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Wave‐influenced deltas, with large‐scale arcuate shapes and demarcated beach ridge complexes, often display an asymmetrical form about their river channel. Here, we use a numerical model to demonstrate that the angles from which waves approach a delta can have a first‐order influence upon its plan‐view morphologic evolution and sedimentary architecture. The directional spread of incoming waves plays a dominant role over fluvial sediment discharge in controlling the width of an active delta lobe, which in turn affects the characteristic rates of delta progradation. Oblique wave approach (and a consequent net alongshore sediment transport) can lead to the development of morphologic asymmetry about the river in a delta's plan‐view form. This plan‐form asymmetry can include the development of discrete breaks in shoreline orientation and the appearance of self‐organized features arising from shoreline instability along the downdrift delta flank, such as spits and migrating shoreline sand waves—features observed on natural deltas. Somewhat surprisingly, waves approaching preferentially from one direction tend to increase sediment deposition updrift of the river. This ‘morphodynamic groin effect’ occurs when the delta's plan‐form aspect ratio is sufficiently large such that the orientation of the shoreline on the downdrift flank is rotated past the angle of maximum alongshore sediment transport, resulting in preferential redirection of fluvial sediment updrift of the river mouth. Key Points Wave approach angle plays a first‐order role in delta morphology Delta lobe width, and therefore progradation rate, are controlled by wave angle Updrift delta flanks trap more sediment, downdrift flanks tend to form spits

Taborda, R. and Silva, A.N., 2024. Modeling shoreline evolution on platform beaches. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 283-288. Charlotte (North Carolina), ISSN 0749-0208. Embayed and shore platform beaches, common along rocky coastlines, are highly vulnerable to changes in oceanographic conditions and sediment supply. Coastal changes in embayed beaches involve sediment redistribution within embayments and exchanges between neighboring embayments, particularly in open or leaky sediment cells. Despite their importance, there is a shortage of shoreline models that couple shoreline evolution with sediment bypassing. The study introduces SEM-PLAT, a shoreline evolution model applicable to both low-lying sandy coasts and shore platform beaches on rocky coasts. Unlike traditional models, SEM-PLAT considers the dynamic behavior of the beach toe over time and sediment exchanges between embayments. It incorporates spatial gradients in wave-induced longshore sediment transport and a dynamic profile model, providing a comprehensive framework for complex shoreline evolution. Applications of SEM-PLAT demonstrate its effectiveness in simulating coastal processes, including beach development, rotation, and sediment bypassing. This model highlights key coastal geomorphological processes and offers a versatile tool for shoreline evolution studies and coastal management strategies.

Coastal catchments, which drain directly to the sea, mediate material fluxes across the land‐sea interface and support species diversity and economic activity in coastal zones. Here, we explore the evolution of coastal catchment divides at the local to global scale from 2000 to 2120 under multiple SLR scenarios using state‐of‐the‐art digital terrain and hydrographic models. We show that coastal catchment area loss due to inundation is partly counteracted by inland migration of coastal catchment boundaries and new coastal catchment formation. Encroaching shorelines intercept runoff from interior watersheds. Runoff within these shoreline runoff capture windows bypasses stream networks and discharges directly to the ocean, resulting in net coastal catchment growth along 14% of the world coastline within a century, even under high sea level rise scenarios. The rate of coastal catchment expansion and formation by shoreline runoff capture is nearly one‐half the rate of coastal catchment area loss from inundation by sea level rise, indicating that shoreline runoff capture plays a key role in coastal catchment evolution. Contrary to the notion of static watershed divides, these results reveal a counterintuitive tendency of geologically rapid expansion and reshaping of coastal catchments in future decades. The findings have important implications for watershed and coastal water quality management, as the dynamic response of coastal drainage boundaries occurs on timescales relevant to coastal planning and decision making.

Tano, A.R..; Dangui, P.N.; Bouo Bella, F-X, Aman, A., and Hauhouot, C., 2024. Monitoring coastal vulnerability using physical and anthropic parameters: The case study of Lahou Kpanda and Grand Bassam, Cote d'Ivoire (Gulf of Guinea). In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 310-314. Charlotte (North Carolina), ISSN 0749-0208. The coastal area of Lahou Kpanda and Grand Bassam, Cote d'Ivoire (Gulf of Guinea) are vulnerable to physical and anthropogenic forcing. The Integrated Coastal Vulnerability Index (ICVI), combining the Coastal Vulnerability Index (CVI) and the Socio-Economic Vulnerability Index (SVI), is used to assess the spatial and temporal dynamics of vulnerability in Lahou Kpanda and Grand Bassam. The results show that the integrated vulnerability index for Grand Bassam is higher than that for Lahou Kpanda. This index increases faster in Grand Bassam than in Lahou Kpanda. That signifies that the Grand Bassam coastline is more exposed to physical forcing and anthropogenic pressure than Lahou Kpanda. The increasing trend in vulnerability is due to rising wave energy, accelerating sea level and the increasing of population density. An assessment of the area's vulnerability for the 2040 and 2050 timeframes indicates an increase in vulnerability. To reduce this vulnerability, adaptation measures such as covering the coastline with mangroves, installing wave power plants, beach nourishment and, in the extreme cases, relocating coastal population should be considered by coastal zone managers and users. This approach could be used to monitor the vulnerability of West African coastline to physical and anthropic forcing.

The evolution of coastal wetlands is a complex process which is difficult to forecast, made more complicated by the addition of changing climatic conditions. Here, long term ecological and geomorphological data are coupled to geotechnical measurements at a coastal wetland in North Inlet estuary, South Carolina. The coupled methodology is presented and discussed in context of understanding coastal wetland system evolution in a changing climate. Specifically, the root shear strength of Spartina alterniflora across a range of elevations was investigated using a cone penetrometer test. Elevation, shear strength, and biomass are shown to be critically interconnected. Root strength was shown to decrease with increased inundation time and decreased elevation (i.e., mudflats). Conversely, the data set illustrates the importance of maintaining key elevation ranges in relation to sea‐level to optimize wetland resilience. Plain Language Summary Coastal wetlands are under increased stress from the effects of climate change. We set out to incorporate measurements from multiple disciplines to better understand how these wetlands evolve under these conditions. The strength (resilience) of the wetlands is directly related to the elevation and vegetation of the wetland. Understanding the relationships we present will assist coastal managers make decisions to better protect coastal wetlands. Key Points Ecological, geomorphological, and geotechnical properties of wetlands are critically interconnected Coupling of interdisciplinary data sets is required for prediction of wetland evolution in a changing climate

The Darss-Zingst Peninsula on the southern Baltic Sea was formed after the Littorina transgression onset about 8000 cal. y BP. It originated from several discrete islands, has been reshaped by littoral currents and wind-induced waves during the last 8000 y, and evolved into a complex lagoon system as seen today; thus, it may serve as an example to study coastal evolution under long-term climate change. A methodology for developing a multiscale process-based morphodynamic model for simulation of decadal to centennial evolution of a wave-dominated coastal environment is presented here. The model consists of eight main modules. The two-dimensional vertically integrated current module, the wave module, the bottom boundary layer module, the sediment transport module, the cliff erosion module, and the nearshore storm module are real-time calculation modules that aim to solve the short-term processes. A bathymetry update module and a long-term control function set, in which the “reduction” concepts and techniques for acceleration of morphological update are implemented, are integrated to extend the effects of short-term processes to a longer-term (yearly) scale. Successful model validation demonstrates that it is capable of simulating the long-term morphological evolution of the southern Baltic coast. Model results indicate that coastline change of the Darss-Zingst Peninsula is dominated by mechanisms that act on different timescales. The coastlines of Darss and Hiddensee Island are mainly reshaped by long-term effects of waves and longshore currents, while coastline change of the Zingst area is a combination of long-term effects of waves and short-term effects caused by extreme wind events.

Antarctica’s ice shelves help to control the flow of glacial ice as it drains into the ocean, meaning that the rate of global sea-level rise is subject to the structural integrity of these fragile, floating extensions of the ice sheet 1 – 3 . Until now, data limitations have made it difficult to monitor the growth and retreat cycles of ice shelves on a large scale, and the full impact of recent calving-front changes on ice-shelf buttressing has not been understood. Here, by combining data from multiple optical and radar satellite sensors, we generate pan-Antarctic, spatially continuous coastlines at roughly annual resolution since 1997. We show that from 1997 to 2021, Antarctica experienced a net loss of 36,701 ± 1,465 square kilometres (1.9 per cent) of ice-shelf area that cannot be fully regained before the next series of major calving events, which are likely to occur in the next decade. Mass loss associated with ice-front retreat (5,874 ± 396 gigatonnes) has been approximately equal to mass change owing to ice-shelf thinning over the past quarter of a century (6,113 ± 452 gigatonnes), meaning that the total mass loss is nearly double that which could be measured by altimetry-based surveys alone. We model the impacts of Antarctica’s recent coastline evolution in the absence of additional feedbacks, and find that calving and thinning have produced equivalent reductions in ice-shelf buttressing since 2007, and that further retreat could produce increasingly significant sea-level rise in the future. Data from multiple satellite sensors show that Antarctica lost almost 37,000 km 2 of ice-shelf area from 1997 to 2021, and that calving losses are as important as ice-shelf thinning.

Orviku, K., Tõnisson, H., Kont, A., Suuroja, S. and Anderson, A., 2013. Retreat rate of cliffs and scarps with different geological properties in various locations along the Estonian coast. Recently reported increased water depths and greater wave heights, perhaps associated with increased storminess, are likely to lead to more active changes, such as increased beach erosion, faster shoreline migration and sediment redistribution. A coastal environment particularly sensitive to the impact of sea-level rise is that of highly erodible cliffs and scarps. As structures are often built close to such formations, it is important to determine the retreat rate of cliffs and scarps. Among other things, knowing the retreat rate can help regulators plan coastal protection measures and can help property owners decide where to place their structures to avoid damage. The principal objective of the current study is to find and analyze the retreat rate of cliffs and scarps in several locations along the Estonian coast. Variable geological conditions, exposure to the sea and human influence are considered. The study was carried out in five different locations along the Estonian coast representing different geological properties, variable human influence and hydrodynamic conditions. Aerial photographs, orthophotos, RTK-GPS, leveling survey and archive data was used to measure the changes on the edges of the scarps and cliffs. It was found that the fastest rate of retreat appears on the location where the softest sediments are exposed to the roughest wave conditions – in Cape Kiipsaare. Here the yearly scarp-line retreat reached over 7 m/y (17 m3/y per meter of shoreline) which is faster than the fastest retreat rate of soft cliffs recorded anywhere else, but still two times lower in terms of the eroded volume of sediments.

The response of coastal barrier islands to relative sea-level rise (SLR) is a long-debated issue. Over centennial and longer periods, regional barrier retreat is generally proportional to the rate of relative SLR. However, over multi-decadal timescales, this simplification does not hold. Field observations along the USA East Coast indicate that barrier retreat rate has at most increased by ~ 45% in the last ~100 years, despite a concurrent ≥200% increase in SLR rate. Using a coastal evolution model, we explain this observation by considering disequilibrium dynamics—the lag in barrier behaviour with respect to SLR. Here we show that modern barrier retreat rate is not controlled by recent SLR (last decades), but rather by the baseline SLR of the past centuries. The cumulative effect of the baseline SLR is to establish a potential retreat, which is then realized by storms and tidal processes in the following centuries. When SLR accelerates, the potential for retreat is first realized through removal of geomorphic capital. After several centuries, barrier retreat accelerates proportionally to the increase in SLR. As such, we predict a committed coastal response: even if SLR remains at present rates, barrier retreat in response to SLR will accelerate by ~50% within a century. The lag dynamics identified here are probably general, and should be included in predictions of barrier-system response to climate change. Coastal evolution simulations suggest that the modern retreat of coastal barrier islands is controlled by cumulative sea-level rise over the past several centuries and will accelerate by 50% within a century, even if sea-level rise remains at present rates.

The attenuation of ocean surface waves during seasonal ice cover is an important control on the evolution of Arctic coastlines. The spatial and temporal variations in this process have been challenging to resolve with conventional sampling using sparse arrays of moorings or buoys. We demonstrate a novel method for persistent observation of wave‐ice interactions using distributed acoustic sensing (DAS) along existing seafloor fiber optic telecommunications cables. DAS measurements span a 36‐km cross‐shore cable on the Beaufort Shelf from Oliktok Point, Alaska. DAS optical sensing of fiber strain‐rate provides a proxy for seafloor pressure, which we calibrate with wave buoy measurements during the ice‐free season (August 2022). We apply this calibration during the ice formation season (November 2021) to obtain unprecedented resolution of variable wave attenuation rates in new, partial ice cover. The location and strength of wave attenuation serve as proxies for ice coverage and thickness, especially during rapidly evolving events. Plain Language Summary Coasts globally are susceptible to erosion by ocean waves. In the Arctic, sea ice near the coast can serve as protection for much of the year. It is particularly challenging to measure waves and ice in this environment, which is necessary to understand the degree of buffering and project future changes. Typical ways of observing waves (e.g., buoys and underwater moorings) have lower success in coastal ice. We show a new way to observe waves and ice in these coastal regions using cables at the seabed deployed for internet connection. With the use of an instrument called an interrogator on shore, fibers in these cables can act like a series of hundreds of wave buoys. This allows us to see that waves are reduced at a variable rate throughout the ice. There are significant opportunities to learn more about the coastal Arctic using this novel technology and method. Key Points Seafloor fiber optic cables can be used to quantify surface waves in seasonally sea ice‐covered oceans High spatial‐resolution wave observations may be used to study wave attenuation in ice at much finer resolution than previously possible The rapid evolution of the location and strength of attenuation serves as proxy for the evolution of ice itself