Coastal Engineering 1992

Spectral evolution of breaking and nearly breaking waves propagating over a submerged trapezoidal bar has been investigated in laboratory experiments. It is found that wave breaking itself does not play a crucial role in the evolution of the spectral shape, but contributes simply by extracting energy roughly in proportion to the local spectral density. For nonbreaking waves, a Boussinesq model with improved dispersion characteristics is found to simulate the wave evolution very well. On the basis of these findings, it is suggested to combine a semi-empirical model for the overall energy dissipation with a nondissipative Boussinesq model so as to obtain a model for simulation of spectral evolution of breaking waves.

Data collected from measurements performed in waves propagating over a trapezoidal bar on a horizontal bottom are used to test a fully nonlinear numerical model. The experiments include both regular and random waves. Wave form evolutions in the shoaling region, the near resonant wave-wave interactions over the bar, and finally the decomposition behind the bar are well predicted. The results provide assurance for the reliability of the numerical model.

Twelve methods used for estimating the directional wave spectrum from heave-pitch-roll data are compared on realistic numerical simulations. These methods are based on different modelling approaches including simple and sophisticated ones: Fourier Series decomposition, Fit to unimodal or bimodal parametric models, Variational fitting technique, Maximum Likelihood Methods, Eigenvector Methods, Maximum Entropy Methods and Bayesian approach. The comparison is performed in terms of practical aspects such as estimation error, computation time, implementation difficulty... This study must be regarded as a preliminary step devoted to the choice of optimal methods for operational in situ measurements.

Two different flow models of the surf zone wave-current dynamics based on Boussinesq and Serre equations have been implemented and tested. Good results were obtained while testing the models against many diffent wave and current data sets. A preliminary calibration was tried but further activities are required to define the proper parameters.

Some basic properties and computational results are presented of a solution method for potential flow problems, with nonlinear waves at the free surface. The results show that stable and accurate results can be obtained for nonlinear wave propagation problems, up to the stage of breaking waves, though no numerical smoothing is applied. Also the interaction with constructions on the bottom can be computed well.

For efficient usage of the available CPU-time, a suitable condition for the time increments in nonlinear computations is given.

Laboratory measurements of irregular wave heights across a bar/trough beach profile are being studied to develop improved probability distributions including the subset of breaking waves. The energy dissipation in breaking waves modeled as a periodic bore is inversely proportional to the wave period and this may explain why the bore model appears to underestimate measured average energy dissipation rates. The study is ongoing and preliminary results for one wave period are presented in this paper.

We describe the sea wave forecasting system presently operational at ECMWF. After a short description of the meteorological and wave models, we address specifically the problems connected to their application to the Mediterranean Sea. We consider in particular two storms, a Mistral and an African storm, whose results provide clear indication of the present forecasting capability in this area.

A numerical model is presented for the prediction of combined refraction-diffraction of waves propagating in the region of slowly varying current and topography. For steady waves, two elliptic-type model equations are derived from the mild-slope equation which can be solved in a similar way to an initial value problem without stability restriction. Therefore, the present model appears to be an efficient tool for irregular wave propagation problem in a large coastal area. Some examples of numerical computations are given for the cases concerning wave-current interaction on a sloping beach and over a mound.

A recently developed numerical method is applied to the study of transient, nonlinear wave propagation in a flume. The nonlinear free surface boundary conditions and the wave generator boundary condition are expanded about the corresponding equilibrium positions by perturbation expansions. The boundary conditions are then satisfied to second order by a numerical integration in time, and the field solution at each time step is obtained by an integral equation method based on Green’s theorem. The propagation characteristics of regular, bichromatic and irregular waves are studied numerically, and the significance of nonlinear effects is highlighted.

A frequency-domain model is developed for elucidating the nonlinear transformation processes of the Fourier amplitudes and phases of normally incident random waves in surf and swash zones. The vertically-integrated continuity and momentum equations which have been used to describe a turbulent bore on a beach are rearranged to derive the equations expressing the cross-shore variations of the Fourier components of normally incident random waves. The derived equations are solved numerically using forcing terms computed from a previously developed time-domain model. The frequency-domain model attempts to quantify the importance of the nonlinear forcing due to the cross-shore variations of instantaneous radiation stress and bottom shear stress as well as the seaward boundary condition related to incoming low frequency waves for generating two-dimensional surf beat in the surf and swash zones.

This paper describes a two-dimensional numercial model capable of simulating non-stationary flows. Special emphasis has been put on wave motion on and in porous structures, e.g. a rubble mound breakwater. Comparisons of numerical simulations with analytical solutions and model test results have confirmed the applicability of this model for studies of waves and currents with regard to coastal structures.

The interaction of steady deep-water gravity waves with a preexisting large-scale curved current has been investigated. In order to investigate the influence of the curvature of the current on the wave field, the current field was represented by a section of an annular current with a particular non-dimensional radius R.

As a first approximation the interaction of a family of linear axi-symmetrical waves and the current was investigated. Exact linear ray solutions were obtained which, in the limit when $\text{R}\to \infty$ , reduce to the analytical straight current solutions of Longuet-Higgins and Stewart (1961).

Spatial distributions of wave crests are examined through numerical simulations of directional random sea surface. As the directional spreading of wave energy becomes narrow, the wave crests become long and the spread of individual crest directions become narrow. Simulations are extended to waves propagating into a planar beach. The areas of wave breaking are identified as the zone of surface elevation higher than the breaking threshold. The lateral spreading speed of breakers is analyzed from consecutive scenes of breaker crest patterns. It is about 30% of the forward advance speed of breakers.

The Particle Image Velocimetry (PIV) technique is reviewed, with special reference to its application to coastal engineering problems. The basic principles are described, and strengths and weaknesses of different implementations considered. Examples of some applications of PIV at Edinburgh are described to illustrate the practicalities of its implementation in a hydrodynamics laboratory. Finally, the limitations to the accuracy of PIV in these applications are reviewed and an outline of some new developments in this area is given.

The aim of these tests was to study wave propagation on a beach, including the surf zone, and nearshore circulation produced by breakers in the presence of a rip channel. The tests were carried out in a multidirectional wave tank. The initial series of tests concerned the case of a plane beach sloping at 1 in 30. The second series was performed with a rip channel excavated in the beach. Conventional wave measurements were taken at 50 different points. Measurements of the multidirectional waves and rip current were taken at 7 points along the channel centre line. During the tests, various types of wave (monochromatic, random monodirectional and multidirectional) were tested and the results obtained were compared with identical starting conditions.

This paper investigates the phenomenon of wave setup both on beaches and within river entrances. Field measurements of the mean water surface through the Brunswick River Entrance on the North Coast of NSW, Australia and on the beach immediately south of the entrance are presented for a variety of incident wave conditions. These include wave heights up to 4m (Deepwater RMS). Data collected show very little setup in the river entrance even though wave breaking occurs across the entrance under relatively small wave conditions. At the same time significant wave setup was measured on the adjacent beach. This resulted in the super-elevation of the beach shoreline level above the mean water level of the adjacent river. This super-elevation has been observed to result in large scour holes as the water finds its way through the entrance training walls.

This study aims to make quantitatively clear the breaking wave characteristics of a solitary wave incident to a submerged obstacle by performing intensive numerical simulations using a boundary integral method. The incident critical wave height, the break point and the breaker height are formulated through regression analyses based on the simulated results and are shown to be determined uniquly by using the regression equations.

This paper deals with 8 years of wave hindcast at 11 wave observation points along the coast of the Japan Sea using a long-term shallow water wave hindcast system, and investigation of its applicability to the estimation of wave climate. Comparison with observations for not only time variations of significant waves but also long-term sea state indices such as yearly-averaged wave height and period. The availability of the present system and the advantages over the deep water wave hindcast system previously developed by the authors are verified by close and more reasonable agreement with the observed data including mean wave direction.

In order to maintain realistic and expected incident waves, an absorbing directional wavemaker has been developed and its performance is examined experimentally. The directional spectrum of the generated waves in the progressive wave field is analysed by the Bayesian Model (BDM), and the directional spectrum of the incident waves in the combined wave field is separated by the Modified Bayesian Model (MBM). Good agreement is shown between the BDM result and the MBM result. In order to make a further check on the angular spreadings of the directional waves in the progressive and combined wave fields, coherence function of the cross spectrum is measured and compared with the target one derived theoretically.

A field directional wave gage has been developed for requirements in coastal, port, and harbor engineering. Uses include planning and design studies, long term wave climatology, and post construction monitoring. The gage provides high quality directional wave spectra measurements from a compact, easily installed instrument. Stand alone installation with long term internal data recording is provided. Real time data access may be simultaneously provided by connecting a cable. Reliable data storage and long term deployment are achieved by performing preliminary data analysis within the instrument.

In order to understand the relationship between entrained air bubbles and energy transfer inside surf zone, a special technique of He-Ne laser and 2D LDV were employed to investigate the characteristics of air bubbles concentration and velocity fields, respectively. The experimental results shows that the concentration profiles of air bubbles decay hyperbolically in the vertical direction and exponentially in the horizontal direction. With appropriate parameter groups, the distributions of air bubbles show a characteristics of similarity. The potential energy, kinematic energy and total energy decrease with the horizontal distance except that the kinematic energy slightly increases between the impinging point and the maximum penetration. Within this region, the energy loss of potential energy and kinematic energy is almost transferred to the air bubbles to merge into the water body.

The frequency-directional deep water wave climate along the Mediterranean coast of Israel was evaluated for the first time by computer numerical analysis using instrumental shallow water measurements. The shallow water data underlying the study were gathered within the period from 1984 through 1991 by two CAS (Cassette Acquisition System) wave measuring stations located off Haifa (North) and Ashkelon (South) along the Mediterranean coast of Israel. The paper includes a brief description of the data gathering, analysis, and processing methods, and it also includes main results of the study.

This paper is to investigate experimentally variation of the potential and kinetic wave energy in the surf zone. First, a cantilever-type velocimeter is newly devised to measure water particle velocities in an air-entrained water body above as well as below the wave trough. Laboratory experiments are carried out, and it is revealed that the kinetic wave energy is larger than the potential one and that some of the potential wave energy can be transferred to the kinetic one at the early stage of wave breaking.

A 2-D numerical model of bottom turbulent boundary layer is described. Trie nonlinear effects associated with wave asymmetry and the nonlinear interaction of waves and currents are taken into account. The model provides a relatively simple procedure for determination of both instantaneous and time-averaged quantities of velocity and friction inside the boundary layer.

Two different aspects of nearshore wave modelling are discussed. The first section details a model valid in deeper water than the usual shallow water wave models. We derive a mild-slope equation in which nonlinearity is retained to second order in ϵ and dispersion is retained to all orders. The resulting parabolic model is then simplified for expedient calculation. This simplified model is compared to the data of Whalin (1971) with favorable results. The second section concerns the role of vector-sum interactions as compared to colinear, near-resonant interactions. We use the angular spectrum model of Kirby (1990) to determine which sort of interaction is dominant in the nearshore wavefield. A steady wave solution of the model and a case of unsteady wave evolution were investigated. Two simplified data sets with different amounts of directional spread were then run through the model. All three tests indicate that vector-sum interactions contribute significantly to wave field evolution.

In this paper, the distance from the mid point between a wave trough and a consecutive wave crest of a zero-crossing wave (a position of wave height bisection) to the still water level is proposed to be an important zero-crossing wave property. Its roles on certain physical properties of the zero-crossing waves are shown through experimental data in the first part of the paper. Its probability distribution is introduced, in the second part, from the combined probability distribution of the amplitudes of consecutive wave trough and crest of irregular waves. In the last part, the theoretical probability distribution for this property is verified with numerically simulated data for many types of wave spectra.

Time dependent forms of the mild-slope wave equation are applied to the propagation of regular and irregular wave trains over variable bathymetry. The model equation of Smith and Sprinks is found to be a robust predictor of irregular waves, if the frequency spread for a single component calculation is not made too large. The model is extended to include forced, low-frequency components, and some preliminary results for bound and free long wave computation are shown.

This publication gives an introduction to the SWADE experimental programme. It presents examples of results of directional ocean wave spectra in polar format obtained by the third generation met/ocean buoy WAVESCAN. Then focus is made on a new algorithm "CUWA" that simulates non-linear Stokes waves propagating through regions of strong surface current.

A time-dependent mild slope equation is derived to simulate the deformation of irregular waves due to refraction, diffraction and breaking. It is based on Berkhoff’s mild slope equation, but the resulting model is capable of simulating the time evolution of irregular wave profiles. The validity of the model is verified through comparisons with experimental data in a wave flume. Application examples for two-dimensional problems are given.

Five comtemporary numerical models on wave-current interactions are evaluated in this paper. The bases of evaluation are mathematical exactness, degree of computational difficulty and practical applicability in terms of the abilities of handling shoaling, refraction, diffraction, reflection and wave-current interaction. Recommendations are given in matrix form on the relative merit of each model.

Random wave tests were performed in a flume to investigate wave transformations above a submerged bar built on a horizontal bottom.

Wave data were analysed in the frequency and time domains. In the time domain, reference was made both to short (f>0.5f_p) and long waves (with f<0.5f_p). This allowed in particular investigation of transformations of long waves passing over the bar.

Experimental results were interpreted using a second-order analytical model, able to separate first- and second-order components from given (measured) variance spectra. The analytical method proved to be conveniently applicable as long as breaking phenomena are not too intense.

Propagation and shoaling of irregular wave trains in shallow water is a nonlinear process, where substantial cross spectral energy transfer can take plane in relatively short distances. This process involves the generation of bound sub- and super-harmonics and near-resonant triad interactions, which are defined as the energy exchange between three interacting wave modes. It turns out, however, that the accuracy of the linear dispersion relation for higher wave numbers is of major importance for the exchange of energy even in shallow water and for this reason we recommend as governing equations a special form of the Boussinesq equations.

This paper develops a hybrid model for random wave transformation by employing a modified spectral model of the KdV equation and a probabilistic bore-type wave breaking model, and compares the numerical predictions with experimental observations. Main results are as follows: 1) Original frequency-domain KdV equation overestimates energy densities, due to over-shoaling term by Green’s law in the equation, even in a region where wave breaking is not seen; 2) Modification of the original KdV equation in order to represent shoaling for linear-dispersive component waves leads to better predictions in the non-breaking region; 3) Damping coefficients in the model equation, either estimated from measured spectral densities or the numerically predicted, are in inverse proportion to the water depth and in proportion to the square of frequency, similar to the viscous damping term of the Burgers equation; 4) The hybrid model developed here can predict transformations of random waves satisfactorily, as indicated by comparison of energy spectra, representative wave heights, periods, and crest heights.

Breaking condition of irregular waves on a slope is studied through a series of labolatory experiment of bichromatic waves. First, breaking condition of individual waves defined by zero-down crossing method is compared with breaking condition of regular waves. An emperical formula is proposed to take into account of the influence of both the depth and width of the following trough. Then it is shown that the breaking condition of regular waves can be applied succesfully when the individual waves are properly defined by paying attention to the nature of the wave crests. Finally these results obtained from the laboratory experiment are tested against the field data with reasonable success.

The development of a mathematical model to calculate the response of a simple oscillating water column wave energy device (OWC) to a known wave climate is described. The power available from the device is calculated and this is compared with results from model tests in a wave flume.

Particle Image Velocimetry (PIV) has been used to map the flow of water within the chamber of the device and vorticity maps have been calculated. The estimation of energy loss in vortices due to viscous dissipation is discussed in detail and is shown to account for as much as 8% of the total energy of an incident wave.

This paper discusses a feature of the generalized gamma distribution which is particularly appropriate for statistical analysis of long-term significant wave height data. The agreement between the cumulative distributions of the data and the generalized gamma distribution is shown to be satisfactory. Methods to estimate the probable extreme sea state (significant wave height) expected in a specified time period as well as the extreme sea state for design consideration of marine systems are presented.

The decomposition phenomenon of a nonlinear wave train passing over a submerged dike has been investigated by a previously developed numerical model. The model, based on the time-dependent boundary element method, employs an effective nonreflective open boundary treatment and can be applied to arbitrary nonlinear wave processes. The results for regular wave incidence indicate that the higher harmonics generated during passage over the dike are transformed into prominent free waves in the trailing side of the dike, revealing the essential mechanism of the observed decomposition phenomenon. The computed wave profiles at various locations agree favorably with experimental observations. The transformation of multicomponent random waves has also been investigated. The results show that a substantial amount of wave energy is transferred into higher frequency components. The power spectrum of the transmitted wave is found to be significantly influenced by the phase differences among the incident components as well as by the incident wave spectrum itself.

A probabilistic calculation model is developed, for the simplicity of inclusion of wave breaking and energy dissipation, to predict the transformation of directionally-spreading random waves by using parabolic refraction-diffraction equations. The numerical predictions are compared with the experimental observations of random wave transformation over an elliptic shoal by Vincent and Briggs (1989); the predictions agree well with the observations under the non-breaking condition, however, the agreement is poor under the wave breaking condition.

This paper presents the experience and results with a slope array of wavestaffs specially designed and built for directional wave measurements from an offshore platform off the Rio de Janeiro coast. We discuss the main features of the system, limitations and noise sources. A promising adaptive technique is introduced.

In this paper, the mechanisms which dissipate the energy of waves propagating on a current are considered. It is shown that the surface slope of an actual uniform current plays an important part for the variation of wave height attenuation rates with the intensity of the current. The surface slope enhances the attenuation of waves propagating on an opposing current and weakens it for a following current. It is also shown that, as the wave attenuation rate increases in stronger opposing currents, it affects the change in height of waves on a gradually varying opposing current to such an extent that we can not ignore the effect.

A simple approach to wave breaking using the concept of surface rollers is introduced in a two-dimensional Boussinesq model. A surface roller represents a passive bulk of water riding on the front of a breaking wave and the vertical redistribution of momemtum associated with the formation and change of surface rollers leads to additional terms in the Boussinesq equations. A simple geometrical method is used for the determination of the shape and location of these rollers at each time step in the simulation. This automatically results in a time-varying break point position in the case of irregular waves. Furthermore, breaking may well cease for example when waves reach a trough inshore of a bar.

Comparison between one-dimensional simulations and experiments shows good agreement for the variation of wave height and mean water surface as well as surface elevation time series throughout the surf zone for both regular and irregular waves. Simulations in two horizontal dimensions are still at the initial stage. A sample simulation is shown.

Field applicabilities of both the parabolic equation model and the energy flux equation model are verified through comaprisons with field data. The results show that the parabolic equation model has fairly good accuracy for estimating the wave height distribution of the actual wave field over a complex bottom topography, but the transformation of directional wave spectra cannot be reproduced satisfactorily in the surf zone. It is also found that the energy flux equation model is applicable for practical use although its basic equation has a shortcoming of not taking into account the diffraction in a strict sense.

This paper describes a two year experimental research programme investigating the influence of non-linear wave-current interactions on wave and current characteristics. The tests focus on the mean and oscillatory velocity components and shear stresses within the bottom boundary layer over a rough bed for cases where waves propagate at right angles to the line of the current flow. Bed shear stresses have been measured directly by means of a novel shear plate device. The aim of the research is to generate a reliable data set for use by modellers.

Results show that currents experience a significant change both in mean bed shear stress and apparent bed roughness when waves are superimposed. However, the oscillatory, wave-induced, bottom shear stress has been shown to be insensitive to the addition of an orthogonal current.

Steep, steady non-linear waves have been generated onto strongly sheared currents. Quantitative, full-field velocity measurements have been made for a number of wave/current combinations using the method of Particle Image Velocimetry (PIV). For one of the combinations, the measured kinematics are compared to the estimate obtained by adding the stretched current profile to the predictions from irrotational theory. The steadiness of the conditions is assessed by calculating the vorticity distribution for different cycles in the wavetrain. Finally, the measured wavelengths for a range of wave frequencies are used to estimate the effective current.

In previously reported laboratory experiments, the authors found that incident waves with the same characteristics in deep water break differently on barred and plane-sloping beaches. For example, waves of greater steepness that plunge on plane beaches tend to collapse on barred beaches, and plunge distance on barred profiles is about half that on a plane sloping beach for a given wave steepness. In the present study, wave height transformation, reflection, and runup of monochromatic and random waves are investigated for barred and plane beach profiles in a wave tank, with deep-water wave steepness varied from 0.0085 to 0.09. For monochromatic and random waves, wave-height to water-depth ratios are higher for waves breaking on bars, whereas just seaward of breaking these ratios are lower than on a plane beach. For plane and barred beaches, the ratios unite in the inner surf zone, and the magnitude and shape of wave spectra are the same at fixed points outside and inside the surf zone, except just shoreward of the break point, where the spectrum on a barred profile has the same shape but contains less energy. Despite differences in breaker-related quantities on barred and plane beach profiles, runup, reflection, and wave height transformation in the surf zone on barred profiles are mainly controlled by the plane beach slope on which the bar or reef is located, with only minor influence by a bar, even for extremely-shaped obstacles such as reefs.

This review of rational predictive methodologies for irregular wave kinematics confirms the crucial importance of the complete nonlinear free surface boundary conditions. Four methods, the global design wave method, the global linear superposition method, the local Wheeler stretching method and the local Fourier approximation method, have been compared for a very large measured wave from hurricane Camille. Free surface boundary condition errors are comparable to the wave height for the design wave and Wheeler stretching methods. They are sharply reduced by the local Fourier approximation method, though not eliminated. Linear superposition fails completely in the crest-trough region.

Modulation instabilities in surface waves on deep water are investigated. Experimental wave elevation records from laboratory tests are analysed, based on simultanous records at different distances from the wavemaker. Initially monochromatic and biohromatic wave trains are seen to gradually change with the propagation, by splitting up into smaller groups. After further propagation, large individual waves, and wave breaking, may occur. Results from tests with irregular (random) waves indicate that the skewness of the record, which is mainly a measure of 2nd order nonlinearities, is closely connected to the wave steepness during the whole propagation, more or less independently of other wave processes going on. The non-linear wave group formation, however, which is related to higher-order instabilities, show a development during the propagation. This may lead to frequency down-shift of the wave energy, combined with energy dissipation and wave breaking.

A nonlinear wave-current model is developed to obtain the velocity and shear stress. The model employing and "empirical velocity deviation" which introduces the modification of the time-mean velocity caused by waves is proposed. With an application of a time-invarient linear eddy viscosity and making use of the truncated Fourier series, a boundary value problem is formulated and is solved numerically. Comparisons among many cases of measured and predicted results show reasonable agreements.

A perturbation analysis is presented in which a series of small amplitude progressive gravity waves interact with a strongly sheared current. The solution, which is extended to a second order of wave steepness, shows that if the time averaged vorticity distribution varies with depth the wave motion becomes rotational. An additional wave component, expressed in terms of the first harmonic, is identified at a second order of wave steepness. This does not arise within an irrotational solution and is quite distinct from the Doppler shift associated with the surface current. Explicit solutions are given for the dispersion equation and the wave induced kinematics. These are found to be very different from the existing irrotational solutions, and suggest that the non-linear wave-current interaction terms can become very important if the current profile is strongly sheared in the vicinity of the water surface. In such cases the underlying velocity field should not be predicted by an irrotational solution based upon an "equivalent" uniform current.

This paper presents an application to the transition region of an integral momentum conservation model incorporating a Reynolds type decomposition for both wave and turbulent fluctuations. With simple parameterizations the model provides both a rough predictive capability for the limiting wave reduction across the transition zone and also an alternative means of examining the partitioning of flow momentum across the region.

Preliminary results of a numerical study of wave-current interactions in SWADE for 20 Oct. 1990 to 31 Oct. 1990 are presented. The results are obtained with the wave model WAVEWATCH, which incorporates both wave-current interactions and a full description of the dynamics wave growth and decay. It is shown that wave-current interactions are expected to be sufficiently strong to be observed in mean wave parameters, but that significant effects of interactions occur close to the Gulf Stream only. Furthermore, wave growth and decay are strongly influenced by the currents. Thus, modelling of wave-current interactions on the scales considered requires a comprehensive assessment of both (conservative) wave-current interactions and of the dynamics of wave growth and decay.

The progressive wave absorber discussed here in this paper contains several porous plates with different porosity. Four arrangements of progressive wave absorbers were compared in wave absorption. The results indicate that of the four arrangements examined, Arrangement 4 is the most effective at absorbing waves, for a relative water depth ranging from 0.05 to 0.5. The results also show that an eight-plate wave absorber is more effective than a six-plate wave absorber. When waves are well within the relative water depth ranging from 0.05 to 0.5, reducing the G value of the rear plates further may provide even greater wave absorption efficiency.

The aim of this paper is to analytically clarify the interrelation among all of the existing cnoidal wave theories of the third order approximation. The result is that the Chappelear theory expressed with two expansion parameters is found to include the other theories. This means that they are able to be derived from the Chappelear theory by changing expansion parameters in the expressions of wave characteristics and integral properties and identifying the definition for wave celerity to be used in the theory. The expressions for the trajectory of a water particle, mass transport velocity and integral properties of waves are newly derived using these theories, and the wave characteristics and integral properties are examined based on the numerical computation and comparison with the experiments. As a result, use of the theory expressed with a single expansion parameter is recommended from a practical viewpoint. The figures describing a limiting range of wave parameters for the application of the above-mentioned theory are also provided by comparing wave characteristics and integral properties of the theory with those of Fenton's Fourier approximation wave theory.

This study aims to make clear the cause and occurrence condition of two-dimensional (2-D) freak waves by solving the hydrodynamic equations of 2-D irrotational flow for nonlinear waves with various spectra corresponding to swell from wind waves and describing the long-time evolution. As a result, it is shown that the third order resonant interaction causes the 2-D freak waves of which surface profiles are very similar with those observed in nature and multiplies the occurrence probability with the decreasing of the spectral bandwith in deep water. Conversely, the feature of the freak waves — single and outstanding wave height — gets prominent with the broadening of the spectral bandwith.

A method for estimating the reflection coefficient is developed for practical uses. In the method, a parametric expression of directional spectra is adopted and the parameters in it are estimated by the maximum likelihood method. The validity of the method is verified by applying it to simulated data. The method is also applied to field data, obtained at Oarai Port, Japan.

A method based on linear wave theory is presented to decompose one-dimensional wave fields into left and right-travelling components using an arbitrary number of wave gauges. Results are presented to show that an increased accuracy is possible if more than three wave gauges are used. The technique uses a least squares scheme with variable weights. Results will also be presented that indicate a further improvement in accuracy is possible by an appropriate choice of the weighting coefficients.

This paper deals with the use of submerged detached breakwaters as beach protection, a use that today has become quite popular. This type of structure has been largely studied both theoretically and through experimental analyses in recent years, however its behaviour has not been completely understood, specially if related to the real irregular wave attacks. In particular some laboratory studies carried out by the authors have pointed out some interesting phenomena associated with the interaction between the nonlinearities of wave transformations in shallow water and submerged breakwaters.

Aiming at discerning between the phenomena related to the structure (beach and breakwater) and flume geometry, a new series of laboratory tests have been carried out in a 50 m long wave flume; these tests and the results obtained are described in this work. Besides the study of the behaviour of submerged structures related to the bounded-long-waves, some current velocities have also been measured during this research through directional micro-propeller fluid meters.

Field observations of waves were conducted inside and outside a harbor in order to study the behavior of surf beats. From the observations, it is confirmed that surf beats propagate as bounded long waves at depths of 13 to 15m, whereas they behave as free waves in the harbor. It is found that the amplitude of bounded long waves become 20% of the ordinary-wave amplitude when the ordinary-waves height is 5 m.

The generation of low-frequency waves (LFW, also known as ‘infragravity waves’) within a two-dimensional surf zone is investigated numerically using a short-wave resolving model. In this simplified model, based on the nonlinear shallow-water equations, breaking waves are represented by ‘bores’, at which there are jumps in both water depth and velocity. Some idealized trains of modulated waves are then used to investigate how LFW may be generated by forcing within the surf zone, as opposed to the mechanisms of bound wave reflection and moving break point forcing. In this way, the process of LFW generation may be examined in some detail. The model is also compared with some measurements of irregular waves in a flume: good agreement is obtained.

This paper is concerned with calculations and field measurements of low frequency or infragravity waves associated with wave grouping (frequencies in the range of 0.005 to 0.04 Hertz). These waves have periods in excess of wind generated waves and they are assuming particular importance now due to the effect they are thought to have on sediment transport in and near the surf zone. However, the impetus for the work described here originated from a need to quantify the magnitude of these waves in intermediate depths typical of harbour entrances: it being generally accepted that long period waves excite harbour resonances and moored ship movements, leading to berth downtime.

Extensive field observations in depths between 8-204 m are used to investigate the sources and variability of infragravity-frequency (nominally 0.005-0.05 Hz) motions on the shelf. The predicted local forcing of ‘bound’ infragravity motions by difference-frequency interactions of swell and sea (Hasselmann, 1962) is verified with array measurements of sea floor pressure in 13 m depth. Observed forced infragravity energy levels agree well with theoretical predictions, but are consistently much lower than the observed total infragravity energy. Wavenumber estimates show that free waves, obeying the surface gravity wave dispersion relation, are frequently the dominant source of energy in the infragravity band. The observed directional properties and cross-shore decay of free wave energy show that refractive trapping, neglected in many current infragravity wave generation models, is of O(l) importance. Both free and forced wave energy levels generally increase with both increasing swell energy and decreasing water depth, but the observed dependencies of free and forced waves are different. The relative contributions of free and forced waves to infragravity energy on the shelf are therefore highly variable. Comparisons of observations in the same water depth at different sites suggest that free wave radiation is relatively stronger from broad, sandy beaches than from rocky, cliffed coasts.

A finite-difference model is used to compare long wave amplitudes arising from two group-forced generation mechanisms in the nearshore: long waves generated at a time-varying breakpoint and the shallow-water extension of the bound long wave. Plane beach results demonstrate that the strong frequency selection in the outgoing wave predicted by the breakpoint-forcing mechanism may not be observable in field data due to this wave’s relatively small size and its predicted phase relation with the bound wave. Over a bar/trough nearshore, it is shown that a strong frequency selection in shoreline amplitudes is not a unique result of the time-varying breakpoint model, but a general result of the interaction between topography and any broad-banded forcing of nearshore long waves.

Three effects of surface gravity waves on storm surges in the North Sea are studied with numerical models. The enhancement of the effective sea surface roughness due to growing waves causes the storm surge to build up more quickly. The maximum effect on the waterlevel along the English and Dutch coast is about 5 % of the total waterlevel elevation due to the storm. The effect of the radiation stress is opposite: it slows down the building up of the surge in the beginning of the storm. The maximum effect of the radiation stress is about 2 %. The enhancement of the bottom drag by swell in shallow water can be considerable. The lack of detailed insight in the local bottom roughness and the turbulence near the bottom defies a quantitative analysis.

Laboratory measurements were performed on cross-shore velocity variations in the surf zone caused by random waves by using a laser Doppler velocimeter. Two-dimensional distributions of undertow and long-wave component velocity were obtained on a uniform slope bed and a bar-type beach. A model was presented to estimate undertow distribution due to random waves on an arbitrary beach topography.

The effect of wave grouping on the occurrence frequency distribution of maximum wave height was investigated on the basis of field observation data. The observed maximum wave height distribution fitted the distribution derived from Weibull distribution and was closely related with not only the wave grouping but also wave non-linearity. In the case of large degrees of wave grouping and wave non-linearity, it was found that the maximum wave height was greater than that estimated by the Rayleigh distribution.

Three field experiments were executed in the Straits of Messina starting in 1990 in order to verify the closed solution for the mechanics of the highest wave groups in a random wind generated sea state (Boccotti, 1984-88-89) . The paper presents the first experiment which was concerned with the first part of the theory: the wave groups in an open sea. An array of nine wave gauges and nine pressure transducers supported by vertical piles provided space-time information on waves generated over a fetch of approximately 10 Km.

The principal aim of this work is to quantify the long period (group) time scales associated with incident wave breaking in the surf zone. A video based sampling technique is employed to distinguish those waves which are breaking from those which are not. The technique relies on the gray tone contrast between higher luminance of turbulent generated bubbles and foam associated with wave breaking, and the darker, unbroken surrounding water. Video image intensity time series, I(x,y,t), are sampled across the width of the surf zone at 10 m increments, from just outside the shore break to the far offshore region of the wave breaking. Outside the point of minimum depth (at the bar crest), the width of the surf zone fluctuates over several hundred meters. In this region, low frequency oscillations in I, phase coupled to the crest of breaking incident waves, are associated with wave groups. Crossshore phase relationships indicate a shoreward progressive group structure up to the crest of the bar. Landward of the bar crest in the trough, low frequencies in I are uncoupled from group modulations seaward of the bar. Video data also show that wave breaking does not cease immediately as waves propagate past the bar crest, but continues well into the deeper water of the trough.

This paper deals with the statistical properties of wave groups in a stationary ergodic normal process. For a narrowband Gaussian process, a method based on Kimura’s theory is developed to estimate the characteristics of wave groups directly from the wave spectrum. For a non-narrowband Gaussian process with an arbitrary bandwidth, a new model is established to predict the formation of the wave groups by means of zero-upcrossing method. Thus the probabilistic structure of the wave groups in a Gaussian process with an arbitrary bandwidth can be determined. Using this model, the mean run length of the wave groups above any amplitude and the probability distribution of run length at any level can be obtained. On the other hand, a representative wave period of the wave group is suggested to describe the time intervals between two successive maxima. The computational data shows that the bandwidth parameter has a significant effect on the statistical properties of wave groups.

The statistical properties of four spectral shape parameters (Q_p, Q_e, κ and ν) and the correlation coefficient between succeeding wave heights (p_HH) are investigated using field data and numerically simulated data. The effects of spectral smoothing, integration range and duration of the data record on estimates of these parameters are discussed. The relation between spectral shape and wave grouping is discussed in relation to Kimura’s theory for group length statistics. A group length distribution independent method for computing this mean group length is introduced. Further, a comparison is made between time and frequency domain estimates of the correlation coefficient between successive wave heights. Observed discrepancies between them are analyzed and an improved method for the spectral computation of this coefficient is suggested.

A mathematical model is presented which describes cross-shore low-frequency motions generated by shoaling and breaking of wave-groups on a beach. The numerical scheme is tested against known analytical solutions for standing waves on a plane beach. Model results are compared with laboratory experiments (Kostense, 1984) which refer to bichromatic carrier waves incident on a plane beach. It is shown that, apart from a good representation of the trends found in the experimental study, for realistic values of the breaking and friction coefficients the computational results also quantitatively agree surprisingly well with the experiments.

Variations of the wave groupiness, cross-correlation between the incident wave envelope and long wave motion, and skewness of the near-bed velocity were measured on a macrotidal beach at Spurn Head, UK, as part of an experiment by the B-BAND (British Beach And Nearshore Dynamics) programme.

Wave groupiness persisted throughout the surf zone, and did not decay immediately at the breakpoint as is often assumed. The crosscorrelation between the incident and long wavefields varied systematically across the nearshore, with negative values outside the surf zone and positive values near the shoreline. Offshore of the breakpoint, the skewness of the cross-shore current was dominated by three contributions - (i) the skewness of the incident waves, (ii) the interaction between the incident wave energy and the mean flow and (iii) the correlation between the incident and long waves. Onshore of the breakpoint, contributions (i) and (ii) remained important, along with the interaction between the long wave energy and the mean flow. The relative importance of these contributions to the skewness was unaffected by the incident wave characteristics.

To understand the cross-shore distribution of the wave groups and the infragravity waves in a storm, field observations have been carried out at the Hazaki Oceanographical Research Facility. The relationship between the wave groups and the infragravity waves is examined. The infragravity waves are generated in the wave breaking process of the wave groups. The observed heights of infragravity waves in the surf zone agree well with the predicted one by modified Symonds’ model, in which a time delay of small wave breaking due to propagation is taken into consideration.

The aim of monitoring mound breakwaters is presented. Available techniques and Sines breakwaters monitoring program are described.

With the aim of providing improved methods for preliminary design of berm breakwaters, a series of physical model tests and a parameter study with special emphasis on the rear side stability of a trunk section have been carried out at the Danish Hydraulic Institute (DHI). The model tests included different geometries of the berm breakwater profile and a range of wave conditions. For each profile, the wave condition resulting in sea side and/or rear side damage was determined. As a hydrodynamic description of the overtopping waves would be very comprehensive, and at present is not available, a surf similarity approach in combination with a force balance for the armour stones has been chosen. A parametric expression for the rear side stability has been established and found to be in fairly good agreement with the model test results.

The influence of the angle of the incoming wave on the stability of a placed block revetment on a filter layer has been investigated. A computer program is described to simulate the flow in the filter layer for various wave conditions. The flow in the filter layer together with the wave conditions determine the loading on the revetment. Two different boundary conditions have been studied, A schemed wave pressure distribution based on results obtained for wave loading perpendicular to the revetment and regular waves measured in a wave basin. The results show that for regular waves the influence of the angle of the incoming wave on the loading of a placed block revetment is small for a revetment with a leakage length equal or larger than the wave height. Oblique incoming waves can result in a considerable increase in loading when the leakage length is much smaller than the wave height and near transitions in the revetment.

The propagation of long-crested and short-crested waves through a gap such as between two breakwaters is affected by diffraction. If the water depth is not uniform, refraction may also affect this penetration. It is shown with a navigation channel between two breakwaters (academic case and a realistic harbour case) that the effects of diffraction are small compared to those of refraction in regions where waves can penetrate with refraction only (e.g. where wave rays can penetrate). This region is relative large for short-crested waves. Outside these regions diffraction is dominant. With another example of waves penetrating through a tidal gap against a strong ebb current, it is shown that the short-crestedness of the waves destroys to a very large extent the waved guide effect of such currents. Both set of experiments show that the inclusion of short-crestedness in the wave computations causes some smoothing of the wave field, and that diffraction is a minor effect in regions with considerable wave motion. This is of some scientific and economic relevance as refraction can readily be combined in wave models with other physical phenomena such as wave generation and dissipation. Moreover, such models require less computer capacity than diffraction models which do not readily absorb wave generation and dissipation.

The slender, complex types of armour units, such as Tetrapods and Dolosse are widely used. Many of the recent failures of such rubble mound breakwaters revealed that there is an inbalance between the strength (structural integrity) of the units and the hydraulic stability (resistance to displacements) of the armour layers.

The paper deals only with Dolos armour and presents the first design diagrammes and formulae where stresses from static, quasistatic and impact loads are implemented as well as the hydraulic stability. The Dolos is treated as a multishape unit where the thickness can be adjusted to the strength needs.

This paper intends to present results of the research work on structural stability of tetrapods done at the University of Hannover. The results are brought in accordance with interpretations from the hydraulic tests made in the large wave flume and prototype realisations. The analysis of the data are supposed to bring a clarification of the similitude problems related to the transfer of the measured impact strains to prototype conditions.

This paper describes a mathematical model of the large but short-lived forces exerted on submerged solid bodies by a wave impacting on a plane impermeable surface nearby. We consider the forces on a hemispherical boulder situated close to a wave impact on (i) a vertical wall and (ii) a steep slope. We show that for certain positions of the body and for a sufficiently strong wave impact the impulsive force on the body can be much greater than either the flow drag or the weight of the boulder. For a body which is free to move under the wave impulse we compute the body’s initial velocity.

Just by placing hollow blocks in orderly patterns, all in the same direction and well interlocked among themselves, not only will their resistance against localized wave actions be greatly increased, but their resistance will vary little from one block to another. Furthermore, the risks of their breakage due to "rocking motions" and of the rapid spreading of damage once initiated, will be essentially eliminated.

To render possible the placement of blocks under the water surface in predetermined positions, in the presence of waves and currents, the blocks should be suspended simultaneously from three or four inclined cables.

A set of nonlinear vertically integrated equations has been derived to predict the transformation of waves over a submerged permeable breakwater on a one-dimensional topography. The square of the relative water depth is assumed to be of the same order as the wave height to water depth ratio and a set of second-order governing equations which are equivalent to the Boussinesq equations is derived. The equations have been applied to simulate non-breaking and breaking wave transformations obtained from laboratory experiments, in the latter incorporating a model for breaking wave energy dissipation. When breaking is nonexistent on the breakwater, the wave height as well as the wave profile is well predicted. However, the disintegrating character of the transmitted waves is weakly predicted. For breaking transformation, the wave profiles are predicted well prior to the lee of the breakwater where disintegration occurs.

Small-scale model tests were conducted to assess the wave transmission characteristics of low-crested breakwaters. The goals of this study are to quantify the wave transmission characteristics of these breakwaters for various structure heights, water depths, and wave conditions. The tests were conducted on cross-sections of solid and rubble breakwater models using both regular and irregular waves. A new parameter (F-Ru)/H_i, is then proposed to represent transmission past a breakwater for all values of breakwater freeboard.

Beach nourishment to provide an erosion buffer and increase amenity is a well established coastal management option and is favoured because it is a relatively "soft" option with few aesthetic drawbacks. This paper describes how enhancement and stabilisation of the natural accretion processes may be achieved by a low-cost beach drainage system. The project described here shows that the watertable and shoreline can be lowered by a drainage system installed in the beachface. A prototype system was installed on Dee Why Beach, New South Wales, Australia in February-March 1991 and has been continuously discharging water until the present (November 1992). A number of minor storms have exposed and caused some damage to drainage material but the system continues to work.

Survey data are being collected at regular intervals to show the effects of the drainage system on the watertable and the morphology of the beach. Analysis of changes in morphology in both drained and undrained segments of the beach shows a significantly more stable beachface in the area of the drained beachface.

Experiments were conducted in a wave flume to study the harmonic evolution of a normally incident linear monochromatic wave train as it propagated over a submerged impermeable obstacle of rectangular cross-section. The reflection and transmission characteristics of the system were studied and compared to a linear scattering model, which was found to overpredict the transmission coefficients. The experiment was also simulated using the fully nonlinear model by Grilli et al. (1989), which performed well given its inviscid potential assumptions.

For many applications it is possible to reduce the wave motion in the protected area sufficiently using the submerged plate as a wave filter. The horizontal submerged plate, which hardly obstructs the cross-section of the flow, cannot be explained by the Wiegel approach at all. A strong pulsating flow opposite to the direction of the wave propagation originates beneath the plate during wave attack. New velocity measurements, carried out with an ultrasonic 3D-probe in the region below the plate, make it now possible to explain the principle much more in detail. They show that the flow phenomenon at the plate is very stable, the flow is nearly as strong if the region below the plate is partly closed.

Flat impact of a solitary wave on a mixed breakwaters is experimentally and numerically studied, using a 2D nonlinear potential flow model. Free surface profiles, internal velocities, instantaneous pressure and pressure envelope on the wall, and on the berm, are analyzed based on both measurements and calculations. Results show, a converging flow occurs above the berm, followed by a small vertical jet, with large acceleration, that is responsible for large impact pressure on the wall. Short duration peak pressures occur above SWL, and quite large pressures also occur on the berm, as far away as twice the local depth from the wall. Maximum pressure force and overturning moment on the wall reach up to 9 and 15 times corresponding hydrostatic values based on water elevation at the wall.

This paper deals with detailed studies on wave-induced pressures on sloping seadykes and revetments. The presented results are found as well from extensive field measurements at the coast of the German Bight as from full - scale laboratory tests in the LARGE WAVE CHANNEL (GWK) at Hannover, Germany. Summerizing the results, a generalisation of shock pressure occurence with respect to deterministic and stochastic charakteristics and a "dynamic" loading model is presented.

In the design of a porous submerged breakwater, the maximum wave energy dissipation within the breakwater is desirable. To calculate the energy dissipation, the process is simulated numerically in this study using the Boundary Integral Element Method (BIEM). The breakwater is idealized as a homogeneous porous medium and the flow inside the breakwater is modeled by a non-linear porous flow model which is linearized iteratively based on the equivalent energy principle in the numerical model. To fully explore the advantage of BIEM, a boundary integral expression for wave energy dissipation developed in an earlier work by the authors is used to replace the traditional domain integral expression. As a result, the efficiency of the numerical model is greatly increased. The numerical model was run for a number of cases and the results show that the maximum wave energy dissipation can be achieved at a practical permeability level (or stone size). The good agreement between the numerical results and the experiment data for non-breaking waves indicates that the wave energy dissipation within porous breakwaters can be adequately predicted by the numerical model.

The interaction of an incident wave with a rubblemound breakwater results in complex flow patterns involving unsteady non-uniform flow. A reshaping or berm breakwater can be described as a mound of rock, often comprised of a wide range of stone sizes, which undergoes reshaping as a result of wave-structure interaction. As a consequence of this wave action, a stable profile is developed. Two major processes occur in the development of he stable profile. First, the overall geometry of the structure responds to the nature of the hydrodynamic loadings. Secondly, this natural sorting leads to consolidation (densification) of the armor layer as stones.

A series of two-dimensional hydraulic model tests was carried out to investigate the stability of rubblemound breakwater crown walls. The effect of seven design parameters on the minimum mass required for a crown wall to remain stable was studied: wave height, wave period, crown wall height, water level, front slope of the breakwater, position of the crown wall and length of stabilizing legs. Observations regarding the type of wave interaction, degree of overtopping, superstructure movement and overall hydraulic stability were studied. The coefficient of friction at the crown wall/breakwater interface was also measured. The crown wall superstructure was located on the crest of a conventional multi-layer breakwater and was subjected to both regular and irregular wave attack. Preliminary analysis of this data set is presented which shows trends established for each of the seven design parameters.

This paper describes the derivation of a stability formula for dolosse based on the physical model test results of Scholtz et. al. (1982) and Holtzhausen et. al. (1990). The derivation of the formula is based on dimensional analysis and subsequent curve fitting with a non-linear multi-variate regression model. The statistical treatment of the data made it also possible to estimate the confidence intervals.

Variables included in the formula are wave height, wave period, percentage displacement, dolos waist-to-height ratio, and armour unit density. Since not enough data were available to describe the effect of armour slope, only data for a slope of 1:1.5 were used. The test conditions and thus the derived formula represents deep water wave attack, that is, without a specific foreshore slope.

In theoretical study, when the maximum run-up on seawall was happened, the shape of the run-up wedge is assumed to be a parabola with its vertex at the bottom of the first wave trough. The another assumptions are the conservation of mass and momentum. In model test, four kinds of dyke slope (1:0.5, 1:1, 1:2, 1:3 )were choiced and the tests of the wind speed from 0 to 16 m/s accompany with a range of wave steepness were completed. The experimental data shows that the general form of the equations to developped was correct. Comparison of the theoretical estimations and the experimental data are coincident very well. Besides, the relation coefficient between the exponential value n of the parabolic runup shape with the surf parameter ( ξ ) was ranged in 0.19 to 0.65 in different kinds of dyke slope have been found also. At last, in general speaking, in spite of the strength of the wind speed, the relative run-up becomes the biggest when the dyke slope was 1:2.

The scattering of small amplitude water waves by an array of vertical cylinders with a solid vertical backwall is studied theoretically and experimentally. In the theoretical study, a method of matched asymptotic expansions is developed without considering real fluid effects. The energy loss due to flow separation near cylinders is modeled by introducing a complex blockage coefficient. The theories are compared with laboratory data.

The preliminary analysis of a set of three-dimensional tests on an infinite beach backed by a seawall is presented. The longshore sediment transport rate in front of the seawall was found to decrease as the beach in front of the seawall eroded. The location of the breaker peaks in the suspended and bed load sediment transport rate moved slightly offshore, and the bedload peak in the swash zone disappeared as the beach eroded. The local ratio of H/d approached a constant value as the beach eroded for most of the tests, however the erosion depth in front of seawalls cannot be simply related to offshore wave height.

Breakwater failures have often been caused by or at least exacerbated by a structural failure of concrete armor units, especially when the units are the more slender type such as dolosse. To aid in the development of a structural design procedure for complex concrete armor units, post-construction monitoring of movement and stress in dolosse has been ongoing on the outer breakwater at Crescent City, California since its rehabilitation in 1986. This paper describes the significance of static stress in large (38-tonne) dolosse and documents the continued rapid growth of dolos static stress in a relatively nested shallow-water breakwater. New data from 1990, 1991 and 1992 have modified the previously suggested conclusion that dolos static stress was increasing at a decreasing rate (Kendall and Melby, 1989). These new data suggest that while dolos movement has continued to subside, static stress has been building approximately linearly.

This paper is divided into two basic sections: (1) general background on dolos design considerations and the monitoring program being carried out at Crescent City, including new techniques for the photogrammetric monitoring of armor unit displacement; and (2) breakage, displacement, and static stress results through the sixth year of monitoring.

A one-dimensional, time-dependent numerical model is developed to simulate the flow over a rough permeable slope as well as the flow inside a permeable underlayer of arbitrary thickness for specified normally-incident irregular waves. The numerical model has been shown to be capable of predicting the time series and spectral characteristics of the reflected waves and waterline oscillations on a 1:3 rough slope with a thick permeable underlayer. The computed results are examined in detail to quantify the hydrodynamic processes which are difficult to measure in experiments. The computed results for the rough permeable and impermeable slopes are also compared to quantify the differences caused solely by the thick permeable underlayer.

Wave interaction with a vertical slotted wave barrier, also called a wave screen or slit-type breakwater, is considered. A theoretical analysis is presented based on application of the continuity, momentum, and energy equations to flow through the slots in the breakwater, accounting for head losses associated with flow constriction and re-expansion. As a result, relatively simple expressions are found for the wave transmission coefficient and for the wave forces on the wall. These are then verified by laboratory experiments with regular waves.

Interaction of transient nonlinear waves (modeled by solitary waves with moderate wave height) with submerged breakwater has been studied both numerically and experimentally. The emphasis is on the comparison between the numerical solution and the laboratory experiments on the wave transformation and the water particle velocity of the induced flow field.

For the numerical analysis, the Boundary Element Method (BEM) has been used for analyzing the wave field induced by the coastal structure. For the laboratory experiments the wave profiles are obtained by resistance type wave gauge; the two dimensional water particle velocities are obtained by a four-beam Laser Doppler Velocimeter (LDV) equipped with frequency shifting and with a fiber optics system. The LDV measurements are directed to obtain the detail of the wave kinematic properties important for ascertaining the dynamics of the modified wave field in the vicinity of the submerged breakwater. This serves as a critical check for the validity of the numerical computations.

Results of the numerical model have been found to compare well with the experimental data for the conditions studied in both the wave profiles and the water particle velocities beneath the waves as they interact with the breakwater.

The outer portion of the Ponta Delgada Breakwater in the Azores was constructed in the sixties, applying an armour layer of 25 t Tetrapods on a slope of 3 in 4. After two decades of recurring damage and repairs, a redesign and rehabilitation were undertaken.

An armour layer of 40 t Tetrapods on a slope 1 in 2 proved to meet the more severe design wave conditions established for the rehabilitation. This was the most attractive solution from cost and constructability viewpoint. To check the risk of breakage of these units under design conditions, the rocking was analysed both in hydraulic model and by means of an analytical simulation program. This allows to assess the actual impact velocities of rocking units and the percentage breakage under given wave conditions.

Rubblemound structures protected from wave action by a layer of quarried rock (stones) are the most common form of breakwaters. While extensive guidelines and procedures exist to select the size of stone there is very little information available on procedures to be followed to assure the quality of the in-place stone. This subject is not covered in depth in the principal breakwater design manuals such as the U.S. Army Corps of Engineers Shore Protection Manual (1984).

The necessity of a dynamic analysis and the dynamic approaches available in the CIS, formerly Soviet Union, for the stability of vertical structures subject to breaking wave impact loads are first briefly discussed. The different steps of the dynamic method recommended by the Russian Design Guidelines VNIIG-77 are presented. The results obtained by using the different static and dynamic methods for a numerical example are compared. Finally the effect of the nonlinear behaviour of the foundation of the structure under impact loads is discussed.

A new rubblemound breakwater cross section design named D-armor breakwater is presented. The D-armor cross section shows a significantly larger active armor area than the conventional cross section. The D-armor breakwater shows a similar resistance to the initiation of damage, but a significant increase of resistance to total failure. The observed structural response has a wave height range about 30% wider than the range corresponding to the conventional breakwater; the new section reshapes to an efficient S-shape armor near the total failure point. The D-armor breakwater appears to be a reasonable first step towards a convenient evolution from the conventional breakwater to more efficient designs; the wider structural response makes it appropriate for construction sites with large uncertainties in the estimation of the worst wave conditions in its lifetime.

Historically, concrete armor unit design has not included conventional structural design methods. The primary reason is the lack of knowledge of the loads and the resulting structural response. Also, complex and random boundary conditions and wave loading made the engineering problem difficult. With recent advances in concrete armor unit stress prediction and measurement methods, we can begin to utilize conventional structural design methods in concrete armor design. This paper adapts conventional structural reliability design methods in the Load and Resistance Factor Design (LRFD) format to allow a unified approach to both reinforced and unreinforced dolos design. Stress prediction methods are validated for several well known structures. Then LRFD methods are described and applied generically for both unreinforced and reinforced dolos design. The reliability methods described herein are adaptable for general concrete armor unit design.

The stability of the armor unit in relation to the wave force acting on a spherical armor unit of a submerged breakwater was discussed experimentally in this paper. Stability models were derived to relate the stable weight of the spherical armor unit with the wave forces acting. The proposed models were in good agreement with the experimental results. And the vicinity around the leading crown-edge was revealed to be the most critical location of the submerged breakwater.

The first part of this article gives an overview of the development works that have been carried out to date along the French coast, covering types, operating principles and impacts. A "philosophy" is identified with regard to the schemes implemented so far and those recommended for the future: rather than static structures that resist the action of the sea, it would often be preferable to substitute dynamic structures and schemes that work in harmony with it. Much research is being carried out on designs of this type. An analysis and summary of this work is given in the second part of this article. Most such work is currently at the experimental stage and no "miracle" solution has been found so far. Local conditions must be examined carefully before deciding to use any of the new alternatives being proposed.

Field analysis of breakwater damage progression has been performed using monitoring programs which included both photographic and topographic surveying. Reliable information on cover blocks displacement were obtained using a metric camera and a digitizer. Measured damage was compared with those estimated using empirical formulae.

A computer model, capable of predicting damage progression, has been also calibrated using in site collected data. Predicted damage has been satisfactory also for long time interval period.

The results of large-scale model tests are presented on the wave energy dissipation in the various layers of an Accropode armoured mound breakwater and on the interaction between external and internal wave motion. An attempt is also made to describe the "discontinuity" of the waterline at the boundary between layers of different porous materials. Wave reflection coefficients of the structure as well as dissipation and transmission coefficients through the different layers are evaluated as a function of the incident wave parameters.

A computer simulation model for the reshaping of dynamically stable breakwaters under normally incident, monochromatic waves has been developed. The proposed model is used to simulate initial reshaping as well as transport on the developed profile. Preliminary validation of the model has been carried out by comparison with data obtained from experimental tests on a berm breakwater.

A high accuracy boundary element method is used to compute the propagation of solitary waves from a constant depth region onto a plane slope. Initial wave heights range from H/h = 0.06 to 0.775, slopes between 1:35 and 1:1.73 (30°) have been investigated. The prebreaking shoaling shows very different characteristics on gentle slopes (1:20 and less) and on steeper slopes.

A diagram constructed on the basis of a large number of numerical experiments gives a simple limit between which waves break on which slopes and which not. Typical examples of the range of wave behavior are shown. Waves that do not break at run up often break during run down. The velocity fields for the two types of breaking are compared and found to be very different. A simple explanation for this is offered.

The results of large-scale model tests on impact loading and dynamic response of a caisson breakwater are presented.

Hydraulic model tests are performed in which the impact loading is induced by breaking waves on the structure. Horizontal impact forces, uplift forces and the related overturning moments are determined. The transmissibility of the impact loads and the accelerations of the structure are investigated (dynamic response)..

The hydraulic model tests are supplemented by pendulum tests on the same caisson breakwater model used in the hydraulic model tests in order to determine the characteristics of the structural model itself. The added mass of water oscillating with the structure, the stiffness of the foundation and the damping ratio are evaluated from these tests.

This paper presents some of the results from a large parametric laboratory study including more than 200 long-duration model tests. The study addresses both the wave forces imposed on the breakwater crown wall as well as the performance of the structure in reducing the wave overtopping. The testing programme includes variations of the sea state parameters and of the geometrical configuration of the breakwater and crown wall. Basic relations between forces/overtopping and the varied parameters are examined and preliminary design guidelines for structures within the tested range of variations are proposed.

A design algorithm for the optimal cost effective rubble mound structures is developed considering extreme wave statistics and wave control functions as well as the stability under the irregular wave attack. In the algorithm, the conventional deterministic design method and the optimization technique, SUMT (Sequential Unconstrained Minimization Techniques) are used to evaluate the minimum cross section of the structure.

The applicabilty and design sensitivity of the algorithm is examined using experimental data on stability, run-up / overtopping and reflection under the various irregular waves that have different wave grouping characteristics. The field conditions not only the construction method but also the costs can be introduced in the cost estimation subroutine.

A fully nonlinear simulation model was developed to predict the wave transformation interacting with a permeable breakwater. The present model was applied to simulate wave transformations due to a rubble-mound breakwater and due to a caisson breakwater covered with armor units and verified by hydraulic model tests. Numerical experiments were also performed to interpret the stability of armor units and the wave-induced pressure on the caisson through the pile of armor units.

To analyze a wave attenuation on a permeable layer, we first examined the applicability of Forchheimer type equation to the fluid motion in the permeable layer through permeability tests in steady and unsteady flows. Then, we investigated the effects of a boundary shear on the surface of the permeable layer on the wave attenuation by solving boundary layer equations around the surface of the layer.

It is found that the permeability and the turbulent drag coefficient in the Forchheimer type equation in the unsteady flow are different from those in the steady flow. We showed that the Forchheimer type equation could linearlize by using an equivalent linear drag coefficient formulated empirically through the permeability test. The effect of the boundary shear on the wave attenuation on the permeable layer was small compared with the effect of energy loss in the permeable layer if the thickness of the layer was relatively large.

It is also found that we can predict the wave attenuation on the permeable layer exactly when the incident wave has a strong linearity.

Results of large-scale model tests on impact loading of a vertical wall by using waves up to 2 m height and 9.4 s period are presented. A classification of the breaker types tested and breaking criteria for waves in front of a vertical wall are suggested. Impact pressure distributions, forces and force impulses induced by plunging breakers on a vertical wall are discussed. The statistical distributions of the impact pressures and forces for different breaker types are also given. Some aspects of the generation mechanisms of impact pressures and the role of air content and its statistical distribution in the impact process are outlined.

Experimental data has been obtained to test the abilities and limitations of existing and new empirical predictive methods for breakwater profile changes under random waves. The thirty data points obtained within this study describe a structure that is neither solely statically nor dynamically stable, and have indicated the difficulties of empirical formulas in accounting for the complex wave and structural interactions affecting breakwater profile development. Data analyses have indicated that current empirical formulas are not able to predict the profile changes very accurately for the data obtained herein. However, qualitative understanding can be obtained based upon the application and adjustment of the formulas to the structure tested herein.

The paper deals with full-scale wave attack on concrete block slope revetments. The tests were carried out in the research facility LARGE WAVE CHANNEL, Germany. The blocks were placed on a filter layer (granular and/or geotextile) preventing the failure of the sandy sub-soil. Stability results are reported. Pressure measurements at special testblocks were used to investigate uplift characteristics of the blocks. Furthermore, the measurements were applied for verifying analytical design procedures.

A report is given on a field measurement campaign on placed block revetments. Four types of measurement are described. Typical results are presented and discussed. The entire campaign shows a consistant image of changing physical properties in the field.

This paper describes a numerical model of wave action onto and into a rubble mound breakwater. The model is constructed of two parts, the wave action on the exterior of the mound in which a boundary element method is used and flow inside the rubble mound in which a finite element method is used. The two parts of the model are coupled by demanding continuity of flow through the front face of the breakwater. The predicted pressures within the core of the rubble mound are compared with data collected from physical model tests.

A flexible submerged breakwater called "flexible mound", made of an elastic membrane bag filled with water, has been developed for wave control in shallow water as an advanced alternative to the conventional rigid submerged design. Experimental studies were carried out to compare the characteristics of the wave dissipation by flexible mound with those by rigid models. The appropriate ranges of important parameters affecting the efficiency of the flexible type were identified. Numerical studies were also conducted to investigate the mechanism of wave absorption by the flexible structure. To verify the stability and utility of the flexible mound, additional experimental studies were performed using a prototype model. A design concept involved in an actual field construction of the flexible breakwater is also presented.

A deepwater caisson breakwater has been developed by the Ministry of Transport, Japan. The new breakwater is a composite breakwater with a cylindrical caisson named as dual cylinder caisson. The caisson has dual cylindrical walls and its outer cylinder has a perforation in the fore half of the upper portion, forming a wave chamber of a doughnut shape bounded by its inner impermeable cylinder. A series of laboratory experiments had been carried out at the Port and Harbour Research Institute from 1985 to 1988. Prototype experiments of the dual cylindrical caisson breakwater have been conducted in order to verify its proposed design method against waves at Sakai Port by the Third District Port Construction Bureau, since 1989. A distinguished attempt in the field experiments was tried to measure the displacement of caisson as well as wave pressures during sliding due to high waves. This attempt was accomplished by a storm occurred on February 17, 1991.

This paper gives a mathematical description of high frequency pressure oscillations which are observed in measurements of water-wave impacts; particularly impact against a vertical wall. Our ultimate aim is to trace the physical origins of the pressure fluctuations which are related to the understanding of the role of fluid compressibility in breaking wave impact pressure. We investigate possible cases by simplifying the geometry and finding the frequency of free oscillations. We ignore the main flow of water since it has a longer time-scale. Our initial model considers compressible aerated water near the wall and compressible non-aerated water with a much higher sound speed further away. This is compared with a simple example of an air pocket trapped against a wall in incompressible water. Comparisons with three experimental results are encouraging.

Water particle velocities in waves running up and down a berm breakwater have been measured for several wave heights and wave periods with a Laser Doppler Velocimeter (LDV).

The measured water particle velocities have been compared with velocities computed with the numerical model ODIFLOCS. There is a fair agreement between the calculated and measured velocities.

When the construction of the Zeebrugge Outer Harbour was finished a full scale monitoring system was realized as a part of the global monitoring and inspection programme.

The monitoring system was designed to follow the water level- and the water pressure fluctuation inside and in front of the breakwater.

A general description is given of the instrumentation of a section of the NW-breakwater followed by a global overview of the data-acquisition system and off-line data processing.

Results from the primary analysis of the raw data of relevant storm measuring sessions are presented.

Three-dimensional physical models of detached rubble-mound breakwaters have been built with separate Total Section, Front Slope, Crest and Back Slope sections. The stability responses of the armor units of this sections have been tested using irregular waves and differents freeboards.

The stability curves relating the level of damage, the stability number, N_s, and the freeboard, have been obtained for each one of the different sections defined on the breakwaters. A distinct behaviour of the different sections have been found. The curves that plot the stability number against the freeboard for a given level of damage shows a minimun for a intermediate freeboard for the Crest and Back Slope sections. The total section stability response is a combination of the response of each one of its components. As a consequence, relative minimums of stability may appear for intermediate freeboards, due mainly to the contribution of the Crest failure to the total stability.

Two main classes of maintenance are discerned: corrective and preventive maintenance. In this classification only the last subclass contains inspection besides repair. When a corrective maintenance strategy is applied, the structure will be repaired after failure. In a preventive maintenance scheme the structure will be repaired at specified intervals defined in time or operational hours before failure occurs. In a more refined strategy the state of the structure is inspected at such intervals. On the basis of the inspection result the decision to repair is taken.

A Finite Element Model for the simulation of the wave-induced flow in a porous structure is presented and applied to three types of structures: homogeneous vertical structure, homogeneous trapezoidal structure and traditional multilayered rubble mound breakwater. The obtained results are related to the motion of the phreatic surface, the pore pressure histories and distributions within the structure as well as to the internal velocity field induced by wave action. The problems to be solved in order to get an improved numerical model are discussed.

The results of an extensive series of permeability experiments originally analysed by Shih (1990) are reinterpreted in the light of new experiments. It is proposed that the Forchheimer equation might not fully describe flow at the high Reynolds numbers found in the interior of rubble material. A new series of tests designed to test for deviations from the Forchheimer equation and investigate the effects of material shape are described. While no evidence can be found to indicate a deviation from the Forchheimer equation a dependency of permeability and the surface roughness the material is demonstrated.

Recently, waterfront development and the mean sea level rise due to greenhouse effect have been noticed, and it has become important to develop a practical method to calculate wave run-up height or wave overtopping rate.

This paper presents new methods for calculating the wave run-up height on and the wave overtopping rate over a seawall located on a complicated bottom profile of sea coast. The proposed methods were tested both in the laboratory and in the field. The predicted results coincide well with the available data.

To limit erosion during severe storms, it is considered to apply a hard core in a dune, prior to beach nourishment. One of the potential structural alternatives is a gabion protection. The behavior of gabions was studied. It appeared that the rigidity is a factor that cannot be neglected in model investigations. Full scale tests have been carried out to establish the flexibility in prototype. A model material was developed to reproduce the flexibility on model scale.

Delft Hydraulics has recently performed various applied research studies in physical scale models on wave runup and overtopping on various structures. Runup has extensively been measured on rock slopes. Runup and overtopping have been measured on smooth slopes, including the influence of berms, roughness on the slope, shallow water, short crested waves and oblique (long and short crested) waves. The paper gives an overall view of the final results, such as design formulas and design graphs.

A 2-dimensional program for simulation of wave motion on coastal structures is described. The program is based on the Volume Of Fluid method and is able to describe fully plunging waves on all kind of structures.

Impact wave pressures acting on a vertical wall were discussed by simultaneous measurements of the pressure and wave shapes at impact.

Experiments confirmed the principal role of adiabatic processes of trapped air bubbles to the generation of impact pressures. The most severe impulsive pressure was observed when breaking waves hit the wall with trapping small air bubbles or a very thin lens-shaped air pocket. The larger the amount of the entrapped air, the lower the magnitude of the impact pressures. Due to the pulsation of the air pocket, damped pressure oscillations were observed immediately after the impact pressure.

A predictive model, taking account of the adiabatic compression processes of the trapped air pocket, predicts fairly well the maximum impact pressure and the frequency of the damped pressure oscillation, in the case when plunging breakers collide against the wall.

A numerical model is developed to predict the stability of rubble bases exposed to wave action. A boundary element method is applied to solve the problem of wave interaction with a caisson and its rubble base, and to calculate the velocity field. The predicted velocities are used to determine the destabilizing forces on individual stones. Theoretical results reveal two local minima in stability: in very shallow water and at intermediate depths. The rubble base stability increases with decreasing incident wave height, the rubble base height and the bench width. Preliminary results also show that the stability depends on the damping properties and that the stability increases with increasing permeability.

The paper discusses the morphological development of the Venice Lagoon since 1850 and, on the basis of analyses of the system, presents models to simulate large scale development of the lagoon and of various sub-basins.

The morphological development consists mainly in a continuous erosion of the selt-mershes and shallow areas, and a filling of canals. Also a general loss of sediment from the lagoon was observed. The main causes were identified in engineering structures like jetties, dredging of artificial canals and maintenance dredging.

These works resulted in a disequilibrium of the natural hydraulic system. In addition, loss of biological protection in shallow areas, due to pollution, has contributed.

Models were prepared on basis of time and partially averaged concentrations of sediment in shallow areas and canals. Averaging was carried on over a full year.

This approach facilitated the building of models of various complexity, which were found to be useful tools in the analysis of the effectiveness of remedial measures.

Sea level oscillations related to astronomical and meteorological tides in the Lagoon of Venice are analysed in order to find evidence of a possible chaotic nature of the phenomenon. On the basis of the analysis of the signal spectrum and by considering the values of the correlation dimension and of the largest Lyapunov coefficient of the attractor of the system, it is possible to infer that tidal oscillations inside the Lagoon of Venice are the result of deterministic dynamics, i.e. of a chaotic system characterized by few degrees of freedom. In the second part of the paper, taking advantage of the chaotic nature of the system, Farmer & Sidorowich's (1987) algorithm is used in order to make predictions of the time development of the system.

The Rete Ondametrica Nazionale (RON) – the Italian Wave Measurement Network – is a system for recording directional wave motions along the Italian coasts, operational since 1st July 1989. The network includes eight waves directional wave Datawell buoys and the corresponding land-based receiving stations. Following an international tender, the Ministry of Public Works appointed TEI SpA for the design and management for the network and for data processing. After three years of continuous operations (1989–1992), it is now possible to make a preliminary general account of the venture.

The prevention of flooding inside the Venice lagoon requires a system to disconnect the North Adriatic sea and the lagoon hydraulically in order to control water level. This paper describe the method followed to define design wave conditions to support the design of the new storm surge barriers. The derivation of design waves was not straightforward because of the presence of an extended continental platform and irregular geografic boundaries.

In the case of long-term morphological models of tidal lagoons, semi-empirical expressions of the residual terms can be found. The relative calibration coefficients may be then identified by comparison with field data and/or with a limited number of simulations carried out on short-term models. In some previous papers, long-term morphological models of a tidal lagoon have been developed with different space-resolution (zero-dimensional and two-dimensional approach) by considering only one equivalent (uniform) sediment grainsize. The zero-dimensional procedure, in particular, has been applied to the Lagoon of Venice. In the present paper the two-dimensional model is reconsidered and extended to the case of particles with different grainsize, ranging from sand to silt.

Two field campaigns (respectively commencing 11th June 1990 and 2nd March 1991) were carried out in the Lagoon of Venice, involving detailed fine-scale temperature and conductivity measurement surveys. The aim of these experiments was to assess the role and influence of the buoyancy introduced around the perimeter, by freshwater inputs, on the dispersion in the lagoonal waters. The investigations showed the following major features: (a) The tidal flow in the canal system is a mixture of barotropic and baroclinic flows; the degree of baroclinicity being dependent on the phase of the tide and on the salinity difference within the canals and was strongest in the areas which had direct freshwater input. (b) The water masses on the shoals appeared to be formed in an orderly explicable way. As the water rose in the channels and reached a point where the water broached the shoals, the salinity of the inflowing water was completely determined by the surface salinity at the point of broachment in the tidal channel. The shallowness of the water of the shoals led to a pseudo potential flow.

The paper describes the relevant set of analogical, mathematical and phisical models used to simulate the hydrodynamics phenomena of the Venice lagoon. The various models are devided in two classes, depending on the scale: the great scale models, to examine the problems interesting the entire lagoon, and the little scale models for the problems localized near the inlets, where the barrages will be built to control the lagoon water level.

This paper gives an overview of the development of design and construction of coastal defence works in Venice. In fact shore protection is one of the tasks of the present large project for the safeguard of Venice lagoon. A brief description is given of the most interesting steps of the new design supported by extensive field measurements and interactive model testing. An introductory review of the old historical structures for the defence of the lidos (in part still existing) is also given to underline the important links with the past experience and the unusual constraints of the present designs.

In the sheet flow region where several layers of grains are mobilized, grain to grain collision performs a main role in the momentum exchange. The relationship between the applied stress and the bulk deformation is not a Newtonian, and depends on the grain concentration and the rate of deformation. Hanes-Bowen (1985) have proposed a granular-fluid model to describe intense bed-load transport in an uni-directional flow. Shibata-Mei (1986) have proposed another granular-fluid model in so-called macro viscous region where the shear rate is low and granular friction is as important as granular collision. Mathematical expressions to describe velocity profiles and granular discharge have been deduced. These studies provide physical insight into the mechanism of sheet flow.

During the SUPERTANK data collection project, a mobile, vertical array of five Optical Backscatterance Sensors was used to measure sand suspension in the outer surf zone. Test conditions included both regular and random waves, and two different wave energy levels. Examination of the data reveals significant cross-shore variation in both the structure of the time-dependent concentration, as well as mean suspended load.

The interaction of beaches and seawalls is a highly controversial subject today. Many of the arguments both "for" and "against" the construction of seawalls have been speculative. Few are based on actual field or laboratory measurements. This paper is part of a continuing study at one location, which intends to shed some light on this controversy using statistical analysis of real field data.

Sediment auto-suspension criteria (specifying the limit between eroding, selfaccelerating flow and depositing, decelerating flow depending on the slope angle and particle settling velocity) differ by two orders of magnitude for different models in use. Experiments suggest that the results from ordinary density currents are applicable to turbidity currents. In the present study, models based upon well-known turbulence closures are applied in order to obtain a realistic description of turbidity currents:

A two-equation (k-ε) model predicts phase plane behaviour in accordance with results from theoretical work reported in the literature, and with limits for auto-suspension within the range of conventional estimates. However, by its design, this model and simpler gradient diffusion models are unable to produce turbulent diffusion of sediments up through the level of the velocity maximum.

A model with second-moment Reynolds stress turbulence closure is applied. This model proves to overcome the problem of vanishing turbulent diffusivity in the velocity maximum and give plausible results for vertical distribution of flow parameters in turbidity currents.

The fluctuations of sediment concentration and velocity during a wave period may play an important role in cross-shore sediment transport. In this study, the contribution of the fluctuations was estimated by measuring time-varying sediment concentration and velocity under laboratory conditions. The results showed that the contribution can only be neglected if the mean flow is relatively strong compared to the wave orbital motion.

In the present report experimental results about the efficiency of a submerged structure are presented. The experiment, carried out with random waves, covered about 2500 hours until equilibrium profile was reached. The most significant results are the good behaviour of the tested breakwater as a sand holding structure and its slowing effect produced on the shoreline backing, whereas the final position of the shoreline was nearly the same with and without breakwater.

Three quantitative equilibrium beach profiles models are presented for random wave fields. Two models follow the work of Larson where improvements to the spilling breaker assumption are made with spectral estimations of wave breaking. The third model is established by imposing a no-net sediment transport condition on Bailard’s (1982) cross-shore sediment transport formulation. Modelling the flow field as in Roelvink and Stive (1989), an equilibrium solution is achieved which includes a longshore bar.

The British Beach And Nearshore Dynamics (B-BAND) programme is a three year collaborative research project aimed at improving understanding of surf zone sediment transport processes. Field studies were carried out on dissipative, intermediate and reflective beaches during both neap and spring tides (tidal range up to 9m), and during storm wave (H_b > 3m) conditions.

The field research system comprises up to 7 pressure transducers (PT’s), 11 electromagnetic current meters (EMCM's) and 12 optical backscatter sensors (OBS's). The focal point of the instrument array was a 1600m² box which was instrumented at each corner and designed to allow the calculation of alongshore and cross-shore suspended sediment fluxes through the box.

The largest sediment transport rates (up to 0.6 kgm^-2s^-1) occurred in the inner surf zone of the dissipative beach during storm conditions and showed strong offshore-directed sand transport at infragravity frequencies. The extent to which infragravity oscillations developed was seen to vary inversely with the degree of beach reflectivity, and directly with the incident breaker height. Sediment transport patterns often exhibited strong tidal asymmetry, attributed to the effects of beach dewatering and to a lag between hydrodynamics and bedform alteration.

A laboratory study was conducted to investigate mechanisms of bar formation with particular focus on infragravity wave and break point mechanisms. With one exception, all tests commenced with a planar beach composed of fine sand. Infragravity (IG) waves, the result of a biharmonic primary wave spectrum, were generated and documented. For various frequency differences of the components of the primary spectrum and thus the frequencies of the IG wave, the changes in nodal/antinodal positions were compared with the changes in positions of the bar formed during the experiment. It was found that the bar position experienced relatively small movements whereas the nodal/antinodal positions changed substantially as expected with the difference frequency of the primary waves. The approximately constant bar position was interpreted as due to the relatively constant primary wave height characteristics. The effects of the wave spectrum and wave height distribution on bar formation were investigated. The shape of the wave height probability distribution function was found to exert a noticeable control on the degree of bar relief, with those distributions characterized by a substantial concentration near the maximum wave height causing the more prominent bars. This is interpreted in terms of a transport influence function which, if held stationary, would result in a narrow prominent bar. The distributions with a small concentration near the maximum wave height resulted in a less prominent bar. A conceptual model is proposed which incorporates the transport distribution function and which results in bar characteristics which depend on the initial conditions.

Experiments were conducted on initiation and transport rate of sheet flow under asymmetric oscillations. Values of net sand transport rates under asymmetric oscillations and superimposed currents were also measured. In this paper, based on physical interpretations, a new parameter representing the observed transport mechanism is derived. Using this parameter a general transport formula is then presented and applied to estimating the net transport rate and its direction; fairly good agreement with the experimental results is observed. It is shown that the newly introduced parameter together with the sediment Reynolds number can fairly well express the inception of sheet flow.

Early 1991, Statoil started with the installation of a 40 inch diameter gas pipeline between the Sleipner and later Troll field in the Norvegian sector of the North Sea and the harbour of Zeebrugge on the Belgian coast.

The connection between the offshore and the onshore pipeline was performed in August 1991, in the landfall area of Zeebrugge. The design and the construction of the landfall in the nearshore area required an extensive survey and engineering program taking the environmental parameters and the coastal processes into account.

The performance of a beach nourishment at "Playa de Castilla" (Huelva, Spain) is evaluated by means of accurate beach profile surveys, visual breaking wave information, buoy-measured wave data and sediment samples. The shoreline recession at the nourished beach due to "profile equilibration" and "spreading out" losses is discussed. The modified equilibrium profile curve proposed by Larson (1991) is shown to accurately describe the profiles with a grain size varying across-shore. The "spreading out" losses measured at "Playa de Castilla" are found to be less than predicted by spreading out formulations. The utilization of borrowed material substantially coarser than the native material is suggested as an explanation.

A project to analyze historic shoreline erosion and to predict future erosion in Florida is discussed in this paper. Information is given concerning the data base and the methods of analysis. Some examples are provided illustrating the use of various analysis tools. The utility of numerical modeling as a newly developed analysis tool is discussed in particular. Some of the general results of the study are noted, as well as conclusions and opinions concerning the effectiveness of the program.

A predictive theory for the formation of ripples under sea waves is presented for a sandy bottom characterized by a large grain-size distribution. The theory is based on a linear stability analysis. The conditions for the amplification or decay of bottom perturbations are determined and the experimentally observed sorting effect due to the presence of the bedforms is modelled. A comparison between the experimental data available in literature and the present results is attempted.

Full scale laboratory flows producing vigorous bed load transport are conducted at varying periods but constant maximum velocities. The time-varying sediment transport in the first half cycle is measured using video imaging of dyed natural sand. The acceleration of the fluid (proportional to the frequency of the oscillation in these experiments) is found to significantly affect the velocity of the sediment response (bedload transport), and the phase and the absolute magnitude of fluid velocity associated with the initiation of sediment motion.

The boundary layer approximation solution by Mei and Foda (1981) is applied to and its applicability is confirmed for the porewater pressure variation in a seabed under a breaking wave in a surf zone. Then the approximate solution is modified to take into account effects of the wave-induced bottom shear which is not negligible in the surf zone. This modified solution is applied to estimate the terms in the right hand side of the momentum equations for the solid skeleton under the breaking wave. The instability proposed by Madsen (1974) is discussed based on the estimated results. It is suggested that the instability just after the wave crest passing is more likely to occur than the instability just before the crest passing. Just after the crest passing, the horizontal gradient of the porewater pressure is large, while the vertical effective stress is small.

The present paper briefly presents 6 different models for short term coastal profile modelling for direct incoming waves. The models have been tested against measured profile evolutions from a large wave flume. Features such as wave height distribution, cross shore current profiles and sediment transport are compared and discussed.

In the previous paper, a fixed ripple model with a sharp crest was used to investigate the characteristics of oscillatory flow in the vicinity of wavy boundary. The above ripple model is useful to proof the adaptability of the analytical treatment presented by Longuet-Higgins (1981) and to extend our knowledge on the present subject. However the stated model is too simple to represent the real shape of sand ripples appeared on the sea bottom. From such a view point, in the present study another fixed ripple model with a round crest was selected. This model has the shape almost similar to the previous one except in the vicinity of the crest.

A two-dimensional LDV was used to measure the flow velocity at preset grid points. By using these velocity data the vorticity at each grid point was calculated and the equivorticity lines were drawn for the sharp crest ripple as well as the round crest ripple at various phases of oscillatory flow. Then the circulation outside the vortex was evaluated. Based on the available data the temporal variation of the circulation was discussed quantitatively. Finally criteria of vortex formation were introduced and the physical meaning of these criteria was discussed.

To investigate the mechanism of beach erosion in a storm, a daily survey of beach profile and the measurement of infragravity waves near the shoreline have been carried out in a field during two and half years. Analyses of these data reveal that the infragravity waves and the level rising of water table play a important role in the berm erosion in a storm. The infragravity waves run up beyond the berm crest to the backshore. The swashed water permeates into the beach, which contributes to a high water table. The permeated water rises to the surface of foreshore, where the beach is eroded by the backwash of infragravity waves.

In this paper the coupling of a quasi-3D model for the suspended sediment transport with a quasi-3d model for the wave driven flow is presented. The quasi-3d model for the transport is based on an asymptotic solution of the wave-averaged convection-diffusion equation while the quasi-3D wave driven current model is based on a profile function technique. The resulting model is a low cost but detailed alternative to a full 3D model. An application is presented concerning cross-shore transport. Preliminary conclusions are drawn.

The process of sediment sorting under rough sea state was made clear in the cross-shore direction. Field observation reveals that ripples can be formed under high shear stress in which the Shields number is more than two. The plane bed condition is observed at narrow area of wave breaking. Strong undertow distorts the shape of ripples. The criterion of bed configuration given by Kaneko (1981) is good agreement with the field data which were rearranged with significant wave characteristics. The criterion of Komar and Miller (1975) is also applicable with mean wave ones.

For the prognostication of sediment flow during storm period an investigator has to know if there are any microforms at the bottom in a certain place and under certain wave conditions, and what are their characteristics.

In the summer of 1991, a multi-institutional cooperative laboratory data collection project called SUPERTANK was conducted to investigate cross-shore hydrodynamic and sediment transport processes using the large wave channel located at Oregon State University, Corvallis, Oregon. The channel is 104 m long, 3.7 m wide, and 4.6 m deep, into which a 76-m long sandy beach was emplaced. SUPERTANK is believed to be the most densely and comprehensively instrumented nearshore processes data collection project performed in the laboratory or the field. At the peak of data collection, the channel was instrumented with 16 resistance wave gages, 10 capacitance wave gages, 18 two-component electromagnetic current meters, 34 optical backscatter sensors (OBS), 10 pore-pressure gages, 3 acoustic sediment concentration profilers, 1 acoustic-Doppler current profiler, 1 four-ring acoustic benthic stress gage, 1 laser Doppler velocimeter, 5 video cameras, and 2 underwater video cameras. Broad- and narrow-band random waves and monochromatic waves were run with zero-moment wave heights in the range of 0.2 to 1.0 m and with peak spectral periods in the range of 3 to 10 sec. The wave generator absorbed waves at the peak spectral frequency that were reflected from the beach and structures such as dunes and seawalls. Twenty major data collection runs were made, most defined as starting from a new beach profile, and approximately 350 profile surveys were taken to record beach response during the 129 hr of wave action. This paper gives an overview of the SUPERTANK project and presents example results.

This paper describes an attempt at investigating the actual time scale needed to form beach cusps, and the issue whether beach cusps are accretionary features or erosional ones. Data was collected through a field experiment. The experiment was conducted by tracking the process of beach cusp formation on a beach face, which had been flattened in advance by erasing previously formed beach cusps with a bulldozer. New beach cusps gradually developed with every high tide and attained a similar size to the previous ones after three tides.

This paper presents empirical predictive expressions describing the cross-shore movement of linear nearshore bars, based on intensive analysis of survey data from Duck, North Carolina. The analysis centers on 300 beach profile surveys taken at approximately 2-week intervals for the continuous period from 1981 to 1989, together with accurate measurements of the wave conditions. The geometry and dynamics of bars derived from the surveys are related to wave characteristics, and criteria previously developed by the authors to predict beach erosion and accretion are found to be applicable to bar movement if a multiplicative empirical coefficient in each criterion is modified. The results indicate that onshore movement of bars is more probable than previously estimated. The implication is that linear bars formed of dredged material are more likely to move onshore to nourish the surf zone and beach than previously thought.

The Punta Umbria spit is one of the most didactic case studies for spits which can be found along the Spanish coast. The problem the spit presents came to light in the past and has arisen once again causing difficulties for navigation in the channel. The solution adopted for the problem in the past was not totally correct from all points of view, as will be seen later in this study, and, for that reason, the problem has come up once again. This report was undertaken in the facilities which the Ports and Coasts Research Center of the CEDEX has in Madrid.

Both the conventional Principal Component Analysis (PCA) and the Complex Principal Component Analysis (CPCA) were applied to analyze six nearshore profiles in Siuslaw, Oregon. Results indicated that the first two components derived from CPCA always outperformed those derived from PCA. This suggests that CPCA is a better method of describing the seasonal variation in nearshore bathymetry. The relative performance of CPCA on different profiles depended upon the coherence of the variation within those profiles. Furthermore, the concept of an absolute amount of variance was used in explaining the spatial variation of the predictability of principal components.

Sediment samples and beach profile evolution data, collected along one profile line at "El Puntal" Spit, Santander, Spain, are studied by means of Principal Component Analysis (PCA). This analysis technique is used to separate the temporal, spatial and grain size distribution variability of the data. The results show that there is a seasonality in the grain size distribution affecting the fine sand as well as the coarse sand. The variations of the coarse sand percentage, which occur mostly within the bar-berm area, consist of an increase, in the bar zone in winter and in the berm zone in summer. The fine sand presents a different behavior, changing all along the profile, increasing its percentage offshore the bar in winter, and in the foreshore in summer. Thus, the sediment just relocates in the cross-shore direction.

Further, a "master" grain size distribution, which is constructed by adding all the grain samples, taken from all over the profile, is shown to be constant in time. It is suggested that the "master" grain distribution should be used in coastal engineering formulation.

Three-Mode Principal Component Analysis is applied to bathymetric data from a beach nourishment at "Playa de Castilla", Huelva, Spain. This approach is used to separate the temporal and spatial variability of the beach shoreface. The method is shown to describe variations occurring in the cross-shore and in the alongshore direction as well as temporal variations. The results of the analysis show a clear seasonality in the shoreface variations, with bar-berm processes involved in the cross-shore direction and complex sand variations in the alongshore direction. These alongshore variations are induced by the nourished area which avoids the formation of a uniform bar along the beach resulting in a complex sediment redistribution. The results also show an erosion trend in "Playa de Castilla". This erosion, however, is not related to the "spreading out" losses at the nourished beach but with the background erosion.

The mechanism whereby sediment particles are suspended under broken waves in the surfzone is investigated through experimental data analysis and computational modelling. The concentration measurements referred to comprise continuous transmissometer and optical backscatter sensor (OBS) values recorded in the field as well as a large database of time-averaged recordings. The measurements analysis, which included a unique set of laboratory observations derived from a specially designed vertical mixing apparatus, clearly highlight the preeminent role of wave breaker turbulence in the suspension process. The wave period averaged turbulence structure is found to be well predicted by a two equation (k, ε) turbulence model. With the parametrization of the bottom reference concentration using relevant breaker and bottom generated turbulence variables, a scalar extension of the k, ε model is effective in predicting published time-averaged suspended sediment distributions. Analytical relations founded on the assumption of a predominately diffusive turbulent transport regime furthermore display favourable predictive capabilities.

Field observations on the grain size distribution of suspended sediment in a surf zone has been carried out at Fukiage beach in 1990 and 1991. In these observations, a suction pump has been used to sample a sufficient amount of suspended sediment for grain size analysis. The instrument designed for the data collection worked well. Vertical distributions of sediment concentration for several grain sizes which compose suspended sediment are obtained. This enable us to do numerical simulations of beach evolution taking the composite character of suspended sediments into consideration. Results are compared with the ones obtained by conventional simulation method which assumes single grain size composition of beach materials, and discussed. The vertical distribution profiles of the concentration of suspended sediments are also compared with existing models and discussed.

The paper describes the development and application to laboratory and North Sea field data of a series of random wave and current computer models of bed boundary layer flows and associated suspended sediment concentrations. The EC-funded (MAST 1) work is part of a larger project, which also includes the laboratory testing of a new seabed shear stress meter (SSM) and the field collection of nearbed data using a special boundary layer rig (STABLE). Both two-dimensional (2DV) and one-dimensional (1DV) hydrodynamic models are described based on a mixing length closure but including simulation techniques to enable the inclusion of both long and short-crested random waves and steady currents. A 1DV suspended sediment model is also described with realistic boundary conditions to enable the simulation of vortex entrainment from seabed ripples. Application of the various models to the SSM and STABLE data shows realistic results.

Direct and nearly continuous measurements of bed position changes, near-bed velocities and suspended sand concentrations have been made at a single location on a macro tidal beach in the south west of England. The study was conducted in 0.5-2.25 m water depth under low-energy swell conditions with weak currents present. Bed positions and suspended sand concentrations were measured using the 3 transducers of a multi-frequency acoustic backscatter sensor with 5 mm vertical resolution. Large (upto 10 cm) and rapid (upto 1.0 cm min^-1) changes in bed elevation were observed in association with local hydrodynamic forcing, bedform development and bedform migration. Large-scale bedforms observed under breaking waves were highly mobile with measured migration rates of upto 2.2 cm min^-1. Suspended sediment concentrations and transport rates are particularly sensitive to changes in bed position changes and subject to potentially large errors (upto 30%) without compensation for bed elevation changes relative to sensor position.

The Oregon Inlet Terminal Groin was completed in 1991. The groin was built to provide protection to the bridge crossing the inlet. A detailed monitoring program has analyzed shoreline position with the use of aerial photographs collected every two months. To date, no adverse impacts of the groin have been found on the shoreline within a 6 mile distance downdrift of the groin.

A discrete vortex model has been applied to describe plunging breakers. The wave breaking is represented by a jet of water impinging on the surface in front of the wave crest. The suspension of sediment has been modelled by a mixed diffusion - convection scheme. Preliminary results in the form of vector plots of the flow field and concentration profiles are presented.

An extensive experimental project has been undertaken, in two parts, to measure both the formation of shingle beach profiles due to wave attack and the wave velocity fields using the technique of Particle Image Velocimetry (PIV). The former was achieved with moveable beach experiments carried out in the wave basin at HR Wallingford, and the latter on models in the 9.75m wave flume in The University of Edinburgh. Waves of several JONSWAP spectra, reflecting storm conditions, were allowed to impinge normally on an initial slope of 1:7, the resulting profiles were found to reach dynamic equilibrium after about 3000 wave periods. These profiles were modelled at The University of Edinburgh for the wave velocity measurements using the relatively new technique of PIV. This technique has the benefit of providing very accurate, full-field, instantaneous velocity data. In these experiments monochromatic waves were measured on smooth, impermeable beaches although the extension to multi-frequency waves on rough, permeable beaches is planned for the near future. The effect of the increased backwash component typical of these steeper beaches is dealt with in some detail.

The South Baltic Sea coastal zone investigated in the years 1983-1989 belongs to multi-bar dissipative ones, with an average slope of 1.5% and sand grain size D₅₀=0.22 mm. EOF have exhibited the most common locations of bars (e_2x) and the most intensive bed changes (e_3x). Particularly conspicuous are the bed changes about the inner bar (depths about 3 m). Radioisotopic irydium glass tracers have been employed in three different subzones of the shore profile; 50-60 m from shoreline (depths h of 0.8-1.2 m), 200-250 m (h=2-3 m), and some 350-450 m (h=4-5 m), respectively.

During storms the most intensive sediment motion occurs in the second subzone, where the longshore sediment transport rate q reaches 40 to 100 kg/(mh). Closer to shoreline (first subzone), the transport rate ranges from 15 to 40 kg/ (m-h), while the smallest rate (q ≈ 3.5-20 kg/(m-h)) is encountered in the third subzone. Under conditions of weak or moderate oblique waves (e.g. mean wave period and height $\overline{T}\le 3-4$ s and $\overline{H}\le 0.2$ m in the second subzone), the longshore mode also prevailed but the ratio of longshore to cross-shore rate was lower, about 1.7:1 (13.5 versus 8 kg/(mh)).

Core samples of tracer sand have provided estimates of the vertical extent and distribution of transport rate in the bed layer. It has been found that the thickness of the bed sublayer in which all grains move in bulk reaches δ ≈ 2-5 cm during storms, versus a few grain diameters to 1.5 cm under weak and moderate waves.

Velocity measurements have been made with a Laser Doppler Anemometer in oscillatory flow over rippled beds. The ripples were naturally formed in an oscillating tray rig and then stabilised.

Both large-scale mixing, repeatable from cycle to cycle, and turbulence were found to have a significant effect on the velocity profile. Large-scale mixing, which is associated with vortex formulation and ejection, was seen to dominate in the immediate vicinity of the bed but turbulent mixing appeared to be more important at large height. The variation in turbulence intensity with height was found to be qualitatively similar to that previously observed with three-dimensional roughness in oscillatory flow. Time-mean velocities are not well predicted by existing theory. The present measurements show only two recirculating cells per ripple wavelength.

Wave-induced transient porewater pressures were measured near a seabed surface at a coast facing the Japan Sea. The data are compared with the solution using a boundary layer approximation by Mei and Foda (1981). The effective bulk modulus of porewater, β, is estimated 1.0×10⁸ N/m² so that the solution matches the observation. A similar analysis is done for the field data obtained by Zen et al. (1989) at a coast facing the Pacific Ocean. The value of β scatters from 1.2×10⁷ N/m² to 1.0×10⁸ N/m².

Laboratory experiments as well as numerical modeling were conducted for sand transport under non-breaking grouping waves. Experiments showed that the direction of net transport of fine sand was onshore under grouping waves although it was offshore under monochromatic waves with equivalent wave height. It was also revealed that the long wave bounded to wave group plays an important role in particular for suspended load. A numerical model was developed on the basis of the second-order Stokes wave theory and one-dimensional diffusion equation of sand concentration. The validity of the model was confirmed with experimental data.

When the surface waves propagate in shallow water region, the bottom boundary layer may be turbulent because of sand ripples or other kind of roughness of sea bed. But before the flow becomes fully developed turbulence, there is a state, in a certain range of the Reynolds number, in which the flow is still laminar but has separation and complex structure of vortex. This is termed as quasi-turburent flow in the present paper. The flow structure of this boundary layer affects the mass transport and sedimataion.

In the present paper, we use a numerical method to solve the boundary layer of oscillatary flow over ripples. When we discuss the overall wave field, the sand ripples can be considered as ruoghness of the bollom and the flow with the separation and the vortex can be considered as disturbance around mean flow. Therefore, to discuss the averaged flow structure of wave field, the mass transport for example, it is necessary to know some kind of statistical properties of the boundary layer. A particular attention is paid to investigate the mean velocity, the Reynolds stress and turbulent viscosity. It is found that the turbulent viscosity varies along the time during the period of the oscillation. And not only it diverses as the space derivative of the mean velocity diminishes, but also it has a complex distribution in space and time.

The effect of long period wave to local sand transport rate in the surf zone is analyzed by laboratory and numerical experiments. In the laboratory experiment, surface profile, near-bottom velocity and suspended sand concentration are measured simultaneously and resultant net sand transport rate is measured by mass difference during the experimental runs. It appears that the net sand transport rate is determined by three driving forces which are undertow, long wave and short wave. In mild slope condition, the effect of long wave becomes large. In order to simulate this process, a new numerical model is formulated.

The variation of the foreshore in Iwo-Jima is studied by analyzing a series of aerial photographs taken seasonally for the past 4 years since 1987, and data of various surveys obtained for the past 10 years since 1982. These observations are compared with results of numerical analysis of the effects of storm waves on the foreshore. the findings obtained through these analyses are: (1)The island is still rising at a yearly rate of more than 30 cm/year; (2)The foreshore is eroded in summer and fall when typhoons often hit the island, but is restored back in winter and spring of the following year. The seasonal variation of the foreshore area ranges from 300,000 m² to 600,000 m² depending on the magnitude and frequency of the typhoons hitting the island in a year; (3)The foreshore area is increasing at a rate of 50,000 m²/year which is caused by the upheaval of the island; (4)A one-line model can be applicable for the prediction of the short-term variation of the shoreline caused by storm waves.

First results towards the development of a predictive method of cross-shore spreading of beach and shore nourishments are described. Present interest in nourishment as an appropriate answer to long-term erosion motivates special attention for the time evolution of the cross-shore spreading. Hallermeier’s (1981) annual shoreward boundary, D₁, of the shoal zone is probably the most applied quantitative boundary for the seaward extent of nourishments. The extension of this concept to include time-dependency is a logical and necessary step to improve our understanding of nourishment performance. Moreover, insight into the precise cross-shore variation of the spreading process is lacking.

By application of a detailed process-based, cross-shore morphodynamic model and some inductive assumptions the spreading process is studied as a function of time. The results give qualitative and quantitative indications of the spreading process, in particular concerning the evolution character of the spreading and the relation between the nourishment foot and closure depth.

In the Netherlands a political decision has been made to maintain the coastline of 1990. Also, the required funds are available to do so. Thus the main purpose of nourishment in the Netherlands is to combat chronic erosion.

Field measurements have been carried out at the mouth of the Nanakita River in Japan. the maximum velocity at the throat section was kept constant, 1 m/sec, although the river mouth topography changed much rapidly in a week. It therefore seems that the equilibrium condition at the river mouth can be expressed in terms of the maximum velocity. The wave set-up height measured in the river mouth was also analyzed and was found to be responsible for the intrusion of sand into the mouth.

Experiments have been performed in a large wave flume in order to measure sediment transport rate of fine sand under combined regular waves and current. Instantaneous velocities and concentrations are measured using ultrasonic velocimeters and optical turbidity probes. Suspended transport rates, as obtained from vertical integration of measured fluxes, are decomposed into a mean current and an oscillatory wave components. Under waves only, the wave contribution is in the direction of wave propagation. Under combined waves and current, the wave contribution is found to systematically oppose the direction of superimposed mean current.

This paper presents a numerical model for computing time-dependent near-shore hydrographic changes including beach profile responses. The time scale of the model is suitable for storm events to seasonal changes. The model is very stable and is capable of handling complicated topographies including inlets and irregularly-shaped structures such as curved jetties and breakwaters.

The basic approach is similar to many previous investigations utilizing a hydrodynamic model to drive a sediment transport model. The hydrodynamic model computes fully interacted current and wave fields based on coupled mild slope wave equation and depth-averaged circulation equations. The sediment transport model is of energetic type treating the rate of sediment as the summation of two energetic mechanisms one due to the mean current and the other due to the wave induced turbulence.

The model has been successful comparing with the evolution of beach profiles in large wave tank tests as well as other 2-dimensional numerical models of profile evolution. The model is able to predict the bar formation realistically without introducing constraints such as the bar genesis. At present the model consists of four modulars that apply separately for the situation of beach with no subaerial structure but could include non-reflective bottom structure, beach with shore-connected structures, beach with shore detached structures and beach-inlet system. Test applications are presented here with some comparisons with field data and 3-D movable bed experiments.

Longshore sand transport rate has been computed, for 2,520 cases covering field- and laboratory-scale conditions, using a general formula for local transport rate in a coexistent wave-current field proposed by the present author. The computed total transport rate has been well related to the alongshore component of wave power and two other parameters. Cross-shore distributions of the longshore transport rate have also been studied.

This paper compares the results of measurements obtained from two field experiments performed to determine the effect of waves and currents (w+c) on the transport of sand in suspension. One set of measurements are from an estuary (Maplin Sands) and the other are from the surf zone (Boscombe Pier). The vertical and temporal variation in and the correlation between some of the hydrodynamic and sediment dynamic parameters are discussed.

The numerical model for three-dimensional beach change prediction is constructed to simulate a pocket beach formation. The model consists of three modules of waves, currents (include beach change) and sediment transport. Wave transformation module is based on the mild slope equation of hyperbolic type, current module is horizontally two dimensional with direct interaction with sea bottom change which is evaluated by sediment transport model formulated by Bailard.

Numerical simulation of pocket beach formation was performed under two conditions of an artificial pocket beach formation which is the typical case of beach stabilization by headlands and an empirical pocket beach which is made by combining an equilibrium bay and beach profile.

A survey and a critical review of existing sediment transport data in waves and/or currents has been performed. Special emphasis has been given to the applicability of the data sets for the calibration and/or verification of sediment transport models. Only data sets dealing with non-cohesive sediment have been considered in this review. The eventual need for further experimental research is discussed under the light of the results from the present study.

The present Dutch coastal defence policy is aimed at a full compensation of shoreline retreat, mostly by means of beach nourishment. For some parts of the coast with a small dune ridge attacked by severe erosion, a so-called ’seaward coastal defence strategy’ might be more profitable. According to this strategy, measures will be taken to influence the morphological system in such a way that erosion is prevented, which will result in a stable or even progressive coastline.

An analytical policy design was chosen at the onset of the study. A number of seaward coastal defence measures will be tested following a series of selected criteria, such as effects on morphological, financial and construction aspects as well as effects on recreation and ecology. The study works from ‘coarse’ (entire province of Zeeland, SW-Netherlands; different coastal defence alternatives) to ‘fine’ (selected location; preferred coastal defence alternative). This has resulted in conclusions and recommendations with regard to the feasibility of a pilot project with a perched beach in the ‘Cadzand’ area.

Experience has been obtained on the construction of sand fills in water as part of several types of structures in the Netherlands. These include the following: closure of dams, artificial islands or coastal extensions, covering of pipelines, trench back fills and the foundation of submerged tunnels and caissons.

Mathematical and experimental modelling of sediment transport processes in the coastal environment is presented. The convection-diffusion equation for suspended sediment particles has been used to compute the vertical distribution of the time-averaged concentrations. The computed results are compared with measured values of laboratory and field experiments (surf zone Dutch coast).

A two-hour set of wave-current bottom boundary layer data collected at a dredged material placement site is examined with regard to establishing whether readily measured variables such as turbulent and wave kinetic energy (TWKE) correlate with more difficult to measure near bottom data. The data, collected in Mobile Bay, Gulf of Mexico, consisted of acoustic concentration profile data and velocity measurements at 50 and 114cm above bottom. The Reynolds Stress did not correlate well with any of the near bottom data including vertical flux and total water column mass. TWKE was a much more solid correlate with these variables but still was weak in correlating with near bottom mass. The wave kinetic energy was a solid correlate with near bottom data, particularly the mass in the bottom 5cm.

We investigated the occurrence of FIG waves generated by a shear instability of steady longshore current on a uniformly sloping beach so that we can discuss the characteristic of Fig waves with respect to a wave breaking. We also carried out experiment to investigate cross-shore distribution of lateral mixing coefficient that determines the cross-shore profile of longshore current.

It is found that the occurrence and characteristic of FIG waves depend on a cross-shore profile of steady longshore current on the uniformly sloping beach as well as those on a beach of a constant depth analyzed by Bowen et al.(1989). The bottom slope affects FIG waves indirectly through the cross-shore profile of longshore current. The measured lateral mixing coefficient, which also gives influence on longshore currents, becomes maximum within the surf zone and decreases rapidly toward offshore. The locus where the maximum longshore current occurs, that plays an important role in the generation of FIG waves, depends on the surf similarity parameter of the incident wave.

The growth of shear instabilities in the longshore current to finite amplitude is studied. It is shown, by considering near-critical conditions and the self-interaction of the fastest growing mode (FGM), that the basic flow is supercritical and that, therefore, the disturbance may be expected to evolve to a finite size, with frequency equal to that predicted by linear stability theory, and final amplitude proportional to the linear growth rate. This is consistent with observation. The mean flow may therefore also be expected to evolve to a new form.

The set-up and preliminary results of a series of model investigations on dune breaching is presented. Based on these 2DV-tests the insight into the processes related to the lowering of the crown of a sandy dam during overflow conditions has been enlarged significantly. Although dam erosion is mainly due to transport processes on the inner slope, the angle of the outer upstream slope showed to be very important also. Coarser sand results in larger erosion rates, whereas the effect of packing is only minor.

Suspension of sand in the surf zone is intermittent. Especially striking in a time series of concentration are periods of intense suspension, suspension events, when the concentration is an order of magnitude greater than the mean. We used field data collected in the inner half of the surf zone during a large storm (greater than 1.5 m wave heights and 13 second periods) to define and describe suspension events and determine the contribution of events to the sediment transport.

Large suspension events were found throughout the inner half of the surf zone, occurred about once every 1 to 2 minutes, and each had a duration of about 5 seconds. These events tended to occur during onshore flow under the wave crest, resulting in an onshore contribution to the suspended-sediment transport. Even though large events occurred less than 10 percent of the total time, at some locations onshore transport associated with suspension events was greater than the offshore directed transport during non-event periods, causing the net suspended sediment transport to be onshore. Events and longshore velocity were not correlated. However, events did increase the longshore suspended-sediment transport by approximately the amount they increase the mean concentration, ranging from 15 to 55 percent depending on the definition used for events. Because of the lack of correlation, the longshore suspended-sediment transport can be adequately modeled as the vertical integration of the product of the time-averaged longshore velocity and the time-averaged concentration.

The profile performance and the conditions giving rise to overtopping and overwashing of shingle barrier beaches have been examined in an extensive programme of field work and physical model studies. The hydraulic performance of Hurst Spit, on the south coast of the UK, has been examined in detail, and the studies have been used to design a management programme for this barrier beach. This has included the design of a beach replenishment scheme and quantification of overtopping thresholds and alarm conditions, for a range of beach geometries. An extensive series of 3-dimensional physical model tests are discussed and a dimensionless parametric framework is suggested, which provides a method of estimating the conditions that will result in crest accumulation, breaching and crest lowering of shingle barrier beaches, for a wide range of beach geometries.

This paper presents an analytical solution of water waves propagating over submerged vegetation and a mathematical expression for vegetation motion swayed by the water waves.

Puerto Miranda oil terminal, located in the Maracaibo Strait, Venezuela (see figures 1 and 2), is one of the main Venezuelan oil industry loading facilities of crude oils. Ships access the terminal from the Gulf of Venezuela by a 40 km long, 300 m wide and 13.7 m depth main channel, which is periodically dredged in order to keep the design depth. A secondary channel leads from the main channel to the terminal itself (See figure 3). Over the last few years the increase in sedimentation rates in the secondary channel has motivated the need for studies that would determine alternatives to reduce dredging costs.

A previous work [0], based on the circulation and sedimentation patterns in the area under study, proposed the construction of a new access channel with a different orientation regarding the prevailing current direction, that would reduce the sedimentation rate and dredging frequency.

The Venezuelan oil industry through its R & D filiate (INTEVEP), has developed a 2-D finite element mathematical model to simulate suspended sediment transport and a 2-D finite difference circulation model for coastal regions.

In this work, these models are applied to determine the evolution of the secondary old and new dredged access channels to Puerto Miranda oil terminal. Both models were calibrated and validated with field data and results are presented for the complex circulation and sedimentation patterns that occur in the area of Puerto Miranda terminal.

The settlement of mud lumps dumped in oceans from barges was studied theoretically and the results were compared with data from field and laboratory experiments. The settling pattern and the load of initial turbidity were estimated by a non-dimensional dispersion index and the rate of turbidity load.

The Port of Lisbon authority is aiming at the reception of container ships of the fourth generation. For that a deeper and wider artificial channel has to be dredged through the outer bar. The set of studies undertaken (data collection, site investigations, mathematical and physical modelling) put into evidence the importance of the opening of a secondary bar, some 50 years ago, over the general morphological behaviour of the estuary entrance. So a recommendation has been made to close it using an artificial sand dike.

A dispersive mixing caused by the interaction of the longshore currents and the undertow is found to exist in the nearshore region. It is found to depend critically on the depth variation of both the cross-shore and the longshore currents. The effect is calculated for the simplest possible current profiles which yield a non-zero contribution. It is demonstrated that the dispersive mixing totally dominates the mixing in the nearshore region, exceeding the effect of turbulence by an order of magnitude even inside the surf-zone. In consequence, accounting for this interaction of the nearshore currents makes it possible to model longshore currents using realistic turbulent mixing levels. The vertical variation of those currents become part of the results provided. The predicted depth variation of the longshore currents is shown to be consistent with the only set of such measurements presently available.

Beach erosion has recently been recognized as accelerating due to change in sediment sources from rivers. This can be considered as reduction processes of river deltas. In this paper, the formation and reduction processes of river deltas are first investigated theoretically by introducing the non-uniformity of longshore sediment transport into the equation of continuity of shoreline changes. Theoretical solutions to shoreline changes in the formation and reduction processes are well explained. Secondly, experiments both on the formation and reduction processes were carried out. The theoretical results of the processes compared favorably with the experimental ones.

An eigenfunction expansion method is used to analyze the propagation of a plane wave train along a rectangular channel, the side walls which are provided with regularly spaced thin vertical strips. The presence of such strips may produce cross-channel seiching and energy dissipation. The method is extended to take into account the dissipation of energy at each pair of strips. Analytical solutions are obtained for the general case. Theoretical results of wave attenuation along the channel are compared to laboratory experiments, Battjes (1965).

Investigation for mechanism of the local scouraround a large circular cylinder installed on the uniform bottom slope due to waves and currents were performed experimentally and numerically.

This paper presents an efficient and economic technique to obtain vertical profiles for surf-zone wave-induced currents. The current-wave bottom boundary layer is solved in a parameterized manner, while employing a power series aproximation to obtain the solution in the middle layer (extending up to trough level). This "profile extraction technic" has been coupled to a 2DH surf-zone circulation model which is also concisely described. The paper ends with a brief discussion of some obtained results part of the calibration work which is a very much on going task.

Comprehensive field measurements were made of the vertical current structure on a barred beach profile at the DELILAH project during October of 1990. The current was measured with five electromagnetic current meters mounted on a mobile sled which was stationed at three to eight cross-shore positions. The incident directional wave spectra, bathymetry, tide, wind, and cross-shore wave transformation were also measured. A numerical model was developed to calculate the random wave transformation based on the model of Dally, Dean, and Dalrymple (1985) (Larson and Kraus 1991) and the local vertical current structure (Putrevu and Svendsen 1991). The model predicted the shape of the current profiles well with a root-mean-square error in velocity of 5.9 cm/sec. The model tended to underpredict the velocity over the bar crest .

A comprehensive review is presented of scour around pipelines in the case of non-cohesive sediment. The review is organized in four main sections, namely the two-dimensional scour, the three-dimensional scour, the effect of scour on forces on and vibrations of pipelines and the mathematical modelling of scour process. Over sixty works were included in the review.

Two sophisticated research models, previously used and validated in internal flows, are now applied to sediment laden flows: they give a thorough insight into the vertical distribution of sediment concentration, flow-sediment interaction, stratification and inhibition of vertical mixing. The Reynolds stress model is well adapted to investigate stratification due to density effects: it gives information on turbulent fluxes of momentum and concentration, eddy diffusivity and eddy viscosity profiles, reduction of the bottom shear stress due to the presence of sediment. Results show that suspended sediments affect turbulence even at low concentrations of 1g/l. A dimensional analysis seems to indicate that these stratification effects are not well accounted for in laboratory experiments.

The two-phase flow model enables to describe the vertical profile of sediment in its continuity, from the water surface down to/through the bed, without any definition of the bed water interface. Cohesive sediment processes such as deposition, erosion or consolidation are treated as flow-particles interactions: thus, the model helps in identifying the governing parameters -flow size and density, effective stress- and does not require the classical empirical laws commonly used to describe these processes.

Mean currents have impotant roles in sediment transport. The mean currents around a large circular cylinder are carefully measured. The theoretical mass transport rate is verified experimentally, and the movement of sediment on a flat and smooth bed can be numerically simulated well. On the contrary, the currents on sand ripples are quite different with the theoretical value. The currents are caused by the interaction of the return flow and the mass transport on sand ripples.

Siltation mechanism in a 14km long approach channel on large scale muddy tidal flat is studied based on field investigations and numerical simulation. Natural conditions such as river discharge, waves, tides, tidal currents, and bed materials were measured over one year. The morphological change shows some relations with the grain size distribution of bed materials and current flow patterns. The net movement pattern of bed materials in the muddy tidal flat is given by the analysis of the field data. From the numerical simulation, it is revealed that the resuspended bed materials by waves from the surrounding tidal flat play an important role in the siltation process of the approach channel.

Observations by Gonzalez et al. (1984) and Gonzalez (1984) of swell penetrating the entrance of the Columbia River provide an excellent opportunity to test linear wave theory for wave - current interactions. In the present study a two-dimensional wave model for short-crested waves based on the linear wave theory is used. The model includes the propagation effects of currents and also generation and dissipation of the waves. The results agree fairly well with the wave observations in the river entrance, in spite of an uncertainty in the bathymetry and currents. Numerical experiments show that waves from westerly directions are focused in the entrance by refraction on a bar in front of the entrance and that current induced wave guide effects enhance this focusing in ebb conditions.

An attempt was made, using a 3-dimensional turbulent model coupled with a comparatively simple depth averaged sand transport model, to assess the computational feasibility of predicting sediment transport in a dredged trench, caused by a steady flow passing across the trench. A sophisticated computer software package was used to simulate 3-dimensional turbulent flow by the finite element method. A Profile Model, which discretized the transport process to enable sucessive computation of the flow field, was used for morphological evolution of the channel bed. A physical model was built and tested to validate the numerical models.

High stress or upper-plane-bed condition may be encountered in rivers in flood, large flows in estuaries, and closures or breaches of cofferdams or dykes. Because of very high rate of sediment transport with this type of flow, it has a disproportionate effect on both topographic features and engineering works.

Along the silty coast of the Jiangsu Province, it was found that on the coast stretch which we call the "Radial Sandbanks" coast stretch, deepwater port sites could be created if suitable tidal inlets were selected and provisions were made to maintain the required deepwater areas for port development.

A research project was started to study the behaviour of cohesive sediments at the Delft University of Technology in 1989. An existing flume was modified to study the liquefaction and erosion of China Clay due to waves and current. China Clay is an artificial mud, mainly consisting of kaolinite. Among other things, the experimental results showed that fluid mud was generated by wave action if the wave height exceeded a threshold value; the threshold value increases as the consolidation period increases. Waves were significantly damped when a fluid mud layer was present and the damping was only little influenced by a current. Furthermore, the fluid mud is transported very easily by a current and hardly any mud was entrained into the water layer during this process. The pore pressure showed a transient decrease when the mud started to liquefy, succeeded by a gradual build-up of an excess pore pressure to compensate for the vanishing effective stress. Finally, it was found that observations or measurements made at a sidewall during an experiment only give a rough indication of the physical processes away from the sidewall; measurements carried out far from a wall have to be used for a quantitative description of the bulk processes in the bed.

This paper first presents a literature review of consolidation theories. A link between sedimentation and consolidation models is pointed out and a more general formulation is suggested. The constitutive relationships between the void ratio and the effective stress or the permeability are discussed from experimental data available in literature. Then a numerical modelling is used to simulate settling column tests. At last field measurements of mud characteristics are presented.

Measurements of density and pore pressures for consolidation experiments on estuarine mud are analyzed. Results for bulk permeability, local permeability and effective stress are presented and simple relationships between each of these parameters and the density are proposed. The problems associated with the accuracy of the measurements and their consequences on the determination of closure equations for consolidation models are discussed.

Hydraulic tests of the erosion by waves of a shore profile made from intact samples of till, a cohesive material comprising a large part of the Great Lakes shorelines, have been completed. Over 1000 h of testing in a laboratory flume with random depth-limited breaking waves, varying conditions of sand cover, and varying mean water levels have been run. The vertical erosion rates of the till were measured along the centreline of the 8 m long, 0.35 m wide and 0.25 m thick till profile; its initial shape was the equilibrium form y = Ax^2/3 common on sandy beaches. Some of the important findings are that this type of hydraulic test is viable, the role of sand in the erosion process is similar to its role in unidirectional flow model tests but the thickness and volatility of the sand layer are also factors, the main effect of varying water levels is to shift the zone of erosion activity up and down the profile, and that erosion can occur in the absence of sand if the rate of wave energy dissipation is high enough (plunging breakers, steep slopes).

Particle Image Velocimetry (PIV) has been applied successfully to give quantitative, full field measurements of instantaneous velocity fields for oscillatory flows past a model of a pipeline above a plane bed. The application of PIV to this problem is discussed, and results for the case of KC = 20 with gap ratios 1.0 and 0.1 are presented in the form of velocity vector maps, and contour plots of vorticity distribution.

Shear instabilities of the longshore current are examined as a possible source of non-zero $\overline{\mathit{u\text{'}v\text{'}}}$ values (mixing) within the surfzone. This term is calculated using model generated stream functions whose amplitudes are calibrated with the observed turbulent kinetic energy spectrum. Data from the DELILAH experiment, conducted at the barred beach at Duck, North Carolina is used. Excellent agreement is found between the predicted range of shear instabilities and observations as seen in frequency-wave number plots. Maximum predicted values for $\overline{{\mathit{u\text{'}}}^{\mathit{2}}}\text{,}\overline{{\mathit{v\text{'}}}^2}$ and $\overline{\mathit{u\text{'}v\text{'}}}$ are .04, .20, and .03 m²/s².

Most longshore current models assume a spatially constant bottom friction coefficient which is solved for empirically. Considerable range in values is found in the literature. Given the extreme variation of fluid flow characteristics across the surf-zone, this assumption of constancy seems perhaps unrealistic.

A novel and cost-effective technique for measuring sediment concentrations in high energy surf zones, using a helicopter, was developed and applied at Walker Bay, South Africa. Using this technique, which involved an innovatively operated suspended sediment sampler (TASSS), 280 sediment samples and hours of continuous sediment concentration measurements (with a transmissometer) were acquired at several levels. Currents and waves were also measured at several positions along a cross-shore section. The helicopter was also used to successfully survey the nearshore area using a new method. Spectral analysis of wave and concentration data show responses of the sediment concentration to incident and infragravity waves beyond the surf zone, while suspension is seen to be more intermittent in the surf zone. The concentration profiles beyond the surf zone exhibited typical exponential distributions. Reasonable correlation between the TASSS and the transmissometer was found.

Navigational channels are frequently maintained by the use of jetties. These stabilized channels often form long straight waterways which permit the passage of tidal flows and waves into harbors, lagoons, or rivers. This paper concerns the decay of the waves down the channel due to energy losses within jetties. The analysis involves the use of an impedance boundary conditions at the channel side walls to model the wave dissipation there. The wave motion is described by an eigenfunction expansion for the velocity potential within the channel, with and without tidal currents.

For the case that the water wave length is long with respect to the channel width and no currents are present, the wave height decay down the channel can be described by an exponential decay, H = H_o e^-Γx, where Γ = γx/(2Kb), γ is a (real) damping factor, k is the wave number, and 2b is the width of the channel. For the case of a mean current in the channel, the same expression results, but for a different form of the wave number, (Eq. 24).

This model is specifically conceived to work in estuarine environments characterized by strong tidal currents. It operates on a microcomputer and it is conceived to work with minimal input. The model determines the velocity and radius of the dense sediment cloud, formed by the release of sediments from a scow, during its downfall in the water column. These parameters are used to determine the proportion of sediments settling at the point of impact. Sediments maintained in suspension by the high level of turbulence following impact on the bottom form a density current that spreads out radially. The performance of the model was verified by a series of experiments carried out in the St Lawrence Estuary to monitor the disposal of dredged spoil from a 400 m³ scow.

In order to solve water circulation and solute transport-diffusion problems in two-dimensional hydrodynamical systems a comprehensive simulator, composed by two finite element models, has been developed. In particular the first model, which is of semi-implicit kind, solves hydrodynamical shallow water equations whereas the second, which is an Eulearian-Lagrangian method (ELM), is based on the Modified Method of Characteristics (MMOC) combined with Galerkin finite element method. Semiimplicit procedures for hydrodynamical models are sometimes used with finite differences but are quite rare with finite elements. Nevertheless they have a lot of advantages compared to the others, principally linked to a considerable time saving. This is determined by the fact that the systems of equations in the unknown levels and velocities are uncoupled and the time step is not constrained by Courant-Friedrichs-Levy stability criterion. It can be demonstrated that in the linear case the hydrodynamic model is indefinitely stable and good accuracy can be achieved for velocity fielAOn the other side, the proposed transport-dispersion model presents interesting features, among which the possibility to obtain good results in mass conservation and minimum numerical oscillations or grid orientation problems even under sharp front conditions. In these papers we shall discuss only the approximation method of transport-dispersion model, showing the theoretical fundamentals and some of its applications.

This paper summarises the studies carried out about sedimentation and erosion problems of Yakakent Fishery Habor. Since the start of the construction of the harbor, accretion in the west coast and erosion in the east coast occurs. Additionally, the entrance of the harbor shoals. As a result of accretion at the west coast shoreline moved towards sea and about 300meters of the breakwater was on land. Erosion at the east coast of the harbor caused collapse of two houses which were about 20meters inside the original shoreline. After identifying the causes, precautions for sedimentation and erosion problems are again studied using one-line model and a series of precautions are recommended.

The rheological properties of mud play an important role in the motion of bed mud due to waves, currents, or combined waves and currents. In this paper, a dynamic rotary shear meter is developed to measure the shear stress in the mud under an arbitrary time history of the shear rate. Kaolinite is tested as an example of bed material and its rheology model is proposed. Another experiment is performed to confirm the predominance of the mud mass transport mode over the suspended mud transport mode in the wave-induced transport. Further experiments examine the role of pressure as an external force of the motion of the bed mud and measure some characteristics of waves on the mud bed. Finally, based on the empirical rheology model, a numerical model is developed to predict the motion of the bed mud, and resulting mud mass transport and wave damping. The calculated mud mass transport velocity and wave height change agree well with measurement.

In the present study, with the ultimate objective of developing a numerical model of siltation in a cooling water intake basin of a power plant, the settling velocities of non-uniform sediments are investigated using the settling tube tests. The critical shear stress for deposition of suspended silt and the vertical concentration profile of suspended sediments are investigated on the basis of field data. The depositon rate as well as the grain size distribution of deposited sediments were reproduced satisfactorily by a one-dimensional model.

In order to investigate the role of consolidation processes on the sediment transport in a macrotidal estuary, a simple vertical model of fluid mud consolidation has been coupled to a cross-averaged sediment transport model in the Loire estuary. Simulations show that sediment patterns (turbidity maximum and fluid mud location) are few dependent on consolidation. On the other hand, the consolidation influences the residual deposition after a spring/neap tidal cycle and thus the net transport of sediment through the estuary. It is pointed out that consolidation is in competition with turbulence damping so that both processes have to be considered when predictive simulations are wanted.

The response of a sandy seabed to surface water waves, with a special emphasis to wave-induced excess pore water pressure oscillations is studied here in relation to the vertical stability of submarine buried pipelines. The main object of the paper is to present a study of the distribution patern of the pore water pressure acting around the pipeline, and to calculate the seepage force, the up-lift force particularly, affecting the pipeline stability, under the assumption of compressible both the pore fluid and soil skeleton, for the case of an arbitrary seabed depth as well as for the infinite thickness of the subsoil.

This study aims to establish the effective and economical construction scheme of the rubble mounds which are constructed by discharging a large amount of rubble from hopper barge. Since the plane scatter of the landing rubble on the sea floor directly depends on the random drift force exerted on the settling rubble, the statistical properties for the scattering range of the settling rubble in the still water are fully investigated in experiments. On the basic of the experiments and the discrete block method which equipped to cope with the steeper slope of rubble mound than the angle of repose for rubble, a numerical technique to simulate the spatial geometry of the discharged rubble on the sea floor taking the angle of repose for the rubble into account is developed. An optimum interval of the discharge sites of the barge which makes the uneven property of the mound’s surface minimum is discussed in connection with the change in the the design water depth of breakwater and the discharge times.

A row of vortices forms in an offshore zone when two-dimensional regular surface waves run up on a sloping flat bed. It is called the offshore vortex train. The vortices begin to appear near a breaking point. Moving in the offshore direction, they develop and increase their horizontal length scale through the vortex merging. The vortex train forms due to the shear instability between onshore and offshore drift-currents. After reaching a location of the offshore side, however, they decay rapidly because of the decrease of shear strain rate between the drift-currents. The formation region has been investigated on the basis of visual experiments for three bed slopes. The formation does not depend on the type of wave breaking but is observed when the steepness of deep water waves is smaller than 4.2 × 10⁻². The horizontal length scale of the vortices and the velocity of the vortex movement have also been evaluated empirically.

The variation of floc size has been measured during spring and neap tides at a height of 0.5 m above the bed in the turbidity maximum of the Tamar Estuary, UK. Two size populations were present. Small flocs were eroded from the bed during spring flood tides and were transported up estuary. Large flocs were dominant at other times, particularly just after high water when differential settling concentrated large flocs near the tip of the salt intrusion.

In this paper we have given general formulas for conventions and diffusion in a wave boundary layer. As an example we have examined a localized cloud in a bidirectional wave system which may represent an obliquely incident and reflected wave system near a sea wall. The cloud drifts to the nodal line close to its initial position. When the particle cloud is initially midway between two nodal lines along the y axis. The cloud then bifurcates towards the two nodal lines on each side while the peaks diminish. Future improvements must include better models of turbulence, deposition and resuspension. For fine cohesive sediments possible coagulation is worth studying. Finally it is interesting to examine dispersion in the surf zone where breaking wave induce longshore currents.

A new, quantitative framework is presented for the modelling of suspended sediment concentration distributions. It accounts for large scale mixing (convection) as well as small scale mixing. The small scale mixing is modelled in terms of gradient diffusion as usual. It is shown how the new, combined convection-diffusion model can explain the different $\overline{c}(z)$-distributions of different sediment sizes in the same flow. Also, the dependence of the $\overline{c}(z)$-distribution shape on wave period and sediment settling velocity is explained for oscillatory flow over ripples. It is shown that individual Fourier components of c_n(z,t) behave differently in diffusion dominated and in convection dominated flows. This makes it possible to determine the dominant entrainment mechanism (convection or diffusion) on the basis of concentration time series taken simultaneously at different levels.

The paper discusses criteria for safe working and safe mooring conditions for various types of seagoing vessels. These criteria are based on acceptable movements for moored ships in harbours and have been established by a working group under the Permanent International Association of Navigation Congresses (PIANC).

The existing criteria for defining allowable levels of wave agitation in Canadian harbours are outlined in the Guidelines of Harbour Accommodation (Fisheries and Oceans). These criteria were developed based on a previous study which concentrated primarily on recreational harbours. However, it was realized that fishing vessels, when berthed or moored, may be able to tolerate a greater degree of wave agitation than pleasure craft because of the different characteristics and functions of the two types of vessels. Furthermore, fishermen tend to have more liberal tolerance limits to wave agitation than pleasure craft owners, and have more rugged craft. To develop new allowable wave agitation criteria for commercial fishing harbours in Atlantic Canada, a field measurement programme was conducted in selected harbours. The objective was to determine the threshold values at which the wave climate at both the service/offloading area and mooring area creates either dangerous, difficult or unacceptable working conditions. This was determined to be the point at which operations must cease or the vessel had to be removed to a more protected area. Wave measurement gauges were installed at two locations within two study harbours, and a wave rider buoy was used to measure nearshore waves for each harbour site. A procedure was also developed whereby daily field observations were taken and recorded by the harbour master. Particular emphasis was given to the wave climate events which rendered the facilities less than adequate, unsafe or unusable. By correlating the harbour masters field observations with the measured wave data, the threshold values for unacceptable wave agitation were determined, and new wave agitation criteria for fishing harbours recommended.

The Damietta sediment-formed promontory is located on the eastern half of the Nile Delta, about 40 km west of the Suez Canal breakwaters at Port Said. Following a long period of accretion, the promontory began to erode early this century with shoreline recession rates reaching a maximum of 38 m/yr. This paper documents the shoreline changes, the coastal processes responsible for those changes, and the protective measures that have been erected to control the erosion.

The Nile Delta coast is a dynamic system formed by the Nile River sediments discharged into the Mediterranean Sea through the historic seven branches of the Nile. The central headland at Burullus began to erode around the 10th century upon abandonment of the old Nile branch which had been providing sediment to this area. Commencing in the early 20th century the nine barrages along the main river were constructed which initiated a general erosional trend along the Nile Delta with concentrations around the Rosetta and Damietta promontories. This alarming erosion has been aggravated since the erection of the Aswan High Dam in 1964, which trapped essentially all of the flood sediments in its storage basin.

Eighty beach profiles, covering the Delta coast, have been surveyed twice per year since 1976 and surveying is continuing to the present. A computer program was developed to analyze the collected profile data. This program calculates the accretion/erosion quantities and the movement of various contour lines up to 6 meters depth. The results have shown that the changes do not follow a clear pattern except at the Rosetta and Damietta promontories and around the El Burullus area where consistent erosion is evident.

Before construction of the various Nile River dams, the position of the Nile Delta shoreline was in equilibrium between the sediment supplied by the river and the transport of sediment along the coast. Following dam construction sediment yield from the river has virtually ceased. In the absence of sediment from the river, currents, waves and winds are actively eroding the delta. Extensive beach profiling shows that the primary locus of erosion, in excess of 10 × 10⁶m³ yr, is from the Rosetta promontory. This material is carried eastward in part by wave action but predominantly by currents of the east Mediterranean gyre which sweep across the shallow delta shelf with speeds up to 100 cm/sec. Divergence of the current downcoast from Rosetta and Burullus promontories results in formation of accretionary blankets of sand that episodically impinge on the shoreline. Individual blankets of sand form 1.5 m thick covers over the residual profile in depths of 6 to 4 m, and extend for 2 to 4 km along the shore. The sand blankets move progressively downcoast at rates of 0.5 to 1 km/yr, generating series of accretion/erosion waves along the shoreline.

The erosion/accretion/erosion shoreline change is commonly 50 to 100 m and has a periodicity of 3 to 8 years. When the accretionary phase of the wave has passed downcoast, the shoreline returns to its previous form and exhibits a "residual" equilibrium profile. In its residual form, the beach profile goes through characteristic adjustments to seasonal wave climate, exhibiting an equilibrium winter profile with a pronounced bar and a summer profile when the bar tends to migrate onshore. When the nearshore is blanketed with sand during the accretionary part of the cycle, the profile is in disequilibrium with wave forcing and frequently shows several, irregularly spaced bars and troughs. Although the year to year shoreline changes associated with the accretion/erosion waves are large, 0(50 m/yr), the long-term (decadal) changes based on successive residual profiles from the erosion portion of the cycle are relatively moderate, say 0(2 m/yr).

Findings from this study suggest that the coastal current augmented by waves may transport 10 - 20 million m³/yr of sandy sediment, while the longshore sand transport near the shore is about 1 million m³/yr. Thus it appears that the blankets of moving sand that episodically impinge on these relatively shallow (6 m deep) profiles are only revealing the "toe of the elephant." Additional study is needed at depths of 20 m or more to resolve this problem.

The Boston Outfall, presently under construction in Massachusetts, U.S.A., is the world’s largest tunnel outfall. The outfall represents the latest in tunnel outfall technology and when completed will discharge up to 1300 million gallons per day of secondary treated effluent through a system of seabed diffusers, nine and a half miles off the coast of Boston. Installation of the 55 diffusers and risers are nearing completion, with the construction of the outfall tunnel just commencing. The Outfall is a major component of the Boston Harbor Clean-up Project.

This paper presents a description of the design and construction of the deepwater Boston Outfall.

A description is given of a new large project of artificial beach nourishment protected by a submerged sill carried out at Lido di Ostia near Rome in 1989-1991. After a review of the main aspects of the design (supported by model tests) and construction, details are given of the ongoing field monitoring program. Collected data has been used to verify the predictions of numerical models of cross-shore and longshore evolution of the perched beach. Useful preliminary lessons have been drawn from this unconventional experience of coastal protection.

For more than 200 years aeolian processes have removed sand from the Bate Bay coastal compartment. This ongoing loss resulted in long term recession of the 5.5km beach. By the mid 1970’s the recession threatened both public and private assets. A detailed coastal process study was undertaken to develop a management plan aimed at halting the recessional trend. The plan was progressively implemented over a period of 14 years. The result is that the foreshores of Bate Bay are now stable. The management strategy adopted has not only protected the public and private assets but has also enhanced the recreational amenity of the area. Throughout the project monitoring was undertaken of both the coastal process and the management options. These monitoring programs have provided useful information on the pragmatic application of traditional study techniques and on the effectiveness of the selected management options.

The sea-sand mining has been carried out in the coast of western part of Japan since the early 1970’s. Mined sea-sand is mainly used as fine aggregate of concrete structures. Mining a large amount of sea-sand near the coast induces the possibility of beach erosion and devastation of fishing grounds. In order to evaluate its influence on coastal environment, the present situation of sea-sand mining has been investigated in seven prefectures of Kyushu island in Japan. The sea-sand mining in Kyushu Island is classified into two types. One is the mining in the sea areas where sea-sand reserves are limited. In these areas, the compatibility between the sea-sand mining and the protection of coastal environment will become very important in future. The other is the type that sea-sand has been supplied constantly from rivers or other sea areas. In this case, it will be the most important to keep the balance between the amount of mined sea-sand and that of supplied one.

Investigation of the failure mechanism of the Patras breakwater extension revealed that the seismic loading of the mound was amplified considerably due to the soft foundation soil. This loading induced the overriding of the low safety factors of the structure. Approximate analytical expressions were obtained for the hydrodynamic loading during earthquakes. These were in good agreement with previous results. Recommendations for the completion of the works were given to the harbor authority.

An extended field of 15 long rubble stone groins was constructed in two increments of work at Westhampton Beach, New York, in 1965-66 (11 groins) and in 1969-70 (4 groins), as part of a hurricane storm-protection project. A third increment of work completing the protection to a downdrift point of closure was not undertaken due to political decisions. In addition, the dune and beach fill which was to have been placed in the first 10 groin compartments to complete the protection was not accomplished due to local economic problems. No construction work has been undertaken since 1970. During the 26 years following completion of the original 11 groins, substantial portions of the groin field have been filled naturally by trapping of sediment that moves alongshore with a net rate directed to the west. However, the shore area downdrift of the last westerly groin in the unconstructed increment of work has experienced inordinate recession because of insufficient bypassing of sediment to this area. This paper describes the functioning of the groin field, examining both the extreme downdrift recession and the equally dramatic accretion and beach build up in the groin field, drawing lessons on groin functional design from this historic project.

In 1990 Posford Duvivier were commissioned by the National Rivers Authority to collect, audit and place on a database 550 years of tide data from 15 locations on and in the vicinity of the Humber Estuary, UK. As part of this project 373 years of the data, from 10 locations (key stations), were analysed for trends in relative sea level. The areas covered in the trend analysis included: linear trend estimates on yearly average high tide levels from all the key stations; an examination of variations in trends with location and time; and an examination of the correlation between high water trends, mean tide level trends and low water trends. This paper discusses the trend analysis.

There is a potential sand transport capacity from northern part of Barcelona coast to southern part. This sand transport capacity has been evaluated by means of the CERC formula to be about 89,000 m³ near Barcelona city.

An investigation regarding the coastal changes over a period of about 50 years, as depicted from waterline and beach bluff fluctuations was conducted at Hadera-Sdot Yam beach, located at the central sector of the Southeastern Mediterranean coast of Israel. The study was conducted to assess the sedimentological impact of the breakwaters of a neighboring cooling basin, recently built. Processing and analysis methods used, as well as the main findings and conclusions are presented.

The coast between Torre Mattarelle and Torre San Gennaro (Italy) is deeply eroded. The recent construction of a thermalelectric power plant changed the natural morphodynamic characteristics and the erosion rate. Interventions on the coast were needed. This paper refers about the phases of design and construction of the maritime defence works and tries to call attention about the need of an extensive study before the construction of a power station along the coast.