Rip Currents Research Articles

Loose and Limited Concepts: Using Coauthor Network Analysis to Identify Potential Gaps in the Understanding of Barrier Islands

Houser, C.; Smith, A.; George, E.; Lehner, J., and Lunardi, B., 2021. Loose and limited concepts: Using coauthor network analysis to identify potential gaps in the understanding of barrier islands. Journal of Coastal Research, 37(4), 873–881. Coconut Creek (Florida), ISSN 0749-0208.Understanding of coastal geomorphology expands through collaborative social networks that are expressed through coauthorship. This technical communication examines the structure of coauthorship networks and research on barrier islands with a focus on nearshore bars, rip currents, swash, beach-dune interaction, foredunes, and the backbarrier. Coauthorship in coastal geomorphology is largely based on regional organizational networks and academic lineages, which may limit the cross-fertilization of ideas and techniques that would allow for an improved understanding of barrier island response to storms and sea-level rise. It is also argued that the lack of collaboration has an influence on field sampling strategies and the development of process-based models and machine learning algorithms to predict coastal barrier evolution that ultimately inform coastal management practices.

Short communication: evidence for geologic control of rip channels along Prince Edward Island, Canada

ABSTRACT Rip currents can move unsuspecting swimmers offshore rapidly and represent a significant risk to beach users worldwide, including along the northern coast of Prince Edward Island (PEI), Canada. Although many rip currents are ephemeral and/or spatially variable in response to changes in the nearshore bar morphology and wave and tidal forcing, it is possible for rip channels to be geologically controlled and quasi-permanent in morphology, location, and flow. Several rip channels along the northern coast of PEI appear in the same location from year to year and correspond to elongated lakes, rivers, or swales behind the modern coastal dune system. Given their persistent location and alignment with back dune hydrology, ground-penetrating radar surveys were collected along Brackley and Cavendish Beaches in July 2019 to determine whether persistent rip channels are associated with now-buried river channels extending beneath the modern dunes and continuing offshore. Strong reflectors similar to V-shaped river valleys are present in alongshore transects at both beaches. These infilled valleys align with back-dune hydrology and persistent rip channels, suggesting modern rip channels are structurally controlled and maintained by antecedent geology. This link provides important guidance to beach access management and the distribution of lifesaving strategies along the affected beaches.

Analysis of Rip Current Characteristics Using Dye Tracking Method

Rip currents are strong water channels flowing away from the shoreline. They can occur on any shore with breaking waves. Rip currents play a significant role in changing the topography of shallow water regions by transporting large amounts of bed material offshore. Moreover, they pose a significant danger for people living in nearshore zones and surfers and cause hundreds of deaths annually worldwide. Therefore, rip current generation characteristics have been investigated to prevent casualties. In this study, a GPS drifter survey was chosen as the investigation method; however, a few drawbacks were discovered, such as low accuracy due to the GPS drifter becoming trapped in the surf zone. Therefore, drones and dyes were used to overcome the drawbacks of drifter methods. The results of dye tracking and the 3D wave-induced current numerical simulation were compared; the velocity and formation of the rip current were found to be relatively similar. With the technological advancements and invention of new survey equipment, the survey techniques also evolve, and this paper shows that the disadvantages of the GPS-based Lagrangian method can be overcome using a dye-mounted drone, which observes the rip current easily and accurately.

Rip current hazard at coastal recreational beaches in China

Rip current has become the primary coastal hazard globally. This work presents the operational investigation of nation-wide rip current hazard and its implications for the beach recreational safety in China. Accumulated domestic surfzone fatalities were reported more than the marine disaster casualties over recent ten years. The surfzone accident has high occurrence frequency in the southern regions and reaches its peak from July to August. The spatial distribution of comprehensive hazard levels at 101 major coastal beaches is evaluated based on the proposed risk index system. The methodology involves multiple approaches of statistical analysis and field survey. Southern provinces feature higher rip current hazard than the north due to larger wave, lower tidal range, and more dynamic littoral morphology. The rip current prominently contributes to the demographic variations of beach drowning statistics. The occurrence probability of rip currents could be high in either hotter or cooler weather while the seasonal shift depends on both wave climate and the local shoreline profile. Enhancing public awareness of the rip current hazard has been proved to be a very effective way decreasing surfzone accidents.

HISEA-1: The First C-Band SAR Miniaturized Satellite for Ocean and Coastal Observation

On 22 December 2020, HISEA-1, the first C-band SAR small satellite for ocean remote sensing, was launched from the coastal Wenchang launch site. Though small in weight, the images it produced have a high spatial resolution of 1 m and a large observation width of 100 km. The first batch of images obtained within the first week after the launch confirmed the rich information in the data, including sea ice, wind, wave, rip currents, vortexes, ships, and oil film on the sea, as well as landmark buildings. Furthermore, geometric characteristics of sea ice, wind vector, ocean wave parameter, 3D features of buildings, and some air-sea interface phenomena in dark spots could also be detected after relevant processing. All these indicate that HISEA-1 could be a reliable, remarkable, and powerful instrument for observing oceans and lands.

Monsoonal influences on rip current hazards at recreational beaches along Pahang coastline, Malaysia

Rip current is a type of wave-inducing current that forms nearshore and flows towards the sea. It is a major global hazard in the marine environment that had claimed the lives of hundreds of people due to drowning and recorded thousands of rescue missions around the world. In Malaysia, the Pahang coastline recorded over 30 drowning cases due to rip currents from 2006 to 2018. However, studies on rip current especially on the east coast of Peninsular Malaysia are very limited. Therefore, this study was conducted to classify the beach morphodynamics associated with rip current formations during the southwest monsoon (SWM) and northeast monsoon (NEM) along the Pahang coastline. Five recreational beaches were selected along the Pahang coastline, namely Balok (B1), Batu Hitam (B2), Teluk Cempedak (B3), Sepat (B4), and Air Leleh (B5) as the study site. Sediment samples and beach profile were collected for both monsoonal seasons. It was found that the Pahang coastline was composed of rip-dominant intermediate beaches with several beaches categorised as barred (B), low tide terrace with rip (LTTR), and low tide bar and rip (LTBR). As intermediate beaches are known as rip current dominated beaches, most beaches at Pahang coastline are found to be composed of different risk level of rip current such as high risk (B3 and B5), moderate risk (B1 and B2) and mixed risk (B4). The findings in this study provide useful insights for coastal management planning along the Pahang coastline and the development of beach safety and rescue missions in the event of an emergency related to rip current.

Warm and Cool Nearshore Plumes Connecting the Surf Zone to the Inner Shelf

AbstractCross‐shore transport of larvae, pollutants, and sediment between the surf zone and the inner shelf is important for coastal water quality and ecosystems. Rip currents are known to be a dominant pathway for exchange, but the effects of horizontal temperature and salinity gradients are not well understood. Airborne visible and infrared imaging performed on the California coast shows warm and cool plumes driven by rip currents in the surf zone and extending onto the shelf, with temperature differences of approximately 1°C. The airborne imagery and modeled temperatures and tracers indicate that warm plumes exhibit more lateral spreading and transport material in a buoyant near‐surface layer, whereas cool plumes move offshore in a subsurface layer. The average cross‐shore extent of warm plumes at the surface is approximately one surfzone width larger than for cool plumes. Future work may explore the sensitivity of nearshore plumes to density patterns, wave forcing, and bathymetry.

Tridimensional nonhydrostatic transient rip currents in a wave-resolving model

Flash rips and surf eddies are transient horizontal structures of the order of 10 to 100 m, which can be generated in the surfzone in the absence of bathymetric irregularities. They are traditionally evaluated in a depth averaged setting which involves intrinsic horizontal shear instabilities and the direct generation of vorticity by short-crested waves. In this article, we revisit the processes of surf eddy generation with a new three-dimensional wave resolution model (CROCO) and provide a plausible demonstration of new 3D non-hydrostatic instability and turbulent cascade. We first present a quick overview of a compressible free surface approach suitable for nearshore dynamics. Its ability to simulate the propagation of surface gravity waves and nearshore wave-driven circulation is validated by two laboratory experiments. Next, we present a real world application from Grand Popo Beach, Benin, forced by waves with frequency and directional spreading. The generation of surf eddies by the 3D model differs from depth-averaged models, due to the vertical shear associated with shallow breaking waves. In this case, the generation of eddies from both horizontal shear instability and the breaking of short-crested waves is hampered, the former by stretching the alongshore current and the latter by inhibiting the inverse energy cascade. Instead, the vertical shear flow is subjected to forced wave group variability and Kelvin–Helmholtz type instability at an inflection point. Primary and secondary instabilities generate spanwise and streamwise vorticity connecting small-scale eddies to larger horizontal surfzone structures. Streamwise filaments, appearing as 5 m wide ribs or mini-rips, can extend beyond the surfzone but with moderate energy. These results appear consistent with the velocity spectra and observed patterns of tracers and suspended sediments at Grand Popo Beach. The timescale associated with the mean shear-induced turbulence is several times the wave period and suggests an intermediate range between breaker-induced turbulence and large-scale surf eddies.

Simulations of the Surf Zone Eddy Field and Cross‐Shore Exchange on a Nonidealized Bathymetry

AbstractX‐band radar observations from the 2017 Inner Shelf Dynamics Experiment (ISDE) in central California show multiple persistent and pulsatory rip currents on a relatively straight coastline with alongshore‐varying bathymetry. Although past studies have assessed the characteristics of transient rip currents on alongshore uniform beaches, the relative balance of transient versus steady rip current behavior on nonuniform beaches in realistic wave conditions remains poorly understood. Here, a phase‐resolving Boussinesq‐type wave model (funwaveC) is used to assess the role of alongshore‐varying bathymetry and incident conditions in controlling mean and transient surf zone vorticity and velocity fields and their effect on surf zone exchange. The model simulates wave conditions chosen from the ISDE observations and utilizes both an alongshore‐varying bathymetry estimated from the ISDE radar observations and a uniform bathymetry. Results show that the variable bathymetry significantly increases the alongshore‐ and time‐averaged kinetic energy but that this increase is primarily due to the increase in the standing component resulting from mean circulation patterns, with only small changes in the transient component. A variable bathymetry also increases the spectral energy of surf zone vorticity and time‐averaged vorticity forcing at large spatial scales (>100 m). Wave directional spreading has a large impact on the alongshore‐ and time‐averaged enstrophy and on the spectral energy of surf zone vorticity and vorticity forcing at smaller spatial scales (<100 m). In the presence of a directionally spread wavefield, an alongshore‐varying bathymetry slightly increases the total exchange velocity but has little effect on its transient component.

Detached breakwaters, yes or not? A modelling approach to evaluate and plan their removal

Detached breakwaters have been widely employed as a measure against beach erosion and for coastal protection. However, this type of structures may cause different critical issues, and the advantages are not always evident. Water stagnation, rip currents development in the gaps between multiple structures, and obstruction of the natural panorama are well-recognised issues. However, their removal is always problematic because it is generally associated with rapid erosion of the beach and high costs. This work proposes a modelling approach to obtain a preliminary evaluation of a theoretical removal intervention and discusses its possible consequences. The study case is the Moneglia beach, a tourist beach located on the eastern Ligurian coast, NW Italy. The beach is characterised by the presence of three detached breakwaters, arranged over the entire length of the beach. A dataset consisting of LiDAR data, multibeam data, single-beam data and DGPS data was used to obtain an accurate digital elevation model (DEM) of the study area. Subsequently, the XBeach model was used to simulate three scenarios: i) state-of-the-art scenario (S0), ii) detached breakwaters removal scenario (S1), iii) detached breakwaters removal scenario + nourishment (S1N). The S1 scenario was implemented to evaluate the beach morphodynamic response in the case of a removal intervention. S1N was implemented to simulate a beach recovery plan through a beach nourishment intervention. Once the S1N final scenario was obtained, XBeach was implemented to get a comparison with the sea flooding hazard in the S0 and S1 scenarios. The sea flooding hazard assessment was performed considering storm events with a return time of 50 and 100 years, respectively. The results showed both the potential of the XBeach model as a tool and the sustainability of a theoretical detached breakwater removal intervention.

Adaptive third order Adams-Bashforth time integration for extended Boussinesq equations

We develop the third-order adaptive Adams-Bashforth time integration and the second-order finite difference equation for variable time steps. We incorporate these schemes in the Celeris Advent software to discretize and solve the 2D extended Boussinesq equations. This software uses a hybrid finite volume – finite difference scheme and leverages the GPU to solve the equations faster than real-time while concurrently visualizing them. The newly added adaptive scheme significantly improves the robustness of the model while providing faster computational performance. We simulate several benchmarks using the adaptive time stepping scheme of Celeris Advent and demonstrate the capability of the software in modeling wave-breaking, wave runup, irregular waves, and rip currents. Program SummaryProgram title: Celeris Advent (v.1.3.4)CPC Library link to program files:https://doi.org/10.17632/pwsjdsgz89.1Licensing provisions: GNU General Public License 3Programming language: C++, HLSLNature of problem: Celeris Advent started a new paradigm in nearshore wave simulations and enabled researchers and engineers to run a Boussinesq-type model, faster than real-time and in an interactive environment. For simplicity, we assumed a fixed time step in our first implementation of Celeris Advent. This fixed time step often needs to be chosen conservatively such that the model can resolve the most extreme cases during the experiment. In practical simulations, such as simulating coastal fields, the superposition of boundary and initial conditions may cause rare but extreme conditions, requiring a very small time step that is too conservative during most of the simulation.Solution method: We developed adaptive third order Adams-Bashforth time integration to let Celeris Advent solve the extended Boussinesq equations with a variable time step, allowing it to decrease the time step only when necessary. The adaptive equations are presented in a generic format and therefore can be used for solving other equations as well.Additional comments including restrictions and unusual features: The new version of the Celeris Advent with the adaptive time integration runs ∼3 times faster for the standard conical island benchmark, allowing Celeris Advent simulate this benchmark on a 200×200 grid an order of magnitude faster than real-time on a consumer-level gaming laptop. For a field simulation benchmark, with rare but extreme events, the new version runs ∼25 times faster.

On the swimming strategies to escape a rip current: a mathematical approach

Rip currents represent significant hazards to swimmers all around the world. The danger arises when a misinformed swimmer uses an inadequate strategy to escape the rip, such as fighting the current directly. This can lead to fatigue, panic, and in some cases drowning. There exists a range of strategies put forward by experts (both lifeguards and scientists) to escape rip currents. However, these recommendations are based on a limited number of scientific studies and there is still much discrepancy surrounding the best strategy to escape a rip. Thus, here we present a simple, physics-based theoretical model aimed at assessing different escape strategies in terms of their associated ‘energetic cost’ (in work and power) for any given rip current and swimmer’s proficiency level. Many combinations of swimmers and rips are considered, including both idealised and a realistic rip current. Our quantitative results back the common knowledge that swimming against the rip (which is strongly discouraged by lifeguards) is almost universally the worst possible strategy, especially when compared against strategies favoured by experts, such as floating with the current before attempting to swim back to the shore. For a realistic rip, our results suggest that swimming directly against the rip can require several times more power from the swimmer than other strategies advised by lifeguards, thus lending further scientific support to experts’ recommendations. This study may help promote education around the dangers posed by rip currents and how best to address them.

Investigation of rip current processes along Visakhapatnam beaches, east coast of India: A study based on GNSS drifters and dye experiments

Rip currents are known as one of the most dangerous hazards on sandy beaches worldwide. Indian beaches are least explored to study the variability of rip currents in space and time. The present study is the first attempt made to understand its dynamics by utilizing indigenously developed GNSS (Global Navigation Satellite System) drifters and Rhodamine-B dye experiments. The Rama Krishna (RK) and Rushikonda Beaches of Visakhapatnam are chosen for this study, due to a recorded number of rip current-related drowning cases observed during the past decade. Few experiments were conducted during pre- and post-monsoon seasons of 2018. Drifters work on the Lagrangian principle, where they measure the current velocities along their paths driven by the surface currents. Error analysis of drifter measurements showed that they are capable of resolving surf zone motions very accurately. Strong rip currents were observed in few locations in the study area, where at times current velocities reached ~1 ms−1. Also, Rhodamine-B dye was released into the rip current prone zones along with the drifters and observed that the dye patches also followed the drifters. From these experiments, it has been observed that the rip currents are relatively strong during the post-monsoon season, which could be due to the change in the beach morphology. Similar experiments with more number of drifters would help in understanding rip current dynamics and would help in reducing rip current drowning in the beaches.

Numerical study of rip currents interlaced with multichannel sandbars

Rip currents have become one of the primary coastal hazards globally. In the present work, the dynamics of a multichannel rip system are revealed by a group of numerical simulations over truncated sandbar bathymetry under varying wave conditions. It is found that increasing wave height may disperse rip currents due to strong wave-current shear in opposite directions and the resulting microbreaking, which is contrary to the widely accepted proportional theory. The pump-feed phenomenon between adjacent channels shows that rip currents might be absent in small channels when water flows through neighboring broader pathways. Rip currents are indicated highly sensitive to wave direction and deflect into undulant alongshore currents around sandbars as waves deviate from normal incidence. The decay of rip currents with wave angle did not show a clear dependence on channel width, which was found in previous studies. Vortices usually appear near bar-channel edges and by sides of rip currents. The magnitude of the vortex is not explicitly related to the wave height but increases with the wave angle. The water setup shoreward by sandbars substantially increases with wave angle, while the surface depression over rip channels is less observed. This indicates a lower pressure differential to drive feeder flows toward the channels and explains why rip currents cannot persist when incident waves become slightly oblique.

The self-similar stratified inner-shelf response to transient rip-current-induced mixing

Abstract

A preliminary studies to assess public knowledge of beach safety in east coast Malaysia.

Rip currents are one of the coastal hazards that put Malaysian beachgoers in a risky position. Most of the drowning accidents that occur at beaches worldwide are closely associated with this phenomenon. Research on rip currents is needed to build an effective measuring tool to overcome these issues. However, to date, research on rip currents is mainly focused on its physical aspects, commonly concentrating on the processes that influence and relate to the rips’ generation. As an effort to minimize the negative consequences exerted by the rips, there is an urgent need to enhance the rip-related research in the social sciences field. Comprehensive research that includes all fields might produce more beneficial and reliable information. Therefore, this study intends to examine the level of public understanding of rip currents and beach safety knowledge of the Teluk Cempedak Beach. A questionnaire comprising 5 sections and 31 questions was developed as the primary tool in this study. A total of 60 beachgoers have been surveyed for this preliminary study through a questionnaire to investigate their demographic profile, frequency of visiting the beach, swimming ability, and their knowledge of rip currents and beach safety. The results show that the beachgoers have poor knowledge of rip currents. Conversely, they are observed to have higher beach safety knowledge. Also, the findings help in filling the research gaps of this study in terms of the instrument used for the data collection procedure. Above all, an extension of this study may contribute to the development of beneficial tools in assessing public knowledge on beach safety and rip currents throughout Malaysian beaches.Supplementary informationThe online version contains supplementary material available at (10.1007/s11069-021-04613-z).

Quantifying Optically Derived Two-Dimensional Wave-Averaged Currents in the Surf Zone

Complex two-dimensional nearshore current patterns are generated by feedbacks between sub-aqueous morphology and momentum imparted on the water column by breaking waves, winds, and tides. These non-stationary features, such as rip currents and circulation cells, respond to changing environmental conditions and underlying morphology. However, using fixed instruments to observe nearshore currents is limiting due to the high costs and logistics necessary to achieve adequate spatial sampling resolution. A new technique for processing surf-zone imagery, WAMFlow, quantifies fluid velocities to reveal complex, multi-scale (10 s–1000 s meters) nearshore surface circulation patterns. We apply the concept of a wave-averaged movie (WAM) to measure surf-zone circulation patterns on spatial scales of kilometers in the alongshore and 100 s of meters in the cross-shore. The approach uses a rolling average of 2 Hz optical imagery, removing the dominant optical clutter of incident waves, to leave the residual foam or water turbidity features carried by the flow. These residual features are tracked as quasi-passive tracers in space and time using optical flow, which solves for u and v as a function of image intensity gradients in x, y, and t. Surf zone drifters were deployed over multiple days with varying nearshore circulations to validate the optically derived flow patterns. Root mean square error are reduced to 0.1 m per second after filtering based on image attributes. The optically derived patterns captured longshore currents, rip currents, and gyres within the surf zone. Quantifying nearshore circulation patterns using low-cost image platforms and open-source computer vision algorithms presents the potential to further our understanding of fundamental surf zone dynamics.

Automated rip current detection with region based convolutional neural networks

This paper presents a machine learning approach for the automatic identification of rip currents with breaking waves. Rip currents are dangerous fast moving currents of water that result in many deaths by sweeping people out to sea. Most people do not know how to recognize rip currents in order to avoid them. Furthermore, efforts to forecast rip currents are hindered by lack of observations to help train and validate hazard models. The presence of web cams and smart phones have made video and still imagery of the coast ubiquitous and provide a potential source of rip current observations. These same devices could aid public awareness of the presence of rip currents. What is lacking is a method to detect the presence or absence of rip currents from coastal imagery. This paper provides expert labeled training and test data for rip currents. We use Faster R–CNN and a custom temporal aggregation stage to make detections from still images or videos with higher measured accuracy than both humans and other methods of rip current detection previously reported in the literature.

Laboratory experiment of evolution of rip current according to the duration of successive ends of breaking wave crests

Laboratory experiment of evolution of rip current according to the duration of successive ends of breaking wave crests

Beachgoers' ability to identify rip currents at a beach in situ

Abstract. Rip currents (“rips”) are the leading cause of drowning on surf beaches worldwide. A major contributing factor is that many beachgoers are unable to identify rip currents. Previous research has attempted to quantify beachgoers' rip identification ability using photographs of rip currents without identifying whether this usefully translates into an ability to identify a rip current in situ at the beach. This study is the first to compare beachgoers ability to identify rip currents in photographs and in situ at a beach in New Zealand (Muriwai Beach) where a channel rip current was present. Only 22 % of respondents were able to identify the in situ rip current. The highest rates of success were for males (33 %), New Zealand residents (25 %), and local beach users (29 %). Of all respondents who were successful at identifying the rip current in situ, 62 % were active surfers/bodyboarders, and 28 % were active beach swimmers. Of the respondents who were able to identify a rip current in two photographs, only 34 % were able to translate this into a successful in situ rip identification, which suggests that the ability to identify rip currents by beachgoers is worse than reported by previous studies involving photographs. This study highlights the difficulty of successfully identifying a rip current in reality and that photographs are not necessarily a useful means of teaching individuals to identify rip currents. It advocates for the use of more immersive and realistic education strategies, such as the use of virtual reality headsets showing moving imagery (videos) of rip currents in order to improve rip identification ability.