modelling rip current flow and bather escape strategies across a transverse bar and rip channel morphology abstract rip currents are a hazard to bathers on surf beaches worldwide yet due to logistical and ethical concerns there has been minimal examination of how bathers caught in them should attempt to escape this study presents the first numerical model of simulated bathers escaping from a rip current an understanding of the underlying coastal geomorphology and hydrodynamics form a critical basis for the model with the intention that outcomes of the model should be evaluated from a physical science perspective field observations of a transverse bar rip channel were used as model inputs escape simulations were performed with moderate energy h s 1 m oblique offshore wave forcing used to generate two non stationary asymmetric flow fields dominant surfzone exits and dominant recirculation the model treats bathers as particles that move with the underlying flow with an additional swimming velocity added iterating until a safety condition based on depth and current speed is satisfied or until a maximum time limit is reached simulations compared the strategies of stay afloat and various fixed swim directions using two bather heights and four swim speeds up to 0 4 m s the overall optimal escape strategy was to swim parallel in the direction of alongshore flow time to safety was less for i recirculating flow ii taller bathers and iii greater swim speeds across all simulations 44 of floaters reached safety within 10 min while 80 of slow swimmers 0 2 m s succeeded in the same time interval this suggests that slow sustainable swimming may be a preferable escape action to floating optimal swim direction varied with start location from onshore near the shoreline parallel to shore mid rip channel and diagonally onshore outer rip channel at lower swim speeds the optimal swim direction had greater dependence on the underlying flow field as opposed to distance to safety therefore choice of direction is more complex for slower swimmers critically no strategy succeeded in all scenarios at all locations across the surfzone and small changes to input conditions water level start time and location swim direction had major impacts on outcomes future modelling efforts should examine additional surf zone rip current morphologies and wave tide inputs with a goal of determining generalised rip escape principles that may be communicated to the general public

a self similar scaling for cross shelf exchange driven by transient rip currents transient rip currents episodic offshore flows from the surf zone to the inner shelf present a recreational beach hazard and exchange material across the nearshore ocean the magnitude and offshore extent of transient rip current induced exchange and its relative importance to other inner shelf exchange processes are poorly understood here 120 model simulations with random normally incident directionally spread waves spanning a range of beach slopes and wave conditions show that the transient rip current exchange velocity is self similar the nondimensional exchange velocity surf zone flushing time and cross shore decay length scale are scaled by beach slope and wave properties depending strongly on wave directional spread transient rip current driven exchange can be compared to other cross shelf exchange processes for example transient rip current driven exchange is stronger than wave induced stokes drift driven exchange up to six surf zone widths from shore

field observations on the morphodynamic evolution of a low energy rip current system abstract a field experiment was conducted at palm beach nsw australia to investigate morphodynamic relationships operating within a rip current system during a near complete sequence of beach state evolution under decreasing energy conditions observations and measurements were obtained from nearshore surveys multiple dye releases oblique photographs and the deployment of various combinations of nine ducted impellor flow meters and five pressure sensors over a seven day period in rip and feeder channels the dataset provides a unique opportunity to assess and quantify aspects of the accretionary model of wright and short mar geol 56 1984 93 118 for intermediate beaches the morphology of the main rip channel exhibited distinct sequential adjustments with a narrowing of channel width an increase in channel depth a reduction in the cross sectional area available for rip flow and an increase in morphological relief rip flow velocity increased during the observed evolution and was also modulated by the tide experiencing maximums at low tide and minimums at high tide morphologic and kinematic adjustments of the rip system were most pronounced during the transition to a transverse bar and rip state the existence of a dominant feeder in a twin feeder and rip system contributed to the migration and establishment of a rip head over the seaward slope of the opposite longshore bar net erosion in the rip channel was balanced by net deposition in the feeder channels and bar crests and qualitative observations suggest that this rip head bar both receives transported sediments from the rip channel and contributes sediments to the ongoing accretion of the beach system a direct relationship was found to exist between rip morphology and flow with rip velocity increasing as cross sectional rip channel area decreases and these results are incorporated in a conceptual modification of the model of wright and short the results of this study are restricted to a subset of commonly occurring beaches but show that accretionary beach state evolution on intermediate beaches is indeed characterised by an increase in rip current velocity the nature of which can be linked to morphologic control in addition the rip head bar is identified as a potentially key component of low energy rip system evolution

laboratory experiment on rip current circulations over a moveable bed drifter measurements 1 this study describes a laboratory experiment on rip current circulations over a moveable bed rip current characteristics over eight contrasting nature like beach morphologies are investigated the seabed varied from reasonably alongshore uniform to strongly alongshore nonuniform with crescentic patterns and bar rip morphologies representative of a full morphological down state sequence the same offshore shore normal waves were generated by the wavemaker for the eight situations with the same mean water level to study the sensitivity of rip current characteristics as a function of the beach morphology only in each case a 30 to 60 min video run was used to track a large number of drifters released within the surf zone results show the presence of classic rip current patterns with counterrotating cells and a relatively narrow offshore directed jet varying from shore normal to strongly skewed wave driven circulations were strongly unstable computed standard deviations of flow intensity and direction provide high resolution information on the spatial variability of rip current instabilities highly pulsating and weakly directionally variable offshore directed flow is observed in the rip neck for well developed bar rip morphologies that turns into a weakly pulsating and highly directional variable rip current flow with decreasing beach alongshore nonuniformity proposing a definition of rip current intensity based on the rip current circulation geometry rip current intensity was found to linearly increase with increasing measure of beach alongshore nonuniformity within both the low energy and moderate energy rip current regimes to date our laboratory experiment provides the first extensive quantitative rip current information during a full down state sequence for a given wave condition

extreme erosion on high energy embayed beaches influence of megarips and storm grouping abstract megarips have long been recognised as an important yet poorly documented mechanism of beach erosion on high energy embayed beaches the persistence and cumulative effect of megarips during storm groups are described from three embayed beaches arrifana mt clerigo and amoreira exposed to high energy wave conditions in the mesotidal bedrock dominated southwestern coast of portugal morphological changes determined by topographic monitoring and supplemented by interpretation of digital imagery over two years revealed the development of storm induced megarips which exerted a major influence on beach erosion differences in megarip influence within and between beaches are related to embayment geometry and orientation which significantly influence the nearshore wave field rip location is topographically controlled being determined by alongshore variations in breaking wave height and obliquity along with interaction of wave driven circulation patterns and embayment nearshore topography moderate beach sand loss during individual storms was linked to the development of megarips with associated rip neck and feeder channels extreme erosion however occurred when megarips and feeder channels persisted during successive storms promoting continued erosion and seaward sediment export observations show that once initiated megarip channels persist for several months and continue to act as conduits for offshore sediment transport under non storm conditions the maintenance of such rip circulation systems driven by morphodynamic feedback reduces beach recovery ability until the rip neck and feeder channels are infilled

petrology and major element geochemistry of peru margin phosphorites and associated diagenetic minerals authigenesis in modern organic rich sediments abstract new petrographic and major element geochemical data from modern peru margin upper slope outer shelf phosphorites are presented which provide insight into their origin and paragenetic relationship with other authigenic minerals glauconite pyrite and dolomite occurring in organic rich sediments glauconites are precipitated relatively early following the partial reduction of ferric iron and following this process phosphate pyrite and then dolomite precipitation take place at progressively deeper levels in the sediment in association with microbial reduction of sulfate as in many ancient economic phosphorite deposits the phosphatic facies here consist of nodules crusts coatings and strata composed of phosphatic pelletal grains ooids structureless grains intraclasts clumps and biogenic grains in association with organic rich biosiliceous sediments all are considered to have formed within a few centimeters or within a few tens of centimeters below the sediment water interface important factors that influence which morphology will tend to develop include the amount of available pore space the presence of suitable nucleation sites the amount and size of siliciclastic detritus incorporated as inclusions and the relative solution chemistries of the precipitating solutions bacterial mediation may play an important but as yet unspecified role in the precipitation process textural data and factor analysis of chemical data suggest that structureless pellets are relatively inclusion free na f mg co3 substituted pore water precipitates whereas ooids are inclusion rich pore water precipitates poor in lattice substituted components variations in nodular cement birefringence and crystallinity are suggested to have been produced by similar lattice substitutions that directly reflect pore water carbonate ion concentrations and thus relative degrees of organic matter degradation phosphate and dolomite are intimately mixed yet mineralogically distinct phases in phosphatized dolomicrites depth stratified threshold carbonate ion concentrations may control the lower limit at which phosphatic minerals may precipitate below depths of a few centimeters excessive carbonate ion concentrations and diminished reactive iron and sulfate concentrations favor the development of dolomite while precluding further development of phosphatic minerals and pyrite periodic sediment reorganization bioturbation current winnowing and erosion mass wasting etc plays an important role in both concentrating pelletal grains and maintaining nodules and crusts at critical depth levels in the sediment as well as mixing ordered mineral parageneses into complicated sequences

topographically controlled breaking wave induced macrovortices part 2 changing geometries this is the second part of a series examining the behaviour of breaking wave induced macrovortices the first part examined theoretically general behaviours during startup conditions and gave computational results for macrovortex generation and their evolution on widely spaced breakwaters in this paper we extend and test qualitatively and quantitatively some of the basic results of part 1 in particular the initial longshore vortex transport for a wide range of geometries ranging from narrow rip current topographies to isolated breakwaters accounting for the presence of a shoreline is found to be necessary for the representation of longshore vortex transport results show vortex motion ranging from strongly offshore in the case of a narrow rip current to strongly longshore in the case of an isolated breakwater even with the significant approximations inherent in the analytical predictions numerical computations using time domain boussinesq type equations and laboratory experiments confirm the trends part 3 examines the horizontal mixing features of wave induced flows over isolated single breakwater configuration or multiple ripcurrent configuration submerged structures

morphodynamics of a large scale rip current system at muriwai beach new zealand abstract field measurements of rip spacing nearshore morphology water surface elevation and eulerian and lagrangian flows were made in order to investigate the morphodynamics of a large scale rip current system at muriwai beach new zealand muriwai is a high energy meso tidal beach characterised by modal breaker wave heights of 2 5 m and incident wave periods of 10 15 s the monitored rip system was characterised by a 400 m long 75 m wide longshore feeder channel and a 150 m wide rip neck channel oriented obliquely to the shore and extending over a distance of almost 400 m during the experiment the beach evolved from a longshore bar trough and rip state to a transverse bar and rip configuration mean eulerian flow velocities obtained from ducted flowmeters deployed on the margin of the feeder channel and rip neck were on the order of 1 m s 1 and instantaneous flows were commonly in excess of 2 m s 1 mean lagrangian surface flow velocities extending from the base of the feeder through to the rip head were obtained by tracking rip floaters and were on the order of 0 7 m s 1 with maximums in the rip neck region of 1 4 m s 1 a distinct tidal modulation of rip current flow existed with maximum velocities occurring at low tide and minimum velocities at high tide comparison with other rip studies suggests that although the magnitude of the morphodynamic and hydrodynamic processes occurring within large scale rip systems is extreme the behaviour of these rip systems is very similar to low energy rips with much smaller spatial scales there is evidence to suggest that distinct morphodynamic scaling relationships exist between these environments

a lead isotopic study of circum antarctic manganese nodules abstract lead isotope ratios in manganese nodules from the circum antarctic ocean display systematic geographical variations eastward in the direction of current movement from south of australia they progressively decrease in the pacific sector and into the western atlantic sector until 30 w from this longitude lead isotope ratios increase in the eastern atlantic sector and reach their highest values in the indian sector near 110 e south of western australia they abruptly decrease these two lead isotope domains correspond closely to the circum antarctic neodymium isotope domains previously recognized by albarede and goldstein 1992 however the intraocean isotopic variations are much clearer for pb than nd reflecting the shorter oceanic residence time of pb 102 y compared with nd 103 y and confirming that pb is a much more sensitive marine tracer throughout the circum antarctic ocean the lead isotopic changes follow the pattern of present day oceanic circulation the pb shows an overall continental signature which is strongest in the indian sector the most probable candidate as the source of the continental signal is north atlantic deep water nadw which enters the circum antarctic in the south atlantic as nadw mixes with circumpolar water lead isotope ratios increase eastward in the indian sector reflecting progressive loss of the pacific derived pb signal the abrupt decrease of lead isotope ratios between the indian and pacific sectors appears to be a consequence of addition of pacific seawater through the pacific lead isotope ratios gradually decrease eastward approaching values of east pacific rise metalliferous sediments ocean ridge basalts and south pacific mn nodules this trend results from an increasing influence of pacific ocean water containing a component derived from pacific volcanism the pacific signature persists into the argentine basin in the southwest atlantic ocean reflecting significant input of water from the drake passage northward into the atlantic the pacific pb component is seen in the atlantic and indian oceans near southern africa as well as in the atlantic and indian sectors of the circum antarctic lead and neodymium isotopes correlate in the atlantic indian sectors but not in the pacific sector reflecting differences in residence times and modes of water mass mixing the renewal of circum antarctic water occurs on a timescale which is short compared to the residence time of nd but long compared to pb as a result dissolved pb is subject to considerable changes over the timescale of circumpolar current movement while nd is less easily affected nadw is added locally in the south atlantic and moves eastward as a water mass as nadw mixes with circumpolar water cpw through the indian sector changes affecting nd pb in nadw and cpw occur in tandem and neodymium and lead isotopes are correlated through the pacific sector gradual addition of pacific seawater occurs over a large region and nd pb relationships are not coupled because simple isotopic mixing systematics are not conserved there neodymium and lead isotopes vary independently the consistency of lead isotope variations with present day ocean bottom water circulation is remarkable considering that the mn nodules as sampled reflect the integrated flux of pb over 105 106 y the oceanic mixing time is 103 y the residence time for pb is 102 y and the circulation time of the circumantarctic ocean is 30 y processes occurring over such different timescales can show such a relationship only if the system is stable over the longest time interval thus on average element sources and ocean circulation through the pleistocene have been similar to the present day despite significant perturbations during glacial periods

rip currents under obliquely incident wind waves and tidal longshore currents abstract a field experiment on the nature of rip currents was conducted on the dutch coast which differs from previous rip current study sites because it is a wind sea dominated environment with mostly obliquely incident waves and tidally driven longshore currents during the experiment three distinct flow patterns obtained with gps tracked drifter instruments were observed 1 a locally governed circulation cell 2 an offshore current that is deflected shore parallel outside the surf zone and 3 a meandering longshore current the transition from rip currents flow patterns 1 and 2 to meandering longshore currents flow pattern 3 occurred gradually within the tidal cycle with longshore currents prevalent at mid to high tide rip currents at this site appeared at depressions in the surf zone bar and typically occurred when the water level fell below nap equivalent to msl even in the presence of obliquely incident waves and tidally driven longshore currents hindcast simulations of the drifter experiments were performed with the numerical model xbeach and showed good agreement with field observations the model was subsequently used to investigate the influence of tidal water level fluctuations longshore currents and obliquely incident waves on rip currents rip currents were initiated when the water level dropped below a specific threshold with the magnitude of the rip current associated with the water level the strength of the tidal current and its orientation with respect to the incident waves governed the offshore extent and orientation of the rip current in contrast to other studies that suggest that rip currents solely occur under shore normal or slightly oblique waves in this study both observations and numerical model simulations indicate that rip currents can exist under large angles of wave incidence when the rip channel is sufficiently wide and the wave height is small

infragravity rip current pulsations 1 the origins of rip current pulsations within the infragravity frequency band 0 004 0 04 hz are determined from measurements made with arrays of colocated pressure and velocity sensors deployed on a beach with persistent rip current channels the observations indicate significant energy in cross shore infragravity velocities that varies spatially in the alongshore due to the presence of rip channels infragravity velocities are smaller within the rip channel than on the shore connected shoal owing to differences in water depth rip current pulsations at infragravity frequencies are linked to standing infragravity motions but not to the ponding and subsequent release of water by wave group pumping

boussinesq modelling of transient rip currents the flow on a plane beach with a random directionally spread wave field was simulated with a boussinesq model the random wave spectra were directionally symmetric with their central direction perpendicular to the beach so no constant longshore current was generated variable wave averaged currents were generated because of the spatially variable wave field and sometimes formed offshore directed rip currents that appear in variable longshore locations the rip currents are associated with a vortex pair which is generated within the surfzone and subsequently propagates offshore analysis of the vorticity balance show that the main vorticity input occurs within the inner surfzone three different beach slopes and four different wave spectra are simulated the frequency duration and intensity of the transient rips depend on both the beach slope and the incident wave spectra the results have important engineering implications for the transport of material in the nearshore zone in particular on longshore uniform beaches

vortical surf zone velocity fluctuations with 0 10 min period observations of velocity fluctuations with periods between about 4 and 30 min thus longer than infragravity waves and referred to as very low frequency vlf surf zone motions are described and compared with numerical simulations the vlf motions discussed here exclude instabilities generated by the wave driven alongshore current velocity shear that occur in the same frequency range by selecting cases with weak alongshore currents only numerical simulations are based on the linear shallow water equations including friction and forced by nonlinear difference frequency interactions between incident sea and swell waves the model is initialized with sea and swell frequency directional spectra observed seaward of the surf zone modeled and observed vlf velocity fluctuation magnitudes agree within a factor of 2 both increase approximately linearly with increasing incident wave height and rapidly decay seaward of the surf zone observed frequency wave number f ky spectra of vlf velocity fluctuations estimated with instrumented alongshore arrays are energetic in a broad range of ky in the vortical band observed and modeled vlf pressure fluctuations are relatively weak still the model momentum balance suggests that vlf pressure gradients are as important as the nonlinear wave group forcing by sea and swell in accelerating decelerating the vlf velocities model calculations demonstrate that the vlf f ky response is a function of the modulations of short wave forcing associated with the frequency directional distribution of the incident sea and swell spectra this results in vlf motions which span the surf zone and have o 50 1000 m alongshore scales with o 200 2000 s time scales given the fact that modulations of short waves resulting from directionally spread incident waves are common during field conditions we expect vlfs to be ubiquitous

a simplified model of rip currents systems around discontinuous submerged barriers although in the last years several numerical models have been shown to be able to reproduce rip currents around discontinuous submerged barriers only few simple methods of practical use are available for estimating main flow parameters like the current intensity and the mean water levels in terms of geometrical barrier and gap dimensions parameters and wave characteristics the aim of this paper is to present a simplified model to be used for an easy estimate of these important rip currents parameters the model which is based on rough simplifications considers the area between the shoreline and the barrier as a reservoir in which water is pumped by breaking short waves across the barrier and from which water flows out at the gap four equations mass and momentum conservation across the barrier free discharge at the gap and balance of water pumped towards the shore and freely flowing offshore are used to derive one single model equation that can be solved for the wave set up and subsequently used for rip current velocity calculation two free parameters appear in this equation which respectively account for energy losses at the gap cv and bed friction the proposed model is validated against available laboratory experiments to show its ability in providing reasonable estimates of the desired parameters that may be considered by engineers adequate at the preliminary design stage of submerged breakwaters and that can be used for evaluating hydrodynamics on barred beaches

lagrangian observations of circulation on an embayed beach with headland rip currents abstract this study describes the first comprehensive measurements of nearshore current patterns across the entire extent of an embayed beach bounded by headland rip currents a field experiment at whale beach nsw australia provides valuable insights into i embayment wide spatial and temporal flow behaviour ii rates of cross and alongshore water exchange and iii the influence of geological control by headlands on morphology and circulation lagrangian flow data was obtained using 34 gps drifters with 293 individual deployments over a single ebbing tidal cycle during moderate low energy h s 1 m oblique wave forcing in situ wave and current data and bathymetric data were also collected beach morphology was dominated by a large mid beach rip channel with lesser headland rip channels mean flow rates were 0 6 ms 1 in the mid beach channel and 0 4 ms 1 in the headland channels with the majority of cross shore water volume flux 60 through the central channel a weak alongshore current o 0 1 ms 1 was forced by the oblique offshore wave angle rip current velocities flow variability and rate of surfzone exits by lagrangian drifters increased as water level decreased transient currents on a planar bar along the northern half of the beach with velocity standard deviation up to 0 2 ms 1 were not tidally modulated lagrangian time series were used to differentiate four current regimes rip cell rip head planar bar and offshore low energy zone based on mean velocity velocity variability and degree of tidal modulation an increase in surfzone exit rates by drifters was observed from south upwave to north downwave with exit rates per drifter deployment of 22 at the south headland rip 65 at the mid beach open rip and 80 at the north headland rip the high rate of drifter exits contrasts previous observations on open coast beaches observed flow behaviours are attributed to wave shadowing at the upwave protected end of the beach and longshore currents forced by oblique waves deflected offshore at the downwave headland these field observations are in good agreement with recent numerical modelling a relationship between bathymetric variability and current intensity was determined with cross shore average mean velocity correlating with a parameterisation of bathymetric alongshore non uniformity this study demonstrates that flow behaviour and exchange rates can vary along the length of an embayed beach due to geological control this research has implications for transport of organisms nutrients and pollutants is relevant to beach safety practitioners and can be used in calibration of numerical models

ripex observations of a rip current system rip current kinematics and beach morphodynamics were measured for 44 days at sand city monterey bay ca using 15 instruments composed of co located velocity and pressure sensors acoustic doppler current profilers and kinematic gps surveys the morphology consisted of a low tide terrace with incised quasi periodic rip channels representative of transverse bars offshore 17 m depth significant wave height and peak period ranged 0 20 3 0 m and 5 20 s the mean wave direction was consistently near 08 resulting in rip channel morphology which evolved in response to the changing wave characteristics an inverse relationship between sediment accreting on the transverse bar and eroding in the rip channel was found the spatial distribution of sediment is reflected in the background rip current flow field the mean velocity magnitudes within the rip channel transverse bars increased offshore onshore with decreasing tidal elevations and increased with increasing sea swell energy eulerian averaged flows were predominantly shoreward on the transverse bars and seaward within the rip channel throughout the experiment resulting in a persistent cellular circulation except during low wave energy the rip current spacing to the rip channel width was less than or equal to two which suggests that the rip currents are influenced by each other and that no two dimensional bar return flow should be present the vertical velocity profile on the bar indicated that the flow was predominantly shoreward the flow field within the surf zone was depth uniform except for significant shear occurring near the surface owing to stokes drift the wave induced transport hypothesis is evaluated d 2005 elsevier b v all rights reserved

nearshore circulation over transverse bar and rip morphology with oblique wave forcing there 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 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

transient rip currents and nearshore circulation on a swell dominated beach 1 eulerian and lagrangian measurements of nearshore circulation on a longshore uniform beach with perpendicularly incident swell waves are described both the eulerian and lagrangian data show a variable rotational part of the current field that is distinct from but coexists with that due to infragravity waves a well defined feature of the flow field includes transient rip currents which occur in varying locations and are not topographically controlled drifter trajectories show that the rips behave like a shallow plane jet consisting of a constrained neck region that flows into a spreading head region there is continuous modulation of the flow within the rip neck estimates of the length scale across the rip neck using two particle statistics are 20 30 m well defined discrete vortex features are observed at the initiation point of one of the necks and in one of the rip heads estimated dispersion values suggest that mixing is greatly enhanced outside the surf zone by the intermittent presence of the rip heads the dispersion calculated from both inside and outside the surf zone appears to show scale dependence with a power law close to 4 3 in a similar way to oceanic turbulence at much larger scales

mean lagrangian flow behavior on an open coast rip channeled beach a new perspective article i nfo the accepted view of rip currents is that they are an efficient mechanism for transporting material out of the surf zone previous rip current campaigns on natural beaches have focused on eulerian measurements with sparse in situ pressure and current meter arrays here for the first time spatially synoptic estimates of rip current flow patterns vorticity and lagrangian transport behavior are measured in the field using a fleet of 30 position tracking surfzone drifters during multiple rip current occurrences on an open coast beach in monterey ca contrary to the classic view shepard et al 1941 the rip current flow field consisted of semi enclosed large scale vortices that retained the drifters and resulted in a high number of lagrangian observations that are temporally and spatially repeated approximately 19 of the drifters deployed in the rip currents exited the surf zone per hour on average during the experiments the observed surf zone retention of drifters is consistent with measurements from different open coast beach rip current systems 14 at meso macrotidal truc vert france and 16 at macrotidal perranporth united kingdom the three hour average cross shore rip current velocity at monterey was 30 cm s with peak time averaged velocities of 40 60 cm s depending on wave and tidal conditions drifters that episodically exited the surf zone were transported approximately 2 surf zone widths offshore at 20 cm s published by elsevier b v

low energy rip currents associated with small bathymetric variations we show for the first time that low energy waves can induce a rip current system over subtle alongshore bathymetric variations comprehensive field measurements across a rip current that morphologically migrated 12 m day through a coherent cross and alongshore array of co located pressure and velocity sensors were obtained the rip current is associated with a small bathymetric surfzone non uniformity 1 in 300 alongshore variation the circulation was kinematically non uniform for 5 of the time over the course of the 20 day experiment and was present at low tides associated with increases in rip current activity the presence of the rip current and mild sloped rip channel induce statistically significant alongshore variations in hrms wave direction directional spreading infragravity waves and very low frequency motions changes in the directional spreading are correlated with the presence of very low frequency motions influenced by the presence of the rip current