Surf Zone Currents Research Articles

New insights into combined surfzone, embayment, and estuarine bathing hazards

Abstract. Rip currents are the single largest cause of beach safety incidents globally, but where an estuary mouth intersects a beach, additional flows are created that can exceed the speed of a typical rip current, significantly increasing the hazard level for bathers. However, there is a paucity of observations of surfzone currents at estuary mouth beaches, and our understanding and ability to predict how the bathing hazard varies under different wave and tide conditions are therefore limited. Using field observations and process-based XBeach modelling at an embayed, estuary mouth beach, we demonstrate how surfzone currents can be driven by combinations of estuary discharge and wave-driven bathymetric and boundary rip currents under various combinations of wave and tide forcing. While previous studies have demonstrated the high hazard that rip currents pose, typically during lower stages of the tide, here we demonstrate that an estuary mouth beach can exhibit flows reaching 1.5 m s−1 – up to 50 % stronger than typical rip current flows – with a high proportion (> 60 %) of simulated bathers exiting the surfzone during the upper half of the tidal cycle. The three-dimensional ebb shoal delta was found to strongly control surfzone currents by (1) providing a conduit for estuary flows that connect to headland boundary rips and (2) acting as a nearshore bar system to generate wave-driven “river channel bathymetric rips”. Despite significant spatio-temporal variability in the position of the river channels on the beach face, it was possible to hindcast the timing and severity of past bathing incidents from model simulations, providing a means to forewarn bathers of hazardous flows.

Wave-driven current and vortex patterns at an open beach: Insights from phase-resolving numerical computations and Lagrangian measurements

Wave-driven currents have a substantial impact on local circulation patterns in and across the surf zone, and are responsible for cross-shore and longshore exchange of mass and momentum over a broad range of spatial and temporal scales. Nearshore currents may drive sediment transport, lead to beach erosion, and also affect the spread of bacteria and other marine microorganisms, as well as the distribution of pollutants such as chemicals and microplastics. In addition, surf zone currents can cause hazardous conditions for beach-goers in the form of rip currents.It is known from previous work (Chen et al., 2003; Feddersen et al., 2011; Hally-Rosendahl and Feddersen, 2016) that Boussinesq-type models in combination with appropriate boundary conditions and wave breaking capabilities can function as powerful tools for the analysis of circulation patterns in the surf zone. In the present work, data from a recent field campaign reported on in Bjørnestad et al. (2021) are used to further validate the capability of Boussinesq systems to simulate nearshore dynamics.The numerical model is then used to study the influence of tidal elevation, peak direction and directional spread of the incoming wavefield on the quantity, extent, and circulatory magnitude of the nearshore circulation. In addition, fundamental features such as horizontal eddies are investigated, and comparisons are made to solid-body rotation and irrotational vortices.Overall, it is observed that local variations in the bathymetry across the surf zone are the controlling factor regarding the size of these circulations, and an increasing tidal level, which can be seen as a uniform offset to the bathymetry, favors the generation of larger vortex patterns. For a given tidal stage, the directional spread of the incoming wavefield has the most pronounced influence on the size and strength of the nearshore eddies while the peak direction has the strongest effect on the total number of circulations.

The Roles of Bathymetry and Waves in Rip‐Channel Dynamics

AbstractThe behavior and predictability of rip currents (strong, wave‐driven offshore‐directed surfzone currents) have been studied for decades. However, few studies have examined the effects of rip channel morphology on the rip generation or have compared morphodynamic models with observations. Here, simulations conducted with the numerical morphodynamic model MIKE21 reproduce observed trends in flows and bathymetric evolution for two channels dredged across a nearshore sandbar and terrace on an ocean beach near Duck, NC, USA. Channel dimensions, wave conditions, and flows differed between the two cases. In one case, a strong rip current was driven by moderate height, near‐normally incident waves over an approximately 1‐m deep channel with relatively little bathymetric evolution. In the other case, no rip was generated by the large, near‐normally incident waves over the shallower (∼0.5 m) channel, and the channel migrated in the direction of the mean flow and eventually filled in. The model simulated the flow directions, the generation (or not) of rip currents, and the morphological evolution of the channels reasonably well. Model simulations were then conducted for different combinations of the two channel geometries and two wave conditions to examine the relative importance of the waves and morphology to the rip current evolution. The different bathymetries were the dominant factor controlling the flow, whereas both the initial morphology and wave conditions were important for channel evolution. In addition, channel dimensions affected the spatial distribution of rip current forcings and the relative importance of terms.

Forecasting coastal evolution on time-scales of days to decades

Increasing pressures on coastal environments induced by sea level rise and coastal squeeze has meant that tracking the morphological evolution of sedimentary coasts from the last known survey, pre-empting storm impacts and forecasting potential beach recovery following extreme events is of substantial and increasing societal importance. Equilibrium models for forecasting coastal evolution have figured prominently in the literature in the past two decades and show a strong potential for fulfilling this societal need. In particular some very skilful shoreline evolution models have been proposed based on equilibrium concepts. These models are stable, simple and permit long-term (O(10) years) predictions of coastal change. However, equilibrium models are typically highly empirical and in many cases do not consider explicitly the impact of dynamic sea level, which is modulated by tides, surge and global sea level rise. Equilibrium-based models of shoreline evolution have shown particular promise, but these models generally do not consider the role of the sub- and supra-tidal morphology on coastal evolution (e.g. the importance of coastal dune systems). This contribution presents a new model for Forecasting Coastal Evolution (ForCE), which addresses these issues. The model algorithm adopts a reduced complexity but fundamentally physics-based approach, whilst maintaining equilibrium principles. Unlike, most prior models, the sub- and supra-tidal areas are represented explicitly in the model, as are sea level variations. Sediment transport is equated directly with the disequilibrium in wave energy dissipation flux, leading to a sediment transport formulation that negates the normal intermediate step of computing surfzone currents, generally required in process models. Two components of sediment transport are considered: The first is forced by the turbulent kinetic energy associated with wave breaking and the second diffusive term, is related to a sea bed-slope disequilibrium. The first component perturbs the equilibrium profile and dominates in the surfzone, whilst that latter component plays an important role in beach recovery. Equations are developed for a depth-averaged, beach profile model, assuming longshore uniformity. These computational efficient and stable equations facilitate long forecasts (>decade) and easy comparisons with a field data at cross-shore transport dominated field sites. At the test field site, the model is capable of reproducing qualitative observations of nearshore sand-bar dynamics and quantitative comparisons with measured coastal state indicators including both the shoreline displacement (r = 0.90, N.M.S.E. = 0.145) and intertidal beach volume (r = 0.87).

High‐Energy Surf Zone Currents and Headland Rips at a Geologically Constrained Mesotidal Beach

AbstractWe analyze Eulerian and Lagrangian measurements of wave‐induced circulation collected during a 3‐week field experiment at a high‐energy mesotidal barred beach with the presence of a 500‐m headland and a submerged reef. Small changes in wave and tide conditions were found to largely impact circulation patterns. Three main regimes were identified depending on offshore wave obliquity: (1) Under shore‐normal configuration, the flow was dominated by cross‐shore motions, except for moderate waves at low tide, with the presence of a quasi‐steady circulation cell on the reef. (2) Under shadowed configuration, an onshore‐directed current flowing away from the headland and a weak oscillating eddy were present outside and inside the shadow region, respectively. (3) Under deflection configuration, a deflection rip flowing against the headland and extending well beyond the surf zone was present, with activity maximized around low tide for moderate waves. Under 4‐m oblique waves, the deflection rip was active regardless of the tide with mean depth‐averaged velocities up to 0.7 m/s 800‐m offshore in 12‐m depth, with energetic low‐frequency fluctuations. Our results emphasize the ability of deflection rips to transport materials far offshore, suggesting that such rips can transport sediment beyond the depth of closure. This study indicates that a wide variety of wave‐driven circulation patterns can occur and sometimes coexist on beaches with prominent geological settings. Changes in the dominant driving mechanism can occur as a result of small changes in wave and tide conditions, resulting in more spatially and temporally variable circulation than along open sandy beaches.

Field Evidence of Inverse Energy Cascades in the Surfzone

AbstractLow-frequency currents and eddies transport sediment, pathogens, larvae, and heat along the coast and between the shoreline and deeper water. Here, low-frequency currents (between 0.1 and 4.0 mHz) observed in shallow surfzone waters for 120 days during a wide range of wave conditions are compared with theories for generation by instabilities of alongshore currents, by ocean-wave-induced sea surface modulations, and by a nonlinear transfer of energy from breaking waves to low-frequency motions via a two-dimensional inverse energy cascade. For these data, the low-frequency currents are not strongly correlated with shear of the alongshore current, with the strength of the alongshore current, or with wave-group statistics. In contrast, on many occasions, the low-frequency currents are consistent with an inverse energy cascade from breaking waves. The energy of the low-frequency surfzone currents increases with the directional spread of the wave field, consistent with vorticity injection by short-crested breaking waves, and structure functions increase with spatial lags, consistent with a cascade of energy from few-meter-scale vortices to larger-scale motions. These results include the first field evidence for the inverse energy cascade in the surfzone and suggest that breaking waves and nonlinear energy transfers should be considered when estimating nearshore transport processes across and along the coast.

Extremely Low Frequency (0.1 to 1.0 mHz) Surf Zone Currents

AbstractLow‐frequency surf zone eddies disperse material between the shoreline and the continental shelf, and velocity fluctuations with frequencies as low as a few mHz have been observed previously on several beaches. Here spectral estimates of surf zone currents are extended to an order of magnitude lower frequency, resolving an extremely low frequency peak of approximately 0.5 mHz that is observed for a range of beaches and wave conditions. The magnitude of the 0.5‐mHz peak increases with increasing wave energy and with spatial inhomogeneity of bathymetry or currents. The 0.5‐mHz peak may indicate the frequency for which nonlinear energy transfers from higher‐frequency, smaller‐scale motions are balanced by dissipative processes and thus may be the low‐frequency limit of the hypothesized 2‐D cascade of energy from breaking waves to lower frequency motions.

Rip current circulation and surf zone retention on a double barred beach

Rip currents have an important control on the exchange of water and advected materials such as sediment and pollutants, between the surf zone and inner shelf. Concurrent in situ Eulerian and Lagrangian (GPS drifter) data of surf zone waves and currents were combined with video data on wave breaking patterns over the inner and outer bars on a high energy, double-barred beach. The data collectively show how the occurrence of wave breaking over the outer bar changes the behavior of a channel rip current, and the exchange process. On both days, there was a prominent clockwise eddy in the surf zone, for which the seaward-heading portion formed a rip current in a well-defined channel rip, incised into the inner bar. Exit rate (measured with drifters) from the surf zone to inner shelf decreased significantly with increased wave breaking over the outer bar, from 71% exits to 6% over the two days. Exit rate appears to be driven by the balance between wave breaking over the inner and outer bars and pulsing of currents within the surf zone. Under higher wave conditions, there were stronger pulsations in surf zone currents and more surf zone exits. However, higher wave conditions caused wave breaking over the outer bar. This breaking increases vorticity around the outside of the surf zone eddy, which increases surf zone retention. This is in contrast to previous studies showing that vorticity is highest at the center of surf zone eddies. Under such conditions, drifter exits were rare, and occurred due to vortex shedding. During lower incident wave conditions, eddy vorticity was lower, and drifters could relatively freely exit the surf zone. This is one of the few studies that investigate surf zone circulation on a high energy, double-barred beach.

Bathymetric Controls on Rotational Surfzone Currents

AbstractA multibeach Lagrangian data set was used to determine bathymetric controls on flow variability within the surfzone. Seven microtidal flow regimes were examined, six containing rip channels, under moderate shore normal waves. Three selected zones exemplified varying bathymetric control: (i) a alongshore uniform zone; (ii) a shallow rip channel at an oblique angle to shore normal; and (iii) a deep, shore‐normal rip channel. Bathymetric variables included alongshore nonuniformity (φ) and channel angle relative to shore normal (α). Low‐frequency flow (0.01 Hz) was described by velocity (U), velocity standard deviation (σU), angular deviation (σθ), and bias in direction of eddy rotation (ζbias). Observations of the exemplar zones indicated the following: (i) near‐zero mean flow with transient eddies within the alongshore uniform zone; (ii) low mean flow with high ζbias within the oblique channel; and (iii) strong mean flow with low ζbias in the deep channel. Bathymetry and flow variables were spatially averaged and linearly correlated, scaling for wave forcing. Normalized flow variables were found to be interdependent and were correlated with bathymetric variability, with [U ∝ φ], [(U/σU) ∝ φ], and [σθ ∝ − φ], all with (R2 ≥ 0.8). A correlation was determined between α and ζbias (R2 ≥ 0.7, increasing as zone width is decreased), with peak ζbias within oblique channels. Based on these results, a conceptual model is introduced to predict flow behavior for known bathymetry. Surfzone currents were found to span a dynamic continuum from transient eddies on alongshore uniform bathymetry, to channelized rip currents, forced by bathymetric three‐dimensionality and mediated by channel geometry.

Pulsations in Surf Zone Currents on a High Energy Mesotidal Beach in New Zealand

ABSTRACT Gallop, S.L.; Bryan, K.R.; Pitman, S.J.; Ranasinghe, R., and Sandwell, D., 2016. Pulsations in surf zone currents on a high energy mesotidal beach in New Zealand. 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. 378–382. Coconut Creek (Florida), ISSN 0749-0208. The exchange of material between the surf zone and continental shelf can be driven by pulsations in rip current velocities. However, there is a poor understanding of the relationship of these pulsations to surf zone morphology and material exchange. Moreover, understanding of rip current dynamics has focused mainly on single-barred beaches in an intermediate state, and there have been few studies on high energy beaches. Therefore, this paper undertakes preliminary research on surf zone current velocity pulsations, on a high energy beach in New Zealand. This initial analysis presents...

Effects of reef roughness on wave setup and surf zone currents

ABSTRACT Franklin, G.L., Marino-Tapia, I. and Torres-Freyermuth, A., 2013. Effects of reef roughness on wave setup and surf zone currents. Circulation in reef systems controls an important number of key processes, such as the transport and dispersion of larvae, nutrients, and sediments. In fringing reef systems, where a shallow lagoon backs onto the reef crest, circulation appears to be dominated by wave breaking. Despite the identified importance of wave driven flows within reef systems, there is a lack of detailed knowledge on these processes within the surf zone of reef crests and the effects reef roughness has on these flows. A numerical study, using two-dimensional (2DV) simulations, was carried out in order to improve the understanding of wave-driven flows in the surf zone of a fringing reef. The model used is Cornell Breaking Wave and Structures (COBRAS), which solves the Reynolds-Averaged Navier-Stokes (RANS) equations with a turbulence closure scheme. The effect of different reef roughness on wav...

Numerical simulation of wave-induced currents combined with parabolic mild-slope equation in curvilinear coordinates

Researches on breaking-induced currents by waves are summarized firstly in this paper. Then, a combined numerical model in orthogonal curvilinear coordinates is presented to simulate wave-induced current in areas with curved boundary or irregular coastline. The proposed wave-induced current model includes a nearshore current module established through orthogonal curvilinear transformation form of shallow water equations and a wave module based on the curvilinear parabolic approximation wave equation. The wave module actually serves as the driving force to provide the current module with required radiation stresses. The Crank-Nicolson finite difference scheme and the alternating directions implicit method are used to solve the wave and current module, respectively. The established surf zone currents model is validated by two numerical experiments about longshore currents and rip currents in basins with rip channel and breakwater. The numerical results are compared with the measured data and published numerical results.

Análise Dos Riscos Ao Banho De Mar No Município De Pontal Do Paraná - PR – Temporada 2003/2004

This work aims to analyze the features related to bather safety at Pontal do Paraná – PR. The study is concentrated on environmental risks, on bather behavior and spatial distribution of bather rescue. A GIS was structured with information about beaches infrastructure, the permanent and temporary risks, bather’s density in each beach, the safeguards houses and rescue statistics. Generally Pontal do Paraná bathers are neglect with their security. Only 54% of them to bath in patrolled places, 74% don’t ask for the lifeguard’s information about the sea condition and 17% don’t observe the sea condition before bather. About the bather capability of swimming was found that 50% of the bathers don’t know to swim. Despite this, 44% of the bathers go to the sea with the water at level of their thorax or above. This finding may help explain the large amount of rescue. The most part of bathers ignore the environmental risks of sea bathing like: surf zone currents; tides which continually change water depth and current velocities; wind-driven currents, and rip currents. So the hazards during sea bathing happen by an equivocated perception of the beach environment. The GIS show be useful to understand the relationship among the behavior of the bather on the beach, the physics parameters that drive the beach morphodynamic and the available lifeguards patrolling infrastructure.

Low-Cost Handheld Global Positioning System for Measuring Surf-Zone Currents

Abstract Low-cost, handheld, L1 (1575.42 MHz) global positioning systems (GPSs) provide scientists with the opportunity to acquire position and velocity estimates at reduced expense (order of [O]$100), size (∼cell phone), weight (O[70 g]), and engineering time. Two different low-cost, handheld GPS units and four different position-correcting configurations are evaluated here to determine their practicality in measuring surf-zone currents. Three of the simpler configurations result in relative position and velocity errors of O(2 m) and O(0.5 m s−1) for stationary tests. Surf-zone position and velocity signal-to-noise spectral ratios for the three configurations suggest that only motions <0.01 Hz can be confidently estimated for these surf-zone systems. For the fourth configuration, a GPS handheld unit that internally records GPS carrier phase is postprocessed using more sophisticated software for position corrections to obtain absolute position and velocity estimates. Simple modifications are required to i...

Surf zone currents over irregular bathymetry: Drifter observations and numerical simulations

Surf zone currents over irregular bathymetry were observed with GPS‐tracked drifters and modeled with the depth‐integrated nonlinear shallow water equations. Trajectories of drifters released in 1–2 m depth sometimes defined rip currents and surf zone eddies, features that have been difficult to resolve with fixed instruments. The drifter‐delineated surf zone circulation evolved as the tidal level changed during each 4–6 hour deployment. In one case, as the tide dropped, a shore normal rip current present for the first 2 hours evolved to a more shore parallel flow. In a second case, on a rising tide a well‐developed bifurcated rip current was replaced by a weak, amorphous circulation. Rip current velocities were strongest near the surf zone edge and decayed by an order of magnitude within 2 surf zone widths from the shoreline. An eddy was observed to persist over a bathymetric depression within the surf zone for at least 1 hour. Observed and numerically simulated drifter trajectories define similar flow features, but the observed and modeled velocities differed by roughly a factor of 2, and flow evolution observed during roughly 0.5 m changes in tidal level were reproduced only if the simulated water levels varied by about 1 m. The alongshore momentum balance was spatially variable, with wave forcing balanced by pressure gradient, friction, and advective terms. The cross‐shore momentum balance was everywhere dominated by wave forcing and pressure gradient terms of about equal magnitude. In the vicinity of a simulated rip current the residual of the cross‐shore wave forcing and pressure gradient increased and was balanced by advection terms.

Locating sources of surf zone pollution: a mass budget analysis of fecal indicator bacteria at Huntington Beach, California.

The surf zone is the unique environment where ocean meets land and a place of critical ecological, economic, and recreational importance. In the United States, this natural resource is increasingly off-limits to the public due to elevated concentrations of fecal indicator bacteria and other contaminants, the sources of which are often unknown. In this paper, we describe an approach for calculating mass budgets of pollutants in the surf zone from shoreline monitoring data. The analysis reveals that fecal indicator bacteria pollution in the surf zone at several contiguous beaches in Orange County, California, originates from well-defined locations along the shore, including the tidal outlets of the Santa Ana River and Talbert Marsh. Fecal pollution flows into the ocean from the Santa Ana River and Talbert Marsh outlets during ebb tides and from there is transported parallel to the shoreline by wave-driven surf zone currents and/or offshore tidal currents, frequently contaminating >5 km of the surf zone. The methodology developed here for locating and quantifying sources of surf zone pollution should be applicable to a wide array of contaminants and coastal settings.

A Numerical Simulation of Wave-Generated Surf Zone Currents

A numerical modelling protocol for the formation of wave-induced littoral currents is described. The method comprised the synthesis of a steady-state wave transformation program driving a hydrodynamic program. The model was validated with field measurements of bathymetry, waves and currents obtained over a six hour period from a small, but energetic rip on Narrabeen Beach, Sydney.

Temporal and spatial variations of surf-zone currents and suspended sediment concentration

Temporal and spatial variations of surf-zone currents and suspended sediment concentrations were investigated at the U.S. Army Engineer Research and Development Center's Large-scale Sediment Transport Facility (LSTF). A longshore-uniform fine-sand beach, 35 m alongshore, 20 m cross-shore, and 25 cm thick was placed in the facility for these experiments. Two unidirectional, long-crested irregular wave conditions were examined, one resulted in predominantly spilling breakers and one in plunging breakers. Waves and currents, and sediment concentrations were measured at 20 and 16 Hz, respectively, at various longshore and cross-shore locations and throughout the water column. Both currents and sediment concentrations exhibit great temporal and spatial variations in the surf zone. The variation patterns, however, of the longshore current, cross-shore current, and sediment concentration are substantially different. Caution should be exercised when averaging these parameters over time and space. For the two wave cases examined, the temporal variations of longshore current, including those at principal incident-wave frequencies, were relatively small across most of the surf zone. Over 70% of the variations are within approximately ±60% of the mean value. The wave motion, with a strong peak at principal incident-wave frequencies, dominated the temporal variations of cross-shore current. Temporal variations of suspended sediment concentration under the irregular waves were episodic, characterized by occasional large values induced by suspension events or due to horizontal advection. The variance of the concentration at the peak incident-wave frequency was not significant except very near the bed. Time-averaged longshore-current profiles over the predominantly rippled sand bed were logarithmic in shape below the wave trough. Depth-averaged longshore current (excluding the portion of water column above wave trough) matched well with the current measured at an elevation of 1/3 of the water depth from the bed. Time-averaged cross-shore current profiles were characterized by an onshore mass flux near the surface, and a balancing offshore flow below the wave-trough level (undertow). Sediment concentration decreased very rapidly upward through the water column across most of the surf zone except at the plunging breaker line where relatively homogeneous concentration was measured throughout much of the water column above 4 cm from the bed. Depth-averaged sediment concentration over the range from 1 cm above the bed to the bottom of wave trough roughly equaled the concentration measured at an elevation from the bed equal to 20% of the still-water depth. A reasonable estimate of the time-averaged longshore sediment flux was obtained from the product of time-averaged profiles of longshore current and sediment concentration. Accurate estimates of time-averaged cross-shore sediment flux, however, could not be obtained from the product of time-averaged current and concentration.

Tidal and diurnal periodicity in macrocrustaceans and demersal fish of an exposed sandy beach, with special emphasis on juvenile plaice Pleuronectes platessa

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 225:263-274 (2002) - doi:10.3354/meps225263 Tidal and diurnal periodicity in macrocrustaceans and demersal fish of an exposed sandy beach, with special emphasis on juvenile plaice Pleuronectes platessa Bregje Beyst, Jan Vanaverbeke*, Magda Vincx, Jan Mees** Marine Biology Section, Biology Department, Ghent University, K.L. Ledeganckstraat 35, 9000 Gent, Belgium *Corresponding author. E-mail: jan.vanaverbeke@rug.ac.be **Present address: Flanders Marine Institute, Victorialaan 3, \f\f8400 Oostende, Belgium ABSTRACT: Macrocrustaceans and juvenile demersal fish were sampled in spring of 1997 in the surf zone of an exposed sandy beach on the Belgian coast. Three consecutive 24 h cycles were sampled to investigate tidal, diurnal and semi-lunar distribution patterns within the epibenthic community. Multivariate statistical techniques and 3-way ANOVA were used to evaluate the effects of the environmental variables measured. The most important variable correlated with the variation in epibenthic catch density was the state of the tide (ebb and flood), but light intensity (day and night) was also important. The individual catch density of several species differed significantly over the three 24 h cycles. Despite the strong turbulent conditions of the site studied, clear tidal (e.g. the brown shrimp Crangon crangon, juvenile plaice Pleuronectes platessa) and diurnal (e.g. juvenile sole Solea solea and clupeids, caught mainly during the night/day respectively) periodicities of many macrocrustacean and demersal fish species were observed. Nevertheless, the extremely turbulent conditions of the surf zone possibly affect the behaviour of many species (e.g. juvenile brown shrimp are not able to bury themselves as the water retreats). To investigate whether the high dynamics of the surf zone suppress the ability of juvenile plaice to actively search for food, stomach contents were analysed. Also, the interaction with potential prey was investigated: the hyperbenthic fauna was sampled simultaneously and macrobenthic data were available from the literature. Clearly, the Belgian sandy beaches are used as a feeding ground by I-group plaice. An opportunistic utilisation of available food resources is suggested. I-group plaice migrate high up the beach during the flood tide to profit from the rich macrobenthic intertidal area, while the 0-group feeds mainly on the most abundant hyper- and macrobenthic organisms from somewhat deeper water. The presence of the 0-group in the intertidal area is possibly linked to refuge for predators or influenced by the strong surf zone currents. KEY WORDS: Surf zone · Sandy beach · Pleuronectes platessa · Crangon crangon · Feeding periodicity · Stomach content analyses · Tidal migration Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 225. Online publication date: January 11, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Surf Zone Currents

A large fraction of the water-wave energy incident on beaches is dissipated as the waves break and travel towards the shore through the surf zone. However, the momentum associated with the incident waves is not destroyed and drives other motions within the surf zone. An analysis is given of the unsteady and irregular currents that may occur in the surf zone. The forcing due to a discrete group of waves, and the vorticity of the surf-zone currents are the major topics. In particular, the almost two-dimensional nature of the flow implies that significant eddies are likely to be generated. There is evidence that eddies arise from long-shore currents, and the combination of eddies of opposite sign gives rip currents. It is noted that generation of vorticity by non-uniformities in bores may be a useful way of considering the forcing of surf zone motion. Expressions for the rate of increase in the circulation about material circuits and the vorticity generated at bores are derived.