Rip Current System Research Articles

Modeling Rip Current Systems around Multiple Submerged Breakwaters

Multiple submerged breakwaters (MSBWs) are commonly used coastal protection structures due to their specific advantages over the emerged ones. Rip currents, as the inevitable natural hazard in the gaps of these constructions, are investigated numerically in the present study. A fully nonlinear mild-slope equation (NMSE) model possessing both fully nonlinear and fully dispersive properties is validated and adopted in the simulations. With four monochromatic wave conditions of different wave heights, periods and incidences representing low-energy, typical, storm and oblique waves tested, the flow patterns and the low-frequency oscillations of the rip currents are studied. For the convenience of risk assessment, the rip risk level is divided into three degrees according to the maximum rip flow speed. The effects of the configurations of the MSBWs on the rip current system as well as the rip risk level are examined, considering different breakwater widths, heights, forms, gap widths and gap numbers. Simulation results suggest that the cross-shore configurations of MSBWs influence the rip risk level by inducing different wave energy dissipations but the longshore configurations of MSBWs by changing flow field patterns.

Flow characteristics of the rip current system adjacent to a coastal vertical structure for irregular waves

Rip currents are common hazards found on many beaches around the world. The present research examines the rip current flow features adjacent to a coastal vertical structure with total reflection function to the incident waves. The laboratory experiments were conducted over the planar beach for both regular and irregular waves to explore the specific phenomenon for the irregular waves, and a higher-order Boussinesq equation model was adopted in the simulations to analyze the formation mechanism of the flow features. The study results show that, the standing wave pattern for the irregular wave is much weaker than that for the regular wave with inducing only one apparent node rip at the first node line in the reflection wave area. Moreover, the specific “single-vortex” flow pattern was formed in the crossing wave field for the irregular wave tests. This specific flow pattern is found essentially induced by the larger wave reflection rate of the vertical structure, which leads to the strong lateral flow against the downstream longshore current. This specific flow pattern prefers to present for the smaller wave incident angles and larger wave heights and periods, and leads to the feeding flow volume rates discharged more in the form of lateral flow. The C-shaped lateral flow is found mainly induced by the longshore gradient of the wave set-up instead of the non-uniform wave radiation stress nearshore.

Flow Characteristics of the Rip Current System near a Shore-Normal Structure with Regular Waves

Rip currents are the strong narrow seaward current produced by waves breaking on the coast. Of the many types of rip currents, the present study investigates, experimentally and numerically, the rip current system produced by the wave reflection on a finite-length shore-normal structure (corresponding to groin, jetty and headland in a real-word environment) with strong wave reflection strength. The incident wave condition of an obliquely propagating monochromatic surface gravity wave is considered for the bottom topographies of planar and barred beaches without or with a rip channel. The corresponding laboratory experiment was conducted and used to validate the numerical model. A set of higher order Boussinesq equations is used to reproduce the experimental observation and produce the results for the related prototype cases, with the latter considering more factors which may influence the formation and evolution of rip current flow patterns. The resulting rip current system contains two parts: the node rips formed due to the presence of the longshore standing wave in the wave reflection field and the deflection rip formed due to the interaction between the incoming longshore current and the reflection wave field mentioned above. A new formation mechanism of the deflection rip has been proposed, i.e., the deflection rip is formed by the meeting and then deflection of the longshore current and lateral flow. The effects of different wave reflection strengths of the structure, wave incident angles and bathymetric conditions on the pattern and flow volume of the deflection rip are also studied.

Morphodynamics of Rip Current Systems at Haeundae Beach, Korea

Lee, J. and Hong, S., 2023. Morphodynamics of rip current systems at Haeundae Beach, Korea. Journal of Coastal Research, 39(1), 199–206. Charlotte (North Carolina), ISSN 0749-0208. Rip current generation and beach morphodynamics were measured for about 60 days at Haeundae Beach, Busan, Korea, using various instruments comprising co-located velocity and pressure sensors, ADCPs, and kinematic GPS surveys. Rip currents are narrow currents initiated close to the shoreline that flow strongly in a seaward direction through the surf zone and beyond. It is generally accepted that rip currents arise mostly from the variation of wave height alongshore attritutable to wave refraction over inhomogeneous bathymetry. Field measurement was performed to clarify the generation mechanism of rip currents at Haeundae Beach, Korea. The creation and destruction of sandbars could be identified clearly using data from a photogrammetric survey taken from the roof of a high building during the summer season. In this study, a surf-zone depth survey was performed periodically using Network Real-Time Kinematic GPS, a device that can provide a detailed topographic survey of the surf-zone region. Using these data, we perform a correlation analysis between rip current generation and surf-zone morphological variation.

A numerical study of arsenic contamination at the Bagnoli bay seabed by a semi-anthropogenic source. Analysis of current regime

Bagnoli Coroglio is an urban district of the City of Naples (South Italy), which fronts the Tyrrhenian Sea for nearly 3 km. It is part of the Campi Flegrei caldera, one of the most explosive volcanic areas in Europe. The need for redeveloping the site after the intense industrial activities of the twentieth century has prompted a remarkable research effort to investigate the pollution's degree, nature, and extent at both the land and seafloor.This article focuses on releasing thermal waters from a natural channel as a source of arsenic contamination in the Bagnoli marine sediments; the thermal waters originate from the nearby Agnano hot-springs and have been conveying artificially to the track since the mid-XIX century. As a first part of the outcomes, the work describes the flow regime that characterizes the marine area.The analysis has been conducted via numerical simulations carried out with the software package Delft3D, developed by Deltares, which employs dynamically interfacing modules to account for wave propagation, generation of currents, and presence of coastal structures. Climatic inputs to the software (waves, winds, and tide) have specifically been gathered and analyzed within this research.The numerical study has permitted to furnish, for the first time, a clear and systematic view of the hydrodynamic forcings that characterize the area under investigation. In particular, a leading role in the transport of pollutants could be played by rip current systems, whose characteristics vary with climate intensity (waves and wind) and coastal structures characteristics.Due to its inherently dynamic nature, the proposed approach seems especially desirable in situations where different contamination sources are compared. As such, it could be successfully applied to other sites also.

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

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.

PERFORMANCES OF THE RIP CURRENT WARNING SYSTEM AT THE HAEUNDAE COAST OF SOUTH KOREA

Haeundae is one of the most beautiful beaches in Korea, and is also notorious for frequent and strong rip currents. Every recent year in this beach, hundreds of swimmers rescued from rip currents have been reported. The large-scale Haeundae rip current is known to be a kind of transient rip currents which is hardly predicted. The successive ends of wave-crest pattern (i.e., honeycomb wave-crest pattern(Dalrymple et al., 2011)), which generate rip current, are mainly formed by two-directional wave trains due to the refraction of incident swells over submerged shoals and ridges of the Haeundae coast. Many people are caught by the rip current in the relatively calm sea and weather conditions. The incident waves generating rip currents are nearly monochromatic with the wave period of 7-13 seconds. These swells are supposed to be generated by distant typhoons formed in the Philippine Sea. Some of them might propagate with dispersion and dissipation during the travel toward the south coast of the Korean Peninsula, especially to the Haeundae coast. In order to protect the swimmers from the rip current accidents, Choi et al. (2014) proposed a method for a rip current warning system, and Korea Hydrographic and Oceanographic Administration (KHOA) has established and operated the rip current warning system to the Haeundae beach. The rip current warning system estimates the rip current risk level based on the real-time incident wave conditions measured near the beach and the database pre-calculated by a numerical model according to various wave and tide conditions and the topography of the Haeundae coast. The Boussinesq wave model, FUNWAVE (Wei et al., 1999; Choi et al., 2015) was utilized for resolving the ends of the wave crests. This study showed the performance of the forecast and warning system of the rip current at the Haeundae coast of South Korea.

Persistent Differences in Horizontal Gradients in Phytoplankton Concentration Maintained by Surf Zone Hydrodynamics

Surf zones, regions of breaking waves, are at the interface between the shore and coastal ocean. Surf zone hydrodynamics may affect delivery of phytoplankton subsidies to the intertidal zone. Over a month of daily sampling at an intermediate surf zone with bathymetric rip currents and a reflective surf zone, we measured surf zone hydrodynamics and compared concentrations of coastal phytoplankton taxa in the surf zones to concentrations offshore. At the intermediate surf zone, ~80% of the variability in the concentration of coastal phytoplankton taxa within the surf zone was explained by their variation offshore; however, concentrations were much higher and lower than those offshore in samples from a bathymetric rip current and over the adjacent shoal, respectively. Hydrodynamics at this intermediate surf zone did not hinder the delivery of coastal phytoplankton to the surf zone, but the bathymetric rip current system appeared to redistribute phytoplankton concentrating them within eddies. At the reflective shore, we sampled surf zones at a beach and two adjacent rocky intertidal sites. Concentrations of typical coastal phytoplankton taxa were usually an order of magnitude or more lower than those offshore, even when offshore samples were collected just 20 m beyond the breakers. The phytoplankton assemblages inside and outside the surf zone often appeared to be disconnected. Surf zone hydrodynamics at the steep, reflective shore coupled with low phytoplankton concentrations in near-surface water appeared to limit delivery of phytoplankton subsidies to the surf zone. Surf zone hydrodynamics may be a key factor in the alongshore variation in phytoplankton subsidies to coastal communities.

Determining How Offshore Shoals Control Rip Current Generation in an Embayed Beach

ABSTRACT Wu, G.; Liang, B.; Li H.; Lee, D.-Y., and Guo, W., 2017. Determining how offshore shoals control rip current generation in an embayed beach. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 224–228. Coconut Creek (Florida), ISSN 0749-0208. In this study, the generation of rip currents at Haeundae Beach, Korea, is investigated using an advanced, non-hydrostatic wave-resolving model SWASH. It is found that the presence of offshore shoals leads to strong wave refraction, creating significant alongshore wave height variations and mega-scale rip current systems. The modeled rip currents occurring locations correspond well with the low wave height areas. The rip currents persist even if the surf zone rip-channel topography is smoothed, with very similar spatial patterns and occurring locations compared with those generated under the original bathymetry. We argue that the mega-sca...

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 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...

Examining rip current escape strategies in non-traditional beach morphologies

Rip currents are a significant hazard on global surf beaches and are a factor in hundreds of drowning fatalities each year. Contemporary rip current safety information often idealises rip currents as part of a Transverse Bar Rip (TBR) morphology with rip channels bound by shallow, shore-connected bars. Real-world conditions frequently differ from this model, with potential implications for rip current escape strategies promoted to, and undertaken by, the general public. This study describes outcomes of rip current escape strategies conducted at North Cronulla Beach, NSW, Australia, over two distinct morphologies; a mixed Low Tide Terrace/Transverse Bar Rip (LTT/TBR) and a Rhythmic Bar Beach (RBB) system lacking shore-connected bars. Swimmers attempted to escape by adopting one of three pre-determined strategies: Stay Afloat, Swim Parallel and Swim Onshore. A total of 100 escape attempts were conducted, with the RBB system experiencing longer duration ( $$\bar{t}$$ = 2.4 min) escapes than the LTT system ( $$\bar{t}$$ = 0.8 min). The RBB system was associated with a higher rate of action failure, particularly for Stay Afloat, due to a lack of shore connectivity of adjacent bars. Swim Parallel was of lower duration ( $$\bar{t}$$ RIP1 = 0.66, $$\bar{t}$$ RIP2 = 2.68 min) in both systems, but durations and distances to safety in the RBB system often exceeded swimming abilities of weaker bathers. Although Swim Onshore was more successful ( $$\bar{t}$$ RIP1 = 0.22, $$\bar{t}$$ RIP2 = 1.65 min) than Swim Parallel, promotion of such a strategy is strongly discouraged in conventional safety advice. Results suggest that contemporary rip current escape strategies may be inappropriate in non-TBR rip current systems and that alternative strategies should be considered, including Swim Onshore and a greater focus on preventative strategies, particularly in relation to bathers with limited swimming ability.

Numerical study of the secondary circulations in rip current systems

To investigate the mechanism of secondary circulations in rip current systems, and to explore the relationship between wave conditions and secondary circulation intensity, a series of numerical experiments is performed using coupled nearshore wave model and circulation model. In these experiments, the rip currents and secondary circulations generated above barred beaches with rip channels are simulated. A comparison experiment is conducted to investigate the formation and hydrodynamics of the secondary circulations. Model results indicate that the secondary circulations consist of alongshore flows driven by wave set-up near the shoreline, part of the feeder currents driven by the wave set-up over the bars, and onshore flows at the end of the rip channel driven by wave breaking and convection. The existence of the secondary circulation barely affects the rip current, but narrows and intensifies the feeder currents. Three groups of experiments of varying incident wave conditions are performed to investigate the relationship between wave conditions and secondary circulation intensity. The velocity of the alongshore flow of the secondary circulation is sensitive to the variation of the incident wave height and water depth. It is also found that the alongshore flow intensity is in direct proportion to the alongshore variation of the wave height gradient between the bars and the shoreline.

A Rip Current Warning System Based on Real-Time Observations for Haeundae Beach, Korea

Choi, J.; Lim, C.H., and Yoon, S.B., 2014. A rip current warning system based on real-time observations for Haeundae Beach, Korea.A real-time rip current warning system was studied to help mitigate against rip current accidents at Haeundae Beach. The system produces a real time sequence of index representing the risk and the likelihood of rip current based on the real time observations such as waves, currents, and tide. The index is estimated by using the rip current likelihoods derived from the results of various numerical simulations with various sea conditions, the parameters of which correspond to the observation quantities. The rip current warning system is operated by taking into account the effect of wave height, wave period, wave direction, wave spectrum (i.e., frequency-directional spreading), longshore currents, and tidal elevation on the rip current likelihood. The real-time wave and tidal observations at the Haeundae coast in 2012 were applied to the rip current warning system, and its performances at several real events observed from the video cameras were presented and analyzed.

Introduction to KMA Operational Forecasting System for Rip Current

ABSTRACT Eom, H.; Yun, J.H.; Jeong, C.K.; Seo, J.W., and You, S.H., 2014. Introduction to KMA operational forecasting system for rip current. A rip current, commonly referred to simply as a rip, is a strong channel of sea water flowing seaward from the near the shore, typically through the surf line. Rip currents can be found on the Haeundae Beach every year and make a very large number of rescues each year (106 in 2009, 144 in 2010 and 220 in 2012). The main reasons that it is present on the Haeundae Beach are the geographical factor, wide surf zone and mild slope, and meteorological factor, seasonal southern wind and normal waves. When waves travel normal from deep to shallow water, there is a greater than normal transport of wave energy into a surf zone which may result in an elevated rip current risk. Korea Meteorological Administration (KMA) developed a rip current forecast system that considers bathymetric and meteorological effect through Research and Development program. The system is based on hig...

Physical modeling of three‐dimensional intermediate beach morphodynamics

Experiments have been performed in a large wave tank in order to study the morphodynamics of rip current systems. Both accretive and erosive shore‐normal wave conditions were applied, the beach evolving through all the states within the intermediate beach classification, under the so‐called down‐state (accretive) and up‐state (erosive) morphological transitions. Results show that any prescribed change in the wave conditions drastically increases the rate at which the morphology changes. The surf zone morphology tends toward a steady state when running a given wave climate for a long duration. We quantitatively describe a full down‐state sequence characterized by the progressive evolution of an alongshore‐uniform bar successively into a crescentic plan shape, a bar and rip channel morphology, and a terrace. From the analysis of a large data set of dense Eulerian measurements and bathymetric surveys, we depict several feedback mechanisms associated with wave‐driven rip current circulation, wave nonlinearities and the seabed evolution. At first, a positive feedback mechanism drives a rapid increase in the rate of morphological change, beach three‐dimensionality, and rip intensity. By the time the sandbar evolves into a bar and rip morphology, a negative feedback mechanism, characterized by a decaying beach change rate and an increasing beach alongshore uniformity, overwhelms the former mechanism. An erosive sequence characterized by both an overall offshore bar migration and an increase in beach three‐dimensionality is also described.

Nearshore circulation over transverse bar and rip morphology with oblique wave forcing

ABSTRACTThere is a paucity of field data to describe the transition in nearshore circulation between alongshore, meandering and rip current systems. A combination of in‐situ current meters and surf zone drifters are used to characterize the nearshore circulation over a transverse bar and rip morphology at Pensacola Beach, Florida in the presence of relatively low energy oblique waves. Current speeds vary in response to the relative wave height ratio (Hs/h), which defines the degree and extent of breaking over the shoal. In the absence of wave breaking the nearshore circulation was dominated by an alongshore current driven by the oblique waves. As waves begin to break across the shoal (0.2<Hs/ h<0.5) the nearshore circulation is characterized by a meandering alongshore current. As conditions became more dissipative (Hs/h>0.5), the meandering current is replaced by an unsteady rip circulation that moves offshore between the shoals before turning alongshore in the direction of wave advance outside the surf zone. The increase in wave dissipation is associated with an increase in very low frequency (VLF) variations in the current speed across the shoal and in the rip channel that caused the circulation to oscillate between an offshore and an alongshore flow. The unsteady nature of the nearshore circulation is responsible for 55% of all surf zone exits under these more dissipative conditions. In contrast, only 29% of the drifters released from the shoal exited the surf zone and bypassed the adjacent shoal with the alongshore‐meandering current. While the currents had a low velocity (maximum of ~0.4 m s‐1) and would not pose a significant hazard to the average swimmer, the results of this study suggest that the transverse bar and rip morphology is sufficient to create an alongshore variation in wave dissipation that forces alongshore meandering and low‐energy rip circulation systems under oblique wave forcing. Copyright © 2013 John Wiley & Sons, Ltd.

A Study on a Predictive Index for Dangerous Rip Current Generation at Haeundae Beach

Lee, J.Y. Jun, K. C., Lee, S. C and Lee, J.L.Haeundae beach draws one million visitors every summer season, and more than 100 people are rescued from rip currents every year. Beachgoers are unexpectedly carried away seawards, as far as 50 ~ 100 meters from shore, where swimming is restricted for safety reasons. Rescuers have strengthened lookout measures at several spots where dangerous rip currents have occurred. The determination of a predictive index for rip currents is vitally important for the protection of human life. Such an index allows governmental agencies to issue rip current warnings directly to the public, and allows for the establishment of preventative measures according to the magnitude of the rip current threat. We apply a modified rip current predictive index suitable for Haeundae - using wave height, wave period, and incident wave angle from the north. Compared with wave data acquired for the summer of 2011, the result of NERiPS-H (NEarshore Rip current Predictive System at Haeundae) index is reasonable and appropriate. Unfortunately, we have insufficient observed wave data. So, our NERIPS-H method has insufficient reliability. This lack of wave data will be addressed by additional intensive field surveys. Additional intensive field experiments were carried out at Haeundae Beach from June to August, 2012 for the collection of data. This in-situ measurement data will be used to improve the reliability of rip current predictive guidance.

SPH MODELING OF MEAN VELOCITY CIRCULATION IN A RIP CURRENT SYSTEM

A Lagrangian numerical model called Smoothed Particle Hydrodynamics is used to analyze rip current system generated by a single bar and a rip channel. The pattern of the wave-induced circulation cell over the bar, the oppositely-rotating circulation cell on-shore and a strong seaward-directed current in the rip channel is modeled numerically. The mean horizontal variations of rip current system as well as three-dimensional circulations are studied. The results in three-dimensional space reveal the wave-current interaction and flow patterns in different parts of rip channel, bar, and the trough located near shore. For comparison to experimental data, Eulerian nodes are introduced to the numerical model and SPH interpolation over neighboring Lagrangian particles is implemented to find fluid parameters at those specific nodes. This methodology leads to a better understanding of depth-integrated flows and a more accurate comparison of numerical results with experimental results. Model predictions are compared to laboratory measurements of Drønen et al. (2002) and show good agreement, including mean velocity profiles, mean surface elevation and three-dimensional velocity components.

Surf zone diffusivity on a rip‐channeled beach

Absolute and relative diffusivity are measured on a rip‐channeled beach using 30 position‐tracking drifters released in clusters (4–12 drifters) deployed on 7 days with different wave forcing and tidal elevations at Sand City, Monterey Bay, California. Diffusivity and dispersion were found to be larger on days with rip current flow patterns and larger waves. Rip currents cause material to diffuse quickly for t < 90 s in the cross shore (κxx = 5.4–6.1 m2/s) before decreasing to an asymptotic oscillation (κxx = 0.9–2.2 m2/s), while alongshore material diffusion is initially (t < 170 s) smaller than cross‐shore diffusion and asymptotes at a larger value (κyy = 2.8–3.8 m2/s). The cross‐ and alongshore absolute diffusivity modulate at ∼300 s corresponding to the average circulation time for a rip current. Two‐particle relative dispersion (Dp) grows like Dp2 ∼ t4/3 and the relative diffusivity (Kp) is scale dependent, Kp ∼ d0.2 (d is particle separation). Cluster relative diffusion (Ke) ranged from 1.0 to 4.5 m2/s and cluster relative dispersions (De) are significantly correlated with two‐particle relative dispersions (DS) [R2 > 0.9]. Two independent methods are used to measure the small‐scale turbulent diffusion contribution (kxy), which are found significantly correlated (R2 = 0.95) with each other and calculated surf zone wave breaking induced turbulent eddy viscosity. Here kxy is small relative to the total dispersion (Ke/kxy = 3–30), indicating that the shear flow is the primary mechanism responsible for dispersion in a rip current system.