Rip Currents Research Articles

Rip current occurrences in meso tidal surf zones at a coastal stretch along the central west coast of India

Currents in the surfzone were measured and modeled along a coastal stretch on the central west coast of India. Wave and tide were the primary forcings for the numerical model, which was validated with the measurements. The rip current occurrences concerning the prevailing coastal processes are attempted, and the instances where the rip currents can prevail are identified. The wave height, wave period, wave direction, and water level in the nearshore waters were correlated with the rip current (>0.2 m/s) occurrence. The wave period around 7–8 s and the wave direction between 240° and 275° significantly contributed to the rip currents over the entire study region. Along Sinquerim and Candolim beach stretch, a high prevalence of rip currents is observed for wave heights in the range between 1.4 and 1.6 m. In contrast, in Candolim and Baga beaches, the rip current prevalence is greater for wave heights ranging between 0.4 and 0.7 m. In comparison, the tide level between 0.5 and 1 m was significant along the Sinquerim–Candolim stretch. In contrast, tide levels between 0.75 and 2 m were significant in rip current occurrence for the Calangute and Baga stretch.

Identification of coastal typology: potential resources and hazards

Coastal areas are unique ecosystems because of the potential for abundant natural resources and hazards that can cause losses. Therefore, this study aims to identify the typology and coastal dynamics of Kukup, Ngrawe, Sepanjang, Drini, and Krakal, Indonesia, for analyzing the potential of natural resources and hazards. A rapid-integrated assessment was carried out to identify typology, genesis, and dynamics of coastal areas by conducting field surveys at locations that have been determined by purposive sampling. The results showed that wave erosion coast was formed in Ngrawe, Kukup, Drini, and Krakal. The marine deposition coast was formed in Ngrawe, Kukup, Sepanjang, Drini, and Krakal. Moreover, the coast built by organism can be found in Sepanjang, Drini, and Krakal. In contrast, the structurally shaped coast was formed in the western part of the Krakal. The coastal dynamics begin with geodynamic processes that form structurally shaped coast, hydrodynamics that form marine deposition coast, wave erosion coast, and ecodynamics that form coast built by organism typology. The potential of natural resources consists of fishery potential, agriculture, and natural beauty for tourism objects. In contrast, the potential hazards consist of earthquakes, tsunamis, tidal waves, rockfall, rip currents, topographic changes, and land-use changes. The coastal area management planning recommendations were Spatial Planning Regulation, Early Warning System, Evacuation Route and assembly point (shelter), Digital-based Information Dissemination, and building retrofitting.

Identifying risk factors and implications for beach drowning prevention amongst an Australian multicultural community.

Multicultural communities in Australia are recognised as a priority area for drowning prevention, but no evidence-based study has addressed their knowledge of beach safety. This study used an online survey tool to identify and examine risk factors relating to swimming ability, beach visitation characteristics and behaviour, and beach safety knowledge of the Australian Southern Asian community to assist in the development of future beach safety interventions. Data was obtained through 249 online and in-person surveys of people aged > 18 years. Most respondents reported poor swimming ability (80%), often swam in in the absence of lifeguards (77%), did not understand the rip current hazard (58%), but reported that they entered the water (76%) when visiting beaches. Close to one-quarter (28%) had not heard, or didn’t know the purpose, of the red and yellow beach flags, which identify lifeguard supervised areas on Australian beaches. Length of time living in Australia is an important beach safety consideration for this community, with minimal differences in terms of gender and age. Those who have lived < 10 years in Australia visit beaches more frequently and are less likely to have participated in swimming lessons, be able to swim, heard of the flags or swim between them, understand rip currents, or have participated in a beach safety program. Very few (3%) respondents received beach safety information from within their own community. The importance of beach safety education and swimming lessons within the Southern Asian community should be prioritised for new and recent migrants to Australia.

Flow-Based Rip Current Detection and Visualization

Rip currents are like rivers of fast-moving water that can quickly carry the unwary out to sea. They are not easy to recognize, especially to the untrained observer. Other than in-situ current measurements, there exists a number of methods that analyzes images and videos to detect rip currents. Most of these techniques base their detection on the appearance of rip currents such as foamy pattern, discoloration of water, and locations of breaking waves. Leading methods use either image processing or machine learning of images and/or video input. In this paper, we analyze the behavior of water movement rather than simply its appearance to detect rip currents. Specifically, we investigated several flow visualization methods and tune them to detect rip currents. Based on our study, we recommend two methods that allowed us to detect rip currents where other methods have failed. And because the methods originated as visualization techniques, any presence of rip currents are automatically highlighted. We also evaluated these two methods against previously annotated results by rip current experts, and found that our detections were sufficiently sensitive that some expert annotations were relabeled.

Exploring RPAS potentiality using a RGB camera to understand short term variation on sandy beaches

Remotely Piloted Aircraft Systems (RPAS) is a low-cost and useful alternative to track spatial-temporal variations in a rapidly changing environment. However, there is a lack of studies on beach geomorphology characterization in association with visible spectrum reflectance potentialities. The objective of this study was to embrace this technology for coastal change detection. For this purpose, the data set samples are covering the winter season of 2019. The materials used were digital orthophotos, digital terrain models, and geomorphological parameters, such as the Relative Tide Range (RTR) and Omega (Ω). The goals are to (i) classify the beach morphodynamics; (ii) identify the berms, cusps, and rip current channels; (iii) extract RGB indexes to detect the shoreline variability; (iv) assess beach profiles and (v) evaluate the volume of sediments. The study area, Paiva beach, is located in the Northeast of Brazil, which presents significant morphodynamic variations. The results indicate three morphodynamic stages, namely: Rhythmic Bar and Beach (RBB); Transverse Bar and Rip (TBR), and Low Tide Terrace (LTT). The wave climate for the region averaged Dir of 120°, Tp of 9 s, and Hs of 1.8 m. Between June and July, the shoreline had the most significant advance with 51% of the beach extension. On the other hand, between July and August, the beach registered a considerable 88% retreat. The profiles showed a maximum variation of 1.5 m vertically on the berm, a common characteristic of winter profiles, detected in August. For the sediment volume, July and August showed erosion processes with sediment loss of 12,508.58 m3 in the south sector and accretion of 23,052.97 m3 in the north. The planimetric and altimetric mean square error were 2.7 and 4.5 cm, respectively, showing the advantage of high spatial resolution data for morphodynamic classification, and combining it to identify vegetation indexes to detect shoreline variability.

Drowning Risk Analysis Comparing Surf Bather Subgroups

The study assessed the utility of risk analysis for advancing knowledge on drowning risk factors. The setting was unintentional drowning of surf bathers in Australia. Bathers reported earlier exposure to selected risk factors (swimming ability, wave height associated with rip currents and surf bathing experience) and were observed for water exposure (in minutes). These data were then assembled in mathematical models. The analysis forecast relative drowning risk pertaining to risk markers representing selected surf bather subgroups (gender, age and water activity). Contextualized through previous study findings, comparison of results with a gold standard obtained from mortality data generated new surf bather drowning hypotheses suitable for future testing by rigorous analytical epidemiologic designs. The hypotheses were: (1) The male to female comparative surf bather drowning rate is explained primarily by differences in crude water exposure; (2) the association of cardio-vascular medical conditions with surf bather drowning is stronger for older surf bathers compared to younger surf bathers; and (3) other risk contributors to surf bather drowning are: Poorly calibrated perception of bathing ability (overconfidence) and use of alcohol. Nonetheless, drowning rates appear generally consistent with time exposure to water. The study findings may also support drowning prevention strategies targeting risk marker subgroups.

A numerical investigation of wave and current fields along bathymetry with porous media

A three-dimensional non-hydrostatic model based on Volume-Averaged, Reynolds-Averaged Navier–Stokes equations (VARANS) in the σ coordinate is presented. It is coupled with a non-linear k−ε turbulence model. The model's performance on wave interactions with porous structures is validated against laboratory data, including dam-break flows through a porous wall, solitary waves propagating over a submerged permeable obstacle, as well as periodic waves propagating over a submerged porous breakwater with wave breaking. Compared with models that use a volume-of-fluid approach, the high computational efficiency of the present model is demonstrated and stressed. Furthermore, the model is shown to be capable of simulating well wave transformation and wave-driven currents in a reef-lagoon-channel system, using the experimental data of Zheng et al. (2020). Next, the effects on wave-height, mean water level and wave-driven currents, caused by porous layers are studied. It is seen that the porous beds can reduce wave height about 43% on the reef flat, while wave setup is comparable (6% mean difference) between corresponding smooth and porous structures. Velocities of the wave-driven currents on the reef flat and the rip currents in the channel decrease by 16% and 21% with porous media. Moreover, results show only small discrepancies with varied porosities.

A convolutional neural network based model to predict nearshore waves and hydrodynamics

This study proposes a convolutional neural network (CNN) based model to predict waves and hydrodynamics in the nearshore zone. Specifically, we address the so-called next-frame prediction of wave and hydrodynamic conditions using the previous-step conditions. A laboratory experiment on unsteady rip currents is simulated using the non-hydrostatic model SWASH. The simulated wave and hydrodynamic results are divided into two groups. The first group of data is used to train the CNN model, and the second group of data is used to evaluate the trained model by comparing the simulated water surface elevation, cross-shore velocity, and longshore velocity by SWASH with the corresponding prediction by the trained CNN model. The result shows that the CNN model accurately predicts the wave propagation over the offshore slope, wave breaking over the sandbar, and bore propagation over the shore including detailed wave crest bending and separation. Time-averaged water level comparison further confirms that the CNN model captures the wave setup induced by wave breaking. The CNN model also correctly predicts the cross-shore velocity and longshore velocity driven by wave breaking over sandbars and wave–current interaction. Finally, the low-frequency nearshore circulation pattern predicted by the CNN model is also evaluated by time-averaging the velocity field. The comparison shows that the CNN model correctly predicts the distribution of circulation cells and the number of cells, as simulated by the SWASH model. This work serves as a paradigm to integrate traditional coastal modeling with machine learning to study coastal processes.

Numerical Analysis of Sediment Transport Rates from Rip Currents at an Open Inlet between Low Crested Breakwaters (LCB): The Role of Infra-Gravity Waves

Lee, J.L. and Cho, Y.-J., 2021. Numerical analysis of sediment transport rates from rip currents at an open inlet between Low Crested Breakwaters (LCB): The role of infra-gravity waves. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 489–493. Coconut Creek (Florida), ISSN 0749-0208. Low Crested Breakwaters (LCB), the most preferred structural type in the coastal zone management project by the Korean Ministry of Ocean and Fisheries, has been designed to mitigate beach erosion by high waves occurring only a few times a year. Now that moderate sea conditions are dramatically different from those in rough seas, these poor design practices could interrupt the grand circulation process of natural beaches over the course of a year. As a result, the beach stabilizing effect of LCB often falls short of our expectations. In this study, in order to test this hypothesis, 3-D numerical simulation was carried out to analyze the rip currents and its associated sediment transport at the open inlet between LCB when LCB is subject to infra-gravity waves, which play an indispensable role in the beach restoring process in a mild sea with an annual prevalence rate of over 80%. Numerical results show that in the case of LCB with lower crest freeboard, rip currents gets increased by 2.6 times when compared to the one before the deployment of LCB since the water mass influx toward the down-wave side of LCB by overflowing LCB by the preceding waves is redirected toward the open inlet. The sediment transport rate was estimated using Bailard's model, the most referred cross-shore sediment model in the literature. It was shown that the primary sediment transport mode at the open inlet between LCB was bed load, and sand of 5.62 ×10–5 m3 / m was leaving the inner zone of LCB per unit wave period.

Mechanism of Rip Current Generation at Deoksan Beach, South Korea

Chang, S.-Y.; Kim, J.-H.; Lee, H.-S., and Kim, I., 2021. Mechanism of rip current generation at Deoksan Beach, South Korea. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 295–299. Coconut Creek (Florida), ISSN 0749-0208. The coast serves as a buffer by reducing the energy of high waves and also serves as a leisure space for people. The east coast of Gangwon has become popular for its beach and for surfing in summer. Most beaches are sandy, and they have well-developed crescentic bars owing to exposure to high waves. The study site, Deoksan Beach, had an accident in which two college students drowned owing to rip currents at around 5:40 pm on July 13, 2019. The flow velocity and direction of the rip currents were identified using CCTV images at the time of the accident, and the causes of the currents were analyzed using data obtained from five water depths surveys conducted in 2017. At the time of the accident, the significant wave height was 0.6 m, the period was ∼7.5 s, and the wave direction was 54°. The survey results indicated that an environment suitable for rip current generation existed at this site. A numerical model experiment was conducted using the non-hydrostatic Surface Waves till Shore (SWASH) model to reproduce the occurrence of rip currents at the time of the accident, and the flow (surface: 0.38 m/s, average: 0.3 m/s) was found to be on the offshore side of the accident.

Development of Coastal Safety Mapping System by Vulnerability Assessment of Tidal Creeks

Lee, J.K.; Kim, J.O., and, Oh, Y.S. 2021. Development of coastal safety mapping system by vulnerability assessment of tidal creeks. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 459–463. Coconut Creek (Florida), ISSN 0749-0208. Most coastal accidents occur in coastal areas with heavy traffic, or crowded beaches and tidal flats. In Korea, various leisure activities are conducted throughout the year on beaches. A significant increase in the number of coastal area workers has led to a corresponding increase in the risk of accidents; this makes the employment of effective countermeasures a necessity. A coastal safety map integrates spatial information of dangerous areas and hazards to prevent accidents in the ocean. In addition to its use for safe expansion of coastal leisure activities, coastal safety maps can be used for the prevention of disasters caused by sea conditions such as tidal creeks, heavy swells, and rip currents. In this study, a tidal creek map was created using an Unmanned Aerial Vehicle (UAV) to express the shape of a tidal creek in three dimensions. We designed and implemented a mapping system that identifies places with a high potential for human accidents in tidal flats. The system uses computer vision technology to identify the shape and location of the tidal channel and extract areas with a high probability of accidents, contributing to the development and implementation of comprehensive safety measures.

Analysis of Beach Changes after Construction of Submerged Breakwaters

Lee, H.; Kim, J.; Chang, S., and Kim, I., 2021. Analysis of beach changes after construction of submerged breakwaters. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 300–304. Coconut Creek (Florida), ISSN 0749-0208. This study presents seasonal investigations of submerged breakwaters constructed from 2013 to 2014 as part of a government erosion prevention project in the region of Samcheok-si, South Korea. Parameters, including wave-induced currents, wave heights, beach profiles, and shoreline changes, were investigated to monitor and analyze sand transport trends in the study area. The construction of Gungchon Harbor in 2006 led to the transport of sand from southern Wonpyeong Beach to northern Gungchon Beach, which resulted in an average shoreline retreat of greater than 50 m. However, despite the subsequent construction of the submerged breakwaters, beach erosion continued to occur in adjacent areas. Specifically, a tombolo was generated behind the submerged breakwaters, which led to beach erosion. Rip currents were also typically generated near submerged breakwaters, which play a role in the offshore transportation of sand. Wonpyeong Beach experienced erosion following the construction of Gungchon Harbor, whereas Gungchon Beach exhibited accretion. Moreover, evidence of further erosion was observed near the breakwater construction area. Therefore, this study indicates that detailed monitoring during and after the construction of breakwaters is required to predict potential secondary erosion and understand the erosion mechanism for an optimal breakwater design.

Can the visualization of rip currents prevent drowning accidents? Consideration of the effect of optimism bias

Drowning accidents at beach in Japan are caused by rip currents. To reduce these accidents, a new technology that can detect rip currents and notify beachgoers by using the Internet of Things (IoT) and Artificial Intelligence (AI) was proposed. However, studies on the effect of visualizing rip currents or considering the effect of optimism bias have not been conducted. This study investigates if visualization of rip currents might help in preventing drowning accidents, while considering the effect of optimism bias. The participants were 90 Japanese beachgoers. They were asked to answer questions based on their knowledge of the beach and rip currents, their optimism bias regarding rip currents, and awareness with or without visualization. The results of the analyses suggest that despite optimism bias, the visualization of rip currents increases the tendency of beachgoers to perceive and avoid rip currents. As described above, it was found that by visualizing the rip current, beachgoers were able to perceive and avoid rip currents. In addition, an understanding of rip currents is positively related to the intent to avoid rip currents even when rip currents are visualized. Therefore, it is necessary not only to enhance the avoidance tendency by visualizing rip currents, but also to further enhance knowledge of beachgoers to deepen the understanding of rip currents including the danger associated and methods to avoid them.

Rip currents investigation on a Ligurian pocket beach, NW Mediterranean

Wave-induced currents play a key role in coastal sedimentary and hydrodynamics processes, and in particular, rip currents are probably the most widely studied aspect. Rip currents are characterized by a strong seaward-directed flow, which can transport sediments, planktonic organisms, nutrients, pollutants, and suspended material. However, rip currents are also a hazard for beachgoers and constitute a well known risk to bathers. Several studies have been conducted to describe rip current dynamics and their implications along oceanic beaches, although only a few studies have considered rip dynamics along Mediterranean coasts. This study is an accurate investigation of rip current development in the Levanto pocket beach (Ligurian sea, NW Italy). Coastal video-monitoring, coastal modelling, field surveys, and laboratory analysis are well known methodologies used to study the behaviour of rip currents, but each has its limitations. To overcome this problem, we propose an integrated approach where different tools are integrated among these to obtain mutual validation among several different approaches. The results show how the rip currents investigated in this study can reach and exceed velocities of 1 ms−1, comparable with those of oceanic rip currents, and how these are a key component in the coastal processes that occur along a Mediterranean pocket beach.

Regional Climate Change Impact on Coastal Tourism: A Case Study for the Black Sea Coast of Russia

Regional climate change is one of the key factors that should be taken into account when planning the development of the coastal tourism, including investments and construction of tourism-related infrastructure. A case study for the Black Sea coast of Russia shows a series of potential negative hydrological, meteorological, and biological factors that accompany regional warming of the Black Sea Region, that can impede the development of coastal tourism and devalue billions of dollars in investments by the State, private companies, and individuals. We discuss such natural phenomena as air and sea warming, extreme weather events, coastal upwelling, heavy rains, river plumes, wind and waves, tornado, rip currents, sea-level rise, algal bloom, introduced species, and other features characteristic for the region that seriously impact coastal tourism today, and may intensify in the nearest future. Sporadic occurrence of extreme weather events, unpleasant and sometimes dangerous sea and atmosphere phenomena during the summer tourist season, and from year to year can be of critical psychological importance when choosing your next vacation and tourism destination. The research does not include anthropogenic factors, geopolitical, and socio-economic processes, and the COVID-19 pandemic that play an important role in the sustainable development of coastal tourism as well.

Rip current rescues on unguarded beaches

Rip currents are the greatest danger at surf beaches. Professional lifeguards rescue tens of thousands of people every year at U.S. beaches, but only a small percentage of the nation’s beaches are guarded. Oftentimes it is a young person who is caught in a rip current, and a bystander will attempt a rescue without a flotation device. The U.S. Lifesaving Association strongly suggests that this kind of rescue should not be undertaken because too often the rescuer will drown. Some coastal towns such as Cocoa Beach in Florida are now posting ring buoys on their unguarded beaches with the warning to throw, but not to go into the water. Ring buoys of two different weights were tested for efficiency when thrown in terms of distance and accuracy. The participants threw the ring buoys two different ways: one way of their choosing (un-instructed) and second by Red Cross recommendation (instructed). The buoyancy was also tested for each buoy. While these flotation devices have some merit, they clearly have limitations.

Correspondence of Beach User Perception, Lifesaving Strategies and Rip Currents: Implications for Beach Management

Rip currents at beaches are a public health hazard, with the potential to have serious socio-economic impacts on coastal communities globally, particularly those that depend on tourists. The potential for drowning or rescue depends on a combination of physical and social factors, and this is the first study to examine the relationship amongst the presence and location of rips, beach user intentions and behavior, and the hazard level identified by the lifeguards. Results of a survey administered in the summer of 2019 at Cavendish Beach and Brackley Beaches along the north shore of Prince Edward Island (PEI), Canada, suggests that beach user intention and perception of the rip current hazard may not accurately reflect their actions. Despite being aware of beach hazards, most beach users and in particular the tourists to the area, did not observe beach warnings. Their activity on the beach also appears to be influenced by the design of the beach access and the presence of other beach users. Respondents who could not recall the hazard level defined by beach flags and signs on the boardwalk tended to sit further away from the access point and lifeguards. Most of the respondents were tourists who were at a higher risk of needing rescue or drowning caused by rip currents due to their lack of rip knowledge and familiarity with those beaches. It is argued that the potential for drownings and rescues can be mitigated through changes in the design of the beach access and the distribution of lifeguard resources, but further research into the correspondence of beach user perception, lifesaving strategies and rip currents is required.

Flash rip current driven suspended sediment flushing amplification in depth-integrated modeling framework

Until recently, wave and hydrodynamic properties in the cross-shore direction have been linked to accretive or erosive morphological evolution. However, various uncertainties remain, hindering the full understanding and accurate prediction of the transport direction and quantity of sediment transport in nearshore areas. In this study, we showed that flash rip currents (FRCs) could significantly amplify suspended sediment flushing out of the surf zone by greatly increasing advective flux, even under accretive wave conditions in a depth-integrated modeling framework. Compared to the case without FRCs, where only one-dimensional cross-shore direction waves and currents exist, FRC-driven seaward advective sediment flux increased by approximately O(102) times under normal incoming waves on alongshore uniform beaches, at least for the tested wave and bathymetry conditions. To properly consider the role of FRCs in suspended sediment flushing, short wave related physics, such as nonhydrostatic pressure and frequency dispersion, had to be included. In addition, it was important to accurately predict not only wave properties but also local hydrodynamics that cause erosion and advection. Finally, uniform sandbars prevented beach erosion, even when FRCs occurred on uniform beaches, by dissipating the wave energy closely associated with FRC generation. Therefore, one-dimensional cross-shore direction approaches neglecting the role of FRC-driven sediment transport processes, which are closely related to short wave motions and occur in two-dimensional space, could lead to lower prediction accuracy.

A Bayesian network approach to modelling rip-current drownings and shore-break wave injuries

Abstract. A Bayesian network (BN) approach is used to model and predict shore-break-related injuries and rip-current drowning incidents based on detailed environmental conditions (wave, tide, weather, beach morphology) on the high-energy Gironde coast, southwest France. Six years (2011–2017) of boreal summer (15 June–15 September) surf zone injuries (SZIs) were analysed, comprising 442 (fatal and non-fatal) drownings caused by rip currents and 715 injuries caused by shore-break waves. Environmental conditions at the time of the SZIs were used to train two separate Bayesian networks (BNs), one for rip-current drownings and the other one for shore-break wave injuries. Each BN included two so-called “hidden” exposure and hazard variables, which are not observed yet interact with several of the observed (environmental) variables, which in turn limit the number of BN edges. Both BNs were tested for varying complexity using K-fold cross-validation based on multiple performance metrics. Results show a poor to fair predictive ability of the models according to the different metrics. Shore-break-related injuries appear more predictable than rip-current drowning incidents using the selected predictors within a BN, as the shore-break BN systematically performed better than the rip-current BN. Sensitivity and scenario analyses were performed to address the influence of environmental data variables and their interactions on exposure, hazard and resulting life risk. Most of our findings are in line with earlier SZI and physical hazard-based work; that is, more SZIs are observed for warm sunny days with light winds; long-period waves, with specifically more shore-break-related injuries at high tide and for steep beach profiles; and more rip-current drownings near low tide with near-shore-normal wave incidence and strongly alongshore non-uniform surf zone morphology. The BNs also provided fresh insight, showing that rip-current drowning risk is approximately equally distributed between exposure (variance reduction Vr=14.4 %) and hazard (Vr=17.4 %), while exposure of water user to shore-break waves is much more important (Vr=23.5 %) than the hazard (Vr=10.9 %). Large surf is found to decrease beachgoer exposure to shore-break hazard, while this is not observed for rip currents. Rapid change in tide elevation during days with large tidal range was also found to result in more drowning incidents. We advocate that such BNs, providing a better understanding of hazard, exposure and life risk, can be developed to improve public safety awareness campaigns, in parallel with the development of more skilful risk predictors to anticipate high-life-risk days.

A New Morphodynamic Instability Associated With Cross‐Shore Transport in the Nearshore

AbstractThe existing theory for shore‐transverse rhythmic sand bars relies on morphodynamic instabilities involving the wave‐driven longshore current and rip currents. Intriguingly, transverse finger bars are common on coasts with sediment excess, something not related to those currents. Here we show that, if the actual beach profile is above the equilibrium profile, cross‐shore transport can induce an instability triggered by onshore transport together with wave refraction by the emerging bars. We use a numerical model that filters out the dynamics associated to longshore and rip currents but includes a simplified version of cross‐shore transport and is able to reproduce the formation of shore‐transverse bars. The alongshore spacing scales with the wavelength of the incident waves and the cross‐shore extent is approximately equal to the distance from shore to the depth of closure. The modeled bars compare qualitatively well with observations at El Trabucador back‐barrier beach (Ebro delta, Western Mediterranean Sea).