Search Results (268)

Rhodoliths (from Greek etymology meaning red + stone) are spheroidal accretions composed of various types of crustose coralline red algae that dwell in relatively shallow waters where sunlight allows for photosynthesis. Unlike most other kinds of algae that are attached to the seabed by a holdfast, rhodoliths are free to roll about by circumrotary movements stimulated mainly by gentle wave action and bottom currents, as well as by disruptions by associated fauna. Frequent movement exposes every part of the algal surface to an equitable amount of sunlight, which generally results in an evenly concentric pattern of growth over time. Individual structures may attain a diameter of 10 to 20 cm, representing 100 years of growth or more. Initiation typically involves encrustation by founder cells on a rock pebble or shell fragment. In life, the functional outer surface is red or pink in complexion, whereas the structure’s inner core amounts to dead weight. Chemically, rhodoliths are composed of high magnesium calcite [(Ca,Mg)CO₃], with examples known around many oceanic islands and virtually all continental shelves in the present world. The oldest fossil rhodoliths appeared during the early Cretaceous, 113 million years ago. Geologically, rhodoliths may occur in massive limestone beds composed of densely packed accumulations. Living rhodoliths commonly occur in waters as shallow as −2 to −10 m, as well as seaward in mesophotic waters up to −100 m under exceptional conditions of water clarity. Especially in shallower waters, rhodoliths are vulnerable to transfer by storm waves to supratidal settings, which result in bleaching under direct sunlight and death. Increasingly, marine biologists recognize that rhodolith beds represent a habitat that offers shelter to a community of other algae and diverse marine invertebrates. Full article

Morphological variability on Mediterranean embayed sandy beaches is largely driven by wave storms and episodic sediment inputs from local streams during intense rainfall. While storm impacts are well documented, the combined influence of stream discharge, wave forcing and morphological response remains poorly understood. This study examines these interactions at Castell beach, one of the few non-urbanised, stream-fed embayed beaches on the northwestern Mediterranean, during two high-energy storms with heavy rainfall: December 2019 and January 2020 (Storm Gloria). Morphological changes in the subaerial and submerged beach, and stream dynamics were assessed using repeated RTK–GNSS surveys, orthophotos and echo-sounder bathymetry. Results show the stream mouth shifted along the beach (east, central or west) during heavy rainfall episodes depending on wave direction and pre-existing topography, tending toward more wave-sheltered zones. The storms induced contrasting responses: the first caused slight subaerial accretion, whereas Storm Gloria produced subaerial erosion and nearshore sediment deposition from both beach and stream sources. This material was subsequently reworked and reincorporated into the subaerial beach under calmer conditions, with full recovery by February 2022. These findings highlight the role of stream–wave interactions in sediment dynamics and the capacity of highly protected embayed beaches to adapt to extreme events. Full article

Coastal sandbars play a crucial role in shoreline protection, yet monitoring their dynamics remains challenging due to the cost and limited temporal coverage of traditional surveys. This study assesses the feasibility of using Sentinel-2 multispectral imagery combined with the logarithmic band ratio method to automatically detect submerged sandbar crests along three morphologically distinct beaches on the northwestern Mediterranean coast. Pseudo-bathymetry was derived from log-transformed band ratios of blue-green and blue-red reflectance used to extract the sandbar crest and validated against high-resolution in situ bathymetry. The blue-green band ratio achieved higher accuracy than the blue-red band ratio, which performed slightly better in very shallow waters. Its application across single, single/double, and double shore-parallel bar systems demonstrated the robustness and transferability of the approach. However, the method requires relatively clear or calm water conditions, and breaking-wave foam, sunglint, or cloud cover conditions limit the number of usable satellite images. A temporal analysis at a dissipative beach further revealed coherent bar migration patterns associated with storm events, consistent with observed hydrodynamic forcing. The proposed method is cost-free, computationally efficient, and broadly applicable for large-scale and long-term sandbar monitoring where optical water clarity permits. Its simplicity enables integration into coastal management frameworks, supporting sediment-budget assessment and resilience evaluation in data-limited regions. Full article

Extratropical cyclones are the main drivers of high-energy wave events along the southern coast of Brazil, frequently producing hazardous coastal conditions. Between 2001 and 2020, we identified 51 high-impact coastal storms based on Marine Weather Warnings and ERA5 reanalysis. Events showed a clear seasonal pattern, with the highest occurrence in winter and autumn. Composite analyses revealed that these extreme events are consistently associated with strong meridional pressure gradients and southerly to southeasterly low-level winds, which establish long wind-fetch zones that favor the generation and shore-normal propagation of energetic waves. Significant wave heights typically exceeded 4 m along the entire coastline, with maxima south of 35° S. EOF analyses showed that the dominant mode of variability is a recurrent low-pressure system centered between 40 and 45° S over the southwestern Atlantic. In contrast, the second mode represents the dipole between continental high pressure and oceanic low pressure that intensifies storm-related wave generation. Case studies from 2008 and 2015 confirmed that these synoptic patterns result in prolonged hazardous sea states and coastal impacts, including bar closures at the Port of Rio Grande, totaling 355 h of inoperability. These findings provide a clear characterization of the meteoceanographic patterns associated with high-impact coastal storms in southern Brazil and offer a climatological basis for improving early warning, navigation safety, and coastal risk management. Full article

The transplanting of juvenile and adult mussels onto soft sediments is an emerging technique for the ecological restoration of the biogenic habitat formed by mussels. While these habitats are often found within estuarine systems, the spatial suitability of these environments for restoration is poorly described. The dynamic and variable environmental conditions characteristic of estuaries could represent challenges to the persistence of restored mussel beds. To assess whether there are spatial differences in mussel responses to transplantation within an estuarine environment, six experimental mussel beds of adult green-lipped mussels (Perna canaliculus) were established along an environmental gradient in a small estuarine harbour in northern New Zealand. Transplanted mussel beds were sampled immediately after installation and again at 3 and 9 months later. Minor differences in the density, length and condition index of mussels were identified among the six sites over the course of the study; however, their responses were typically similar across sites. These results suggest that these mussels have the capacity to establish themselves within estuarine environments and that their subsequent performance once transplanted onto the seafloor appears to be determined by other site-specific factors, such as the presence of predators and the degree of exposure to storm waves. Full article

Upper oceans are highly energetic during a severe weather event, with large surface waves and intense ocean currents over areas affected by the storm. An advanced and coupled wave–current modelling system for the northwestern Atlantic (WCMS-NWA) was developed by the Regional Modelling Group at Dalhousie University for simulating surface waves and three-dimensional ocean currents over the eastern Canadian shelf and adjacent waters. Applications of this modelling system during different weather events have been discussed separately in the past. In this overview, the model performances of WCMS-NWA and major hydrodynamics over the study region during 11 severe storms are summarized. Comparisons of model results with in situ oceanographic observations and satellite data demonstrate the suitability and accuracy of WCMS-NWA in simulating ocean circulation and surface waves during normal weather conditions and intense ocean currents and extreme surface waves during severe storm events. It is shown that satisfactory model performance of WCMS-NWA requires reliable temporal–spatial representations of atmospheric forcing and inclusions of interactions between waves and currents (WCIs). Important contributions from WCIs during these severe weather conditions are discussed based on the model results. Full article

Coastal managers worldwide must prepare for changes in annual wave overtopping events due to climate change and sea-level rise. Research often assesses overtopping discharges by extreme events at a sea wall crest, typically using data from physical models or empirical rules based on scaled experiments. Here, we analyse a unique 1-year field dataset of coastal wave overtopping, from SW England, to determine the number of individual waves, regardless of their size, overtopping two locations across a coastal structure. The coastal conditions causing the most frequent overtopping differ from those driving it landward, complicating hazard communications for multiuse infrastructure. These data are the first field observations covering a year of tide, wave and wind conditions that cause overtopping of a vertical sea wall. Storms have a minimal (<2%) contribution to the number of tides associated with overtopping and the prevailing wave direction was not that associated with most overtopping events. Overtopping histograms identify the variability in the most likely time of overtopping relative to high tide for different wave categories across the structure. Sea-level rise, beach lowering and climate change will influence the annual number of waves overtopping in future. Change will be a complex balance between overtopping by different wave categories due to their likelihood of coincidence with water levels that do not cause depth-limitation over the foreshore or (partial-)reflection off the structure. It is possible the number of waves overtopping will reduce at the crest of a sea wall, while more of those overtopping waves will travel further inland. Full article

Approximately 27.6% of Italian beaches are currently affected by erosion, despite the widespread implementation of coastal defence structures. Around 10,500 installations—mainly groins and detached breakwaters—occupy nearly 24.6% of the national shoreline. Although primarily designed to protect tourist beaches, these hard-engineered structures often degrade coastal landscapes, alter nearshore circulation, and pose risks to swimmers. Nevertheless, beaches remain a fundamental asset for the “3S” (Sun, Sea, Sand) tourism sector, which contributes approximately 2.2% to Italy’s GDP, accounting for over 175 million tourists’ overnight stays in 2024, frequently concentrated near protected coastal zones. In this study, drowning incidents along the Italian coastline were analyzed using press reports complemented by official statistics. Between 2016 and 2021, an average of 145 fatalities occurred per bathing season. Sudden drownings following medical emergencies accounted for 41% of cases, non-swimmers for 18%, accidental falls into the water for 3%, and water sports activities for an additional 3%. Rip currents on natural beaches were responsible for 22% of drownings, whereas those generated by coastal defence structures accounted for 12%. A further 12% of non-swimmer fatalities are suspected to have resulted from falls into depressions or channels formed in proximity to these structures. Evidence from previous studies and seabed morphology analyses indicates that coastal defence structures can generate rip currents through two main mechanisms: (1) hydraulic pressure exerted against groins, which drives offshore flow, and (2) water outflow between pairs of breakwaters resulting from wave setup behind them. Both processes, though often less intense, are also observed near submerged structures. The erosional channels formed by these currents may persist well beyond storm events, maintaining dangerous conditions for bathers. As Italy continues to rely predominantly on hard coastal protection measures, improving the understanding of drowning dynamics associated with these structures is crucial. This should be accompanied by regulatory updates requiring designers and coastal managers to systematically assess related hazards and to propose effective mitigation and safety strategies. Full article

This work, conducted within the framework of the international network CRESTE (Coastal Resilience Using Satellites), examines the role of resilience in monitoring coastal evolution across diverse environments in Europe (France, The Netherlands), America (Mexico), Asia (China), and Oceania (Australia). High-resolution morphological datasets, derived from in situ measurements and video monitoring systems, were analyzed for wave- and tide-dominated beaches influenced by both climatic drivers and anthropogenic pressures. Findings indicate that beach resilience is strongly linked to system resistance, which depends on the intensity of climate drivers, including storm frequency, and site-specific conditions related to the type of sediment and its availability, and the presence of anthropogenic activities including coastal structures (e.g., Normandy, Yucatán) and shoreface nourishments (Netherlands). In Batemans Bay (Australia) and Hangzhou Bay (China), assessing the resilience is particularly challenging due to the combined influence of multiple drivers, fluvial inputs, and urban development. Accurate monitoring of coastal resilience across timescales requires accounting for long-term morphological, ecological, and socio-economic processes. This can be enhanced through satellite observations, which, when integrated with in situ measurements, numerical modeling, and artificial intelligence, support a more comprehensive assessment of resilience and refine projections under future climate change and sea-level rise; representing a key focus for further works. Full article

This paper investigates an integrated sensing and communication (ISAC) system operating in a rainfall scenario, where a base station (BS) simultaneously serves multiple communication users and performs rainfall detection. Specifically, considering the fading characteristics of the millimeter-wave (mmWave) channel and the impact of rainfall on the signal propagation link, we adopt the Weibull distribution as the channel model between the nodes. Based on the above, the received signal-to-noise ratio (SNR), channel capacity, bit error rate (BER), and outage probability of the users within the system are analyzed to characterize the communication performance. Furthermore, the sensing capability of the BS is demonstrated through the analysis of the probability of rainfall. Simulation results reveal that increasing the distance between the BS and users significantly degrades their communication performance. Furthermore, the performance is highly sensitive to the rainfall intensity. Specifically, compared to storm conditions, light rain yields an improvement of 16.9 dB in the average user SNR, a 7.2 bps/Hz increase in channel capacity, and a 40.2% reduction in the outage probability. Additionally, an increase in the complex dielectric constant of raindrops substantially reduces the backscattering coefficient at the ISAC BS. Full article

Coastal profile models are frequently used for the computation of storm-induced erosion at (nourished) beaches. Attention is focused on new developments and new validation exercises for the detailed process-based CROSMOR-model for the computation of storm-induced morphological changes in sand and gravel coasts. The following new model improvements are studied: (1) improved runup equations based on the available field data; (2) the inclusion of the uniformity coefficient (C_u = d₆₀/d₁₀) of the bed material affecting the settling velocity of the suspended sediment and thus the suspended sediment transport; (3) the inclusion of hard bottom layers, so that the effect of a submerged breakwater on the beach–dune morphology can be assessed; and (4) the determination of adequate model settings for the accretive and erosive conditions of coarse gravel–shingle types of coasts (sediment range of 2 to 40 mm). The improved model has been extensively validated for sand and gravel coasts using the available field data sets. Furthermore, a series of sensitivity computations have been made to study the numerical parameters (time step, grid size and bed-smoothing) and key physical parameters (sediment size, wave height, wave incidence angle, wave asymmetry and wave-induced undertow), conditions affecting the beach morphodynamic processes. Finally, the model has been used to study various alternative methods of reducing beach erosion. Full article

Extreme weather events, such as typhoons, induce strong wave–current interactions that significantly alter nearshore hydrodynamic conditions, particularly in shallow intertidal zones. This study investigates the influence of wind speed and water depth on wave–current coupling under typhoon conditions in Shenhu Bay, southeastern China—a semi-enclosed bay that hosts multiple ancient forest relics within its intertidal zone. A two-tier numerical modeling framework was developed, comprising a regional-scale hydrodynamic model and a localized high-resolution model centered on a protective structure. Validation data were obtained from in situ field observations. Three structural scenarios were tested: fully intact, bottom-blocked, and damaged. Results indicate that wave-induced radiation stress plays a dominant role in enhancing flow velocities when wind speeds exceed 6 m/s, with wave contributions approaching 100% across all water depths. However, the linear relationship between water depth and wave contribution observed under non-typhoon conditions breaks down under typhoon forcing. A critical depth range was identified, within which wave contribution peaked before declining with further increases in depth—highlighting its potential sensitivity to storm energy. Moreover, structural simulations revealed that bottom-blocked devices, although seemingly more enclosed, may be vulnerable to vertical pressure loading due to insufficient water exchange. In contrast, perforated designs facilitate an internal–external hydrodynamic balance, thereby enhancing protective effect. This study provides both theoretical and practical insights into intertidal structure design and paleo-heritage conservation under extreme hydrodynamic stress. Full article

This study examines the evolution of a beach formed along the coastline of a semi-enclosed, essentially tideless, embayment in the eastern Mediterranean Sea. The analysis revealed that the primary factors influencing its recent evolution are the terrestrial sediment influxes, current nearshore oceanographic conditions, and the existence of coastal constructions. The beach zone is exposed to waves approaching from the south with extreme values of height and period of 7 m and 4.3 s, respectively. Associated morphodynamic characteristics include a closure depth of 7 m, a breaking depth of 4.3 m, and a maximum run-up of 2.4 m. Since the mid-1900s, the shoreline has evolved through an accretional phase from 1960 to 1988, followed by a retreating phase from 1989 to 1997, except in the central part, where progradation has continued. The most recent period (1998–2017) has been relatively stable, though with a slight retreating trend. During storm events, changes to the beach are not uniform along-shore. Gross estimates of beach retreat due to sea level rise induced by climate change threaten the existence of the entire beach (for moderate and extreme IPCC Special Report Emissions Scenarios); however, this does not seem to be the case if riverine sediment influx continues. Full article

Coastal vegetated ecosystems, including tidal marshes, vegetated dunes, and shrub- and forest-dominated wetlands, can mitigate hurricane impacts such as coastal flooding and erosion by increasing surface roughness and reducing wave energy. Land cover maps can be used as input to improve simulations of surface roughness in advanced hydro-morphological models. Consequently, there is a need for efficient tools to develop up-to-date land cover maps that include the accurate distribution of vegetation types prior to an extreme storm. In response, we developed the RUSH tool (Rapid remote sensing Updates of land cover for Storm and Hurricane forecast models). RUSH delivers high-resolution maps of coastal vegetation for near-real-time or historical conditions via a Jupyter Notebook application and a graphical user interface (GUI). The application generates 3 m spatial resolution land cover maps with classes relevant to coastal settings, especially along mainland beaches, headlands, and barrier islands, as follows: (1) open water; (2) emergent wetlands; (3) dune grass; (4) woody wetlands; and (5) bare ground. These maps are developed by applying one of two seasonal random-forest machine learning models to Planet Labs SuperDove multispectral imagery. Cool Season and Warm Season Models were trained on 665 and 594 reference points, respectively, located across study regions in the North Carolina Outer Banks, the Mississippi Delta in Louisiana, and a portion of the Florida Gulf Coast near Apalachicola. Cool Season and Warm Season Models were tested with 666 and 595 independent points, with an overall accuracy of 93% and 94%, respectively. The Jupyter Notebook application provides users with a flexible platform for customization for advanced users, whereas the GUI, designed with user-experience feedback, provides non-experts access to remote sensing capabilities. This application can also be used for long-term coastal geomorphic and ecosystem change assessments. Full article

Understanding the morphodynamic evolution of muddy coasts under complex wave–tidal forcing is crucial for effective coastal management, particularly under the unstable hydrodynamic conditions associated with global climate change. This study employs a one-dimensional Delft3D model to investigate a tidal flat north of Dafeng Port, Jiangsu Province, China, validated with multi-year profile measurements. Under typical conditions, the profile consistently exhibits upper-flat accretion and lower-flat erosion, with threshold values of Hs ≈ 1.2 m and Tp ≈ 4.5 s triggering nonlinear bed-level changes. During storm tides, the profile displays a distinct upper flood-tide and lower ebb-tide response. Long-term simulations suggest that the profile will likely reach dynamic equilibrium by 2026. Overall, this study demonstrates the capability of one-dimensional modeling to capture nonlinear tidal flat evolution and provides valuable insights into the spatially variable morphodynamics of muddy coasts for adaptive management. Full article