RIP CURRENTS AND THEIR CAUSES

"The outworn dogmas of science seem to be particularly concentrated in the discussions of the ocean in geology books". Beginning with this controversial statement, F. P. Shepard in 1936 tried to lay to rest the concept of the undertow, which had been debated in the pages of Science for over a decade. At the same time, he introduced the term, rip current, to describe the rapidly seaward-flowing currents, which were well-known to lifeguards at that time, as these currents were responsible for carrying swimmers offshore at frightening speeds. Subsequent studies by Shepard and his colleagues (Shepard, Emery and LaFond, 1941; Shepard and Inman, 1950a, 1950b) showed that rip currents (1) are caused by longshore variations in incident wave height, (2) are often periodic in both time and in the longshore direction and (3) increase in velocity with increasing wave height. The major reason put forth to explain the variation in wave height was the convergence or divergence of wave rays over offshore bottom topography (such as submarine canyons) or the forced wave height variability caused by coastal structures, such as jetties. McKenzie (1958) and Cooke (1970) in their studies corroborated the findings of the Scripps Institution of Oceanography researchers and also pointed out the persistence of rip currents (once high energy waves in a storm had caused rip channels to be cut into the bottom) after the storm had abated. In fact it appears that on coastlines which are affected by major storms which build offshore bars, that the nearshore circulation may be dominated by the storm-1-induced bottom topography for long afterwards. The researchers up to the late 1960's who attempted to theoretically model rip currents knew the importance of longshore wave height variability and the wave-induced set-up in the formation of rip currents, but it was not until Longuet-Higgins and Stewart (e.g., 1964) codified the wave momentum flux tensor that great strides were made in providing models for rip currents. This paper is intended to categorize and review the more recent theories for rip current generation and to discuss a simple model for rip currents on barred coastlines.

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RIP - CURRENTS

Coastal Engineering Proceedings ◽

10.9753/icce.v13.32 ◽

1972 ◽

Vol 1 (13) ◽

pp. 32

Author(s):

Edward K. Noda

Keyword(s):

Field Data ◽

Bottom Topography ◽

Circulation Pattern ◽

Rip Current ◽

Rip Currents ◽

Nearshore Zone ◽

Circulation Patterns ◽

Hydrodynamic Processes ◽

Wave Induced ◽

Current Circulation

The generation and stabilization of rip - current circulation patterns is considered herein. An analytic model is developed to simulate the wave hydrodynamic processes in the nearshore zone, strongly influenced by the local bottom topography. The wave induced nearshore circulation pattern is computed and the results compared to prototype field data.

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A FIELD AND NUMERICAL STUDY INTO RIP CURRENTS IN WIND-SEA DOMINATED ENVIRONMENTS

Coastal Engineering Proceedings ◽

10.9753/icce.v33.currents.36 ◽

2012 ◽

Vol 1 (33) ◽

pp. 36

Author(s):

Gundula Winter ◽

Ap Van Dongeren ◽

Matthieu De Schipper ◽

Jaap Van Thiel de Vries

Keyword(s):

Surf Zone ◽

Numerical Study ◽

Warning System ◽

Rip Current ◽

Rip Currents ◽

Mean Flow ◽

Flow Properties ◽

Wind Sea ◽

Wave Induced ◽

Made In

Rip currents are wave-induced and off-shore directed flows which occur frequently in the surf zone and can pose a serious threat to swimmers. While the behaviour of rip currents has been studied in swell-dominated environments, less is known about their characteristics in wind-sea dominated environments. This study aims to improve the knowledge on rip currents in these environments such as the Dutch coast. In a field campaign at Egmond aan Zee (The Netherlands), Lagrangian velocities in the surf zone were measured with drifter floats. An extensive dataset of rip current measurements was collected from which parameters that initiate rip currents and affect their mean flow properties were identified. Numerical simulations with XBeach aided to understand and confirm the observations made in the field. A reduction of the hydrodynamic parameters along with simplification of the bathymetry in the model allowed for identification of the governing rip current parameters, which can be the basis for a warning system.

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ARMOUR UNIT STRUCTURAL RESPONSE - A PARAMETRIC STUDY

Coastal Engineering Proceedings ◽

10.9753/icce.v21.176 ◽

1988 ◽

Vol 1 (21) ◽

pp. 176

Author(s):

C. David Anglin ◽

William F. Baird ◽

Etienne P.D. Mansard ◽

R. Douglas Scott ◽

David J. Turcke

Keyword(s):

Wave Height ◽

Parametric Study ◽

Structural Integrity ◽

Design Procedure ◽

Structural Response ◽

Design Parameters ◽

Coastal Structures ◽

Log Normal ◽

Wave Induced ◽

Hydraulic Stability

There is a general lack of knowledge regarding the nature and magnitude of loads acting on armour units used for the protection of rubblemound coastal structures. Thus, a comprehensive design procedure incorporating both the hydraulic stability and the structural integrity of the armour units does not exist. This paper presents the results of a detailed parametric study of the structural response of armour units to wave-induced loading in a physical breakwater model. The effect of the following design parameters is investigated: breakwater slope, armour unit location, wave period and wave height. This research has made a number of significant contributions towards the development of a comprehensive design procedure for concrete armour units. It has identified a linear relationship between the wave-induced stress in the armour units and the incident wave height. In addition, it has shown that the conditional probability of waveinduced stress given wave height can be estimated by a log-normal distribution. Finally, a preliminary design chart has been developed which incorporates both the structural integrity and the hydraulic stability of the armour units.

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

Natural Hazards and Earth System Science ◽

10.5194/nhess-21-2075-2021 ◽

2021 ◽

Vol 21 (7) ◽

pp. 2075-2091

Author(s):

Elias de Korte ◽

Bruno Castelle ◽

Eric Tellier

Keyword(s):

Bayesian Network ◽

Environmental Conditions ◽

Surf Zone ◽

High Energy ◽

Environmental Data ◽

Tidal Range ◽

Boreal Summer ◽

Rip Current ◽

Rip Currents ◽

Awareness Campaigns

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.

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FLUCTUATION OF RIP CURRENT MEASURED IN SHALLOW WATER REGION WITH SMALL TIDAL RANGE

Coastal Engineering Proceedings ◽

10.9753/icce.v32.currents.44 ◽

2011 ◽

Vol 1 (32) ◽

pp. 44

Author(s):

Ichiro Deguchi ◽

Mamoru Arita ◽

Takumi Yoshii

Keyword(s):

Flow Pattern ◽

Wave Height ◽

Bottom Topography ◽

Low Frequency ◽

Field Measurements ◽

Tidal Range ◽

Sudden Increase ◽

Rip Current ◽

Wave Direction ◽

Frequency Fluctuations

Disappearance and formation processes of rip channel are discussed based on the field measurements of wave height, current velocity, bottom topography and flow pattern of near-shore current. Sudden increase in wave height together with the change in the wave direction took place during a half day caused these phenomena and rip current rose and fell according to the transition of the bottom topography. Furthermore, flow pattern of rip current was not steady but transformed itself with low frequency fluctuations of the period of few minutes. It is found that such low frequency fluctuations are caused by the intrinsic fluctuations of the incident waves (grouping waves) through the numerical simulations.

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NEARSHORE CURRENTS ON A PARTIALLY ROCKY SHORE

Coastal Engineering Proceedings ◽

10.9753/icce.v17.65 ◽

1980 ◽

Vol 1 (17) ◽

pp. 65

Author(s):

T.O. Sasaki ◽

H. Igarashi ◽

S. Harikai

Keyword(s):

Rocky Shore ◽

Surf Zone ◽

High Energy ◽

Sandy Beaches ◽

Physical Experiment ◽

Low Energy ◽

Rip Current ◽

Rip Currents ◽

Wave Regime ◽

Wave Refraction

Nearshore circulation on a partially rocky shore at Haranomachi Beach, Fukushima Prefecture, Japan has been studied in terms of field observations and numerical experiments for a low energy wave regime and with a physical experiment for a high energy wave regime. No significant distinctions were found in current velocity and rip current spacing between rocky and sandy beaches for the low energy wave regime, however the positions of rip currents were affected by wave refraction from the offshore exposed rocky bottom. On the other hand, since the surf zone bed is largely occupied by an exposed rocky floor for the high energy wave regime, the circulation exhibited fairly irregular patterns, so that a rip current becomes difficult to define, however the positions of inflow across the breaker line were found to be coincident with wave convergence zone.

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EFFECT OF RIP CURRENT BARRIER ON HARBOR SHOALING

Coastal Engineering Proceedings ◽

10.9753/icce.v19.140 ◽

1984 ◽

Vol 1 (19) ◽

pp. 140 ◽

Cited By ~ 1

Author(s):

Tamio O. Sasaki ◽

Hiroshi Sakuramoto

Keyword(s):

Surf Zone ◽

Cost Effective ◽

High Energy ◽

Rip Current ◽

Rip Currents ◽

Effective Measure ◽

The Pacific ◽

Small Craft ◽

The Pacific Ocean ◽

Cost Effective Measure

Prototype experiments on rip currents and sediment transport around structures were conducted at two fishery harbors on microtidal high energy beaches facing the Pacific Ocean. The purpose of the experiments was to examine the performance and mechanism of rip current barrier structures on harbor shoaling. Based on the results of five experiments, the wave breaker heights during which varied from 1.1 m to 3.0 m, it is concluded that shore-parallel rip current barriers are effective if their length is greater than the surf zone width and if they are located outside the surf zone. When the above conditions are satisfied, the rip current barrier is a cost-effective measure against shoaling of small craft harbors.

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HYDRAULIC APPROACH TO SHORELINE CHANGE DUE TO SUBMERGED BREAKWATER

Coastal Engineering Proceedings ◽

10.9753/icce.v36v.sediment.40 ◽

2020 ◽

pp. 40

Author(s):

Inho Kim ◽

Hyungseok Lee ◽

Jinhoon Kim ◽

Sungyeol Chang

Keyword(s):

Numerical Analysis ◽

Shoreline Change ◽

Beach Erosion ◽

Rip Current ◽

Rip Currents ◽

Induced Current ◽

Beach Profile ◽

Submerged Breakwater ◽

Sand Movement ◽

Wave Induced

The items of investigation include wave induced current, wave height, beach profile, shoreline change, etc. The investigation has been performed seasonally. After the construction of submerged breakwaters, a tombolo was generated behind the submerged breakwaters. This caused beach erosion in the nearby areas. Rip currents are mainly generated near submerged breakwaters, which plays a role in the transportation of sand in the offshore direction. In order to analyze the sand movement, numerical analysis was conducted. The analysis indicated that a strong rip current is generated near submerged breakwaters.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/5p2wiNSMKlM

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

10.5194/nhess-2021-36 ◽

2021 ◽

Author(s):

Elias de Korte ◽

Bruno Castelle ◽

Eric Tellier

Keyword(s):

Bayesian Network ◽

Environmental Conditions ◽

Surf Zone ◽

High Energy ◽

Environmental Data ◽

Tidal Range ◽

Boreal Summer ◽

Rip Current ◽

Rip Currents ◽

Awareness Campaigns

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 one with a hidden hazard and exposure variables. Both BNs were tested for varying complexity using K-fold cross-validation based on multiple performance metrics. Validation (prediction) results slightly improve predictions of SZIs with a poor to fair skill based on a combination of different metrics. Shore-break related injuries appear more predictable than rip current drowning incidents 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, that 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, presumably because it favors the rapid onset of rip current activity and can therefore surprise unsuspecting bathers. 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 skillful risk predictors to anticipate high life-risk days.

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Dynamicity of multi-channel rip currents induced by rhythmic sandbars

10.5194/nhess-2020-97 ◽

2020 ◽

Author(s):

Yao Zhang ◽

Xiao Hong ◽

GuoDong Xu ◽

Xunan Liu ◽

Xinping Chen ◽

...

Keyword(s):

Wave Height ◽

Incident Wave ◽

Probabilistic Models ◽

Numerical Study ◽

Expected Improvement ◽

Rip Current ◽

Rip Currents ◽

Empirical Formulas ◽

Incident Wave Angle ◽

Wave Angle

Abstract. In response to frequent fatal beach drownings, China's first operational attempt on the rip current hazard investigation was made by the National Marine Hazard Mitigation Service (NMHMS). A great number of recreational beaches were found developing rip currents interlaced with rhythmic sandbars, varying by season and location evidenced by satellite images and morphodynamic calculation. Considering insufficient understanding of the multi-channel rip system, case analysis and numerical study were conducted to explore its dynamicity and circulation characteristics under various wave climates in present work. The strength of rip currents was generally proportional to wave height and channel width under certain limits. Increasing wave height was not always a promotion and could even weaken the rip current due to the strong wave-current shear. Interesting pump and feed interactions between adjacent rip currents in the multi-channel system were observed. The rip current might be totally absent in narrow channels when the majority of water flows through neighboring broader pathways. The rip current was highly sensitive to the incident wave angle. Alongshore currents prevailed over the rip current when the wave angle reached 11 degrees to shore normal, which was not favorable to the existence of channeled sandbars. Vortices appeared around the edge of the bar owing to nonuniform wave breaking over rapid-varying bathymetry. The setup water was created shoreward by the sandbar array and substantially increased as the wave deviated from the normal incidence. The water surface depression in the rip channel was not observed as the wave angle increased, which fundamentally explained why the rip current could not persist when the incident wave became slightly oblique. In future, incident wave angle should be further incorporated into empirical formulas or probabilistic models to predict the rip current for expected improvement in accuracy.

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