoll island vulnerability and adaptation to future sea-level rise (SLR). However, limitations associated with traditional numerical models and a lack of available benchmarking data have prevented detailed morphodynamic modeling in reef environments, to date. Here, we apply XBeach-G (non-hydrostatic) to represent sediment transport and morpho-dynamic change on a gravel Motu in Tuvalu. Scaled physical modeling experiments were used to comprehensively analyse model behavior and sensitivity to grain size, ground water conductivity and Nielsen’s phase angle, with multiple combinations producing a close match with wave flume results. XBeach-G was then used to explore island morphological adjustment to SLR, highlighting the complexity and potential associated with representing decadal-scale change in a phase-resoling model. Outputs suggest that island crests can accrete vertically at a similar magnitude to SLR if a near-equilibrium morphology is maintained.

In October 1972, Tropical Cyclone Bebe hit Funafuti Atoll, and a large amount of coral debris was deposited on the reef flat. Although this example shows that coral cays could be formed by storm waves during cyclones, the formation and deformation of a rubble rampart on the reef flat and the resulting deformation of the coral cays are important in the conservation of the atoll. The long-term shoreline changes in Funafuti Atoll were investigated using aerial photographs taken in 1971 and 1984 and satellite image in 2010. Photographs of the formation of the rampart immediately after the cyclone were also collected. In June 2012, site observations were carried out on three islands along with beach surveys. It was concluded that the net increase in the size of the cays was small, suggesting that almost all the coral debris was lost owing to the southwestward longshore transport along the reef edge.

Reef canopies are complex and extremely variable across a range of spatial scales. This variability affects the velocity above as well as within the canopy, and directly impacts the transport of sediment along the bed as well as suspended in the water column. How a canopy affects the transport of sediment is important to understand and predict changes in the position of the adjacent shoreline, particularly as reefs change. In this study, high-resolution seabed complexity models derived from photogrammetry for low roughness and high roughness canopy sites at Moloka’i (Hawai’i) are combined with direct field measurements and three-dimensional numerical modelling to investigate these canopy and sub-canopy impacts on velocity and sediment transport.

This study investigates the morphological change of four sand dominated features in a coral atoll lagoon completely sheltered from ocean waves. Morphological change rates are observed using high-resolution satellite imagery combined with hindcast wind and wave data. The most dynamic feature, the barrier, was located in the south-western corner of the lagoon and is exposed to local, wind driven waves within the lagoon from the dominant easterly trade winds. At times, the barrier showed very rapid rates of movement, with regression rates >0.6 m/day in places. On the more sheltered, eastern side of the lagoon, a large flood tide delta, shows a ∼45° counter-clockwise rotation during the course of the study which coincided with a shift in annual average wind directions to have a stronger southerly component. The results here demonstrate that, even in low energy coral reef environments, rates of change of morphological features are significant on annual-decadal time scales.

The transport of carbonate sediment across reefs to the shoreline is of great interest to the research community and coastal managers alike. This sediment is generated by the breakdown of reef skeletal structure and a critical source for beach nourishment that provides a buffer to coastal flooding as sea levels rise. Understanding the physical processes that are responsible for this flux of sediment to the coast is therefore necessary before we can begin to predict how it may be affected by rising sea levels. Six weeks of high quality physical oceanographic data collected on the fringing reef in the Jurabi UNESCO World Heritage Site in Western Australia provides the opportunity to examine these processes in greater detail than ever before.

The assessment of coastal flood risk on a reef-lined coastline presents several challenges. From the probabilistic side, we need to consider all possible events that could occur in the system, taking into account the different contributions of waves, storm surges, and tides that contribute to the total water level. To estimate reliable flood extents, we need to accurately model the complex wave processes that occur across the reef. To explore the multivariate nature of coastal flooding, we rely on a climate emulator that accounts for climate variability and simulates time series of all the variables involved. Due to the computational constraints to numerically simulate thousands of events, we explore the feasibility of using a recently developed tool, the HyCreWW (Hybrid Coral Reef Wave and Water level) meta-model to estimate wave run-up and flooding extents. Limitation of a 1D assessment are analyzed and results compared with 2D modeling.

Coral reefs generate significant volumes of carbonate sediment that becomes the primary source of beach material along many low-latitude shorelines that protect hundreds of millions of people globally. Despite this fact, there is little understanding of the specific processes that transport the carbonate sediment produced on the outer portions of coral reefs to the shoreline, let alone how those processes may be affected by projected sea-level rise. To better constrain the influence of sea-level rise on waves and sediment transport over a fringing coral reef flat, an experiment was conducted across the large fringing reef off the south shore of Moloka’i, Hawai’i, in the summer of 2018. Here we describe the influence of water levels on waves, currents, and the resulting sediment resuspension and fluxes observed during this field effort.

Low-lying coral reef islands are considered extremely vulnerable to the impacts of climate change. However, future island morphodynamic adjustments in response to anticipated sea level rise and changing wave conditions are currently poorly resolved. Assertions of island vulnerability are based on outputs from flood risk models that simulate sea level rise on present day island topography despite evidence that many reef islands are highly dynamic landforms. Utilizing a physical modelling methodology, three experiment programs were undertaken to model gravel island morphodynamics in response to increasing sea level and changing wave conditions. Modelling outputs present new insights into the modes and styles of island change, primarily the first experimental evidence that reef islands can keep pace with sea level rise through island building driven by washover processes. Results suggest that many islands are less vulnerable to inundation than currently perceived and may endure on reef platforms despite sea level rise.

Sand aprons in the southern Great Barrier Reef are relict sedimentary deposits that presently receive negligible sediment input. The main reason for that seems to be that wave dissipation over the fore reef and reef flat is too high to allow any meaningful sediment transport into the lagoon and sand aprons. Here we present a summary of our comprehensive studies on sand apron sedimentation taking into account sea level fluctuations during the Holocene. We hypothesize the existence of a Goldilocks sea level for sand apron formation and progradation, during which wave energy dissipation over the fore reef and reef flat is such that it still allows sediment transport into the lagoon. Sediments in coral reefs are produced by healthy coral and other organisms; therefore, the Goldilocks window of sand apron formation and progradation must coincide with the suitable environmental conditions.

Accurate and complete representation of sediment characteristics within a numerical model supports model calculations and performance. Furthermore, the sediment transport models must also be applicable in the sedimentary environment being simulated. This work uses a modified instrumented settling column to determine fall velocity of individual grain size classes of natural sediments. These sediments have varying quantities of carbonate material. The measured fall velocity is compared with Soulsby, 1997, and Wu, 2006. Numerical modeling guidance is presented.

Sediment dynamics drive changes in coastal morphology and the habitats formed by these mobile sediments, resulting in impacts to local ecosystems and effecting the management of these natural systems and fisheries. The transport of suspended material in coastal environments is controlled by advective and diffusive processes and understanding the variability of these would lead to a better representation of suspended sediment, and to models that can better describe sediment movement in coastal environments. To this end fieldwork was carried out on intertidal flats in Morecambe Bay, UK, as part of the BLUEcoast project (bluecoastuk.org). The data collected of hydrodynamics and sediment dynamics were applied to the advection-diffusion equation to determine the horizontal diffusion-dispersion. This highlighted the relative importance of different processes on the tidal flats.

As part of the design and construction of a new power plant, a dredged material dispersion study was required to support the Construction Environmental Management Plan (CEMP) as part of the environmental impact assessment (EIA). A coupled hydrodynamic and sediment transport model was developed to model the sediment dispersion from two sources, namely (i) a dredged spoil settling pond, and (ii) a dredger working throughout the project site. Nearby on three sides of the power plant model domain there exists some of the last remaining undisturbed coastal habitats in Dubai including sea grasses, corals and a sea turtle nesting area. Thus, the local authority required very low total suspended solids concentration within the water column within short distances during construction activity. A series of modeling scenarios including combinations of suspended sediment sources with and without mitigating barriers were developed to determine fate of total suspended sediment during dredging operation.

Africa’s coasts are considered one of the most sensitive areas worldwide due to their exposure to natural hazards and high social vulnerability. This study presents the first regional assessment for East Africa that combines level of exposure to coastal hazards and social vulnerability, and considers implications to UNESCO World Heritage Sites. Results indicate that 1340 km (12%) of the Eastern Africa coastline show high or very high exposure to coastal hazards, mainly in Mozambique (625 km) and Madagascar (614 km). Tanzania shows the least level of exposure with 57% of its coastline classified as very low or low exposure. However, coastal habitat loss could increase dramatically the exposure levels in Kenya and Tanzania. Although erosion may be an issue locally, 60% of the Eastern Africa coast is relatively stable. Relative to the regional index, the UNESCO Heritage Sites are not in areas showing high levels of exposure, but some may be if erosion rates increase or natural protection is lost.

We present a possible methodology for forecasting one mode of future coastline changes for a case-study Carolina coastline (USA), and for assessing the uncertainty of the forecasts. We would take advantage of the hybrid methodology developed in Antolinez et al. (2018) to transform surface pressure representative of the wind fields from Global Climate Models into forecasts of the wave conditions affecting the Carolina coastline during the next century. Then, we would translate the downscaled wave data into coastline change using the Coastline Evolution Model (CEM; Ashton and Murray 2006a). We envision incorporating a number of different analysis to investigate (1) the ‘epistemic uncertainly’ (Roy and Oberkampf, 2011) arising from the unknown anthropogenic forcing that could be obtained using several RCPs (Representative Concentration Pathways); (2) the ‘model-form uncertainly’ (Roy and Oberkampf, 2011) in wave hindcasts by using different CMIP5 model runs, and by using several runs with the same initial conditions but with different parameterizations of the physics and discretization of the numerical scheme; (3) uncertainties inherent in the climate system (‘aleatory uncertainties’) involving divergent behaviors over time resulting from the sensitive dependence on initial conditions (effectively chaotic behavior) in atmospheric dynamics. With these analyses of forecast uncertainties, we could evaluate how the balance between model-related and inherent uncertainties shifts as a function of time scale, and define for different time scales which types of forecasts (deterministic or statistical) can be useful.

In view of selecting the most appropriate strategic disaster risk reduction and climate change adaptation measures along the coast of West-Africa, a methodology has been developed. First step is to select hotspots along these coasts and next to determine the most suitable adaptation measures by means of a multi hazard and climate risk assessment and a Cost Benefit Analysis. Hereto not only considering the reduction in coastal erosion and or flooding, but also the impacts on a wide range of other receptors: people, environment, economy etc. The methodology was applied on country level and on selected hotspots in 4 different countries (Bénin, Côte d’Ivoire, Ghana and Togo) and the most desirable measures were defined for each site.

The present study quantifies the potential consequences of the future climate change along the urban beaches of Donostia/San Sebastian. A two-step approach is chosen to conduct the study; first, the effects of the sea level rise in the shoreline retreat is analyzed, and subsequently, the effect of short term processes (wave action) are added to take into account the shoreline variability. Results show a shoreline retreat ranging from 20 m to 33 m due to the sea level rise and a dry beach loss ranging from 43% to 75% due to sea level rise and wave action by the year 2100. The study highlights the relevance of the local wave climate and the present sand buffer to withstand future wave climate changes.

Current- and wave-induced bottom shear stress (BSS) are assessed using numerical models output to evaluate their contribution to the erosive potential of the Estuary and Gulf of St. Lawrence (EGSL) system and to evaluate the impacts of the anticipated reduction of the ice cover. Near-bottom hydrodynamics features explain the distribution of surficial sediment and highly dynamic regions are classified in two categories: (i) strong current-induced BSS drive the sediment-dynamics in narrow channels and tidally-dominated areas (e.g. estuary, Strait of Belle-Isle, J. Cartier Strait); (ii) areas under the influence of waves exhibit higher variability and strongest BSS. Our results show insignificant change on the current-induced BSS and the local increase of wave-induced BSS in response to the expected reduction of the ice cover in the EGSL system. Coastal erosion potential will increase in wave-dominated zones and one may expect higher erosion risk along the New-Brunswick coast and the Magdalen Islands for future ice-reduced winters.

An adaptation pathway is proposed for the Barcelona coast which combine different adaptation measures such as beach nourishment, managed retreat and coastal protection structures. with the general objectives of maintaining beach carrying capacity, enhancing adaptation capacity in areas with existing accommodation space and protecting areas with critical infrastructures. First, the SLR-induced expected impacts are presented for each coastal sector and, then, each adaptation measure is defined, with special emphasis in identifying limits and barriers.

Hurricane Irma made landfall along the southwest coast of Florida on September 10, 2017 with a sustained wind speed of 100 kts, causing extensive coastal erosion and overwash on Keewaydin Island. Pre- and post-LiDAR data analysis shows that the northern and central sections of the island sustained foredune erosion and vegetation loss, while the southern-most spit experienced minimal erosion. Analysis of LiDAR data since 2004 also show persistent erosion for most of the island while southern end is continuously prograding in the direction of the longshore current.

Development of effective adaptation strategies for coping with future coastal hazards necessitates consideration of human-induced alterations to the system, climate-induced changes to environmental forcings, and the feedbacks between these drivers. This study expands on recent county-scale applications of Envision, a stakeholder-driven, spatially explicit decision-making framework for exploring alternative coastal futures, by broadening the scope to the entire Oregon Coast and explicitly incorporating climate variability into forecasted coastal hazards. This variability is introduced through TESLA-EX, a climate emulator capable of producing stochastic time series relevant to forcing the coastal evolution and flooding sub-models in Envision. The resulting outputs from TESLA-EX docked with Envision are designed to help coastal communities develop effective adaptation strategies against coastal hazards, and provide researchers, government officials, and community stakeholders with a quantitative understanding of the relative importance of adaptation decisions and climate variability in driving future changes to their community.

Astronomical high tides, storm surges, local waves and wind can combine to elevate water level above predicted levels at the coast. Numerical modeling tools can help establish complex interactions between different drivers of coastal flooding to provide managers and stakeholders with the best knowledge of coastal hazards. Delft3D-FLOW and WAVE are used to simulate the combined effect of tides, surge, and wind/wave direction on extreme water levels using the Severn Estuary, southwest England as an example. The model confirms event severity and tide-surge concurrence are the most important controls on flood hazard along the estuary shoreline. Estuary morphology amplifies the tide up-estuary to determine where maximum water levels occur, and positive storm surge skewness increases variability in water levels along the shoreline. Stronger winds from a shore-normal direction within the estuary increase significant wave height. The model results provide state-of-the-art assessment for hazard mitigation under present and future climate conditions.

What are the implications of possible substantial sea-level rise for coastal societies? This question often generates negative answers and references to submerged islands and deltas, and flooded cities. However, such views lack consideration of adaptation and especially accommodation and protection options. This paper explores our ability to adapt to 21st century sea-level rise by integrating perspectives from coastal engineering, economics, finance and social sciences, to comparatively analyze a diverse global set of populated coastal cases in terms of (1) technological limits, (2) economic barriers, (3) financing barriers, and (4) social conflict barriers that arise in the face of coastal adaptation. It seems that technical and economically-beneficial options for protection and accommodation are widely available, but the finance and social conflict barriers may be significant constraints. More analysis of all these dimensions of adaptation is required, including their long-term implications for coastal futures.

Cliffs composed of glacial and pre-glacial sediments typify long stretches of the coastline of East Anglia, UK. This paper assesses both long-term and short term retreat as it can be extremely rapid. Long-term average annual cliff retreat is typically 2-5 m a^-1 where cliffs have no protection from storm energetics. However, in single events retreat can be 3-4 times this long-term average. Individual storms deliver short term shocks to both the cliff and the beach system which can have serious socio-economic consequences, particularly significant in areas of critical coastal infrastructure. In this paper we look at two such recent events, the December 5, 2013 North Sea storm surge and the February-March 2018 “beast from the east” and “mini beast”. Each of these events left a large shoreline footprint, but each arose from different underpinning meteorological scenarios. Lessons can be learnt for future management planning.

The improvement of our understanding on the mechanisms involved in alongshore variable dune erosion is crucial for the development of accurate and robust models, which can be used to predict the morphological response of the dune. This study utilizes detailed observations obtained during a moderate storm event that hit the Narrabeen-Collaroy beach in New South Wales, Australia in June 2011, to study the influence of pre-storm subaerial morphology in the observed highly alongshore variable dune erosion response. The morphological alongshore variability observed prior to the storm, was found to govern the erosion response of the dune. In succession a newly developed dune erosion model by DHI is used to further explore the mechanisms involved and asses the model’s performance as a predictive tool. The model was found to accurately describe most of the mechanisms involved in the alongshore variable dune erosion.

A physical model study was conducted to quantify the role belowground biomass serves in stabilizing dunes during wave attack. Model dunes were constructed with biomass ratios ranging from 0.0% to 0.56%. A total of three wave conditions were tested with profile measurements taken before and after each study. The number of overtopping events were quantified in addition to the mass of sediment. The results demonstrate that belowground biomass decreases the dune erosion both along the fore and lee slope and decreases the mass of sediment lost to overtopping events.

Wind is a major driver of sediment transport and subaerial landscape evolution in sandy coastal environments. In addition to building coastal foredunes, aeolian processes can also transport sediment from beaches onto adjacent infrastructure or into navigation channels. For example, aeolian processes consistently blow sediment over a jetty along the central Oregon coast, contributing to shoaling within the Yaquina River inlet. A process-based aeolian sediment transport model is applied to the Yaquina River site to quantify total aeolian sediment transport fluxes contributing to inlet infilling. New capabilities are added to the model to incorporate the influence of grass planting and sand fencing on trapping wind-blown sediment before reaching the inlet. Exploratory proof of concept simulations are completed to assess the efficacy of management interventions on reducing aeolian-driven inlet infilling rates.

The development of coastal transgressive dunefields has been the subject of numerous studies internationally. The extent and volume of dunefield development has been frequently attributed to sediment supply and exposure to onshore/alongshore winds above the threshold to initiate sediment transport. In South Australia, where terrigenous sediment supply is very limited, the nearshore is an important source of carbonate sediments to Holocene barriers to a degree proportional to the wave energy. Here we test the wind and wave control in dunefield development in a variety of environmental settings across South Australia. Wind data (observed and from reanalysis products) and dunefield dimensions have been analyzed along the South Australian coast, and demonstrate that aeolian drift potential is an important control in areas where wave-driven sediment delivery is limited; however, it does not fully explain dunefield development in wave-exposed areas.

Sediment supply to the aeolian coastal system and the capacity of wind to transport sediment are the most important drivers for aeolian sediment transport and the growth of coastal dunes. Both these drivers vary between different locations making it difficult to predict the growth of coastal dunes. In this study we assess two locations where sediment supply, wind driven transport capacity and the response of the coastal dune has been documented. At these locations we have quantified past dune volume changes using measurement and we have used state of the art models to reproduce these changes. Models include both sediment supply and wind driven transport capacity. We have found that the differences in measured dune growth could only partly be explained by sediment supply and transport capacity. Additional processes such as marine influences to dune growth and 3D airflow effects are proposed to be included in future studies.

The storm impacted beach/dune erosion at the hyper-tidal coastal environment, Sefton coast, UK was investigated. A new storm event classification (Hs + TA = 2.4 m) was established based on the variation of wave height (Hs) and water level (TA) using probabilistic methods. Numerical simulations were carried out using the dune erosion model XBeach. Sensitivity analysis using different water levels, wave heights and storm durations indicated that water level dominates the beach/dune erosion compared to wave height on this coast. A comparison of storm impacts between the new classification and the official storm definition (Hs = 2.5 m) was carried out simulating an observed high severity storm event. The storm event defined by Hs and TA produced higher dune erosion compared with the official definition. Work is currently in progress to further validate the storm classification using Hs and TA.

A cellular automata model is used to evaluate the impact of shoal attachment processes on dune growth. We explore ten different idealized scenarios of beach width changes due to shoal attachment related to the magnitude of the shoal-driven beach width increase and the rate of dispersion alongshore. For all scenarios, shoals attach the coast with a cyclic period of 15 years in an average beach width of 100 meters. Simulations were carried out for a model time of 90 years. Results show that in only three scenarios, shoal attachment yielded a significant increase in dune growth. Scenarios that significantly changed dune growth presented the slowest rate of spreading and the three largest beach width increase tested. This suggests that local change in dune growth due to shoal attachment are closely related to the shoal capacity of significantly increasing beach width and the longshore capacity of sediment transport.

This study investigates the relationship between grain-size distributions and sediment transport processes at Ängelholm Beach in southwest Sweden. In total, 308 longshore and cross-shore distributed sediment samples are analysed with respect to median grain size and sorting. The longshore sediment transport is almost unidirectional from north to south. Its gradients cause erosion in the north and accretion in the south. The longshore transport sorts the sediment, leading to coarsening in eroding areas and deposition of finer sediment in accreting areas. In the eroding part of the beach, the aeolian transport is limited, and the median grain sizes on the beach are coarser than in the dunes. In the accreting part of the beach, where the dunes are prograding, sediment within the range of dune-building grain-sizes is mostly available at the beach. The results support that sediment supply of appropriate grain sizes is an important factor controlling the long-term dune evolution.

Airborne lidar, in-situ measurements, and numerical modeling are used to quantify foredune evolution and to discern the relative importance of the physical and environmental factors driving alongshore variability in dune evolution. The study region consists of 4 low lying barrier islands on the Outer Banks of North Carolina. Beach and dune morphometrics extracted from lidar indicate vertical dune accretion rates at multidecadal and interannual timescales ranging from 0.02–0.04 m/year and 0.05–0.11 m/year, respectively. In-situ topographic measurements across these 4 islands provide annual scale patterns in dune growth and erosion. These data are complemented by measurements of the local grain size and the dominant grass species and density in the dune. There is spatial variability in the morphological, physical, and ecological characteristics across the study site, as well as the rate of dune response at the annual scales. The numerical model Aeolis is applied to two locations within the study area to begin to investigate the relative roles of spatially variable grain size and wind climate on foredune growth rates between 2016 and 2017. Preliminary findings indicate that modeled sediment transport is on the same order of magnitude as the field observations of dune volume change. A sensitivity study indicates that aeolian sediment transport at these sites is more sensitive to median grain size than sorting of the local sediment distribution. Additionally, the model suggests that aeolian transport to the dune is controlled largely by high magnitude, cross-shore oriented winds, which are largely dictated by the local shoreline orientation.

In 2015, the characteristics and impacts of a sustained energetic event were measured at the USACE FRF facility in Duck, NC. Combined large waves and high water levels in early October resulted in variable dune erosion where dramatic change occurred in the center of the FRF property while the north property dunes were not impacted. Detailed hydrodynamic data for the shoaling and breaking regions and the swash zone are available during he event along a single transect at the FRF. These data are compared with numerical predictions from the one-dimensional CSHORE model in for wave height and runup statistics. With a suitably calibrated wave computation, the morphology change is predicted with CSHORE and is found to compare well with measured measured dune erosion on transects in both the center and north FRF property.

The morphological change in the backshore during the 28-year period from 1987 to 2014 was investigated at the Hasaki coast in Japan. In the backshore, accumulation continuously took place, and the sand volume monotonously increased. In the temporal variation of the sand volume, the long-period components were predominant, but there was a small peak of energy at a period of approximately1 year. A positive correlation between the monthly-averaged volume change rate and the parameter U_Q (= U²U_c, U is the measured total wind velocity and U_c is its landward component), which is assumed to represent the landward aeolian sediment transport rate, was observed. However, the values in February and March were outliers. The factors that are not included in U_Q such as vegetation and the difference between the influences of the landward and seaward winds on aeolian sand transport due to a coastal dune may be the causes.

One of the measures to mitigate retreat of sandy shorelines is the implementation of a sand nourishment. For the design and acceptance of such a sandy strategy, sound information is required on the expected coastal behavior at time scales from storms to decades for both the subaqueous and subaerial areas. A seamlessly integrated morphodynamic model is applied by coupling morpho-dynamic models for the subaqueous and subaerial areas. This study focuses on the impact of interacting marine and aeolian of processes on the predicted dune growth rates at the Sand Engine. Results show that coupling marine processes, as waves, surge levels and especially the subaqueous bed changes, with aeolian processes are paramount for realistic predictions of coastal dune development.

Early coastal dune erosion predictions are essential to avoid potential flood consequences but most dune erosion numerical models are computationally expensive, hence their application in Early Warning Systems is limited. Here, based on a combination of optimally sampled synthetic sea storms with a calibrated and validated XBeach model, we develop a surrogate model capable of producing fast and accurate dune erosion predictions under storm conditions when water level and wave forecasts are available. The analysis is performed on Dauphin Island, AL where we train Multiple Linear Regression Models with oceanographic forcing from the selected sea storms (i.e., XBeach input) and predicted changes in the dune system (i.e., XBeach output). Surrogate model performance is assessed with a rigorous k-fold cross validation. Although changes in the location of dune features are not well predicted, the model attains good performance when predicting changes in dune elevation, barrier-island width and area.

Coast lines can be reinforced with sand. The natural evolution of constructed dune areas and applied measures is not yet well known. The current research uses 3 years of data of a stretch of 6 km recently constructed foreshore beach area extending 850 m in cross-shore direction and with a general maximum dune height around 12 m above mean sea level. The prevailing winds are on- and alongshore. It was found that these dunes behave similar to natural dunes. Most sand deposits were seen on the seaward side of the dune complex, widening the dune area. The seaward side quickly evolved into a naturally looking dune ridge. Little sand was deposited on top of the dunes and hardly any sand was deposited on the landward side of the dune area, meeting the ‘no-hinder-due-to aeolian-transport’ requirements during the design phase. The findings can be used for future dune constructions.

In order to improve the current aeolian modeling, a process-based model is developed by implementing biological and physical processes adapted from different existing models. The current version of the model is capable of simulating barchan and parabolic dunes and the initial stage of coastal dune formation: Embryo dunes. Potentially the model can be used to determine the influence of tidal ranges, storm frequencies, armoring, salinity and precipitation on dune building processes. This will result in a greater insight in the general behavior of coastal systems and on the other hand the model can also be used for engineering purposes.

Analysis of a 13-year long, high-resolution data series on beach profiles, surveyed from 1981 to 1993 by the Army Field Research Facility (FRF) at Duck, North Carolina, in the United States, was analyzed in order to understand the temporal and spatial characteristics of the dune response. Various statistical methods were employed in this analysis. The profile survey data set was analyzed with regard to sand volume change and its relationship to seasonal storms and aeolian sand transport. The results showed how the sediment transport and morphological change of the dune were driven through the combined action by waves, water levels, and wind.

Storm surge and large waves combine to erode beaches, cause marsh and coral decay, and inundate low-elevation areas, resulting in hazards to coastal communities and loss of natural resources. The USGS, in collaboration with NOAA, is developing a real-time system to provide ∼ 6-day forecasts of total water levels (TWLs) combining tides, storm surge, and wave runup. TWL is compared with dune elevations along sandy coastlines to obtain regional flood and coastal hazard forecasts. The predictions are available online (https://coastal.er.usgs.gov/hurricanes/research/twlviewer/) and provide intuitive representations of regional coastal risk. Current efforts include 1) assessing skill by comparing forecasts with observations along sandy coastlines and 2) developing methods more appropriate for non-sandy coastlines (e.g., rocky, reef, marsh, cliff, and built shorelines). The vision of this work is to provide a tool for short- to medium-term coastal hazard forecasts to inform planners and emergency responders along nearly the entire US coastline.

Mobile sediments form the first line of coastal defense against inundation and damage to infrastructure along approximately 30% of the world’s coastlines. These mobile sediments are responsible for both dissipating wave energy and providing sufficient freeboard to prevent flooding. Thus, the intertidal beach volume (V) is a useful state indicator of the health and resilience of the coastline. This parameter is usually measured directly by surveys. However, these surveys are costly, and even when conducted, are rarely frequent enough to keep adequate track of the current resilience of the coast. The recent emergence of simple and skillful equilibrium models (Davidson et al., 2011, Yates et al., 2011, Davidson et al., 2013, Splinter et al., 2013) now presents an opportunity to predict the evolution of V, bridging the gap between expensive and relatively infrequent surveys by keeping track of the resilience of the coastline and providing the initial conditions for subsequent probabilistic forecasts (Davidson et al., 2018). This contribution describes such an operational forecasting system – where an equilibrium model is forced using wave data provided by the Met Office – capable of both tracking and predicting future beach volume changes on both short (e.g. 7-day) and long (e.g. multi-annual) time-scales.

Model predictions of severe storm impacts provide coastal residents, emergency managers, and partner organizations valuable predictive information for planning and response to extreme storm events. The foundation of this work is a USGS-developed numerical model to forecast storm-induced coastal water levels and expected coastal change, including dune erosion, overwash, and inundation. The model is operated in three modes: generalized scenarios, real-time storms, and an operational forecast, with each mode requiring slightly different water level inputs. To evaluate and improve the accuracy of the models, we collect data on water levels and coastal change. In particular, observations before, after, and during storm conditions are used to test the different model applications. Forecast validation for Hurricanes Matthew (2016) and Irma (2017) illustrate three cases with demonstrated forecast skill and three cases with poor skill, and reveal elements of the modeling and/or testing approach which require improvement.

The breaking of short waves in the nearshore can contribute to storm surges substantially, while this process is not always represented in storm surge models. Recent studies reported that the dissipation of short waves over the ebb shoals of shallow inlets or large estuaries can drive a setup that propagates at the scale of the whole lagoon or estuary. To investigate this phenomenon, we implemented the numerical modelling system SCHISM to simulate the sea state and the storm surge associated with the violent extratropical storm Klaus, which impacted the Southern Bay of Biscay in 2009. When wave forces are activated, storm surges predictions are improved by more than 50% at the Arcachon Lagoon and the Adour Estuary. The model results in the inlet region reveal that wave forces can dominate the momentum balance and drive a wave setup that extends over the whole lagoon, while being slightly tidally modulated.

The USGS provides model predictions of severe storm impacts prior to landfall based on pre-storm morphology and predicted total water levels, including waves and surge. Presented in near real time on the USGS Coastal Change Hazard Portal, they provide coastal residents, scientists, and emergency managers valuable coastal response information. iCoast – Did the Coast Change?, an online tool for comparing pre- and post-storm photography, allows volunteer citizen scientists to help researchers classify storm impacts through aerial photography. Using spatially matched pre- and post-storm image pairs from Hurricane Sandy, iCoast users identified the coastal processes seen in each image. These classifications were compared to the predictive model probabilities just prior to Sandy’s landfall. User classifications agreed with the model predictions with a high degree of confidence for dune erosion and overwash. However, for inundation, user classifications, limited to observations of island breaching, were less confident and should be used with caution.

Adaptation to sea-level rise is a major challenge as future sea levels are highly uncertain. While rises of up to 1-m by 2100 are explicit in assessments such as the Intergovernmental Panel on Climate Change, larger and faster rises are also plausible, but less likely. Hence, taking an adaptive (or learning) approach to adaptation is attractive. This means we select a sea-level rise trajectory and a set of appropriate adaptations that could manage this rise. However, if sea-level rise is faster than expected, we need to adapt more rapidly. The success of this approach requires monitoring of sea-level rise and detection of conditions that deviate from expectations so appropriate corrections can be made. This paper considers the utility of this approach based on a project on the UK, which is linked to the adaptive management of London’s tidal flood defenses, including a toolbox to apply the approach.

On the 1^st of March the extratropical storm Emma impacted the Iberian Peninsula with significant damages along the south Portuguese and Spanish coast. In central sector of Faro Beach a maximum vertical erosion of approximately 3 m was observed together with the damages in local infrastructure and houses. The morphological and impact data collected from the above event were used to validate and analyze the accuracy and variability of a combined Early Warning and Bayesian Network system. The obtained results show that the Bayesian Network outputs in terms of both hazards and consequences are in good agreement with the filed data. Furthermore, both the accuracy and the variance of the outputs for the given storm conditions is small. The over-predictions of consequences can be considered as a safety aspect for the decision makers.

An operational, real-time coastal flood warning system for southwest England has been developed that is capable of predicting wave runup elevation and overtopping volumes along the coastline of southwest England, which features embayed, sandy, gravel, and engineered profiles. The model has a 1-km Delft3D wave and hydrodynamic model at its core and uses empirical equations to predict wave runup on beaches, and overwash volumes on beaches with coastal structures. The empirical approach used is highly computationally efficient. The prediction and plotting of coastal flooding hazard for all 186 profiles in the current database takes less than 20 minutes using a single computational core, once inshore wave conditions have been predicted (total modelling time is ∼3 hours). Although the model was developed as an operational forecast, it can also be used for strategic purposes, for example to investigate the effects of climate change on coastal flooding hazard into the future.

An operational coastal-circulation-wave forecast system was developed for the express purpose of hydrodynamic predictions. To better represent the uncertainties in the atmospheric forcing, winds and pressure are obtained from a deterministic high-resolution regional weather forecast model (NAM), and six statistical analyses -- three from an ensemble high-resolution regional weather forecast model, SREF, and three from a global ensemble lower-resolution weather forecast models, GEFS. The ensemble system, which is currently running operationally for the east coast of Central Florida, resolves the IRL estuarine system in fine scale. The forecast skill of the ensemble predictions is assessed for a forecast cycle in January 2019. With respect to the ensembles, it is found that predicted water levels in the open-ocean have less variability, while wave height forecasts are more sensitive to variations in the individual members. Inside the estuary, the predicted water level is relatively sensitive to the different forcing.

Many coastal marshes exhibit degradation from decreased sediment inputs, erosion, and sea level rise. Resource managers seek to restore marshes via introduction of sediments directly onto the marsh surface to stabilize the marsh platform while allowing for rapid vegetation recovery. However questions regarding placement techniques and associated restoration trajectory persist, limiting widespread application. In response, research evaluated marsh conditions following sediment application. These studies indicate improvements in soil physicochemical characteristics and other factors supporting plant establishment. Additional research examining changes in marsh hydrology show that sediment placement increased elevation and reduced inundation, further promoting vegetation biomass production. Results suggest that engineering practices simulating natural processes of periodic storm driven sediment deposition onto the marsh surface may improve restoration outcomes compared with no-action or traditional restoration approaches.

St. Bernard Parish has experienced high rates of shoreline erosion due to its direct exposure to wind-driven waves in an open-bay environment. Wave action from storms have converted the vegetated lands along the project shoreline into open waters and increasing wind fetch. To combat the high shoreline retreat, a living shoreline breakwater system, consisting of different artificial reef products, was constructed along a portion of the shoreline in Eloi Bay. A model was developed to compute the shoreline retreat rate of the marsh edge when protected by these artificial reef breakwaters using a combination of empirical and numerical methods. The model was validated using measured shoreline retreat for unprotected and protected reaches of the shoreline.

Tidal processes that regulate sediment accretion rates strongly influence the evolution of salt marshes. The assessment of the erosion and deposition balance is therefore crucial to find out the best restoration strategies. This work presents the first results of an integrated approach for monitoring channels’ morphodynamics over a six-year time frame in a low energy restored salt marsh at Poplar Island (Maryland, USA). The combined use of an Unmanned Aerial Vehicle (UAV) and traditional GPS cross sections surveys was adopted to detect the current shape of the channels. Due to the site extent of 400 m by 400 m, three missions were performed flying at a 40 m altitude. The comparison with the initial as-built survey showed the effects of erosion and deposition phenomena. The technique provided reliable results at low cost, allowing an accurate assessment of the morphodynamics over time, thanks to both high spatial resolution and the precise imageries georeferencing.

This paper presents a numerical study of wave attenuation, setup, and runup by using the CSHORE model with newly-developed capabilities for simulating interaction of waves, currents, and vegetation in vegetated beaches. A set of experimental cases done by Løvås and Tørum (2001) were simulated to validate both wave and flow models in CSHORE. Through quantifying statistical errors in simulated waves, assessment of model skills shows that the vegetation model in CSHORE reproduced the wave breaking in the cases without vegetation and both wave attenuation and breaking with the presence of vegetation on the beach. Simulated wave setup and runup show reasonable responses of the vegetation model to vegetation resistance.

The aim of this work is to investigate the past, present and future evolution of a land-cover in a sub-tropical estuarine environment, Babitonga Bay (Santa Catarina, Brazil) with the urbanization growing and land use, several types impacts on bay have been reported that reflect on the mangroves. Around Babitonga Bay, there are a population approximately 700,000 inhabitants, with the largest industrial park (Joinville) and the second port system (São Francisco do Sul and Itapoá) in Santa Catarina state, as well as an oil terminal (São Francisco do Sul). Due to the development of the region, in the bay we have been able to study three distinct locations: the sector to the north that is the most preserved the central sector which presents increasing urbanization near the mangrove and the sector 3, in the south, where there is iniciating a small urbanization compared to area 2. Related to the supervised classification presents the increasing urbanization of the city of Joinville in sector 2, presenting some exchange: areas of agriculture and vegetation to urbanized areas and also shows the behavior, evolution and in some places the degradation of the mangrove during the analyzed 31 years. Results demonstrated the most affected area by the pest was the central area, where urbanization is larger, which also suffered anthropic occupation and mangrove removal. This area is suffering evident coastal erosion that is the mangrove has no resilience and capacity of protection, as proved with DSAS results. There are indications of the coastal squeeze process, in the central region of the bay.

The community of Carters Beach, New Zealand, has dealt with dramatic coastal changes since European settlement c1860 and is now facing beach retreat rates of ∼10 m/year (2003–present) which threaten community assets. In planning its response to the immediate threat, the community must also address the long-term threat that sea level rise poses to its low-lying village. The region is not well resourced so to intervene to meet a short-term objective could be an unjustified expense if long-term sea-level rise will overwhelm the area. We developed a high-level adaptative planning pathway for Carters Beach that addresses the changing risk levels and various response options across uncertain timeframes. The pathway allows the community to adapt to each threat without being locked into a set pathway whilst avoiding waiting too long to intervene or unnecessarily exposing the community to foreseeable risks.

The Ghanaian coastline is exposed to low to medium energy waves generating strong nearshore currents that cause erosion and pose risks to coastal dwellers. Harbours, dams and coastal defenses along this coastline disturb its natural equilibrium and causes extreme erosion up to 17 m/yr. The morphological response of micro-tidal beach to waves and erosion controls is studied in Dzita, a coastal community in Ghana using video system and unmanned aerial photography. The results reveal significant sediment lost from the beach through cross-shore wave energy flux. The study finds low sediment transport in the longshore direction compared to the cross-shore direction possibly due to the presence of several groynes and strong rip currents. Predominant erosion occurs between August and September. This beach may continue to erode and maybe rapidly in the future because it has to be the source of sediment to nearby beaches and is also unprotected.

In 2014, three detached breakwaters were implemented at the wave-dominated beach of Le Barcarès, S France, to fight against erosion and submersion hazards. Additionally, beach nourishments are undertaken every summer. Daily video images from Oct 2014 to July 2018 covering an alongshore distance of 1.6 km are used to analyse the response of the shoreline to the structure implementation and to the main forcing factors (SE storms and Tramontane winds). Results show that the breakwaters clearly modified the shoreline shaped by the formation of salients. However, in contrast with the adjacent southern beach, the shoreline is not stabilised and shows rapid short-term variations as well as a great seasonal variability. Nourishment efficiency appears to be clearly linked with the occurrence of storm events that generate a loss of sediment northwards and tramontane winds that favours a southward sediment transport and an increase of sediment volume in the area.

While a clear improvement concerning aesthetic considerations using soft submerged breakwater is undeniable, their design has often focused on wave energy decrease in their lee, overlooking their impact on the dynamics of the nearby nearshore sandbar(s). At the beach of Sète (southeast France), the submerged structure clearly affects the natural net offshore migration cycle (NOM) of the former double barred beach. On the contrary, at Narrowneck (Queensland, Australia), the deployment of a multi-functional submerged structure does not affect the cross-shore sandbar processes. These contrasting behaviors are addressed using high frequency video monitoring. After discussing observations at both field sites, a process-based morphodynamic model provides insight into the morphological sandbars response to artificial reefs.

The Long Beach project is a coastal storm risk management project which has been designed to provide risk reduction against wave attack, erosion, and inundation for homes and businesses along the 10.3 km (6.4 mile) of ocean front on Long Beach Island, NY. The project involved the rehabilitation of 18 existing groins, the construction of 4 new groins, the placement of 3.6 million m³ (4.7 million yd³) of beachfill and dune grass vegetation, and the construction of 65 dune walkovers and vehicular crossovers. Stone work began in June 2016 and was completed in January of 2019. Sand placement began in July 2018 and runs through February 2020. At present the Long Beach project has encompassed two significant periods of wave activity, the September 2017 hurricane season and the March 2018 winter storm season, both of which impacted construction schedule, and structure integrity. Shoreline response was immediate with impoundment on the east (updrift) side of the new and rehabilitated groins. Within a few weeks of completion elevation of the berm east of the groins increased along with seaward movement of the shoreline. Downdrift shorelines remained at a lower berm elevation and at a more landward position. Elevation and shoreline differentials ranged between 1 to 2 m (4 to 6 ft) and 9 to 15 m (30 to 50 ft) east to west across the structures respectively. Ephemeral scour channels were also observed across the head section of the groins and along the western trunk regions. Often active during lower design conditions these features would undermine the structure and result in advanced settling of the stone.

This study aims to understand the development of new ramifications along the spit of Goro (northern Adriatic, Italy) and to present the first results of a new innovative concept that guides the spit growth and favor its formation. The method used combines aerial photos analysis, topobathymetrical and sedimentological maps and numerical simulations. From 2001 to 2017, 261 spit ramifications have been identified. Their dimension, location and occurrence are variable, but four types have been identified. Their formation seems to be related to fluvial sediment discharge, mainly during flood events, and wave’s actions. On the sheltered side of the ramification, sediment deposition occurs. At the final stage, cross-shore transport probably induces an onshore displacement of the ramification that merges with the beach. Finally, the preliminary results of the intervention monitoring are positive and indicate sand accumulation in the shallower zone.

Assessing bedload transport is of particular interest to understand the morphodynamics of active sedimentary systems in coastal areas and remains a scientific challenge. Here we present results illustrating an original approach aimed at obtaining bedload transport values with an extended temporal and spatial coverage, and consisting in recording passive acoustics data from a vessel drifting over the site of interest. It was tested during contrasting hydrodynamic forcing conditions on a shallow submarine dune bank composed of coarse shell sand. Root mean square pressure (P_rms) was computed on the [60–80] kHz frequency band, corresponding to bedload transport. P_rms values were then inverted using an empirical formulation (Thorne, 1986) to estimate the number of moving grains on the seafloor N. Results are promising, with N showing a clear dependency on the magnitude of the current at the bottom of the water column extracted from numerical simulations with a high-resolution hydrodynamic model.

To mitigate the coastal erosion disaster, we developed the ACRs method as a countermeasure. In this study, we investigate the performance of ACRs method by conducting 3D hydraulic experiments so that we can verify it. For this reason, wave analysis, level measurement and sieve analysis of seabed soil samples were carried out. With more researches on wave attenuation effect, coastline deformation tendency, ACRs method can be evaluated as one of the coastline defense method.

The 2.09-kilometer (km) Fort Pierce Shore Protection Project experiences nonuniform erosion. An erosional hotspot along the northernmost 0.7 km requires beach nourishment after about two years of normal wave regimes. This study evaluated two designs for shoreline stabilization—beach nourishment alone and beach nourishment combined with coastal structures—to produce more uniform erosion throughout the beach-nourished project area and increase the nourishment interval. The study applied several validated state-of-the-art numerical models to evaluate the two-dimensional effect of “no structures” and with structures alternatives on hydrodynamics, waves, sediment transport, and beach morphology. Long-term model simulations that used equivalent representative periods to shorten model computation time show a baseline shoreline movement pattern similar to the general historical pattern observed in the project area and coastal structures will retain beach fill longer than baseline.

In Korea, beach erosion is mitigated through the Coastal Maintenance Plan. However, there is an on-going problem of erosion as artificial structures are constructed without the consideration of layout design. This is particularly evident in Bongpo Beach, Goseong, where the loss of sand is worsening owing to the development of the hinterland. This study aims to determine the initial shoreline before construction of a coastal structure in the target area and use the equilibrium shoreline prediction model, which is a fairly useful means of reviewing coastline deformation after construction of the coastal structure, to estimate the initial shoreline after construction of the coastal structure. The results of the field observations of Yate et al. (2009) and 30-year frequency erosion threshold with the equilibrium section equation of Dean (1977) were applied. Through this, we could examine the erosion and sediment tendency for each section and predict the possibility of damaging coastal roads, residential facilities, and coastal forests.

This paper presents a method for predicting the crenulate-shaped shoreline, which is accomplished using a CERC formula on longshore sediment transport based on the distribution of annual wave directions. A simple formula is applied for the wave diffraction behind the structure. The proposed method shows a good agreement with Hsu’s formula for impermeable breakwater and with laboratory observations for the permeable detached breakwater.

The channel shoaling at Bolivar Flare in the Gulf Intracoastal Waterway (GIWW) near the junction with Houston Ship Channel (HSC), Texas, becomes significant in recent years. Approximately 214,000 cubic-meters (280,000 cubic-yards) of sediment were dredged from Bolivar Flare based on the annual maintenance for safe navigation. Supported by the US Army Corps of Engineers (USACE) Regional Sediment Management Program (RSMP), a numerical modeling study was conducted to explore innovative solutions to reduce maintenance cost and identify potential beneficial use options in the area. Model results showed a long breakwater constructed along the north side of Bolivar Flare channel could interrupt effectively sediment transport from Galveston Bay to reduce the channel shoaling rate.

Worldwide, buildings are present at the beach and in the dunes for recreation or habitation. Their presence can affect the beach-dune development, because they affect the airflow and Aeolian sediment transport in their surroundings. This might eventually have repercussions for coastal safety. We start examining these effects by studying the local sedimentation and erosion patterns around buildings. Hereto, we placed scale models of buildings on the beach. The sedimentation and erosion patterns around the models were measured using structure-from-motion photogrammetry. In general, the air flow around bluff bodies like buildings forms a horseshoe vortex. This creates deposition and erosion patterns in a horseshoe shape. For nearly all scale models, the upwind part and downwind tails of the horseshoe showed deposition. The horseshoe deposition at the building sides was sometimes visible, also depending on building orientation. Frequently, smaller erosion and/or deposition areas also developed between the horseshoe deposition and the building.

Storms such as hurricanes generate large storm surges and surface waves in typically low-energy estuarine environments. This enhances sediment transport and affects morphology, impacting navigation and aquatic vegetation. To better understand and predict these impacts, a numerical model corresponding to a 20 km long section of Currituck Sound, a narrow back-barrier estuary in North Carolina, was implemented with a 25 m resolution using Delft3D-SWAN for two 2016 tropical cyclones. Model results compare well with observations from instrumented platforms for both waves and water levels, and the simulated bed shear stress qualitatively matched observed trends in turbidity with considerable spatiotemporal variation. Satellite observations of red and infrared reflectance indicate considerable differences in total suspended matter between the two storms despite similar peak wind speeds. These preliminary results indicate detailed in situ observations and high resolution coupled numerical models can be used to quantify estuarine sediment transport during cyclonic storms.

The objective of this numerical modeling study is to provide a design basis for the final layout of rock groin field at Rockaway Beach. The current study includes numerical modeling of coastal hydrodynamics, wave transformation and sedimentation in the coastal area of the Rockaway Beach to assess coastal hydrodynamic and sediment transport patterns with alternative groins layouts to optimize sediment retention along project shoreline, future re-nourishment needs, and minimize downdrift effect.

Coastal dikes may suffer serious damage from high waves that exceed their design scale. Experiments are carried out to find resilient structures that can mitigate the damage to coastal dikes due to seaward scouring accompanied by unexpected high waves by focusing on the seaward foundation and seaside armoring. Highly resistant structures can be produced by (1) installing sheet piles or soil improvement material together with the seaward foundation, (2) paving beach surfaces adjacent to coastal dikes with coarse gravel to resist scouring, or (3) adding beach nourishment using gravel or sand to cover the seaward foundation.

We present a novel semi-analytical shoreline model comprising of a combination of simpler semi-analytical solutions to the One-Line Model. The purpose of the development of the model is to provide alternative means of simulating complicated coastal systems. In this study, its performance is investigated, firstly, in Calangute, a beach in India where no coastal structures exist, and then in Galveston beach in Texas, which is a considerably more complicated case-study as it includes coastal defence schemes, jetties etc. Results show that except for the wave-induced littoral drift, other unspecified factors might affect significantly and, possibly, in an unpredictable way the beach morphodynamic evolution. To this end, the model, named AMMOS, can incorporate in the modelling process sources or sinks of sediment material to simulate changes in the morphodynamic evolution which cannot be explained though the longshore sediment transport caused by wave action.

In this study, a large-scale experiment on sand dike breaching by wave overtopping and overflow is carried out in a flume of 75.0 m in length, 1.8 m in width and 2.0 m in depth. The dike is 1.0 m high and 1.8 m wide, and is homogeneously built with sand. A 3D laser scanner is used to capture the downstream breach formation and evolution. Two digital cameras are used to record the breaching process. Five water level gauges are adopted to record the head and tail water levels. The sand dike erosion and breaching processes are analyzed to reveal the impacts of wave overtopping. The measured data are useful for understanding the breaching processes and validating numerical models.

Salt marshes and tidal flats contribute valuable ecosystem services, by providing habitats, storing pollutants and reducing flood and erosion risk in the coastal hinterland. However, salt marsh areal extent is decreasing both globally and regionally (e.g. in Northwest Europe). While we know that salt marshes are retreating, this could be occurring due to biological, geochemical and geotechnical properties of the marsh and tidal flat, and/or due to changes in hydrodynamic forcing. Until now, very few studies have assessed how substrate geotechnical properties influence both the erosion processes and the erodibility of the marsh edge and tidal flat surface. Here, we compare frictional and cohesional strength components at two hydrodynamically-similar but sedimentologically-different salt marshes and tidal flats in the UK. As such, we assess how sediment composition and behavior may influence marsh resistance to hydrodynamic forcing.

Erosion of pure kaolinite clay was investigated in the laboratory using a duct-type erosion testing device at the University of Auckland. In total, about 200 sets of erosion rate of seven groups of kaolinite samples with different bulk densities were measured. The erosion rate of each group of kaolinite with a certain bulk density obeys the widely used power law relationship. An empirical formula for critical shear stress for erosion of kaolinite expressed in a power function of dry bulk density was developed. The power law function for erosion rate was revised by considering the relationships of the coefficients of M and n in the function to the critical shear stress for erosion. The predictions by the revised formula agreed well with the measurements of erosion rate of seven groups of kaolinite with different bulk densities.

The uppermost layers of subaqueous sediment beds can be stratified in physical characteristics and geotechnical properties. Such stratification is subject to spatiotemporal variations depending on different hydrodynamic forcing conditions and sediment transport processes, amongst others. The detailed geotechnical properties of such surface layers are still rarely investigated and poorly understood. A geotechnical site characterization of the topmost layers at the Pamunkey River was conducted on July 10 and August 7, 2018, using a portable free fall penetrometer to assess in-situ sediment strength, pore pressure response, and soil stratification. The results show the presence of a loose sediment layer of ∼ 6 cm in thickness overlying a stiffer substratum with a maximum quasi-static bearing capacity (QSBC) of ∼ 9 kPa. The pore pressure response suggested a contractive, fine-grained soil with positive excess pore pressures during penetration. In-situ results were verified by laboratory tests on the gravity core samples. Representative QSBC-depth profiles were developed for both survey dates and were approximately identical with standard deviations < 0.23 kPa, implying temporal stability of the site over the summer.

The study evaluates the spatial distribution and seasonal variations in the sediments and organic matter of the Suape Port-Industrial Complex southern area. The employed parameters were the grain size, carbonate and MOT contents, the elemental and isotopic sedimentary organic matter analysis (COT,NT,δ¹³C,δ¹⁵N).The sediments are, in general, sandy lithoclastic, with low TOM and organic matter from continental, mixed and marine origin conditioned by the sediment types and the distinct inputs which each subenvironment is subjected in the present. The influence of seasonality is more marked in the region of the upper and middle estuary mainly for the total organic matter contents. But overall, there is an increase in CaCO₃ and a decrease in TOM in the dry season due to the low continental contribution. Marine influences are observed in Muro Alto lagoon and in the Ipojuca bay near the estuarine mouth and mainland in upper and middle Ipojuca and Merepe’s estuaries.

Surface sediment erodability and a range of physical and biological properties were examined across Nazareth tidal flat and marsh in St. Lawrence estuary in August 2016, August 2017 and September 2018 to determine the role of biofilms in sediment stabilization and to examine the spatial and annual variability. Erosion threshold (τ_crit) measurements show a strong difference between high and low marsh. The low erodability of high marsh was mediated by a thick biofilm cover, which was characterized with Chl a and carbohydrate fractions (EPS proxies). However, at the lower intertidal areas (low marsh, mudflat, sandflat) correlation between Chl a and τ_crit was weaker and correlation between carbohydrate fractions and τ_crit was non-significant. Our results show that Chl a and EPS are not so good indicators for τ_crit, except for the low marsh/high marsh difference. The erodability patterns remained identical over the three summer campaigns, with no interannual variability.

In the face of sea level rise, perceptions of sediment among sediment managers may shift from a once “nuisance” to a valuable resource. Interviews with over 25 sediment managers at local, regional, state, and federal scales — a co-production method in the research approach of the Sediment Resilient Infrastructure and Sustainable Environments (SedRISE) Project — have illuminated significant challenges to actualizing this sediment-as-a-resource orientation, as well as opportunities for innovation in implementation. By considering information obtained through co-production with end-users, hydrodynamic and biological models have resulted in actionable knowledge, including the identification of promising interventions and optimal timescales. Informed by engagement with end-users, a system dynamics model will aid in the continued assessment of future management practices and scenarios in the two case studies in the Southern California coastal systems of Newport Bay Watershed/Estuary and Tijuana River Watershed/Estuary.

Coastal communities use hard and soft engineering to sustain beach recreation and to protect physical properties and infrastructure. Soft engineering involves external sand placement to widen beaches artificially; this placement is typically termed ‘nourishment’. Hard engineering involves the construction of immovable objects, such as shore-perpendicular groins, which slow alongshore currents and deposit sediments locally at and updrift of the objects. While groins accrete sediment updrift, they also limit downdrift sediment supply, exacerbating erosion and often forcing downdrift communities to respond with new engineering measures. We have developed a coupled geo-economic model to explore how community wealth, size, and groin-induced erosion might affect management choices. Results indicate the wealth of a community and its neighbor determine its strategy, and, in extreme cases, a community’s sustainability along the coast depends directly upon its neighbor’s decisions.

Following the devastating effects of Superstorm Sandy in October 2012, the State of New Jersey adopted and installed large-scale berm-dune structures with the goal of enhancing coastal resilience to future storms. Specifically, artificial dunes have been constructed by the US Army Corps of Engineers in accordance with the FEMA “540-Rule” design. The management goal of dune construction was to mitigate storm-related damages, thereby ensuring continuation and growth of beachfront tourism. Because some communities tend to value aesthetics (i.e. beachfront viewership) over protection or may begin to lower their perceptions of storm damage risks over time, it is unclear whether beachfront communities are willing to afford the costs of maintaining these projects in the future. To tackle this question, we develop a “geo-economic” model that captures the natural processes of beach and dune erosion and migration via storm overwash coupled with engineering interventions of beach nourishment and dune construction. The economic portion of the model accounts for the relationship between property values and berm-dune geometry. By deriving mathematical expressions for optimal berm and dune size as a function of geologic and economic parameters, our model suggests that conflicting preferences for coastal protection versus aesthetics could affect the willingness of property owners to maintain large-scale berm-dune structures in the long-term.

Coral reef islands are small, low-lying landforms that provide the only habitable land for atoll nations and support a range of endemic flora and fauna. Thus, the vulnerability of these islands to projected sea-level rise is a global concern. The internal structure and modes of island accretion are integral in understanding how islands have formed and subsequently, how they will change in the future. This study employs extensive ground penetrating radar (GPR) imaging on a reef island on Huvadhoo Atoll, Maldives, combined with island coring and stratigraphic analyses, in order to infer styles of island accretion. The GPR images imply central core accretion, with vertical accretion occurring on the initial core and progradation occurring outwards in both directions. However, some transects display progradation occurring predominately in one direction, which may also indicate erosional and rollover or overwash processes that could have led to island migration. Furthermore, using inferences of major radar units and boundary changes in signal reflectors combined with detailed subsurface sedimentology, the subsurface stratigraphy of the island sediments was divided into four discrete facies: velu (lagoon infill), finolhu (initial island core), athiri (beach and paleobeach), and muraka (surface layer) facies. The GPR records on KAN provide visual evidence of the mode of island evolution to complement previous theoretical interpretations, and have demonstrated the capability of GPR to discern sedimentary facies, subsurface features, and changes in sediment characteristics on reef islands. Results from this study show past processes of island building and could infer island response to various stages of sea-level change, which has implications for the stability of reef islands in the face of projected sea-level rise.

Swash at the shoreline plays a key role in coastal erosion and inundation and is often dominated by infragravity motions in high energy wave conditions. However, the behaviour of infragravity swash on gravel (as opposed to sandy) beaches remains largely unknown. Here, 40 hours of shoreline video data, collected on a steep (0.14 slope), gravel (median grain size = 5 mm) beach during exceptional high energy conditions, (offshore significant wave height, H₀, up to 3.3 m) are used to investigate the infragravity swash characteristics. Infragravity frequencies were observed in the swash and became dominant over gravity frequency oscillations when H₀ exceeded 1.5 m. Infragravity swash height (S_ig) increased linearly with offshore significant wave height (H₀) according to S_ig = 0.51H₀+0.3. These results demonstrate that infragravity motions can dominate the swash under high energy wave conditions, even on steep gravel beaches.

Native tracer cobbles were tracked on a mixed sand and gravel beach at three temporal scales. Passive Integrated Transponder tags were inserted in 400 cobbles and tracked at monthly intervals over 130 days; tags were inserted in a further 200 cobbles and tracked on days 1, 2, 4, 6 and 16. Despite similar incident wave conditions, opposing directions of dominant sediment transport occurred in the two tag tracer experiments. A new technique was developed using painted cobbles and drone video capture to provide a third set of measurements on 175 tracer cobbles at the scale of individual swash events. Large differences were quantified between net and gross sediment transport rates. Collectively these data provide rare direct comparable measurements of the dynamic and variable nature of sediment transport on gravel beaches across different temporal scales.

Although considered useful forms of coastal defense, few tools and guidelines exist for the design, evaluation and maintenance of composite sand-gravel and sand-cobble beaches. In this paper we attempt to improve upon this through the development of composite beach processes in the non-hydrostatic version of the XBeach model. The results of model developments are compared to observations of morphodynamics made during the DynaRev physical model experiment. The results show that although the inclusion of gravel and cobble morphodynamic processes in the XBeach model leads to accurate predictions of morphological change in some cases, further development of the model is required to account for sand transport within and below the cobble layer. An experimental two-layer bed composition approach, in combination with equations to resolve sand transport within the gravel and cobble matrix, is proposed to overcome these limitations, with preliminary results showing improvement over the existing approach.

An artificial lagoon built on existing unimproved land suffered from poor beach appearance, cloudy/hazy water quality and lagoon basin becoming shallower due to siltation caused by the beaches shedding their surface layers and alongshore transport transporting sediments into the lagoon. Extensive site observations and field data collection including sediment and water quality parameters were carried out to determine the conditions in the lagoon and beaches including ground water levels. Based on field and numerical model results a series of T-head groin structure at the both west and east lagoon entrances is recommended to mitigate excessive wave and resulting siltation in the lagoon during frequent southern storms. It is also recommended that the existing beach profiles should be excavated to accommodate the equilibrium profile by shifting beach crests landward at the lagoon. To provide high quality recreational beaches, characteristics of the fill sand surface layers are recommended to be more uniform and coarser good quality sand having a median grain size of 0.5 mm.

This study applied a sediment tracking methodology within a numerical sediment-transport model that includes bed layering in the computation of morphology change. The temporal scale of sediment exchange between various morphological features of an idealized inlet and its adjacent beaches, and the vertical and horizontal distribution of traced sediments, are examined. An idealized numerical model of a mixed-energy inlet was designed to imitate the Johns Pass tidal inlet in West-central Florida, USA. The analyses of the adjacent beach contribution to tidal inlet sediment bypassing demonstrate various temporal scales on sediment transport and exchange. High energy wave events dominate the temporal scale for sand to be transported from the updrift beach to the ebb-tidal delta, whereas cyclical tidal processes have a significant influence on the spatial pattern of exchange between the shoals and channel features of the tidal inlet. The ability to simulate burial and erosion of tracers allowed identification of offshore sedimentation hotspots such as terminal lobe as well as zones of deposition and active transport in shallow water, such as the updrift channel margin linear bar and the downdrift platform of the ebb-tidal delta. The general sediment bypassing pathway reflects a tidal-driven redistribution following event-driven pulses of wave-induced sediment mobilization. Sediment is transported along the beach during these energetic wave events. Flood- and ebb-tidal currents transports the sediment mobilized by high waves into the inlet channels. This is followed by subsequent gradual redistribution of the deposited channel sediments over the ebb-tidal delta features during fair-weather conditions.

Tidal inlets concentrate socio-economic and environmental challenges so that it is fundamental to better understand and predict the processes controlling their morphological changes. To address these challenges, the application of morphodynamic modelling systems constitutes a promising perspective, although most application use 2DH approach, which prevents to represent adequately the dynamics in sheared flows. This study presents the application of a recently extended 3D morphodynamic modelling system to a mixed energy tidal inlet. The comparison between modelled results with unpublished field measurements reveals that the model is able to reproduce the effect of short waves on velocity profiles, but also the effects of tidal current feedback on the wave field. The analysis of model results further demonstrate that the representation of these wave-current interactions is essential to simulate sediment fluxes and morphological changes.

The Nauset-Monomoy barrier beach system on Cape Cod in southern New England was a single inlet system in 2007 when a second inlet formed in a seemingly more hydraulically efficient location. The system’s tidal hydraulic and geomorphic changes were monitored using data from tide recorders as well as aerial photography and bathymetric surveys. Monthly mean tidal statistics were generated from 6-minute water level data recorded at a station near the head of the basin and another near the first inlet. Analysis of the results indicate that for approximately 5 years the second inlet remained highly flood-dominant and while it significantly increased the system’s tidal prism only later did increasing resistance at the first inlet lead to a notable reduction of tidal range there. Approximately 10 years were required for the second inlet to fully capture the main ebb channel and achieve hydraulic dominance over the system.

A hydrodynamic, sediment transport, and morphology model developed specifically for the Collier Creek region (Collier County, Florida), applied to better understand key processes that occur under existing conditions, and test alternatives to address the rough navigation conditions and high sedimentation rates after channel dredging. The reported problems are ultimately related to the sharp flood-tide flow curvature from Marco River into Collier Creek, and was likely aggravated by the major coastal changes that occurred on regional scales over the last three decades. The observed local problems were reproduced by the developed model, which was then applied to test and refine alternatives. The plan selected for further development includes changes to the dredge template and coastal structures, which improve overall hydraulics, navigation safety, and extend project life of dredging events.