Longshore Current Velocity Research Articles

On reversal of wave-generated longshore currents at tidal frequencies on dissipative beaches contiguous to a mesotidal estuary, S.E coast of Nigeria

Reversals in wave-generated longshore currents in surf zones occur at different temporal and spatial scales. Along coastlines with tidal channel openings with well-developed mouth bars or ebb-tidal deltas, the reversal mechanism is often attributed to the mouth bar – induced refraction of the shoaling waves. This reversal mechanism is characterized by convergence of longshore currents from the adjoining surf zones at the mouth of the tidal channel. Simultaneous half-hourly monitoring of wave-generated longshore currents over 50 successive (daylight) semi-diurnal tidal cycles in beach surf zones adjoining the Qua Iboe River estuary, S.E coast of Nigeria showed the above reversal pattern during flooding stage only. The converse pattern, where the surf zone longshore currents diverged away from the mouth of the estuary, was observed during ebbing stage. Both surf zones showed flow direction inversion with respect to each other, with velocity vector correlation coefficient r > − 0.8 in over 80 % of the data set. Instances of comparable flow direction (<10 %) were also recorded. Tidal processes are implicated in the documented results. Direction-averaged longshore current velocities, typically in the 15–60 cm/s range, attained highest values in both surf zones at about spring tide phase. Also, tidal cycle-residual longshore current maximum and minimum velocities occurred close to spring and neap tide, respectively. Only 30 % of the residual velocities were eastward directed in the up-drift surf zone as against 80 % in the down-drift counterpart. Given the prevailing southwesterly waves, the present results negate the assertion that reversal in longshore current direction in this offset shoreline setting is exclusively a consequence of wave refraction by mouth bar morphology. The reversing pattern of the longshore currents over a tidal cycle is well explained by incorporating interacting effects of shoaling waves with tide-induced oscillations in water level as well as the estuarine flow.

Modeling investigation of wave-induced longshore current distribution patterns on barred beaches

A three-dimensional coupled wave-current model was employed to investigate the wave-induced longshore currents on barred beaches. The modeling system was developed by coupling the finite-volume community ocean model (FVCOM) and the simulating waves nearshore (SWAN) model to fully describe wave-current interactions in the nearshore region. The three-dimensional radiation stress, surface rollers and wave-enhanced turbulent mixing were incorporated as the major wave effects on currents. The model was first evaluated against data collected from multiple sets of laboratory experiments. Diagnostic simulations demonstrated that the contributions of the wave rollers and wave-induced mixing, in addition to the radiation stress, were important for ensuring accurate calculations. Then, the longshore current patterns on barred beaches were investigated through simulations of a series of test cases under controlled conditions. The cross-shore distribution of wave-induced longshore currents, which predominantly occurred within the barred beach surf zone, usually exhibited bimodal characteristics. The maximum peak longshore current velocity was positively correlated with the incident wave height and period. As the bar height and width increased, the first velocity peak of the longshore current strengthened, while the second peak weakened. In most cases, the maximum longshore current velocity on a barred beach coincided with the first peak, which could occur anywhere from the bar-trough region to the bar-crest region, depending on the wave and bar heights. This finding could be used to clarify the cross-shore location discrepancies in the maximum peak longshore current velocity reported in previously published studies.

Numerical Simulations of Effects of the Layout of Permeable Pile Groin Systems on Longshore Currents

Coastal permeable groins have been used to protect beaches from erosion for centuries. However, the hydraulic functioning of permeable groins has not been fully understood and their design heavily depends on engineering experiences. In this study, numerical experiments were executed to investigate the effects of layout configurations of a permeable groin system on longshore currents. The non-hydrostatic SWASH (Simulating WAve till SHore) model was employed to carry out the numerical simulations. Two data sets obtained from physical laboratory experiments with different permeable groin layouts on different slopes are used to validate the accuracy of the model. Then, the longshore current reduction by the permeable groin system with varying configuration parameters (e.g., groin spacing, groin length) was numerically investigated under different environmental conditions (e.g., a slight or a moderate wave climate). From the calculation results of numerical experiments, it is indicated that permeable groins function efficiently to reduce the maximal longshore current velocity under the condition that the groin length ranges from 84% and 109% of the wave breaker zone width. The longshore current reduction rate monotonously decreases with the increase in groin spacing; permeable pile groin functions best to reduce longshore current with the minimal groin spacing-groin length ratio 1:1 among the range between 1:1 and 2:1. When the groin spacing–groin length ratios are 1:1 and 1.5:1, the longshore current reduction is not sensitive to the investigated wave conditions in this study. When the spatial ratio is 2:1, the permeable pile groin system functions worse under a moderate wave climate than under a slight wave climate, from the view of longshore current reduction.

Izmenchivost' kharakteristik pribrezhnogo techeniya u Yuzhnogo berega Kryma v 2017–2019 godakh

This paper aims at specifying peculiarities of the coastal water circulation according to the current monitoring data obtained at the stationary oceanographic platform of the Black Sea hydrophysical sub-satellite testing area of the MHI RAS near the Southern coast of Crimea in 2017–2019. The monitoring was performed using the technology of continuous measurements with a vertically distributed (from the surface to bottom layer) complex of Euler vector-averaging meters of the horizontal current component. The new results are matched to those of the coastal current monitoring obtained for the previous period from 2008 to 2016. For the entire observation period (2008–2019), the annual focused current of coastal waters kept the west-south-western direction, with its vertical structure remaining stable. In 2017–2019, a verifiable decrease was registered in the annual longshore current velocity, on average by 10 % throughout the depth up to 7.8 cm/s at a depth of 5 m and up to 6.4 cm/s at a depth of 20 m. Also, the relevant characteristics of bimodal distribution of direction repeatability within original (nonaveraged) data remained unchanged. Further, for 12 years, the oscillation intensity of the coastal current with periods of 10–13 days or less remained reliably unchanged. While analyzing the vertical structure of averaged for 2017–2019 kinetic energy spectra in the inertial-gravitational fluctuation range, two separate regions are reliably detected of regular oscillations with daily (24 h) and local inertia (about 17 h) periods. The obtained new research results can be used while performing validation calculations of local models of the coastal water circulation in the water area of the Southern coast of Crimea. This includes also planning measures to provide crisis monitoring of the coastal ecotone of the sea due to pollution of the coastal and shelf waters

Experimental study and numerical simulation of mean longshore current for mild slope

In this paper, experimental and numerical studies were performed to investigate the characteristics of longshore current under two mild slopes, the results of which may complement the existing studies, which have mainly focused on steep slopes. The experimental results revealed that the average velocity distribution of the longshore current was significantly different under the two different mild slopes. Under the slope of 1:100, the distribution of the averaged longshore current velocity had a downward concave trend at the nearshore side, while under the slope of 1:40 the trend became convex. In addition, the analysis of the numerical results showed that the distribution of the averaged longshore current velocity was affected by the distribution of the wave height within the surf zone and the bottom friction equations, with the influence of the latter being more significant. For the slope of 1:100, the cross-shore variability of alongshore variability can be calculated using the flow-type bottom friction equation, while for the slope of 1:40, the wave-type bottom friction equation can be used instead. Finally, the secondary breaking wave heights for mild slopes and the distribution of wave set-up are also shown in the study.

The Curve Fit Analysis of Mean Longshore Current Velocity Distribution Under Different Mild Slope Conditions

Studying the distribution of longshore current velocity has important practical significance for coastal sediment transport and nearshore material transport and diffusion. Based on the experimental results of 1:100 slope and 1:40 slope mild slope longshore current, this essay adopts MATLAB software and uses different functions to fit and analyze the mean longshore current velocity distribution under mild slope in two cases. The results show that the maximum value of 1:100 mean longshore current velocity have a concave trend on the nearshore side, three kinds of functions can properly fit the mean longshore current velocity distribution. In the case of 1:40, three kinds of functions cannot appropriately show the mean longshore current velocity distribution. Therefore, the distribution characteristics that the convex trend is on the coastal side of the 1:40 mild slope can be better described by proposing a custom piecewise function and relevant constraints.

Analisa Model Matematik Arus Sejajar Pantai Pada Groin Seri Permeable

This research is the mathematical model has been made with two groins, permeable and impermeable groins, with the variation is in length and distance; 50 meters, 100 meters, 150 meters and 200 meters. A modelling has been done by using the data of physical modeling study by Chen., et al, 2003, and used as input to the simulation of mathematical models using 2D Boussinesq software.Results of the research showed the influence of variation model long distance between the groins, the reduction of longshore current velocity along the coast with an average 59.21% reduction for the double permeable groin with 50 meters long, 76.02% for 100 meters, 79.50% for 150 meters, 80.49% for 200 meters. The reduction of longshore current velocity along the coast are 57.42% for an impermeable groin groin double with 50 meters, 84.61% for 100 meters, 150% for 88.89 meters, and 89.91% for 200 meters. The distance variation between one groin to the other groin has a result that a longer permeable or impermeable groin affects the reduction longshore current velocity along the coast of the Surf Zone with the addition of longshore current velocity reduction occurs along the coast up to 20%. Reduction of longshore current velocity along the coast by the permeable and impermeable groin Permeable and impermeable groins has not been significantly occured in the long-term groin area exceeding Surf zone with an average additional reduction up to 5%. The longshore current velocity approaching the speed of currents along the coast for the existing conditions at a distance up to 2.4 times of length of groins. And the distance between the groins are too close if we compare to the long groins causing the current direction of movement towards the sea (rip Current).

A baroclinic coastal trapped wave event in the Gulf of Naples (Tyrrhenian Sea)

In this study, a baroclinic coastal trapped wave, with period ~ 4.5 days and cross-shore scale ~ 3 km, is identified in the outputs of a very-high-resolution ocean circulation model of the Campania coastal system (central Tyrrhenian Sea; including the Gulfs of Salerno, Naples, and Gaeta). The outputs are from a simulation spanning June 2003, a month in which the surface winds were always weak, except for a strong northeasterly wind event that lasted 1 day (20 June). This event is found to generate a strong upwelling along the Campania coasts, whose relaxation—virtually free, because of the weakness of the winds—produces coastal current fluctuations that propagate to the north, spanning the three gulfs. The dynamics (analyzed with a focus on the Gulf of Naples) is found to share important features with baroclinic Kelvin waves in a two-layer model, such as the sharp cross-shore decrease of the perturbation amplitude and the vertical reversal of the long-shore current velocities. The simulated phase speed, cross-shore extension, and wavelength of the perturbation are also close to those obtained using a two-layer approximation of the dynamics. Moreover, the propagation described by the models is shown to be compatible with current measurements that were made in June 2003 at the southern entrance of the Gulf of Naples. Experimental implications related to the specific oceanographic problem are finally discussed, and an experimental strategy—inspired by our modeling approach—aimed at identifying the phenomenon is proposed.

Controls on Flash Rip Current Hazard on Low-Tide Terraced Tropical Beaches in West Africa

Scott, T.; Castelle, B.; Almar, R.; Senechal, N.; Floc'h, F., and Detandt, G., 2018. Controls on flash rip current hazard on low-tide terraced tropical beaches in West Africa. In: Almar, R.; Almeida, L.P.; Trung Viet, N., and Sall, M. (eds.), Tropical Coastal and Estuarine Dynamics. Journal of Coastal Research, Special Issue No. 81, pp. 92–99. Coconut Creek (Florida), ISSN 0749-0208.Flash rip currents are transient non-fixed offshore-directed jets of water often associated with migrating surf-zone eddies. They can occur on featureless (alongshore-uniform) beaches and are essentially hydrodynamically controlled. Due to their unpredictable nature, they represent one of the most significant hazards to bathers across surf zones worldwide, especially in Tropical West Africa, where high levels of flash rip activity and a lack of a lifeguard service lead to high drowning rates. Recent work has shed light on two contrasting driving mechanisms for non-fixed rips: (1) cascading vortices generated by wave breaking, and (2) shear instabilities of the longshore current. This research provides the first quantitative scientific understanding of wave-driven currents in Tropical West Africa. Specifically, the study focussed on the dynamics of flash rips occurring along alongshore-uniform beach morphology, through the collection of unique Lagrangian field measurements of flash rips. During two periods, February 2013 and March 2014, 13 days of field data collection occurred at Grand Popo beach on the southerly-facing Bight of Benin coast (Gulf of Guinea, West Africa). The experiments measured flash rip currents, nearshore hydrodynamics and morphology at a moderately energetic (long-term average significant wave height, Hs = 1.36 m, and peak wave period Tp = 9.4 s), sandy alongshore-uniform low-tide terraced beach exposed to South Atlantic groundswells and local wind-waves. A suite of GPS drifters, dye-tracking and video confirmed the presence and characteristics of low–high energy flash rips (up to 0.7 m/s) in the surf zone, while in-situ acoustic wave and current measurements from the surf zone and inner-shelf provided metocean forcing conditions (0.8<Hs<1.6 m; 8<Tp<14 s; 1°<Dp<21° (from shore normal)) and longshore current velocities (0.2–0.8 m/s in surf zone). Throughout a range of wave conditions (height/period/angle/directional-spreading) contrasting flash rip behavioural responses were observed (surf zone exits/offshore extent/offshore-directed velocities). This study (1) supports findings of the first rip experiment conducted at this site (Feb 2013) suggesting that flash rip activity is likely to be driven by wave breaking vorticity generation (flash rip activity high under shore-normal wave forcing) and (2) provides further quantitative insights into the role of specific wave/tide forcing characteristics on flash rip activity, specifically the importance of reduced directional spreading and tidal level in controlling increases in offshore extent of flash rip currents. Finally, (3) the observed ubiquity of significant hazardous transient flash rip activity and identification of key behavioural controls can provide a foundation for any future development of rip hazard prediction tools and effective lifeguarding in West Africa.

A process based shape equation for a static equilibrium beach planform

Coastal erosion is a major problem for shorelines everywhere in the world. In order to mitigate beach stability problems it is necessary to determine the equilibrium shape of the beach planform. Current equilibrium planform shape equations are only valid under certain simplifications; for instance, they are unable to predict the effect of nearshore islands and/or rocky bottoms, as well as the effect of several diffraction points. The aim of this paper is to present a new process-based shape equation that is able to overcome those limitations and estimate the static equilibrium shoreline of complex bathymetry beaches. The equation is based on the hypothesis that a pocket beach gets its static equilibrium planform when the mean surf-zone longshore velocity averaged over a period of time is null (V¯=0) in every point along the beach. Based on this hypothesis, the direction of the shoreline that nulls the mean surf zone longshore velocity along the beach is evaluated. Therefore, the shape equation is based on the longshore current velocity formula. The new equilibrium shape equation is applied to two Spanish beaches, namely Milagro beach and Cala Millor beach. Milagro beach has a very smooth bathymetry and the parabolic shape equation developed by Hsu and Evans (1989) is able to predict the equilibrium shoreline. Cala Millor is more complex: it has some rock outcrops along the beach and the parabolic shape equation does not work. The equilibrium shape equation presented in this paper simulates the equilibrium shoreline of both beaches successfully with a high R2 (around 0.96) between the modelled shoreline and the real shoreline in both case studies.

Analysis of Longshore Currents with an Eulerian Nearshore Currents Model

ABSTRACT Chun, H. and Suh, K.-D., 2017. Analysis of longshore currents with an Eulerian nearshore currents model. In the present study, longshore currents are analyzed with the three-dimensional nearshore currents model in the Eulerian framework. It was found that the model was reduced to the classical one-dimensional longshore currents model for a long, straight, uniform coast, which could also be obtained from the Lagrangian nearshore currents model. It indicates that the longshore current velocities calculated by the Eulerian and Lagrangian models are equivalent to each other for a long, straight, uniform coast. In addition, it was shown that longshore currents with a parabolic vertical profile could be reproduced by the wave–current interaction term in the model. The analysis has been confirmed by the numerical experiments on DUCK94. According to the numerical experiment, the depth-averaged velocities from the present numerical model were consistent with those of one-dimensional longshore currents mod...

Influence of Submerged Breakwater on Longshore Currents

Submerged breakwater is a kind of commonly used maritime sheltering structures, so it is necessary to accurately grasp the hydrodynamic characteristics before and after the submerged breakwater. Based on the longshore current experiment in harbor, taking the trapezoid submerged breakwater as the research object, this paper analyzes the influence of submerged breakwater on the mean longshore current by changing the position of submerged breakwater and observes the effect of submerged breakwater on the instability of longshore currents for frequency fluctuation. The results show that the closer the submerged breakwater, cross-shore longshore current velocity has the more obvious tendency to toward the shore. Meanwhile, it will make the upstream direction of longshore current velocity increase and will make the distribution of longshore current velocity in the direction of the whole coast is more uniform. Furthermore, some frequency fluctuation of longshore current instability may strong and new high frequency components of the instability of longshore currents may occur for the increase of the submerged breakwater.

Longshore sediment transport and foreshore change in the swash zone of an estuarine beach

Estuarine beaches often lack well developed surf zones; incident waves break and convert directly to swash on the steep foreshore, resulting in greater influence of the swash zone in generating longshore flows and sediment transport. This study was conducted to evaluate longshore sediment transport in the swash zone of an eroding estuarine beach and relate transport rates to changes in beach position and volume downdrift of a shore-perpendicular structure. Field data were gathered on a sandy beach on the bay side of Fire Island, New York, USA in a short fetch (12–15km) microtidal (mean range 0.21m) environment. Wave and swash processes, beach changes and sediment tracer and trapping experiments were conducted during strong onshore winds in March and April 2012.Daily topographic surveys of the beach revealed pulses of sediment movement alongshore at small temporal (daily) and spatial (5m) scales. The mid foreshore retreated 2.75m from the beginning to the end of the 24days of monitoring. This retreat was associated with a loss of 2.1m3 of sediment per meter of shoreline length. The greatest amount of foreshore retreat during a single storm event was 1.27m, associated with a volume loss of 0.9m3 of sediment per meter. Mean wind speed on that day was 11.3ms−1 with a maximum of 18.2ms−1; significant offshore wave height at the time of maximum wind speed was 0.30m. Mean significant wave heights ranged from 0.12 to 0.26m during the five times when trapping occurred, resulting in mean longshore swash velocities of 0.08 to 0.23ms−1 and transport rates ranging from 0.413 to 1.516m3h−1. The longshore sediment transport rates are similar to rates gathered under similar longshore current velocities on microtidal low energy beaches. Transport rates on beaches in sheltered environments can differ from rates calculated using existing formulas that may be more appropriate for high-energy beaches, where a greater proportion of sediment is transported in the surf zone than in the energetic swash zone under plunging breakers. Transport rates calculated from three existing formulae (Bagnold, 1963, CERC, 1984, Kamphuis, 2002) revealed that estimates from Bagnold compared most favorably with measured rates because of direct measurements of longshore current velocities. Rates of erosion on beaches in short fetch environments can be high despite low wave energies because the low, narrow beaches have little volume, magnifying the importance of seemingly low rates of transport in the swash.

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

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

ANFIS and ANN models for the estimation of wind and wave-induced current velocities at Joeutsu-Ogata coast

In this study, the adaptive network-based fuzzy inference system (ANFIS) and artificial neural network (ANN) were employed to estimate the wind- and wave-induced coastal current velocities. The collected data at the Joeutsu-Ogata coast of the Japan Sea were used to develop the models. In the models, significant wave height, wave period, wind direction, water depth, incident wave angle, and wind speed were considered as the input variables; and longshore and cross-shore current velocities as the output variables. The comparison of the models showed that the ANN model outperforms the ANFIS model. In addition, evaluation of the models versus the multiple linear regression and multiple nonlinear regression with power functions models indicated their acceptable accuracy. A sensitivity test proved the stronger effects of wind speed and wind direction on longshore current velocities. In addition, this test showed great effects of significant wave height on cross-shore currents' velocities. It was concluded that the angle of incident wave, water depth, and significant wave period had weaker influences on the velocity of coastal currents.

An experimental and numerical study of bimodal velocity profile of longshore currents over mild-slope barred beaches

A detailed description is given of the results of laboratory experiments on bimodal velocity profile of longshore currents over two mild-slope barred beaches. The objective is to examine the bimodal longshore current velocity profile for purely wave-driven currents, with emphasis on the second peak and ratio of two peaks. The research focus is on the locations, values and ratios of two velocity peaks for the cases of mild slope beaches. The dependence of its bimodal feature on wave height, wave period and beach slope on the longshore currents are discussed. The 2-D model based on vertically integrated equations (external mode) of Nearshore POM was performed to compute the measured velocity profile. The depth-varying wave-induced residual momentum, the surface rollers, and the lateral mixing the bottom friction are considered, and the effects of lateral mixing, surface rollers and bottom friction on numerical model are discussed.

The Effects of Offshore Wave Energy Flux and Longshore Current Velocity on Medium-Term Shoreline Change at Hasaki, Japan

The relationships between medium-term shoreline fluctuations, offshore wave energy flux and longshore current velocity were investigated on the basis of data sets from 1987 to 2001 (15years). In this analysis, the spectral density of the data was calculated, and the frequency components from the investigated period (15 years) to 1000 days were recomposed and defined as the medium-term fluctuation. A multiple linear regression analysis was performed to evaluate the associations between the medium-term fluctuations of shoreline change rate and that of the major dependent variables, which are the offshore wave energy flux and the longshore current velocity. The results suggested that a medium-term fluctuation of the shoreline change rate at the field was affected by both the medium-term fluctuations of the offshore wave energy flux and the longshore current velocity at approximately the same rate. The fluctuation range of the medium-term shoreline fluctuation was nearly the same range of the seasonal shoreline fluctuation, i.e. approximately 20 m. This indicates that for beach management, not only seasonal shoreline fluctuation but also medium-term shoreline fluctuation is needed to be considered.

Coastal impact induced by a Pelamis wave farm operating in the Portuguese nearshore

The objective of the present work is to evaluate the local and coastal impact of a wave farm based on Pelamis convertors that would operate in the Portuguese nearshore. The target area is the coastal environment located north of Peniche. This sector was found in previous studies as representing a significant hot spot from the point of view of the wave energy. An analysis of the wave climate based on historical buoy data was first carried out. This allowed also a preliminary assessment of the electric power expected to be delivered by a Pelamis device in the coastal area targeted. Two farm configurations are considered and simulations with the SWAN spectral model were performed for each case and also for the actual situation when no wave farm operates. The impact in both geographical and spectral spaces was evaluated for various representative wave patterns. Moreover, in order to estimate the influence of the wave farm on the shoreline dynamics, the nearshore circulation was also evaluated using a Surf model. The results show that the presence of a Pelamis based wave farm operating offshore has a strong influence on the wave conditions immediately down wave, but this influence is usually attenuated at the level of the coastline. On the other hand, it appears also that at the surf zone level the longshore current velocity is in relative terms more sensitive to the presence of the wave farms than the significant wave height.

Advective Diffusion of Contaminants in the Surf Zone

AbstractA theory on the horizontal spreading of contaminants in the surf zone is described in this paper. The surf zone is viewed as a narrow strip comparable to the characteristic wavelength, in which turbulence caused by wave breaking is strong. Flows inside the surf zone consist of both oscillatory motions and a steady current induced by breaking waves. The wave field in the shoaling zone is modeled by the linear theory for monochromatic waves, and it is assumed that the breaking wave height is proportional to the local depth in the surf zone. The simplest scenario of longshore current on a straight beach of constant slope is considered, for which the longshore current velocity is predicted by a slightly modified version of Longuet-Higgins' original theory developed in the 1970s. On the basis of the estimation that the time scale of horizontal diffusion is much longer than the wave period, the perturbation method of multiple scales is applied to derive the transport equation for the advective diffusion...

Surface Roller Effect Affecting on Shear Fluctuations of a SandyDuck Experiment under a Random Wave Environment

Bae, J.S., Kim, H.J., Choi, J., 2013. Surface Roller Effect Affecting on Shear Fluctuations of a SandyDuck Experiment under a Random Wave Environment. In: Conley, D.C., Masselink, G., Russell, P.E. and O’Hare, T.J. (eds.), Proceedings 12 th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 1491-1496, ISSN 0749-0208. Surface roller effect affecting on shear fluctuations of a SandyDuck experiment was investigated under a random wave environment by using the combination of SHORECIRC and SWAN. The surface roller, which is a strong turbulent region of waves that break and tumble shoreward, has been known to be significant for modelling of nearshore waveinduced motions. The surface roller forces to move the maximum of the cross-shore profile of the mean longshore current toward the shore, and it increases longshore current velocity in the sandbar trough region. Consequently its effect improves the predictions of mean nearshore circulations and surface elevation. The surface roller effect, which gives the corrections to surfzone dynamics, plays a significant role on the shear fluctuations of longshore current. In this study, shear fluctuation changes depending on the surface roller effect were numerically analyzed. As a result, since the surface roller effect moves the maximum of the cross-shore profile of the mean longshore current toward the shore, the location of shear fluctuations was moved toward the shore. And the surface roller effect suppressed rapid rip currents or separation of vortices due to shear fluctuation out of the surfzone, and decreased its fluctuation energy.