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Several coastal barriers experienced significant erosion and change in shape throughout the Mediterranean coasts over the past decades, and the issue has become of increasing concern for scientists and policymakers. With reference to a case study and by meteorological and geomorphological investigations, this note aims to define the wind–wave conditions, infer the net longshore transport, and detect the geomorphological processes that shape the landforms of the Cesine Lagoon barrier (South Italy). Despite the importance of the site in coastal defense and environmental conservation, there are still no specific studies. A challenge for this research was to obtain significant results from publicly available sources and simple and inexpensive methods. Geomorphological changes, such as the retreat of dune toes, accretion of washover fans, and formation of gravel beaches, are related to the analyzed wind–wave conditions. The net longshore transport is found in accordance with the direction of the more intense winds. The role of extreme events in the shaping of coastal landforms is yet to be established, even if they greatly increase the vulnerability to flooding of the study area. The results achieved so far are starting points for further data collection and analysis in the perspective of assessing the impact of climate changes and the threatening hazards on the lagoon barrier. [ABSTRACT FROM AUTHOR]

Houston, J.R., 2023. Measured fate of beach nourishment sand. Journal of Coastal Research, 39(3), 407–417. Charlotte (North Carolina), ISSN 0749-0208. The fate of sand placed over a 20-year period in one of the largest series of beach nourishment projects ever conducted in the United States is determined by using direct measurements of elevation vs. distance from dunes to closure depth. Four projects placed 11.25 million m3 of sand from 1998–2017 on a 28.8-km-long shoreline at Panama City on Florida's Gulf of Mexico coast. Profile measurements were available in 1996 following Hurricane Opal and in 2018 after Hurricane Michael, one of the largest hurricanes to strike the United States, which came ashore only 30 km from Panama City beaches. The profiles were about 300 m apart within the project template and extended down to closure depth. After about 20 years, 87 ± 3% of the nourishment sand remained on profiles. Some sand used for nourishment was dredged within closure depth along a 3.6-km section and resulted in sand loss of 4% ± 1% as sand partially refilled the dredged holes. About 9% ± 3% was lost to longshore transport out of the project area. Calculations based on the equilibrium profile concept used in U.S. beach nourishment design predicted beaches should have widened 30.9 m ± 0.9 m and profiles raised 0.69 m ± 0.10 m due to the measured volume of sand remaining on profiles from the start of beach nourishment in 1998 to November 2018 after Hurricane Michael. The measured change in beach width was 32.4 m ± 4.0 m, and the rise was 0.66 m ± 0.05 m. The rise of 0.66–0.69 m is comparable to the 0.81 m mean sea-level rise by the year 2100 projected by the Intergovernmental Panel on Climate Change for its worst-case temperature scenario. [ABSTRACT FROM AUTHOR]

Several coastal barriers experienced significant erosion and change in shape throughout the Mediterranean coasts over the past decades, and the issue has become of increasing concern for scientists and policymakers. With reference to a case study and by meteorological and geomorphological investigations, this note aims to define the wind–wave conditions, infer the net longshore transport, and detect the geomorphological processes that shape the landforms of the Cesine Lagoon barrier (South Italy). Despite the importance of the site in coastal defense and environmental conservation, there are still no specific studies. A challenge for this research was to obtain significant results from publicly available sources and simple and inexpensive methods. Geomorphological changes, such as the retreat of dune toes, accretion of washover fans, and formation of gravel beaches, are related to the analyzed wind–wave conditions. The net longshore transport is found in accordance with the direction of the more intense winds. The role of extreme events in the shaping of coastal landforms is yet to be established, even if they greatly increase the vulnerability to flooding of the study area. The results achieved so far are starting points for further data collection and analysis in the perspective of assessing the impact of climate changes and the threatening hazards on the lagoon barrier.

When longshore transport systems encounter tidal inlets, complex mechanisms are involved in bypassing sand to downdrift barriers. Here, this process is examined at Plum Island Sound and Essex Inlets, Massachusetts, USA. One major finding from this study is that sand is transferred along the coast—especially at tidal inlets—by parcels, in discrete steps, and over decadal-scale periods. The southerly orientation of the main-ebb channel at Plum Island Sound, coupled with the landward migration of bars from the ebb delta to the central portion of the downdrift Castle Neck barrier island, have formed a beach protuberance. During the constructional phase, sand is sequestered at the protuberance and the spit-end of the barrier becomes sediment starved, leading to shoreline retreat and a broadening of the spit platform at the mouth to Essex Bay (downdrift side of Castle Neck). Storm-induced sand transport from erosion of the spit and across the spit platform is washed into Essex Bay, filling channels and enlarging flood deltas. This study illustrates the pathways and processes of sand transfer along the shoreline of a barrier-island/tidal-inlet system and provides an important example of the processes that future hydrodynamic and sediment-transport modeling should strive to replicate. [ABSTRACT FROM AUTHOR]

The analysis of shoreline changes is very important for coastal planning and management. In territories such as Calabria (Italy), characterized by significant anthropogenic pressures and various eroded coasts, the knowledge of the shoreline changes, and the factors that influence them, is necessary for management and planning of coastal areas. In fact, shoreline position is one of the most important indicators of coastal dynamics. From this point of view recent advances in remote sensing and GIS techniques allow to estimate with great precision the shoreline changes over the years. The paper analyzes the shoreline changes near the mouth of the Sant’Agata River (Reggio Calabria, Italy), carried out through the comparison of various cartography data. Furthermore, the paper analyzes the main factors influencing the coastal dynamics in order to identify possible correlation between these factors and the shoreline changes. The analysis of these factors shows that, in this case study, the rainfall regime has a considerable influence on shoreline change. The methodology described in this paper is particularly useful for better understanding the factors that most influence the coastal balance and, therefore, is applicable to many contexts which are similar to the Sant’Agata river mouth.

Beach loss is a growing global challenge that threatens the safety of coastal communities, the health of coastal ecosystems, recreational amenities, and regional economies dependent on tourism. Spatial gradients in longshore sediment transport, or divergence of drift (DoD), is a primary driver of beach width change over multi-annual time scales, but the response of any particular beach can be challenging to characterize and predict. Here we present a new method to characterize DoD using a non-uniform segmentation of the coastline informed by the spatial distribution of longshore transport potential, including the location of physical barriers identified using satellite imagery, and both maxima and reversals in longshore transport potential derived from nearshore wave data. The method demonstrates improved capacity to predict beach width trends at sandy beaches compared to methods that rely on a uniform segmentation of the coastline. In an application to southern California where satellite data documents two decades of beach width change, the non-uniform segmentation method correctly predicts the sign of beach trends at 93% of transects within a littoral cell and achieves a linear correlation between DoD and beach width trends exceeding 0.8. Moreover, we find that a minimum of five years of data are required to establish consistently strong correlations between DoD and beach width changes. Conversely, use of a uniform segmentation is shown to be unreliable for estimating beach width trends due to strong sensitivities to shoreline segment size. This work shows the potential to leverage nearshore wave data and satellite-based beach width data for improved characterization of shoreline dynamics relevant to beach erosion management. • A new shoreline modeling method is presented for estimating divergence of drift. • Segment boundaries are identified using longshore transport characteristics. • Strong correlations were shown between divergence of drift and beach width trends. • A littoral Peclet number characterizes the dominant longshore transport mechanism. [ABSTRACT FROM AUTHOR]

When longshore transport systems encounter tidal inlets, complex mechanisms are involved in bypassing sand to downdrift barriers. Here, this process is examined at Plum Island Sound and Essex Inlets, Massachusetts, USA. One major finding from this study is that sand is transferred along the coast—especially at tidal inlets—by parcels, in discrete steps, and over decadal-scale periods. The southerly orientation of the main-ebb channel at Plum Island Sound, coupled with the landward migration of bars from the ebb delta to the central portion of the downdrift Castle Neck barrier island, have formed a beach protuberance. During the constructional phase, sand is sequestered at the protuberance and the spit-end of the barrier becomes sediment starved, leading to shoreline retreat and a broadening of the spit platform at the mouth to Essex Bay (downdrift side of Castle Neck). Storm-induced sand transport from erosion of the spit and across the spit platform is washed into Essex Bay, filling channels and enlarging flood deltas. This study illustrates the pathways and processes of sand transfer along the shoreline of a barrier-island/tidal-inlet system and provides an important example of the processes that future hydrodynamic and sediment-transport modeling should strive to replicate.

The dune systems are very important from an environmental, landscape, and coastal defense point of view within coastal areas. Currently, dune systems are significantly reduced compared to a few decades ago and, in Europe alone, dune systems have decreased by 70%. During the same period, intense beach erosion processes have often been observed, and, currently, 30% of the world’s coasts are eroding. These processes have various causes, both natural and anthropogenic, and the knowledge of the causes of the erosive processes are very important for an effective planning and management of coastal areas and to correctly plan any interventions on dunes and beaches. The paper, through a case study, analyzes the beach and dune erosive processes, their causes, and the possible interventions. The case study concerns the archaeological site of Kaulon, located on a dune in the Ionian coast of Calabria (Italy). The beach near the site was affected by erosive processes and during the winter of 2013–2014, the site was damaged by two sea storms. To identify the causes of these processes, three erosive factors were analyzed. These factors are anthropogenic pressure, wave climate and sea storms, and river transport. The effects produced by these factors were assessed in terms of shoreline changes and of damage to the beach–dune system, also evaluating the effectiveness of the defense interventions. The main causes of the erosive processes were identified through the cross analysis of erosive factors and their effects. This analysis highlighted that in the second half of the last century the erosive processes are mainly correlated to anthropogenic pressure while, recently, natural factors prevail, especially sea storms. Regarding the interventions, the effects produced by two interventions carried out during the winter of 2013–2014, one built in urgency between the first and second sea storm and the other built a few years after the second sea storm were analyzed. This analysis highlighted that the latter intervention was more effective in defending the site.

Sand spits with distal hooks have been well documented from coasts with low to moderate tidal ranges, unlike high tidal‐range environments. Datasets from 15 LiDAR and 3 UAV surveys between 2009 and 2019 on the Agon spit in Normandy (France), a setting with one of the largest tidal ranges in the world (mean spring tidal range: 11 m), combined with in‐situ hydrodynamic records between 2013 and 2017, highlight a three‐stage pattern of spit hook evolution. Stage 1 (2009–2013) commenced with the onshore migration and attachment of a swash bar, followed by persistent spit accretion updrift of the bar and erosion downdrift because of the slow speed of bar migration in this large tidal‐range environment. In stage 2 (2013–2016), three overwash events and a 220 m‐wide breach culminating in the total destruction of the spit during winter 2015–2016 involved the landward mobilization of thousands of cubic metres of sand. These events occurred during short durations (a few hours) when spring high tides coincided with relatively energetic waves, underscoring the importance of storms in rapid spit morphological change. Strong spring tidal currents maintained the breach. Stage 3 (2016–2019) has involved new hook construction through welding of a swash bar and spit longshore extension, highlighting the resilience of the spit over the 10‐year period, and involving a positive sediment balance of 244 000 m3. The three stages bring out, by virtue of the temporal density of LiDAR and UAV data used, a high detail of spit evolution relative to earlier studies in this macrotidal setting. The large tidal range strongly modulates the role of waves and wave‐generated longshore currents, the main process drivers of spit evolution, by favouring long periods of inertia in the course of the spring–neap tidal cycle, but also brief episodes of significant morphological change when storm waves coincide with spring high tides. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The analysis of shoreline changes is very important for coastal planning and management. In territories such as Calabria (Italy), characterized by significant anthropogenic pressures and various eroded coasts, the knowledge of the shoreline changes, and the factors that influence them, is necessary for management and planning of coastal areas. In fact, shoreline position is one of the most important indicators of coastal dynamics. From this point of view recent advances in remote sensing and GIS techniques allow to estimate with great precision the shoreline changes over the years. The paper analyzes the shoreline changes near the mouth of the Sant'Agata River (Reggio Calabria, Italy), carried out through the comparison of various cartography data. Furthermore, the paper analyzes the main factors influencing the coastal dynamics in order to identify possible correlation between these factors and the shoreline changes. The analysis of these factors shows that, in this case study, the rainfall regime has a considerable influence on shoreline change. The methodology described in this paper is particularly useful for better understanding the factors that most influence the coastal balance and, therefore, is applicable to many contexts which are similar to the Sant'Agata river mouth. [ABSTRACT FROM AUTHOR]

Sea level rise increases the pressure on many coastlines to retreat landwards which will lead to coastlines previously held in position through management, being allowed to retreat where this is no longer affordable or sustainable. Barrier beaches have historically rolled back in response to different hydrodynamic events and sea level rise, but very little is known as to how quickly and how far roll-back is going to occur once management has ceased. Data from more than 40 topographical surveys collected over 7 years along the 1.5 km long, almost swash-aligned shingle barrier at Medmerry (southern England) are used together with hydrodynamic data in a wide-ranging assessment of barrier roll-back. This study shows that roll-back is progressing through time along the barrier in downdrift direction in response to a gradual reduction in cross-sectional area through longshore transport. The Barrier Inertia concept provides a practical means to assess stability/instability for events experienced, but also a tool to assess the short- to medium term risk to the coast downdrift of the immediate study area where flood risk still needs to be managed. Roll-back is influenced particularly by the creation of an artificial tidal breach and removal of its sediment, the elevation of the underlying marsh and clay sediments, the number and severity of storms experienced and the presence of legacy groynes; roll-back has exceeded modelled predictions and expert judgement by an order of magnitude.

Current techniques assessing longshore sediment transport rates have large uncertainties, pleading for the development of alternative and complementary approaches. The present study proposes a method to estimate the decadal average rate of longshore transport at modern ebb‐tidal deltas based on a sediment budget analysis of the outer shoal growth. This transport is obtained as the balance of the other contributions to the shoal with the total sediment input rate obtained from an inverse application of the inlet reservoir model. The method is applied to the Guadiana ebb‐tidal delta, yielding an average longshore sediment transport rate (~85 000 m3 year−1) in good agreement with expectations for the region. It is exemplified that this decadal averaged rate can be used to improve longshore sediment transport expressions in order to study its variability over shorter time scales. At the Guadiana, the yearly longshore sediment transport from the improved formula ranges from ~25 000 m3 (westward) to ~245 000 m3 (eastward) and is related to the North Atlantic Oscillation index. Overall, the proposed method constitutes an alternative tool to constrain the average longshore sediment transport rate over decades in the vicinity of tidal inlets. It is applicable to ebb‐tidal deltas where the outer shoal growth (from an early to a mature stage) is well documented by bathymetric maps, and where the main transport pathways towards the outer shoal can be specified. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study investigates the impact of beach sediment supply on dune volume evolution through data analysis and model simulations of the Kennemer dunes in the Netherlands. A cross-shore sediment transport model (the CS-model) is applied with local time-averaged longshore sediment transport gradients derived from bathymetric and topographic observations. The model is used to study the relative importance of different transport processes on dune volume evolution, assuming that aeolian transport from the beach to the dune is supply-limited. The wave-driven longshore transport gradients are found to explain a large part of the observed variation in the dune evolution within the study area. In accreting parts of the coast, dunes are growing due to sediment supply from longshore transport, whereas in eroding parts, dune growth depends on supply from artificial nourishments. Seasonal constructions on the beach and vegetation removal from the dunes partly impede dune growth along the considered stretch of coast. The model performance is satisfactory, being able to reproduce a considerable part of the large variation in the alongshore dune response observed in the study area. Overall, the results are a promising contribution to the capability of simulating decadal-scale dune evolution, which is important for long-term flood risk assessments and safe designs of nature-based solutions. • Decadal-scale dune volume evolution was successfully simulated with the CS-model. • Long-shore transport gradients and nourishments control dune evolution at this site. • Seasonal beach houses are found to partly impede dune growth. [ABSTRACT FROM AUTHOR]

Abstract A reduced-complexity numerical model, LX-Shore, is developed to simulate shoreline evolution along wave-dominated sandy coasts. The model can handle any sandy shoreline geometries (e.g. sand spits, islands), including non-erodible areas such as coastal defenses and headlands, and is coupled with a spectral wave model to cope with complex nearshore wave fields. Shoreline change is primarily driven by the gradients in total longshore sediment transport and by the cross-shore transport owing to variability in incident wave energy. Application to academic cases and a real coast highlights the potential of LX-Shore to simulate shoreline change on timescales from hours (storm) to decades with low computational cost. LX-Shore opens new perspectives in terms of knowledge on the primary mechanisms locally driving shoreline change and for ensemble-based simulations of future shoreline evolution. Highlights • A new shoreline change model is developed for wave-dominated sandy coasts: LX-Shore. • The numerical implementation allows addressing complex shoreline plan-view shapes. • LX-Shore couples cross-shore and alongshore processes. • LX-Shore simulates shoreline variability up to decades with low computational cost. • LX-Shore can provide new insights into the mechanisms controlling shoreline change. [ABSTRACT FROM AUTHOR]

In the present paper, after a sensitivity analysis, the calibration and verification of a novel morphodynamic model have been conducted based on a high-quality field experiment data base. The morphodynamic model includes a general formula to predict longshore transport and associated coastal morphology over short- and long-term time scales. With respect to the majority of the existing one-line models, which address sandy coastline evolution, the proposed General Shoreline beach model (GSb) is suitable for estimation of shoreline change at a coastal mound made of non-cohesive sediment grains/units as sand, gravel, cobbles, shingle and rock. In order to verify the reliability of the GSb model, a comparison between observed and calculated shorelines in the presence of a temporary groyne deployed at a mixed beach has been performed. The results show that GSb gives a good agreement between observations and predictions, well reproducing the coastal evolution.

In northern Europe, beach erosion, coastal flooding and associated damages to engineering structures are linked to mid-latitude storms that form through cyclogenesis and post-tropical cyclones, when a tropical cyclone moves north from its tropical origin. The present work analyses the hydrodynamic forcing and morphological changes observed at three beaches in the north coast of Northern Ireland (Magilligan, Portrush West’s southern and northern sectors, and Whiterocks), prior to, during, and immediately after post-tropical cyclone Katia. Katia was the second major hurricane of the active 2011 Atlantic hurricane season and impacted the British Isles on the 12–13 September 2011. During the Katia event, offshore wave buoys recorded values in excess of 5 m at the peak of the storm on the 13 September, but nearshore significant wave height ranged from 1 to 3 m, reflecting relevant wave energy dissipation across an extensive and shallow continental shelf. This was especially so at Magilligan, where widespread refraction and attenuation led to reduced shore-normal energy fluxes and very minor morphological changes. Morphological changes were restricted to upper beach erosion and flattening of the foreshore. Longshore transport was evident at Portrush West, with the northern sector experiencing erosion while the southern sector accreted, inducing a short-term rotational response in this embayment. In Whiterocks, berm erosion contributed to a general beach flattening and this resulted in an overall accretion due to sediment influx from the updrift western areas. Taking into account that the post-tropical cyclone Katia produced £100 m ($157 million, 2011 USD) in damage in the United Kingdom alone, the results of the present study represent a contribution to the general database of post-tropical storm response on Northern European coastlines, informing coastal response prediction and damage mitigation.

ABSTRACT Messaros, R.C.; Rosati, J.D.; Buonaiuto, F.; Rasmussen, C.; Vega, A.M., and Bocamazo, L., 2018. Assessing the coastal resilience of Manasquan Inlet to Sea Bright, New Jersey: Regional sediment budget 1992–2003. Assessing the resilience of regional coastal systems requires analysis of the short- and long-term erosion and accretion characteristics of beach material, including natural and anthropogenic sources and sinks. A regional sediment budget provides that accounting and is pivotal to successful management practices that enhance the resilience of coastal systems. The U.S. Army Corps of Engineers, New York District, updated the regional sediment budget for Manasquan Inlet to Sea Bright, New Jersey, for 1992–2003, which reflects the effects of various beach replenishment projects. The study area is approximately 33.8 km long and encompasses two inlets, mainland beaches from Manasquan Inlet to Long Branch, and a barrier-spit landform from Long Branch to Sea Bright. The previous sediment budgets represented a relatively eroded and limited source beach condition. This updated sediment budget is the first to analyze the with-project condition incorporating periodic beach nourishments/renourishments. The shore protection project consisted of an initial fill of approximately 17 Mm3 (million cubic meters) between 1994 and 2002 and additional fill/renourishment of 11 Mm3 between 2008 and 2016. Data for the sediment budget were based on volumetric change of the beach as developed from digitized, historical, aerial shoreline images as well as volumes and location of sediment replenishment (nourishment) activities in this region of the shoreline. Results from this budget indicate a net longshore transport of sediment northward from Manasquan Inlet toward Sea Bright, increasing from 106,000 m3/y just north of Manasquan Inlet to 343,000 m3/y north of Monmouth Beach. This updated sediment budget establishes a good understanding of the beach processes over time, which will enhance the ability to provide better coastal management and resilience for the northern New Jersey shoreline. [ABSTRACT FROM AUTHOR]

The South Lake Worth Inlet Sand Transfer Plant in Palm Beach County, Florida pumps subtidal sediment from the upcurrent to the downcurrent side of the jetty to correct jetty-induced sediment transport disruption. This pumping accounts for 35% of the overall net longshore transport. We investigated if living macrofauna could survive the sediment pumping process. We also examined the effects this activity had on the subtidal macrofaunal invertebrate communities. Subtidal sediment cores were taken near the intake pipe, at the outflow pipe, and just outside the direct effects of the sand transfer plant. Benthic macrofauna and sand grain size were examined and compared. Macrofauna, live and preserved, were confirmed exiting the outflow pipe. Low diversity, low abundance macrofaunal communities were found at all sample sites. Macrofaunal abundance was primarily isopods (79%) and polychaetes (14%). Three isopod and one polychaete species constituted 89% of the community diversity. Both inflow borrow pit and outflow deposition sampling sites exhibited different community structure compared to adjacent control sites. The inflow borrow pit presented a high population of the isopod Eurydice personata . The outflow deposition site had the highest species diversity. The outflow deposition site also showed much coarser mean sediment grain size compared to other sites. The differences found at the sites direct associated with the sand transfer plant demonstrated localized disturbance. We concluded that although the plant disturbs the adjacent community it also helps maintain the macrofaunal community structure and sand grain size on the downdrift side of the South Lake Worth Inlet. Further studies integrating abiotic and biotic components will assist in management practices and our understanding of nearshore systems. [ABSTRACT FROM AUTHOR]

The concept of coastal sediment compartments was first used in the 1960s in the United States. It has since been recognised as appropriate for defining sections of the Australian coast, but had not been uniformly adopted around the nation in the way that has underpinned management, as in other countries. In 2012, the Australian Government supported a project to better understand coastal sediment dynamics using the sediment compartment approach as a framework within which to consider future shoreline behaviour and the impacts of climate change, including rising sea level, changing wave climates and sediment budgets. This paper outlines the sediment compartment project and uses case studies to demonstrate its application. The project consisted of three steps. The first step involved delineation of a hierarchy of coastal sediment compartments following a nationally agreed set of criteria, integrating the onshore/offshore geologic framework with known patterns of sediment movement and those inferred from surface landforms. This identified more than 100 primary compartments bounded by major structural features such as headlands or changes of shoreline orientation. At a finer scale, approximately 350 secondary compartments were identified, many of which encompass smaller scale structural features that define tertiary scale compartments or cells. For verification of this sediment compartments approach to coastal planning and management, the second step of the study comprised case studies of contrasting compartments with different patterns of sediment supply, transport and deposition. The third step, involved embedding all secondary compartments around the continental coast into the Shoreline Explorer, within the CoastAdapt toolbox (National Climate Change Adaption Research Facility). Information regarding the sensitivity of shorelines to change was compiled at the compartment scale, based upon evidence such as substrate, sediment transport attributes and oceanographic forcing, including waves, tides and storm processes. Presentation of information through CoastAdapt within the compartments framework provides a resource to facilitate improved coastal planning and management over different implementation levels, from national strategy scale down to local policy scale. Case studies from several contrasting settings around the Australian coast demonstrated the potential and feasible application of the sediment compartment approach at different spatial and temporal scales. [ABSTRACT FROM AUTHOR]

The Pinetamare Marina, located SE of the mouth of the Volturno River and the Regi Lagni Canal (southern Italy), is interested by silting phenomena due to longshore transport of fluvial sediments. To eliminate this severe problem, the design of the new Marina includes the construction of a sediment trap, placed perpendicular to the breakwater, to prevent the accumulation of the sand sediments at the marina entrance. To study the efficiency of this solution, experiments were performed through a physical model in a wave basin, with appropriate scaling of the geometric characteristics and of the hydrodynamic processes. The experimental tests highlighted that the trap is able to intercept sediments and to mitigate the port silting for about two years, after which it is necessary to dredge the accumulated sand sediments. These sediments are used to compensate the erosion of the beaches downstream the breakwater. [ABSTRACT FROM AUTHOR]

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

Modelling investigations into the local changes in the shoreline resulting from enhanced atmospheric greenhouse gas concentrations and global climate change are important for supporting the planning of coastal mitigation measures. Analysis of Global Climate Model (GCM) and Regional Climate Model (RCM) simulations has shown that Lakes Entrance, a township located at the northern end of Ninety Mile Beach in south-eastern Australia, is situated in a region that may experience noticeable future changes in longshore winds, waves and coastal currents, which could alter the supply of sediments to the shoreline. This paper will demonstrate a downscaling procedure for using the data from GCM and RCM simulations to force a local climate model (LCM) at the beach scale to simulate additional nearshore wind-wave, hydrodynamic and sediment transport processes to estimate future changes. Two types of sediment transport models were used in this study, the simple empirical coastline-type model (CERC equation), and a detailed numerical coastal area-type model (TELEMAC). The two models resolved transport in very different ways, but nevertheless came to similar conclusions on the annual net longshore sediment transport rate. The TELEMAC model, with the Soulsby-Van Rijn formulation, showed the importance of the contribution of storm events to transport. The CERC equation estimates more transport during the period between storms than TELEMAC. The TELEMAC modelled waves, hydrodynamics and bed-evolutions are shown to agree well with the available observations. A new method is introduced to downscale GCM longshore sediment transport projections using wave-transport-directional change parameter to modify directional wave spectra. We developed a semi-empirical equation (NMB-LM) to extrapolate the ~3.7-year TELEMAC, storm dominated transport estimates, to the longer ~30-year hindcast climate. It shows that the shorter TELEMAC modelled period had twice as large annual net longshore sediment transport of the ~30 year hindcast. The CERC equation does not pick up this difference for the two climate periods. Modelled changes to the wave transport are shown to be an order of magnitude larger than changes from storm-tide current and mean sea level changes (0.1 to 0.2 m). Discussion is provided on the limitations of the models and how the projected changes could indicate sediment transport changes in the nearshore zone, which could impact the coastline position.

As a part of the Dredging Operations and Environmental Research (DOER) Program, movable-bed physical model experiments were performed at the U.S. Army Engineer Research and Development Centre's (ERDC), Large-scale Sediment Transport Facility (LSTF) to investigate the fate and evaluate the benefits of nearshore-placed dredged material. The resulting bathymetry was measured with detailed surveys, the migration of the mound was quantified and comprehensive observations of hydrodynamics were obtained. The potential suitability of dredged material placement in the nearshore/surf zone was demonstrated after 10 h of oblique wave attacks. It has been shown that, as the mound was located at the edge of the surf zone, very likely wave breaking induced horizontal circulation may be dominant. A downdrift accretion of the submerged beach was observed, which is due to the transport of part of the sediment suspended by breakers at the mound and captured by the longshore currents. The experiments provided useful validation data for numerical morphological models. [ABSTRACT FROM AUTHOR]

Along many coastlines of the world, beaches provide the primary defence against flooding or erosion with their fate under rising sea levels still only poorly researched. This is particularly the case for the coastline of Southeast England, where ~190 km of shingle barriers protect low-lying hinterland or a coastal plain that is at or barely above the present reach of waves. During the Holocene transgression, these beaches moved into their present position through longshore extension and cross-shore roll back. This process stopped more than a century ago with port developments affecting longshore transport and the construction of groynes to hold the beach in place. This was followed by beach recharge and recycling towards the end of the 20 th century to build up and maintain beaches as coastal defences in their mid 19 th century position. This paper explores the design requirements for these beaches under future sea level rise scenarios of 1 to 5 m using recently developed tools. It shows that the presently still semi-natural beaches have to increase in size with crest height elevations having to rise by at least up to 1.26 times the rate of sea level rise and that due to higher longshore wave power, especially during storm conditions in the future, higher and stronger groynes are needed to hold these larger beaches in place. Future design requirements for beaches are sensitive to foreshore levels and orientation of the beach to the dominant waves with those presently characterised by shallow foreshores and oblique wave approach requiring the biggest adjustments. Required size increases will be difficult to implement due to the built-up nature of the hinterland. The engineering alternative would be to replace beaches with hard structures, a process that has already started where maintaining a beach is no longer economically viable or the residual risk associated with overwashing and an eventual tidal breach has become unacceptable. [ABSTRACT FROM AUTHOR]

Embayed beaches occurring along rocky coasts with headlands controlling hydrosedimentary processes are considered to be constrained sedimentary systems with little longshore sediment transfer between them. Such beaches are likely to narrow under rising sea level and a deficit of fluvial sediment, and because beaches act to dissipate wave energy, cliff erosion is expected to increase. Knowledge of hydrosedimentary processes in fetch-limited environments such as embayed beaches is therefore a fundamental management tool in erosion-prone coastal areas such as the Algarve region (southern Portugal). The main objective of this work is to quantify longshore sediment transport (LST) using a sedimentary tracer and compare the results with the ones derived via empirical formulae from several authors. To achieve this, we establish the spatial and temporal patterns of stained sediment, and relate these to marine climate data over six tidal cycles for three adjacent embayed beaches. The values of displaced sand estimated using tracer and scaled to mixed layer depth were compared with the results of five well-known LST formulae to assess the applicability of each model to mesotidal environments. Of the LST formulae used, the CERC (2013) shows to be the most accurate in our study area. This study demonstrates the efficacy of using tracers for tracking and quantifying the sediment transport and as a basis for assessing the viability of different LST formulae for representing transport in these types of environments. The work also shows the importance of the morphological control of hydrosedimentary processes, including the disruption of longshore drift and the sediment transfer promoted by shore platforms. [ABSTRACT FROM AUTHOR]

Wegner, C.E. and Ellis, J.T., 2017. The influence of sea-level rise on wave-energy dissipation and wave-driven currents at Buck Island Reef National Monument. Modern Caribbean reefs have undergone significant degradation in the past century because of various anthropogenic stressors, which include climate-change-related impacts, hurricanes, and, potentially, sea-level rise. Degraded reefs will be unable to maintain sufficient vertical accretion with substantial increases in sea level, which will alter the hydrodynamics of these systems. A reduction in wave dissipation by reefs has the potential to shift the shorelines behind the reefs, potentially resulting in economic and habitat losses for tropical shorelines. This study focused on a barrier reef with low, live coral cover (<10%) and accretion rates comparable to current rates of sea-level rise in the region (∼1.7 mm/y). Tides served as a proxy for sea-level rise, with the spring high tide representing a future low tide. These findings indicate that at low tide, infragravity wave frequencies (0.004-0.04 Hz) dominate in the lagoon and are a function of wave breaking on the reef. At high tide, the infragravity waves are less prominent. Current velocities were higher at high tide, averaging 0.14 m s−1 vs. 0.11 m s−1 at low tide. The spectral current characteristics correlate with the infragravity wave frequencies and suggest that these waves are a driving force in lagoon circulation. Wave-energy transmission increased at high tide by 20-30% throughout the sampling period. These results suggest that with sea-level rise, infragravity band waves will be reduced and affect the stresses on the sea bed and sediment-transport processes, also allowing larger and more energetic waves to reach the shoreline. [ABSTRACT FROM AUTHOR]

Low-energy, non-tidal lake beaches are known to be subject to longshore morphodynamics, but little is known about how they are driven by wind and wave-driven currents. Lake Markermeer is a shallow (∼ 4 m deep), wind-dominated lake, of approximately 700 km 2. A gradient in wind-induced water level set-up at the leeward shore induces a flow from the shallower to the deeper parts of the lake, thereby generating a large-scale, horizontal circulation. Flow measurements and results from a numerical Delft3D model of the lake show that these circulations impact the nearshore currents greatly, even more than wave-driven longshore currents for most wind conditions. From nearshore measurements at the first study site in lake Markermeer, we found a clear relation between longshore sediment transport capacity and the measured longshore volume flux. The model numerical can predict flow direction and magnitude for any wind condition. Using wind statistics, the net transport capacity for a short period or a long term mean can be predicted. The relation is confirmed for a second study site, which shows a distinct net transport capacity that could not be explained from wave-driven longshore flow alone. Concluding, large-scale lake circulations are of great significance for the morphological development of low-energy, non-tidal beaches in shallow, wind-driven water bodies. Knowledge of these circulations and their dependence on wind characteristics is a crucial factor to better understand and predict sediment losses of lake beaches. • In wind-dominated lakes, bathymetrical variance causes water level set-up gradients. • In shallow lakes, set-up gradients can induce large-scale, horizontal circulations. • Large-scale lake circulations affect longshore sediment transport on lake beaches. • Longshore sediment transport has a significant impact on design and maintenance. [ABSTRACT FROM AUTHOR]

In the present paper, a set of 319 field and laboratory data on longshore transport rate has been gathered, checked, and finally adopted in order to overcome a noticed limitation in the previous version of General Longshore Transport (GLT) procedure for the estimation of Longshore Transport (LT). In particular, the extensive number of additional data, characterized by a wide mobility range, has allowed to obtain a single equation able to determine the longshore transport rate at coastal slopes consisting of loose not-cohesive materials, from reshaping dynamically stable berm breakwaters to sandy beaches. The reliability of the GLT procedure has been assessed by an independent verification with 39 field and laboratory data, for both offshore and breaking wave characteristics as an input. In addition, the GLT procedure has been compared with the van Rijn (2014) formula. • Gathered high quality datasets of longshore transport from field and laboratory experiments. • Calculation of longshore transport rate at slopes consisting of loose not-cohesive materials. • GLT procedure for longshore transport at any coastal mound for both offshore and breaking wave characteristics as an input. • Improvement and verification of the General Longshore Transport procedure on an independent dataset. [ABSTRACT FROM AUTHOR]

The aim of this study is to assess the longshore transport gradients and wave power distribution along the Ilha Comprida beach system and relate it to the distribution of the current erosion process along this barrier island. The study is based on quantitative analysis of the potential longshore drift and the wave power distribution, as well as on the morpho-sedimentary seasonal variations in the beach system. Therefore, the 30-year wave reanalysis database from the global wave generation model WAVEWATCH III (NOAA/NCEP) has been extracted and analyzed for the region, as well as field surveys with topographic measurements and sediment samples. The numerical model MIKE 21 SW has been applied to propagate waves onshore and recognize the longshore transport tendencies and the nearshore wave power distribution. Results show an overall transport trend to the NE, being larger in the southern sector than in the northern sector of the island. Varying transport magnitudes prove to generate gradients in longshore drift. Two positive gradients in the longshore drift, resulting in local sediment losses, are observed. One is found in the central-southern area and another in the northern part of the island. Both areas coincide with erosive spots, as observed through field surveys. The central-southern positive gradient becomes larger and migrates to the south during the most energetic months, while the northern gradient presents only variations in magnitude, being relatively stable in position throughout the year. Nearshore wave power results show two main areas with higher values that coincide with the positive longshore transport gradients. Sediment data presents low temporal variability, although spatial variations have been found reflecting the local hydrodynamic conditions, while the volumetric data shows largest values in the central-northern sector, being smaller in the central-southern and northern regions. Moreover, the central portions are more stable than the extreme portions regarding its seasonal variability. Our findings show that along this wide open stretch of coastline, exposed to the same offshore wave regime, an alternated nearshore wave regime results in areas with hydrodynamic conditions which lead to erosion or accretion. Erosion is caused by negative sediment balance as a function of higher wave power and positive gradients in longshore transport, and accretion due to lower wave power and negative gradients in longshore transport. Our findings help in further understanding the island's long-term evolution and current state of its beaches. [ABSTRACT FROM AUTHOR]

Shoreline erosion is often exacerbated by reduction of sediment inputs because of interference with sediment transport by human structures. We evaluate use of sediment dredged from a navigation channel to establish a feeder beach adjacent to a bulkhead as a solution for addressing erosion of landforms and habitats on sandy estuarine shores. The objectives are to determine how beach volume, position and shape within and downdrift of the fill area change and whether the volumes supplied by dredging match sediment losses caused by human actions. The fill was placed along a 75 m length of shoreline adjacent to a marina in Great South Bay at Fire Island, New York, USA. Changes in beach shape and volume were determined from topographic surveys conducted before and after fill and at half year intervals for 18 months. The quantity of fill was 1747 m 3 . Maximum shoreline advance due to fill emplacement was 20.7 m. The maximum volume placed at any transect was 28.6 m 3 m − 1 of shoreline length. Erosion of the fill occurred rapidly, with landward migration of a conspicuous scarp. The edge of the upland 18 months after the fill was placed was up to 4.6 m farther landward than prior to the fill. Movement of sediment alongshore downdrift of the fill occurred as wave-like pulses, extending the active foreshore bayward, causing accretion of the inner low tide terrace, burying saltmarsh peat outcrops on the foreshore and creating a higher and wider overwash platform over portions of the saltmarshes. Landforms downdrift of the fill area underwent successive stages including erosion (pre-nourishment), accretion, stability (with throughput of sediment) and then erosion. Beach nourishment compensates for human-induced sediment losses. The volume of sediment added from maintenance dredging can slow the rate of erosion but may not prevent long-term shoreline retreat. Restoration and maintenance of coastal landforms and habitats to specific target states at a given location is difficult, but augmenting longshore sediment inputs can allow those locations to undergo cycles of erosion and accretion, creating a variety of landforms and habitats where only erosional forms existed previously. Alternatively, nourishment could occur more frequently and in smaller volumes to reduce fluctuations in accretion-erosion cycles. [ABSTRACT FROM AUTHOR]

Sand nourishments are a widely applied technique to increase beach width for recreation or coastal safety. As the size of these nourishments increases, new questions arise on the adaptation of the coastal system after such large unnatural shapes have been implemented. This paper presents the initial morphological evolution after implementation of a mega-nourishment project at the Dutch coast intended to feed the surrounding beaches. In total 21.5 million m 3 dredged material was used for two shoreface nourishments and a large sandy peninsula. The Sand Engine peninsula, a highly concentrated nourishment of 17 million m 3 of sand in the shape of a sandy hook and protruding 1 km from shore, was measured intensively on a monthly scale in the first 18 months after completion. We examine the rapid bathymetric evolution with concurrent offshore wave forcing to investigate the feeding behaviour of the nourishment to the adjacent coast. Our observations show a large shoreline retreat of O (150 m) along the outer perimeter of the peninsula, with locally up to 300 m retreat. The majority (72%) of the volumetric losses in sediment on the peninsula (1.8 million m 3 ) were compensated by accretion on adjacent coastal sections and dunes, confirming the feeding property of the mega nourishment. Further analyses show that the morphological changes were most pronounced in the first 6 months while the planform curvature reduced and the surf zone slope flattened to pre-nourishment values. In the following 12 months the changes were more moderate. Overall, the feeding property was strongly correlated to incident wave forcing, such that months with high incoming waves resulted in more alongshore spreading. Months with small wave heights resulted in minimal change in sediment distribution alongshore and mostly cross-shore movement of sediment. [ABSTRACT FROM AUTHOR]

Medellín, G.; Mariño-Tapia, I., and Euán-Ávila, J., 2015. The influence of a seawall on postnourishment evolution in a sea-breeze-dominated microtidal beach. The postnourishment beach evolution is evaluated on a sea-breeze-dominated microtidal beach in Yucatan (Mexico). The study area has experienced severe beach erosion due to both alongshore sediment-transport gradients during calm conditions and offshore sediment transport during extreme wave events. Therefore, a shoreline restoration program, including beach nourishment and the removal of groynes, was carried out in 2002. Bimonthly subaerial/intertidal beach profiles measured during 7 years (2002-09), in front of a seawall and at an adjacent beach (nonwalled), are employed to analyze the beach nourishment evolution. Empirical orthogonal function (EOF) analysis of the shoreline time series is performed using the data extracted from the 50 field surveys. The temporal evolution of the EOF analysis shows the following: (1) an abrupt increase in beach width due to nourishment at the study site at the beginning of 2003, (2) followed by a sustained increase (from 2004 to 2007) owing to the sediment advection from a massive beach fill performed up-drift of the study area, and (3) a decrease in beach width from 2007 until the end of the study period. Moreover, the mean profile-volume change is estimated separately for walled and nonwalled beach sections. The nonwalled profiles results are consistent with the temporal evolution described by the EOF analysis. On the other hand, walled beach profiles show a net volume loss from 2002 to 2007, remaining stable during the following 3 years. Consistent with previous studies, seasonal variability of sand volume was found to be greater in front of the seawall with respect to the nonwalled section. Nevertheless, the erosional/despositional rates in the two sections show opposite trends during mean (sea-breeze) wave conditions, being more important in the subaerial beach profiles. The latter implies that swash-zone sediment transport represents an important contribution to the total sediment budget in the study area; hence, seawalls can significantly modify coastal dynamics in sea-breeze-dominated environments. [ABSTRACT FROM AUTHOR]

The General Longshore Transport (GLT) model (Tomasicchio et al., 2013) and the Van Rijn (2014) expression represent the only two available general formulae in literature for the estimation of longshore transport (LT) at sand, gravel and shingle beaches. The GLT model is based on an energy flux approach combined with an empirical relationship between the wave induced forcing and the number of moving elements. An independent verification of the GLT model is performed for the estimation of the total (bulk) LT at shingle beaches. Without any further calibration, the suitability of the GLT model, even for the shingles beach case, is assessed by means of the comparison between the LT predictions and the observations from two field data sets (Chadwick, 1989; Nicholls and Wright, 1991). In most cases the GLT predicts LT rates within a factor of 2 of the observed values. The predictive capability of the GLT model is tested with reference to two different formulae recently proposed in literature (Mil-Homens et al., 2013; Van Rijn, 2014). It is shown that the GLT model gives a better agreement with the observations (Chadwick, 1989; Nicholls and Wright, 1991; Van Hijum and Pilarczyk, 1982) with respect to the other considered formulae. Moreover, long term (annual) field data (Van Wellen et al., 2000) have been used for a further verification. In addition, the GLT model confirms to have a better agreement even for the LT at dynamically stable berm reshaping breakwaters (Lamberti and Tomasicchio, 1997; Van der Meer and Veldman, 1992). [ABSTRACT FROM AUTHOR]

Abstract: Longshore transport of sand, gravel and shingle has been studied using field and laboratory data over a wide range of conditions. A detailed model (CROSMOR) for cross-shore and longshore sediment transport has been used to determine the effects of wave period, grain size, beach/surf zone slope and type of waves (wind waves or swell waves). The longshore transport was found to be proportional to wave height to the power 3.1 (≈H3.1), to grain size to the power −0.6 (≈d50 −0.6) and to beach slope to the power 0.4 (≈tanβ0.4). Regular swell waves yield much larger (factor 1.5) longshore transport rates than irregular wind waves of the same height. It is proposed to take this effect into account by a swell correction factor. Based on all results, a new simple and general (dimensionally correct) expression for longshore transport of sand, gravel and shingle beaches with grain sizes between 0.1 and 100mm has been derived. Short-term and long-term field data of sand, gravel and shingle have been used for verification. In most cases the predicted longshore transport rates are within a factor of 2 of the measured values. The CERC and Kamphuis formulas have also been tested. [Copyright &y& Elsevier]

This study aims to characterize the wave climate near the coastal region of Maputo (Mozambique), and to provide a first assessment of the sediment transport load in this area. A time-series of 13 years' worth of offshore wave data, obtained from reanalysis products, was propagated to the coast. Wave propagation was performed using Linear Wave theory and the numerical model, Simulating WAves Nearshore (SWAN). Propagations with SWAN were carried out considering different scenarios in order to evaluate the influence of parameters such as wind, tidal level, frequency spectrum and numerical mesh resolution on wave characteristics along the coast. The prevalent waves propagated came from between east and southwest directions. Results from linear propagation were used to estimate the potential longshore sediment transport. The Coastal Engineering Research Center formula was applied for a stretch of beach in the Machangulo Peninsula. A net potential rate of longitudinal sediment transport (of the order of 105 m3/year, along an extension of the coast of 21 km) was directed northwards, and was consistent with the frequent wave directions. [ABSTRACT FROM AUTHOR]

Healy, T. and de Lange, W., 2014. Reliability of geomorphic indicators of littoral drift: Examples from the Bay of Plenty, New Zealand. The net direction of littoral drift can be evaluated by multiple lines of evidence, including a range of geomorphic indicators and trends in sediment characteristics. In this article, the processes that influence the longshore transport of sediment are reviewed and assessed by the types of geomorphic indicators and sediment trends that can be expected. Various proxies for measured littoral drift are used to evaluate the littoral drift in the Bay of Plenty, New Zealand. Previous studies, utilising geomorphic indicators and, to a lesser extent, sediment characteristics and simple models of longshore sediment transport, developed a conceptual model of two main littoral drift systems starting at the western and eastern margins of the Bay of Plenty and converging in the vicinity of Ohiwa Harbour, an estuary enclosed by two opposing spits within the bay. Comparison of geomorphic indicators of littoral drift with the results of 30 years of monitoring and investigation demonstrate that geomorphic indicators can be misleading or misinterpreted. Overall, they do not appear to have been reliable for the Bay of Plenty, whereas sediment characteristics have performed better. The published rates of net littoral drift, and also the directions, appear to be too high and are inconsistent with observed patterns of erosion and accretion. Further, the exchange of sediment between the beach and the inner shelf has not been considered. Within the Bay of Plenty the net littoral drift magnitude and direction varies in response to changes in the wave climate associated with climatic variability, particularly the magnitude, frequency, and duration of the La Niña and El Niño extremes of the El Niño-Southern Oscillation. Decadal-scale fluctuations in the patterns of erosion and accretion along the Bay of Plenty coast have also been recognised. Finally, the influence of tectonic effects on geomorphic indicators of littoral drift needs further investigation. [ABSTRACT FROM AUTHOR]