Rip Current Dynamics Research Articles

Tidal and wave modulation of rip current dynamics

Rip currents have become the primary coastal hazard globally with direct implications for surf-zone recreational safety. Among 101 China's recreational beaches, headland bay with large tidal range and wave-dominated sandbar shorelines are identified with high occurrence risk of rip currents by the morphodynamic assessment. The variability of rip current under tidal and wave modulation is explored by the case simulations. At macro-tidal pocket beach, the strongest rip currents occur in ebb, 20%–50% faster than that during flood, while offshore flows are barely developed at low tide. This asymmetry depends on the quasilinear superimposition of wave-driven and tidal currents. Nearshore circulations are found not sensitive to the wave direction in a macro-tidal environment. For sandbar morphology with weak tidal variations, rip currents are best developed towards low tide with maximum topographic effect on wave dissipation and show high sensitivity to the incident wave angle. The magnitude of vortex increases with wave angle but is not explicitly related to wave height. Rip currents are mostly suppressed by oblique incident waves while the offshore flow may get strengthened as incoming waves slightly deviate from normal incidence when the wave height is small. The decay of rip currents with wave angle did not show clear dependence on channel width which was found in other literatures. The incident wave angle should be incorporated into existing statistical methods or probabilistic models to improve the accuracy of rip current prediction.

A 15-year partnership between UK coastal scientists and the international beach lifeguard community

Drowning is a leading cause of unintentional fatalities around the world, yet on beaches is often preventable through public education campaigns and intervention activities from lifeguards. In 2006, the UK beach lifeguarding community approached the Coastal Processes Research Group (CPRG) at University of Plymouth, UK, with a need to better understand the key hazards on UK beaches and how to foresee and manage the associated risks. In some cases there simply was not sufficient scientifically-robust understanding of certain hazards (for example rip currents) available for lifeguard managers to make objective, data-driven decisions on how to manage them. This paper documents the resulting 15-year body of work, and reflects upon the education, outreach, and other research impacts that have been created, and lessons learned along the way. By furthering fundamental coastal processes understanding of such things as beach classification and rip current dynamics, as well as applying science to challenges such as predicting beach life-risk and times of peak bathing hazard, the ongoing collaboration between lifeguards and academics continues to inform beach safety management in a number of countries around the world. Initiating research with clear aims and objectives that are driven by, and developed in conjunction with, the end-user, as opposed to starting with outcomes prescribed to the end-user by academics, has been an important factor in the success (or failure) of these scientific ventures. CPRG's research activities in the field of beach safety has been scientifically rewarding and have achieved significant impacts. We attribute this to: (1) sustained level of high-quality research; (2) continued effort spent on building long-term relationships with end-users; (3) co-creation of dissemination material and tools; (4) acceptance that it takes time and effort to achieve research impact; and (5) critically evaluating and reflecting on the research impacts. Ultimately, the ongoing collaboration has contributed to a ‘continuing trend of decline in accidental fatalities around our coastlines’, and such collaborations in other parts of the world continue to play a vital role in reducing coastal drowning globally.

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.

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.

Rip currents in the southern Baltic Sea multi-bar nearshore zone

Rip currents in the southern Baltic Sea coastal zone are one of the most incompletely known and least explored hydrodynamic phenomena. As they are rare, discussion on their nature, their contribution to the complex pattern of nearshore currents, and their effect on, inter alia, the seafloor transformations is still on-going. Observations made during this study confirmed the occurrence of rip currents at the southern Baltic Sea shore. During field surveys in 2011–2013, Lagrangian measurements taken using novel GPS-tracked drifters revealed several flow events with features characteristic of rip currents. At the same time, numerical calculations produced a three-dimensional wave-current field in the surf zone. Both the measurements and numerical modelling made it possible to follow the rip current dynamics in the area of study and to compare the rip currents observed with those known from other reflective coasts. In addition, wave action-related and bathymetric conditions conducive to the rip current emergence were identified, and the relationship between the rip current velocity, wave regime and local seafloor morphology was explored. The results confirm the theory of rip currents at dissipative shores emerging at the prevalence of fairly flat long waves. Such conditions are typical at swells, i.e., during storm abatement.

Rip current hazard assessment on a sandy beach in Liguria, NW Mediterranean

Rip currents are one of the most significant environmental hazards for beachgoers and are of interest to coastal scientists. Several studies have been conducted to understand rip current dynamics, and several approaches for rip hazard assessment have been proposed. In general, the purpose is to provide knowledge and tools to support authorities and lifeguards in rip current risk prevention. This study proposes the application of an expeditious methodology to evaluate rip current hazard and risk, based on probability theory. The tested area was located along the Alassio beach, a renowned tourist destination located on the western Ligurian coast (NW Italy). A coastal video-monitoring system was used for rip currents individuation, whereas wave data were collected thanks to an oceanographic buoy managed by Regione Liguria. In detail, a yearly analysis was performed to identify the correspondence between rip currents and wave parameters data. The results showed that rip currents occur, in the study area, under moderate wave conditions (0.5 le H_s le 1.34 m; 4.7le T_m le 7.0 s; 150^{circ },hbox {N} le theta _m le 227^{circ } N). Based on this analysis, an easy application of the probability theory was applied to evaluate the level of hazard. Moreover, considering the official tourist data, we also perform an expeditious rip currents risk evaluation. The results showed that the hazard level is considered high at annual time scale and moderate during the tourist season; the risk is related to seasonal presences. The study can propose a tool to support authorities and lifeguards in water safety planning and management.

Pulsations in Surf Zone Currents on a High Energy Mesotidal Beach in New Zealand

ABSTRACT Gallop, S.L.; Bryan, K.R.; Pitman, S.J.; Ranasinghe, R., and Sandwell, D., 2016. Pulsations in surf zone currents on a high energy mesotidal beach in New Zealand. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 378–382. Coconut Creek (Florida), ISSN 0749-0208. The exchange of material between the surf zone and continental shelf can be driven by pulsations in rip current velocities. However, there is a poor understanding of the relationship of these pulsations to surf zone morphology and material exchange. Moreover, understanding of rip current dynamics has focused mainly on single-barred beaches in an intermediate state, and there have been few studies on high energy beaches. Therefore, this paper undertakes preliminary research on surf zone current velocity pulsations, on a high energy beach in New Zealand. This initial analysis presents...

Dynamics of rip currents associated with groynes — field measurements, modelling and implications for beach safety

Rip currents can occur around groynes and other coastal structures (e.g. breakwaters and geological headlands), which provide a boundary to the wave-induced flow field and present a hazard to water users worldwide. Shore-normal groynes are common along drift-aligned coasts. In northern Europe these are often low-energy, fetch-limited environments that are dominated by locally generated wind waves. The presence of boundary-controlled rip currents due to groynes is supported anecdotally in literature, but few field measurements of their presence and dynamics exist. This study provides new quantitative scientific understanding of the dynamics of boundary-controlled rip currents within this setting. A 10-day field experiment at Boscombe beach on the south coast of England measured rip currents and nearshore hydrodynamics around an impermeable groyne field. Observations from both fixed instruments (wave, tide and current metres) and GPS-drifters confirmed the presence and characteristics of hazardous topographic rip currents around a groyne structure during a number of oblique wave events and drift reversals. The strongest offshore-directed rip velocities of up to 1ms−1 (10-min average) and 2ms−1 (instantaneous) were measured on the updrift side of the groyne where the longshore current generated within the embayment was deflected offshore. These strong rip flows were measured under relatively small wave heights (Hs<1m) and presented a significant bathing hazard. A calibrated and validated numerical model (XBeach) was used, in support of measured data, to explore the key environmental controls on rip behaviour across a range of groyne configurations and wave conditions not observed in the field. Key outcomes were that: 1) upstream deflected rip flows were found to be strongly correlated to the alongshore thrust due to wave forcing; 2) the groyne length relative to surf zone width strongly controlled the offshore extent of rip flows, with a significant increase in surf zone exits above a relative groyne length (length/surf width) of 1.25; and 3) rip flows increase up to a relative groyne spacing (spacing/length) of around 4–6, above which alongshore currents are fully developed. These findings have been distilled into some key principals that are relevant to the assessment of boundary-controlled rip hazard on beaches.

Public Understanding and Knowledge of Rip Currents and Beach Safety in the UK

Rip currents present a severe hazard for water users on beaches and account for the greatest cause of lifeguard rescues worldwide. The physical dynamics of rip currents are well studied, and more recently, the social and behavioural science research surrounding human interaction of rip currents has been expanding, providing a social perspective and feeding into public education strategies. The aim of this study was to assess levels of public understanding of rip currents and beach safety on UK beaches. A questionnaire was undertaken (N = 407) during the summer of 2012 on four beaches. Beach users had a poor knowledge of rip currents (n = 263), but those who have been caught in a rip have a higher level of knowledge. Conversely, beach users had a good understanding of what the beach safety flags indicated (n = 314), and most people complied with this flag system (n = 339). In addition, people previously educated on rip currents had a higher knowledge, and lifeguards proved to be the most effective form of education. The study presents an insight into UK beach users’ knowledge of rip currents and provides more evidence with which to pilot a rip current education scheme within the UK.

Public Understanding and Knowledge of Rip Currents and Beach Safety in the UK

Rip currents present a severe hazard for water users on beaches and account for the greatest cause of lifeguard rescues worldwide. The physical dynamics of rip currents are well studied, and more recently, the social and behavioural science research surrounding human interaction of rip currents has been expanding, providing a social perspective and feeding into public education strategies. The aim of this study was to assess levels of public understanding of rip currents and beach safety on UK beaches. A questionnaire was undertaken (N = 407) during the summer of 2012 on four beaches. Beach users had a poor knowledge of rip currents (n = 263), but those who have been caught in a rip before have a higher level of knowledge. Conversely, beach users had a good understanding of what the beach safety flags indicated (n = 314), and most people complied with this flag system (n = 339). In addition, those previously educated on rip currents had a higher knowledge, and lifeguards proved to be the most effective form of education. The study presents an insight into UK beach users’ knowledge of rip currents and provides more evidence with which to pilot a rip current education scheme within the UK.

Non-hydrostatic Modeling of Wave Transformation and Rip Current Circulation: A Case Study for Haeundae Beach, Korea

ABSTRACT Yoon, J. J., 2014. Non-hydrostatic modeling of wave transformation and rip current circulation: a case study for Haeundae Beach, Korea. Haeundae Beach in Busan, South Korea, is one of the most popular destinations in South Korea, but poses the danger of irregular, fast moving rip currents. To investigate the dominant mechanism of rip currents in this region, a numerical simulation was carried out using the non-hydrostatic model Surface WAves till SHore (SWASH), with observed wave and topographical data. In this paper, the applicability of SWASH for modeling the wave transformation and rip current circulation near the shallow foreshore is investigated. Assuming that rip current dynamics are controlled by combination of variations in wave dissipation and morphological flow constriction, we tested the effects of wave parameters, such as wave heights, wave periods, wave directions, and changes in tidal conditions, on rip current generation. The model results showed good agreement with previous studie...

Water-level controls on macro-tidal rip currents

Field measurements and numerical modelling have been used to investigate the water-level control of rip current dynamics on a macro-tidal beach. Field data collected over 32 complete tidal cycles, spanning a range of wave and tide conditions, demonstrate that rip current strength and behaviour is modulated at the semi-diurnal frequency by tide-induced changes in the water-level over bar/rip morphology. Peak flow speeds in the rip neck 〈uv〉 correspond to the time of maximum wave breaking 1.5h before and after low water.Alongshore-directed water surface gradients ∂η/∂y were measured along the feeder channel and around the ends of the inter-tidal bar, with head differences O(0.1m). The numerical model reproduced ∂η/∂y with a good level of skill and showed that ∂η/∂y and 〈uv〉 increase with the proportion of breaking waves Qb over the inter-tidal bar; but 〈uv〉 was maximised during peak Qb, maximum ∂η/∂y occurred when wave breaking moved offshore to the sub-tidal bar and Qb was reduced. Around low water, the forcing of the rip current by the alongshore pressure-driven feeder current was reduced by the decrease in Qb over the bar and feeder regions, but an offshore flow through the rip channel was maintained by a localised intensification of ∂η/∂y around the ends of the inter-tidal bar.

Rip Current Prediction: Development, Validation, and Evaluation of an Operational Tool

ABSTRACT Austin, M.J.; Scott, T.M.; Russell, P.E., and Masselink, G., 2013. Rip current prediction: development, validation, and evaluation of an operational tool. This contribution details the development, validation, and evaluation of an operational rip current prediction tool. Field measurements of rip current dynamics from a macrotidal beach in the southwest U.K. collected over 87 tidal cycles indicate that the rip currents are highly dynamic over a range of temporal and spatial scales. The morphology of the lower intertidal beach face provides the primary spatial control of the rip currents, whereas the variation in the pattern of wave dissipation due to the tidal translation of the surf zone at spring-neap and semidiurnal frequencies is the principle temporal control. The Lagrangian drift pattern associated with the rip currents displays three key behaviors: rotation, alongshore, and exit. Rotation and exit are observed under moderate conditions, whereas strong alongshore-directed currents prevail d...

Temporal observations of rip current circulation on a macro-tidal beach

A field experiment was conducted on a high energy macro-tidal beach (Perranporth, UK) to examine rip current dynamics over a low-tide transverse bar/rip system in response to changing tide and wave conditions. Hydrodynamic data were collected using an array of in situ acoustic doppler current meters and pressure transducers, as well as 12 GPS-tracked Lagrangian surf zone drifters. Inter-tidal and sub-tidal morphology were measured through RTK-GPS and echo-sounder surveys. Data were collected for eight consecutive days (15 tides) over a spring-neap tidal cycle with tidal ranges of 4–6.5 m and offshore significant wave heights of 1–2 m and peak periods of 5–12 s. The hypothesis that rip current dynamics in a macro-tidal setting are controlled by the combination of variations in wave dissipation and morphological flow constriction, modulated by changes in tidal elevation was tested. During the measurement period, rip circulation was characterised by a large rotational surf zone eddy O(200 m) extending offshore from the inner-surf zone to the seaward face of the inter-tidal transverse bar. During high- and mid-tide, water depth over the bars was too deep to allow wave breaking, and a strong longshore current dominated the surf zone. As the water depth decreased towards low-tide, wave breaking was concentrated over the bar crests initiating the rotational rip current eddy. Peak rip flow speeds of 1.3 m s −1 were recorded around low-tide when the joint effects of dissipation and morphological constriction were maximised. At low tide, dissipation over the bar crests was reduced by partial bar-emergence and observations suggested that rip flows were maintained by morphological constriction and the side-drainage of water from the transverse bars.

The dynamics of the littoral zone

We review some of the properties of surface gravity waves and look at their modification as they enter the littoral zone. Theoretical and experimental modeling of processes pertaining to the near shore are discussed and compared with field observations. In particular we review the present knowledge pertaining to the dynamics of rip currents, longshore currents, and computer modeling of beach deformation due to wave‐induced erosion or accretion.

On energy coupling between waves and rip currents

The theory of rip currents has been extended to include energy exchange between the waves and the rip currents that they produce. This added coupling does not modify the flow field appreciably but changes the wave energy distribution across the surf zone. It is also found that for the same flow field the longshore varying energy density at the breaker line (which causes the currents) is now increased: the energy interaction resists the flow, and larger wave perturbations are needed to induce rip currents. A criterion for rip spacing is advanced, based on a minimization of the relative rate of energy dissipation. The results obtained with this criterion do not compare well with observations and indicate that lateral friction, neglected in this model, should play a significant role in the dynamics of rip currents.

Comment on paper by C. K. W. Tam, ‘Dynamics of rip currents’

Comment on paper by C. K. W. Tam, ‘Dynamics of rip currents’

Reply [to “Comment on paper by C. K. W. Tam, ‘Dynamics of rip currents’”

Reply [to “Comment on paper by C. K. W. Tam, ‘Dynamics of rip currents’”

Dynamics of rip currents

The dynamics of rip currents is investigated using a set of shallow water equations with a horizontal eddy viscosity term. A boundary layer analysis is introduced based on the observed fact that rip currents are rather narrow. Similarity solutions of the model equations are found which seem to give reasonable representations of the velocity profile and other characteristics of rip currents. The mechanisms that are believed to be responsible for the formation of rip heads are studied. The turning of rip currents due to the longshore momentum carried by the entrained fluid is analyzed.

A note on the dynamics of rip currents

A vorticity equation is applied to the flow of a rip current that transports water seaward through a surf zone. If a column of water stretches vertically as it moves into deeper water, the magnitude of the vorticity will increase along the streamline. An approximate solution indicates that the width of the current decreases as the depth increases. This action of the nonlinear inertial terms may help to explain the maintenance of a relatively narrow, concentrated pattern of streamlines observed in rips.