Rip Currents Research Articles

The Effect of Stokes Drift and Transient Rip Currents on the Inner Shelf. Part I: No Stratification

AbstractThis is part one of a two-part study focused on Stokes drift and transient rip current (TRC) effects on the unstratified (this paper) and stratified (see Part II) inner shelf. A TRC-generating, wave-resolving model funwaveC is coupled to the 3D, wave-averaged wave and circulation model Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST). Two simulations (R1 and R2) are performed on an unstratified inner shelf and surfzone with typical bathymetry and wave conditions. R1 is a COAWST-only simulation (no TRCs), while R2 has funwaveC–COAWST coupling (with TRCs). R2 and funwaveC vertical vorticity (eddy) statistics are similar, indicating that the model coupling accurately generates TRCs, with TRC-induced eddies out to four surfzone widths offshore. R1 has a two-layered, inner-shelf-to-surfzone-connected, mean Lagrangian circulation, while R2 has separate inner shelf and surfzone circulation cells. The R2, TRC-induced, cross-shore and vertical eddy velocities are stronger than the R1 or R2 mean Lagrangian velocity out to four surfzone widths offshore. The R2, inner-shelf, mean, vertical eddy diffusivity is an order of magnitude larger than R1 out to four surfzone widths offshore. Both R1 and R2 are in a Stokes–Coriolis balance at six surfzone widths offshore, as is R1 at three surfzone widths offshore. For R2, TRC-induced horizontal advection and vertical mixing dominate the cross-shore momentum dynamics at three surfzone widths offshore. The R2 surfzone and inner-shelf cross-shore exchange velocity is 2–10 times larger for R1 because of the TRC-induced stirring. Accurate, unstratified, inner-shelf simulations of pollution, larval, or sediment transport must include transient rip currents. In Part II, the effects of Stokes drift and TRCs on the stratified inner shelf are examined.

Beach Morphodynamics of an Atlantic Coast Embayment: Runkerry Strand, County Antrim

Runkerry Strand is exposed to high energy Atlantic wind and wave processes. Rhythmic topography found on the beach and in the nearshore zone includes beach cusps, rip current channels, longshore rip feeder channels, rip current embayments (giant cusps), transverse and crescentic bars. Changes in beach/nearshore zone morphology are cyclic and although no link with incident wave power was demonstrated, it is suggested that the Australian beach state model is applicable. Sand is moved seawards by rip currents which scour the sea bed. exposing an underlying gravel frame, and returns landwards on migrating crescentic bars which become welded to the upper beach.

Water Safety and Aquatic Recreation among International Tourists in New Zealand

Little is known about the water safety knowledge, attitudes, and behaviors of international tourists holidaying in New Zealand. An online survey was conducted among New Zealand residents (n = 413) and international tourists (n =181) in August 2015. Significantly more New Zealand residents (69%) than tourists (40%) reported swimming at a beach. Tourists were more likely to hold unsafe beliefs related to swimming and boating activity. More tourists agreed that they would swim at a non-patrolled beach. Both residents and visitors had a poor understanding of rip currents at surf beaches. Ways of promoting water safety messaging to address these shortcomings are discussed. Language: en

Case Study of Rip Current Knowledge amongst Students Participating in a Study Abroad Program

Students studying abroad or participating in a foreign exchange often visit a beach during their time abroad, but little is known about their understanding of rip currents and other surf hazards, their behavior, their choices, or if they take precautions when visiting a beach. This study describes the results of a survey of Texas A&M University students who completed a study abroad program between May 2013 and May 2015. Results of the survey suggest that a majority of the students surveyed (~74%) visited at least one beach during their time abroad, and over 50% of students visited more than 2 beaches. The visit to the beach was optional for most of the respondents and most went as part of a group. Decisions about the beaches visited tended to be based on convenience and recommendations from other students, tourists, or locals, and were rarely based on safety. Results of this preliminary study point to a need for implementing proactive beach safety education programs for students studying abroad.

Wave breaking patterns control rip current flow regimes and surfzone retention

Recent research into rip currents has revealed the existence of multiple circulation patterns, meaning that no single escape strategy is appropriate in all situations. Rip circulation is influenced by surfzone morphology, which can be inferred from wave breaking patterns in video imagery. Wave breaking often occurs over the bars adjacent to the rip channel, with little breaking over the seaward end of the rip. However, under varying wave and tide conditions, breaking can also occur at the seaward extent of rip channels. Here, we use this difference as a novel wave dissipation parameter to classify a rip channel as either ‘open’ or ‘closed’ in terms of rip-head wave breaking. A 4-day field study provided Lagrangian rip current data at a macrotidal, dissipative beach monitored by a coastal imaging system. Using this new parameter, rip channels that were identified as closed exhibited a 31% increase in current speeds and 43% increase in horizontal vorticity compared to open channels. The transition between open and closed channels occurred over a single tidal cycle, which altered surfzone retention rates. Closed channels promoted surfzone retention, with <25% of drifters exiting the surfzone. In comparison, open channels were more conducive to exchange, with exit rates up to 91%. Analysis of the Royal National Lifeboat Institution lifeguard rip incident database showed that open rips were disproportionately represented in the occurrence of rescue events, and calculated here to be twice as dangerous as closed rips. The use of this new open/closed parameter could be used by surf lifesaving organisations, and may have implications for the cross-shore exchange of sediment and pollutants.

Surfzone hydrodynamics as a key determinant of spatial variation in rocky intertidal communities.

Larvae of intertidal species develop at sea and must return to adult habitats to replenish populations. Similarly, nutrients, detritus and plankton provide important subsidies spurring growth and reproduction of macroalgae and filter-feeding invertebrates that form the foundation of intertidal communities. Together, these factors determine the density and intensity of interactions among community members. We hypothesized that spatial variation in surfzone hydrodynamics affects the delivery of plankton subsidies. We compared entire zooplankton communities inside and outside the surf zone daily while monitoring physical conditions for one month each at two shores with different surfzone characteristics. Opposite cross-shore distributions of larvae and other zooplankters occurred at the two sites: zooplankton was much more abundant inside the mildly sloping dissipative surf zone (DSZ) with rip currents and was more abundant outside the steep reflective surf zone (RSZ). Biophysical numerical simulations demonstrated that zooplankters were concentrated in rip channels of the DSZ and were mostly unable to enter the RSZ, indicating the hydrodynamic processes behind the observed spatial variation of zooplankters in the surf zone. Differences in the concentration of larvae and other zooplankters between the inner shelf and surf zone may be an underappreciated, key determinant of spatial variation in inshore communities.

Rip current tomography based on reciprocal sound transmissions using reflective waves

In order to monitor the occurrence of rip current in beaches, an acoustic measurement system for rip currents based on passive reciprocal sound transmissions using reflective waves was designed and developed. The offshore current velocity V is given by V = C0 2/L*(t21-t12)/2 where C0 is sound speed, L is the distance between the transducers, t21 is travel time at onshore transmission, and t12 is travel time at offshore transmission. The typical components of the measurement system consisted of one modified dual-frequency sounder, two broad-band acoustic transducers, six sound reflectors, and a data acquisition network. The frequency, source level, and transmission interval of transmitted signal was 50 kHz, 1 kW (max), and 2 s, respectively. The typical monitoring area is 30 m wide and 90 m long, and the depth is 1 m. This system simply required the precise position measurement of two transducers and sound reflectors. The sound speed was determined by the direct travel times between the transducers. When the field tests were conducted at Uradome Beach in Tottori Prefecture of Japan in September of 2014, the phases of sound signals were so stable to allow the automatic peak and/or phase tracking. The obtained and reconstructed velocity data were consistent with those by EM current meters.

Morphodynamic changes as an impact of human intervention at the Ras El-Bar-Damietta Harbor coast, NW Damietta Promontory, Nile Delta, Egypt

Due to the absence of a national strategic plan for coastal management, the Nile Delta coast is no longer described as a fully dissipative, divergent, low-gradient beach face composed of fine to very fine sand. Instead, new patterns have emerged depending on rock type, geomorphology of the coast, direction of the shoreline in relation to waves and current, and the implemented defense measures. This study attempts to record the morphodynamic changes which occurred due to human intervention. Landsat satellite images acquired for the periods of time of 1973, 1984, 1989, 2003, and 2015 are used together with geomorphologic observations in order to monitor the changes along the coastal strip between Ras El-Bar and Damietta Harbor. This study reveals two beach segments; one of which lies to the east, it is protected with detached breakwater system, and shows average shoreline accretions of +4.73 myr−1, +5.0 myr−1, and +0.89myr−1 during the periods of 1984–1998, 1998–2003, and 2003–2015 respectively. This segment still has the geomorphologic imprints of the dissipative beach, wave divergence, low-gradient beach face, fine grained sand and spilling breakers. The second is to the west, between the detached breakwaters and the eastern jetty of the Damietta Harbor. It is an erosional segment with shoreline retreat of −7.43 myr−1, −10.90 myr−1, and −3.11myr−1 for the same periods. This segment shows intermediate “d” beach or intermediate-reflective, wave convergence, rip currents, with the characteristic steep sloped and cuspate beach face, cliffy, reworked sediments of coarse grained sands, mud clasts, discoidal gravels, shelly beach, and plunging breakings. The presence of convergent waves along this segment confirms the concept of an emergence of a new wave pattern of reversed eddy which enhances the steepness of the beach face, accelerates erosion, and increases the possibility of drowning of swimmers at Ras El-Bar resort. Under such circumstances the plunge step approaches the shore and its shell content forced by wave to accumulate forming the shelly beach. To secure the coastal strip against erosion and sea level changes the detached breakwaters should be extended to reach the eastern jetty of the Damietta Harbor. The protection of this segment is a matter of interest for investment projects related to industries and trading along the Damietta Harbor as well as the touristic investments at Ras El-Bar, as one of the important tourist destinations in Egypt. Millions of pounds spent by beach visitors and investment annually provide significant input to local and regional economy. Hazards associated with the morphodynamic effects on recreational beaches can influence the suitably of any given stretch of coast as a recreational resource, and thus impact tourist money spent in addition to the safety and well-being of beach visitors.

A mixed solution for a highly protected coast (Punta Marina, Northern Adriatic Sea, Italy)

Spatial data collected over three years are presented to assess the impacts of a mixed intervention carried out in a low sandy microtidal highly protected beach (Punta Marina, Italy). Coastal erosion started in the 1980s, principally due to reduction of fluvial sediment discharges, wave attack, and both anthropic and natural subsidence. The intervention consisted in a small beach nourishment, shallow feeder berm construction, and the placement of an artificial reef to retain the sand fill. Topo-bathymetrical surveys with Real-Time Kinematic (RTK) GPS, multi-beam surveys, sediment samplings, wave data records, dive inspections and numerical simulations were undertaken over a 3-year monitoring period to analyse the process-response mechanism of this intervention, to assess the main factors affecting the performance of the mixed intervention and the possibility of using fine sediments for nourishment practices.The results reveal a generally positive impact characterised by short-term beach stability that was mostly due to the feeder berm effect. The beach nourishment had a short but direct effect on the beach width, while the feeder berm dissipated wave energy and successively fed the nearshore with eroded sediment. On the other hand, the artificial reef did not retain the sand, but rather induced rip currents that increased eddy circulation and, therefore, promoted the loss of offshore sediment. Settlement and scouring problems were also observed and the structure's failure induced safety problems.The results confirm that a feeder berm operation carried out with fine sediment represents a good solution, although particular attention must be paid to the relationship between sediment grain sizes, volume, and location of the nourishment, as they are the key factors for good performance. Finally, the cross-shore sediment transport represents a critical factor that controls the coastal evolution of beaches bounded by hard structures and assimilated to the littoral cell. Consequently, it should be better integrated within the nourishment design and model setting.

Sistem Informasi Geografis Risiko Kemunculan Rip Current Menggunakan Decision Tree C4.5

One of the dangers that occur at the beach is rip current. Rip current poses significant danger for beachgoers. This paper proposes a method to predict the rip current's occurence risk by using decision tree generated using C4.5 algorithm. The output from the decision tree is rip current's occurrence risk. The case study for this research is the beach located at Rote Island, Rote Ndao, Nusa Tenggara Timur. Evaluation result shows that the accuracy is 0.84, and the precision is 0.61. The average recall value is 0.68 and the average F-measure is 0.59 in the range 0 to 1.

The Assesement of Rip Current at Kerachut Beach Using Hydrodynamic Modelling

KerachutBeach is a beautiful beach in Penang National Park (PNP). However this beach is categorisedas one of dangerous beach for swimming activities in Malaysia due to the drowning incidents reported almost every year. The steep beach slope and rip current were among the factors that lead to this incident. Using bathymetry profile, current, tidal and sediment data collected at site incorporated with UKMO wave data analysis,the hydrodynamic pattern was simulated using Mike 21 modelling software. Result from the model showed the evidence of rip current existence along the coastline. It showed that this rip current eventsoccurred during spring tide phase when the flow change from Flood to Ebb. During this period, the current tend to move parallel to the shoreline with maximum speed of 0.3m/s which is capable to swipe away a swimmer. The bathymetry profile at Kerachutis very steep and dangerous to swimmers since there is a 4 meter sudden plunge just meters away from the shoreline.

Shoreline variability of an urban beach fronted by a beachrock reef from video imagery

This contribution presents the results of a study on the shoreline variability of a natural perched urban beach (Ammoudara, N. Crete, Greece). Shoreline variability was monitored in high spatio-temporal resolution using time series of coastal video images and a novel, fully automated 2-D shoreline detection algorithm. Ten-month video monitoring showed that cross-shore shoreline change was, in some areas, up to 8 m with adjacent sections of the shoreline showing contrasting patterns of beach loss or gain. Variability increased in spring/early summer and stabilized until the end of the summer when partial beach recovery commenced. Correlation of the patterns of beach change with wave forcing (as recorded at an offshore wave buoy) is not straightforward; the only discernible association was that particularly energetic waves from the northern sector can trigger changes in the patterns of shoreline variability and that increased variability might be sustained by increases in offshore wave steepness. It was also found that the fronting beachrock reef exerts significant geological control on beach hydrodynamics. Hydrodynamic modelling and observations during an energetic event showed that the reef can filter wave energy in a highly differential manner, depending on its local architecture. In some areas, the reef allows only low-energy waves to impinge on the shoreline, whereas elsewhere penetration of higher waves is facilitated by the low elevation and limited width of the reef or by the presence of an inlet. Wave/reef interaction can also generate complex circulation patterns, including rip currents that appeared to be also constrained by the reef architecture.

Rip currents: The dangers of nuclear-armed submarine proliferation

ABSTRACTWhen it comes to nuclear-armed submarines, the global status quo is transforming rapidly. During the Cold War and its immediate aftermath, there was more or less a dynamic equilibrium, in which sea-based nuclear forces were limited to the navies of the United States, Russia, France, the United Kingdom, and to some degree, China. But over the past several years, new players have entered the scene – including India, Pakistan, North Korea, and Israel – which means that stability is becoming challenged while the number of weapons in the arsenals of newer nuclear powers increases. This is ironic because the principal purpose of sea-based nuclear forces, in theory, is to bolster deterrence stability by increasing the survivability of one’s arsenal. Yet these weapons, when brandished by countries locked in enduring rivalries and frozen conflicts, could just as easily provoke miscalculation and accidental war due to chance encounters between nuclear-capable submarines and opposing naval forces, lapses in human judgment, and imperfect command and control.

Modeling surfzone to inner‐shelf tracer exchange

AbstractA near‐shoreline, continuous dye release at an approximately alongshore‐uniform beach (IB09 experiment) is simulated with the wave‐resolving Boussinesq model funwaveC. The model generates surfzone eddies and transient rip currents but does not resolve inner‐shelf vertical variation or stratification. The funwaveC model reproduces well the observed surfzone and inner‐shelf dye observations over roughly 350 m cross‐shore and 2 km alongshore. Dye is advected alongshore by wave‐ and wind‐driven currents similarly in the observations and model. Near‐shoreline mean dye concentration decays downstream as a power law with similar observed (−0.33) and modeled (−0.38) exponents. Observed and modeled cross‐shore mean dye profiles are similar, though modeled inner‐shelf dye is somewhat elevated. Observed and modeled alongshore dye transports agree, though with compensating surfzone and inner‐shelf errors later in the release. For times &lt;3.5 h (before observed and modeled dye advects beyond the model alongshore domain), observed and modeled dye budgets are similar to each other and close to within 10%, and half the observed and modeled dye is exported to the inner‐shelf. Later in the release, surfzone and inner‐shelf dye masses are under and overpredicted, respectively. Model‐data differences may be due to the model's lack of vertical variation, stratification, or tide. The good overall model‐data agreement indicates that nearshore tracer transport and dispersion are realistically simulated over 5 h and 2 km alongshore, and that the model transient rip currents accurately induce cross‐shore exchange between the surfzone and inner‐shelf.

Variation in the abundance of Pseudo-nitzschia and domoic acid with surf zone type

Most harmful algal blooms (HAB) originate away from the shore and, for them to endanger human health, they must be first transported to shore after which they must enter the surf zone where they can be feed upon by filter feeders. The last step in this sequence, entrance into the surf zone, depends on surf zone hydrodynamics. During two 30-day periods, we sampled Pseudo-nitzschia and particulate domoic acid (pDA) in and offshore of a more dissipative surf zone at Sand City, California (2010) and sampled Pseudo-nitzschia in and out of reflective surf zones at a beach and rocky shores at Carmel River State Beach, California (2011). At Sand City, we measured domoic acid in sand crabs, Emerita analoga. In the more dissipative surf zone, concentrations of Pseudo-nitzschia and pDA were an order of magnitude higher in samples from a rip current than in samples collected just seaward of the surf zone and were 1000 times more abundant than in samples from the shoals separating rip currents. Domoic acid was present in all the Emerita samples and varied directly with the concentration of pDA and Pseudo-nitzschia in the rip current. In the more reflective surf zones, Pseudo-nitzschia concentrations were 1–2 orders of magnitude lower than in samples from 125 and 20m from shore. Surf zone hydrodynamics affects the ingress of Pseudo-nitzschia into surf zones and the exposure of intertidal organisms to HABs on the inner shelf.

Impacts of wave and tidal forcing on 3D nearshore processes on natural beaches. Part I: Flow and turbulence fields

The major objective of this study was to develop further understanding of 3D nearshore hydrodynamics under a variety of wave and tidal forcing conditions. The main tool used was a comprehensive 3D numerical model – combining the flow module of Delft3D with the WAVE solver of XBeach – of nearshore hydro- and morphodynamics that can simulate flow, sediment transport, and morphological evolution. Surf-swash zone hydrodynamics were modeled using the 3D Navier-Stokes equations, combined with various turbulence models (k-e, k-L, ATM and H-LES). Sediment transport and resulting foreshore profile changes were approximated using different sediment transport relations that consider both bed- and suspended-load transport of non-cohesive sediments. The numerical set-up was tested against field data, with good agreement found. Different numerical experiments under a range of bed characteristics and incident wave and tidal conditions were run to test the model’s capability to reproduce 3D flow, wave propagation, sediment transport and morphodynamics in the nearshore at the field scale. The results were interpreted according to existing understanding of surf and swash zone processes. Our numerical experiments confirm that the angle between the crest line of the approaching wave and the shoreline defines the direction and strength of the longshore current, while the longshore current velocity varies across the nearshore zone. The model simulates the undertow, hydraulic cell and rip-current patterns generated by radiation stresses and longshore variability in wave heights. Numerical results show that a non-uniform seabed is crucial for generation of rip currents in the nearshore (when bed slope is uniform, rips are not generated). Increasing the wave height increases the peaks of eddy viscosity and TKE (turbulent kinetic energy), while increasing the tidal amplitude reduces these peaks. Wave and tide interaction has most striking effects on the foreshore profile with the formation of the intertidal bar. High values of eddy viscosity, TKE and wave set-up are spread offshore for coarser grain sizes. Beach profile steepness modifies the nearshore circulation pattern, significantly enhancing the vertical component of the flow. The local recirculation within the longshore current in the inshore region causes a transient offshore shift and strengthening of the longshore current. Overall, the analysis shows that, with reasonable hypotheses, it is possible to simulate the nearshore hydrodynamics subjected to oceanic forcing, consistent with existing understanding of this area. Part II of this work presents 3D nearshore morphodynamics induced by the tides and waves.

The Application of a Rip Current Warning Decision-Process System, Haeundae Beach, South Korea

ABSTRACT Lee, J.; Cho, W.C., and Lee, J.L., 2016. The Application of a Rip Current Warning Decision-Process System, Haeundae Beach, South Korea. 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. 1167 - 1171. Coconut Creek (Florida), ISSN 0749-0208. Rip currents have the potential to pull swimmers into deep water, beyond offshore sand bars, posing a significant danger to beach goers worldwide. At Haeundae Beach in Busan, a south eastern region of South Korea, many rip current events have recently occurred, resulting in a number of people requiring rescue from these fast moving, seaward currents in 2014. The main objective of this study was to provide a warning decision-process for the occurrence of rip currents, to aid in the protection of human life in the areas where these rip currents occur. The rip current warning decision-process system develope...

Rip Current Zoning Map to Manage Safety at Haeundae Beach, South Korea

ABSTRACT Lee, G.; Hong, S.; Lee, C.; Kim, J., and Lee, J., 2016. Rip current zoning map to manage safety at Haeundae Beach, Korea. 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. 1452-1456. Coconut Creek (Florida), ISSN 0749-0208. Rip currents are well-known in South Korea. Between July and August 2012, rescue workers covering Busan's beaches were on high alert for rip currents. Rescuers pay particular attention to Haeundae Beach near the Paradise Hotel because it is the frequent site of these currents. In July and August of 2012, 62 fast-moving rip currents were observed with maximum speeds of 2.5 m/s. During this period 187 people were rescued at Haeundae Beach after being dragged into deeper waters by these currents; fortunately, no casualties were reported. Authorities caution that ideal weather conditions for rip currents will persist, so this...

Rip Currents Generated by Distant Typhoons at Haeundae Beach of Korea: Forecast and Warning

ABSTRACT Yoon, S.B.; Song, J.H.; Roh, M., and Choi, J., 2016. Rip Currents Generated by Distant Typhoon at Haeundae Beach of Korea: Forecast and Warning. 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. 1417 - 1421. Coconut Creek (Florida), ISSN 0749-0208. A rip current warning system, which estimates the rip current risk level based on the real-time incident wave conditions measured near the beach and the database pre-calculated using the Boussinesq wave model (Choi et al., 2014), has been in operation at several beaches in South Korea. The warning system has been proved to be highly effective to reduce the rip current accidents in the beaches. However, it also suffers from the shortage of lead time of issuing the warning. In this study, the warning system was improved by forecasting the wave condition at the beach in advance with sufficiently lon...

Study on Rip Current Generated by Submerged Breakwaters: Field Observation and Numerical Simulation

ABSTRACT Kim, I.H.; Lee, W.D.; Shin, S.; Kim, J.H.; Hur, D.S., and Cho, W.C., 2016. The Study on Rip Current Generated by Submerged Breakwaters: Field Observation and Numerical Simulation. 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. 1352 - 1356. Coconut Creek (Florida), ISSN 0749-0208. Jetties and submerged breakwaters have been constructed at Gangmun beach, Korea, for the past several years in order to protect the beach and to secure the estuary channel. However, drowning accidents due to rip currents have often occurred in the gap between the jetty and the submerged breakwater. In this study, field observations and numerical simulations were performed to understand the mechanism of the rip current occurrences at Gangmun beach. The field investigation included the geomorphological change as well as the rip current occurrences. Three-dimension...