NEARSHORE CURRENTS ON A PARTIALLY ROCKY SHORE

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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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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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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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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MODELING SPILLED OIL PARTITIONING IN NEARSHORE AND SURF ZONE AREAS

International Oil Spill Conference Proceedings ◽

10.7901/2169-3358-1985-1-379 ◽

1985 ◽

Vol 1985 (1) ◽

pp. 379-383 ◽

Cited By ~ 4

Author(s):

Erich R. Gundlach ◽

Timothy W. Kana ◽

Paul D. Boehm

Keyword(s):

Wave Energy ◽

Surf Zone ◽

High Energy ◽

Sandy Beaches ◽

Coarse Grained ◽

Tidal Range ◽

Incoming Wave ◽

Fine Grained ◽

Beach Sediments ◽

Rocky Coasts

ABSTRACT The shoreline of a potential spill impact area can be divided into units, each with a specific geomorphology. As oil enters each unit, it will (to varying extents) evaporate, dissolve, interact with suspended particles and sink, biodegrade, photo-oxidize, be transported to the next unit, or strand on the shoreline. In the last case, oil will reenter the aquatic system after a given time and again be exposed to these same processes. For modeling purposes, the world's shorelines can be divided into sedimentary beaches and tectonic rocky coasts, varying in wave energy and tidal range. The size of beach sediments can range from very coarse grained (gravels) to very fine grained (silts and clays). Coarse-grained shorelines have higher incoming wave energy than fine-grained areas. Along all coasts, several partitioning components remain relatively constant for medium to light crude oils, e.g., evaporation (30 to 50 percent) and biodegradation/photo-oxidation (0 to 5 percent). Others may vary substantially. For instance, sedimentation may reach 10 to 20 percent in fine-grained estuaries, but only 0 to 2 percent along high energy coasts having very coarse-grained bottom sediments. Similarly, along sandy beaches the stranding of oil along the shoreline may reach 25 to 35 percent, as compared to only 1 to 2 percent along steep, rocky coasts. Dissolution, in general, does not vary so radically, being approximately 10 to 15 percent along high-energy rocky coasts, as compared to 5 to 10 percent in sheltered estuaries that do not have the mixing energy to drive additional oil into the water column.

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Occurrence features of Rip current at Ha My (Dien Ban district) and Tam Thanh (Tam Ky city) beaches, Quang Nam province

Tạp chí Khoa học và Công nghệ Biển ◽

10.15625/1859-3097/19/4a/14587 ◽

2019 ◽

Vol 19 (4A) ◽

pp. 43-53

Author(s):

Le Dinh Mau ◽

Nguyen Van Tuan ◽

Nguyen Chi Cong ◽

Tran Van Binh ◽

Pham Ba Trung ◽

...

Keyword(s):

Wave Energy ◽

Surf Zone ◽

Transition Period ◽

Current System ◽

Southwest Monsoon ◽

Northeast Monsoon ◽

Rip Current ◽

Rip Currents ◽

Open Sea ◽

Study Results

Rip current is a relatively strong, narrow current flowing outward from the beach through the surf zone and presenting a hazard to swimmers. This paper presents some occurrence features of Rip current at main swimming beaches in Quang Nam province, Central Vietnam. Study results show that most of swimming beaches along Quang Nam province coast are directly opposed to open sea and strongly affected by swell. Therefore, Rip current system can occur at any time in the year with large dimension and intensity. During Northeast monsoon (November to March) beach morphology is considerably changed by strong wave action, thus the strongest rip current is formed. However, in this period careful swimmers can easily identify where that rip current occurs along the beach. During the transition period from Northeast monsoon to Southwest monsoon (April to May) wave energy is reduced, thus Rip current intensity is also decreased. During Southwest monsoon (June to August) wave energy is not strong and beach is accreted, therefore some Rip currents remain at reasonable morphology places along the beach. During the transition period from Southwest monsoon to Northeast monsoon (September to October) Rip current can occur at deep places along the beach with characteristics of narrow dimension, thus causing more danger to swimmer. Especially, dangerous rip current is caused by swell which comes from active region of tropical cyclone in open sea. In this period wave field in the nearshore region is not rough, thus most of swimmers are not cautious when swimming at dangerous rip current places.

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Self-organization mechanisms for the formation of nearshore crescentic and transverse sand bars

Journal of Fluid Mechanics ◽

10.1017/s002211200200112x ◽

2002 ◽

Vol 465 ◽

pp. 379-410 ◽

Cited By ~ 64

Author(s):

M. CABALLERIA ◽

G. COCO ◽

A. FALQUÉS ◽

D. A. HUNTLEY

Keyword(s):

Surf Zone ◽

Sediment Concentration ◽

High Energy ◽

Feedback Mechanism ◽

Energy Conditions ◽

Wave Refraction ◽

Sand Bars ◽

Coastal Marine ◽

Planar Slope ◽

First Time

The formation and development of transverse and crescentic sand bars in the coastal marine environment has been investigated by means of a nonlinear numerical model based on the shallow-water equations and on a simplified sediment transport parameterization. By assuming normally approaching waves and a saturated surf zone, rhythmic patterns develop from a planar slope where random perturbations of small amplitude have been superimposed. Two types of bedforms appear: one is a crescentic bar pattern centred around the breakpoint and the other, herein modelled for the first time, is a transverse bar pattern. The feedback mechanism related to the formation and development of the patterns can be explained by coupling the water and sediment conservation equations. Basically, the waves stir up the sediment and keep it in suspension with a certain cross-shore distribution of depth-averaged concentration. Then, a current flowing with (against) the gradient of sediment concentration produces erosion (deposition). It is shown that inside the surf zone, these currents may occur due to the wave refraction and to the redistribution of wave breaking produced by the growing bedforms. Numerical simulations have been performed in order to understand the sensitivity of the pattern formation to the parameterization and to relate the hydro-morphodynamic input conditions to which of the patterns develops. It is suggested that crescentic bar growth would be favoured by high-energy conditions and fine sediment while transverse bars would grow for milder waves and coarser sediment. In intermediate conditions mixed patterns may occur.

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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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RIP CURRENTS AND THEIR CAUSES

Coastal Engineering Proceedings ◽

10.9753/icce.v16.83 ◽

1978 ◽

Vol 1 (16) ◽

pp. 83 ◽

Cited By ~ 2

Author(s):

Robert A. Dalrymple

Keyword(s):

Wave Height ◽

Bottom Topography ◽

High Energy ◽

Rip Current ◽

Rip Currents ◽

Coastal Structures ◽

Submarine Canyons ◽

Set Up ◽

Wave Induced ◽

Made In

"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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Analysis of Rip Current Characteristics Using Dye Tracking Method

Atmosphere ◽

10.3390/atmos12060719 ◽

2021 ◽

Vol 12 (6) ◽

pp. 719

Author(s):

Hyun Dong Kim ◽

Kyu-Han Kim

Keyword(s):

Surf Zone ◽

Breaking Waves ◽

Rip Current ◽

Rip Currents ◽

Induced Current ◽

Tracking Method ◽

Survey Techniques ◽

Current Characteristics ◽

Bed Material ◽

Wave Induced

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.

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