Coastal Engineering 1988

Abstract

A theoretical solution is developed for the interaction of second-order Stokes waves with a large vertical circular cylinder in water of finite depth. The solution is obtained in terms of the velocity potential such that any kinematic or dynamic quantity of interest may be derived, consistent to the second perturbation order. In this study, the second-order wave field around the cylinder is determined, showing the modification of the incident Stokes waves by wave-wave and wave-structure interactions, both in the reflection-dominated up-wave region and in the diffraction-dominated down-wave region. The theory is then compared to experimental data for wave runup and rundown amplitudes on the cylinder as well as for wave crest and trough envelopes in the up-wave and down-wave regions.

Abstract

Part 1

A finite element model has been developed to study the effect of currents on the wave propagation in and around arbitrarily shaped harbours of variable depth. The model solves an elliptic mild-slope type of equation for time-harmonic waves, and thus circumvents the limitations of existing models for wave-current interaction in coastal areas, which apply a parabolic approximation. Numerical examples are presented, both for schematized cases, as the effect of "rip currents" on normal incident waves on a sloping beach, and for a realistic geometry.

Field investigations were performed in order to show the effect of wave diffraction by breakwaters through directional wave spectra measurements in a harbor, and to estimate the reflection coefficient by resolving the incident and reflected wave energy in front of a composite type breakwater. Combinations of an ultrasonic wave gage (USW) and an electromagnetic current meter (EMC) were used to measure the synchronized data of the water surface elevation and two horizontal velocities. The EMLM (Extended Maximum Likelihood Method) was applied for the calculation of the directional wave spectrum, and the modified EMLM for an incident and reflection wave field was applied for the estimation of the reflection coefficient. Through the estimated directional wave spectra, the effect of wave diffraction by breakwaters were discussed and the reflection coefficient was estimated at about 0.9. As a result, the applicability of the field investigation method and the modified EMLM were verified.

A new directioal spectral estimation method using a Bayesian approach is proposed. The proposed method is examined for numerical simulation data, and the validity of the method is discussed. Some examples of the directional spectra estimated from field observation data attained at an offshore oil rig utilizing seven wave probes are also shown in this report. The major conclusions of the report are : (1) The proposed method can be applied for more than four arbitrarily mixed instrument array measurements. (2) It has a higher resolution power than other existing methods for estimating directional spectrum. (3) It is a better method for estimating directional spectra from the cross-power spectra contaminated with estimation errors. (4.) It is more adaptable to reformulation of the estimation equations as the study of structures of directional spectrum progesses.

A numerical comparison study is carried out on a variety of methods for synthesizing pseudo-random Gaussian wave records for laboratory wave generation. Three nonharmonic superposition methods and three time domain filtering procedures are compared to a harmonic FFT technique. The synthesis methods are evaluated on the basis of a statistical analysis of 16 standard wave parameters obtained from a set of 200 wave records. Second order group-bounded long wave components are also investigated.

The results of a 1:40 scale physical model investigation into the shoaling process are described. The model simulated a nearly constant slope of 1:40 with wave measurements made at a depth of approximately 25 and 9 m. Two hundred individual tests were undertaken, with four offshore significant wave heights as the only test variant. The results indicate that the most severe nearshore wave conditions do not occur with the worst offshore conditions. There is evidence of a significant increase in low frequency wave energy in the nearshore zone.

Based on the concept of linear superposition, the model for combined wave refraction and diffraction developed by Liu et al. is extended to the situation of permeable deached breakwaters in a slowly varying water depth. Two cases are investigated which include a semi-infinite permeable breakwater and a single permeable breakwater. Laboratory results with a particular transmission coefficient in a wave basin are used to compare with the theoretical results. Fair agreements are found.

A technique to decompose colocated random field measurements of wave elevation and current velocity into incoming (shoreward propagating) and outgoing (seaward propagating) components is presented. This decomposition technique, which is less sensitive to noise, enables us to determine the frequency dependent reflection coefficients and also the relative phase between the incoming and outgoing waves. The method is applied to C²S² and NSTS data sets, from beaches with wide ranging characteristics and wave regimes. The results demonstrate the selective nature of beach absorption/reflection characteristics but are inconclusive in terms of a proper parameterization of reflections on natural beaches.

The swash oscillation, waves and water particle velocity in the surf zone were measured by using 16 mm memo-motion cameras and electromagnetic current meters. It was inferred that incident waves form two-dimensional standing waves with the anti-node in the swash slope. Separation of the incident waves and reflected waves was attempted with good results using small amplitude long wave theory. Reflection coefficient of individual waves ranged between 0.3 and 1.0. The joint distribution of wave heights and periods in the swash oscillation exhibited different distribution from that in and outside the surf zone. This indicates that simple application of wave to wave transformation model fails in the swash zone.

This paper deals with the effect of wave action on the water purification near a permeable breakwater. When determining standards for water purification, three indexes are usually taken into account: the diffusion coefficient, the concentration reflection ratio and the reaeration coefficient.

In our study, the values of the diffusion coefficients Kx near the breakwater ranged from about 10^-1 cm² /sec to 7x10cm² /sec. The effect of aeration caused by setting up a permeable breakwater was limited to within a distance of only one wave length at either side of the breakwater. As a result, values of the reaeration coefficients were then estimated to be in the order of 10^-5 - 10^-4 /sec.

This paper discusses the development from first principles of a first-order solution for non-breaking waves on a gently sloping bottom. The theory is derived in a similar fashion as was done by Swart and Loubser (1978) for vocoidal waves on a horizontal bottom. The resulting covocoidal theory was compared to an extensive data set for waves over a sloping bottom (Nelson, 1981) and is tested for analytical validity. It adheres exactly to continuity and the kinematic free surface boundary condition, and shows comparable errors in the dynamic free surface boundary condition to that found for the better, general horizontal bed wave theories.

A large amount of wave records measured at four different locations of the Spanish shores have been analysed from the point of view of wave group formation. The influence of wave climate and depth on the results is studied. The results are compared with existing theories for runs of waves, SIWEH and envelope functions. Characteristics of extreme groups are also considered.

This is a study of the maximum runup of single long waves on plane beaches. Laboratory data are presented that suggest that solitary waves attain the higher runup distances than other single long waves with identical generation characteristics, such as energy or momentum. These results suggest that solitary waves may provide a limiting condition for long wave runup on plane beaches.

The separation of boundary layer occurs periodically near a breaking point when incident waves climbing up a sloping bed are about to break. Not the breaker but the separation forms an unsteady coherent eddy, which suspends a large amount of bed material. A row of steady vortices has been found along the water surface of an offshore zone. Its formation is due to the shear instability between shoreward steady flow induced near the bed and offshore steady flow near the water surface. Moving in the offshore direction, the steady vortices repeat amalgamation each other and increase their intervals at the order of mean water depth. They decay after reaching to the region where the shear rate is not enough between the two steady flows. This shear instability may be excited by the periodic separation of boundary layer.

Two Fourier models for the propagation of surface waves are reported, which are theoretically valid for angles of propagation up to ±90° with respect to normal incidence. This is a great improvement in comparison with the present parabolic models. The first model is based on the assumption of straight and parallel depth contours, and the second one is the extension to the case of irregular bathymetry.

The objective of this work is to understand the evolution and main features of the wave climate in the offshore area off Rio de Janeiro State - Brazil, using point measurements. Several spectral models are compared with the data and criteria absed on jonswap and Mitsuyasu relationships are established to identity situations of combine sea and swell from different directions. The Toba model is used to get friction wind values from the spectra for comparison with measued winds. After understanding the main features of the wave climate and using visual observations for wave direction and the spectral informaton, a distribution of average energy vs direction is calculated.

An extensive series of experiments has been carried out at the laboratory in order to study rectangular harbour oscillation excited by incident long waves. Attention is focused on the effect of head loss entrance on resonant response attenuation. A "gross" quadratic hydraulic head loss coefficient is defined and information about it, resulting from tests, is provided. Experimental conditions used in this piece of work seem to be realistic under suitable scaling for Northern Spain harbours.

This paper summaries the initial stages in the development of a mathematical model of wave action on slopes. The model calculates water surface elevation and depth averaged velocity on the slope, and uses this data to estimate the level of wave run-up. The model has been validated by comparing its results with those from similar models, and from a physical model. Examples are presented of these comparisons, which were found to be in good agreement in most cases.

Since wave energy dissipation in the surf zone is a stochastic process closed mathematical formulations cannot be expected. The dissipation was computed using several analytical and/or empirical approaches and compared with prototype measurements in the Big Wave Flume (GWK) in Hannover as well as with field measurements from the west coast, of the Island of Sylt/North Sea. Generally good agreements were found for moderate energy dissipation conditions (spilling-breaker), whereas in the case of plunging breakers, however, the fitting is not solved satisfactory.

Specific consideration is given to the dependence of Fourier wave solutions on both truncation order and the number of free surface nodes. Solution dependence is quantified by a comprehensive set of numerical experiments over a typical range of wave height, water depth, truncation order and overspecification values. Integral error measures include the rms free surface boundary condition errors and a slope error that identifies non-physical positive slope segments in the wave profile between crest and trough. Summary error diagrams are presented as a guide to the adoption of suitable truncation orders and overspecification for Fourier solutions. The truncation order is the crucial parameter but there is measurable advantage is some small overspecification.

In the scope of a joint research program dealing with erosion problems of the island of Sylt in the North Sea, wave measurements with two pitch-and-roll buoys are carried out in order to obtain more detailed information on the sea state with regard to wave dependent morphological processes.

The instrumentation is described. Results from the directional analysis of closely spaced buoys are compared, showing good agreement in significant parameters and in distributions in the frequency range. Differences between wave and wind directions are discussed. A method of separating double peak spectra by fitting theoretical shallow water spectra to the measured energy density distributions is presented.

A wave overtopping rate from a sea dike of various toe depths is formulated based on a weir model in an unidirectional flow. To evaluated the wave overtopping rate from a seadike on an artificial reef by the weir model, a numerical procedure for predicting wave transformations including the effect of forced wave breaking on the reef is constructed. After confirming the applicability of the model through experiments with regular and irregular waves, the effect of artificial reef on wave overtopping is discussed. So-called individual wave analysis method is shown to he applicable to the wave overtopping caused by irregular waves.

A 2-D numerical model has been developed to simulate wave propagation prior to breaking. This non linear hydrodynamic model works in connection with various spectral analysis routines. This paper intends to study the propagation effects on the wave time-series and on the corresponding spectral density functions in order to gain insight on both the spectral description of waves and irregular wave propagation.

Measurements have been made of wave height decay in a rough bottomed flume for waves alone and for waves combined with 3 following currents. Tests have also been carried out to quantify energy dissipation at the sidewalls under these conditions. Results show that waves attenuate less rapidly when propagating on a following current, with a corresponding reduction in wave-current friction factor. A simple method is suggested by which wave attenuation in the presence of following and opposing currents can be predicted.

A numerical computation method for a wave field coexisting with a current is presented to study wave-current interaction on a slowly varying bottom topography. Derivation is given for a new set of time-dependent mildslope equations extended to a wave and current coexisting field, which can deal with wave deformation due to combined refraction, diffraction, reflection and breaking as well as to wave-current interaction. Discussion is made on the numerical computation schemes, boundary conditions and breaking conditions. Some examples of the numerical computations are shown for wave and current coexisting fields.

The dynamics of nearshore circulations is investigated using mass, momentum and energy conservation equations with bottom friction, lateral mixing and wave-current interaction. By means of introducing a perturbation expansion for the mean variables, the first-order solutions are found in the surf and offshore zones according to the boundary conditions at the coast.

It is found that:(l) The rip velocity attains a maximum value in the offshore region near the break point as Yr* becomes larger. (2) The longshore velocities become higher in the surf zone and lower in the offshore region with increasing Yr*. (3) The rip and longshore velocities in the surf zone become relatively smaller due to the effects of the bottom friction, and that the rip and longshore velocities in the surf zone become smaller due to the wave-current interaction.

Wave height change of the zero-down-cross waves on uniform slopes were examined experimentally. The properties of shoaling, breaking and decay after breaking for a total of about 4,000 irregular waves of the Pierson-Moskowitz type on 4 different slopes (1/10, 1/20, 1/30 and 1/50) were investigated. The shoaling property of the zero-down-cross waves can be approximated by the linear wave theory. However, the properties of breaking and decay after breaking differ considerably from those for periodic waves. The wave height water depth ratio (H/d) at the breaking point for the zero-down-cross waves is about 30% smaller than that for periodic waves on average despite the slopes. Wave height decay after breaking also differs from that for periodic waves and can be classified into three regions, i.e. shoaling, plunging and bore regions. Experimental equations for the breaking condition and wave height change after breaking are proposed in the study. A new definition of water depth for the zero-crossing wave analysis which can reduce the fluctuation in the plotted data is also proposed.

The performance of two numerical wave propagation models has been investigated by comparison with field data. The first model is a refractiondiffraction model based on the parabolic equation method. The second is a refraction model based on the wave action equation, using a regular grid. Two field situations, viz. a tidal inlet and a river estuary along the Dutch coast, were used to determine the influence of the local wind on waves behind an island and a breaker zone. It may be concluded from the results of the computations and measurements that a much better agreement is obtained when wave growth due to wind is properly accounted for in the numerical models. In complicated coastal areas the models perform well for both engineering and research purposes.

Stokes (1847) showed that finite amplitude progressing waves cause a net drift of fluid, in the direction of wave motion, which occurs in the upper portion of the water column. In a closed wave flume this drift must be accompanied by a return flow toward the wave generator to satisfy the conservation of mass. This study presents Eulerian velocity and water surface measurements soon after the onset of wave motion from 12 locations in a large scale flume. Waves with .67 ≤ kh ≤ 2.29 and .09 ≤ H/h ≤ .39 were produced in a water depth of 3.5 meters. Superimposing the return flow theory of Kim (1984) with seventh order stream function theory is shown to improve the velocity predictions. The measured return flows are a function of time and depth and agree with Kim’s theory as a first approximation. The mean water surface set-down agrees with the theory of Brevik (1979) except for the nearly deep water waves.

Coastal hydrodynamic analyses are basic for the planning and assessment of activities in that area. An important application of these analyses is harbour lay-out and location. In this paper, hydrodynamic results of a numerical model based on Boussinesq-type equations are presented in the issue of Computer Aided Harbour Engineering. This model achleves overall second-order accuracy and has efficient modules of pre- and post-processing of information. The model has been used as a CAD tool for the planning and design of Spanish harbours. Its flexibility and economy of operation allow the model to be used, in the future, as a module of a global expert system for CAD harbour lay-out. This global expert system will provide a fully automatic design process. The output of this system will consist in the final optimized harbour configuration, considering all Imposed constraints and requirements.

In order to establish a model of the vertical distribution of the undertow, laboratory experiments were performed on uniform slopes of 1/20 and 1/30. The turbulent velocity in the surf zone including the area close to the bottom was measured by using a two-component laser doppler velocimeter. The distributions of the mean Reynolds stress and the mean eddy viscosity coefficient were calculated. Based on the experimental results, a model to predict the vertical profile of the undertow was presented.

Based on the linearized form of the boundary layer equations and a simple eddy viscosity formulation of shear stress, the turbulent bottom boundary layer flow is obtained for a wave motion specified by its directional spectrum. Closure is obtained by requiring the solution to reduce, in the limit, to that of a simple harmonic wave. The resulting dissipation is obtained in spectral form with a single friction factor determined from knowledge of the bottom roughness and an equivalent monochromatic wave having the same root-mean-square near-bottom orbital velocity and excursion amplitude as the specified wave spectrum. The total spectral dissipation rate is obtained by integration and compared with the average dissipation obtained from a model considering the statistics of individual waves defined by their maximum orbital velocity and zero-crossing period. The agreement between the two different evaluations of total spectral dissipation supports the validity of the spectral dissipation model.

Effects of instationary depths and currents in tides on shelf seas on wind wave propagation are investigated using two numerical models in two academical situations representing shelf sea conditions. It is shown that changes in absolute frequency, which are induced by the instationarity of depth and current, are significant in contrast to what is usually assumed. If these changes are neglected large and unpredictable errors may occur in calculated changes of wavenumber and amplitude.

In the individual wave analysis of short-crested irregular waves, the wave direction of an individual wave is an important quantity as well as the wave height and period. In this paper, the joint probability density of the wave height and direction is derived theoretically on the assumption of a narrow-banded frequency spectrum. A field experiment was carried out to examine the validity of the theory. The measured joint distribution agreed well with that predicted by the theory.

A new, efficient and cheap method is described for obtaining field measurements of surf zone mean water levels. The method applies manometer tubes rather than the traditional pressure transducers. Together with simple stilling well measurements of the water table the results obtained from manometer tubes demonstrate for the first time a complete mean water level profile, from offshore of the break-point to the back-beach region.

While some previous studies have provided information about the average position of the waterline, the present study is the first to provide comprehensive field data on the position of the shoreline defined as the intersection of the mean water surface and the sand. The difference between average position of the waterline and the shoreline is not trivial.

This is a study of the maximum runup of cnoidal waves on plane beaches. An approximate theory is described for determining the maximum runup of nonbreaking cnoidal waves. It is shown that the linear and nonlinear theory predict mathematically identical maximum runup heights. An asymptotic result is derived for the maximum runup of solitary waves, which are one limiting form of cnoidal waves. A series of laboratory experiments is described to support the theory. Other numerical results are presented that suggest that the runup of cnoidal waves is significantly higher than the runup of monochromatic waves with the same waveheight and wavelength. Preliminary laboratory data are also presented which suggest that, for certain cnoidal waves, the maximum runup is not a monotonically varying function of the normalized wavelength.

The application of an advanced third generation wave model to the Mediterranean Sea is described. The model is based on the physical description of the wind wave evolution, avoiding any shortcoming in the estimate of the single terms that contribute to the energy budget. The capability of the model to respond to any meteorological situation is illustrated by applying it to a severe storm occurred in January 1987. The results show that the crucial point for the final accuracy lies in the correct evaluation of the wind field.

A numerical model is presented for nearshore wave deformation due to shoaling and breaking, and to decay and recovery in the surf zone. The model is based on a set of time-dependent mild slope equations including a term of wave energy dissipation caused by breaking. Its applicability is demonstrated by comparisons between the computations and the measurements of cross-shore distributions of the wave height and potential energy over typical beach configurations.

An efficient numerical model is presented for calculating the refraction and shoaling of finite-amplitude waves over an irregular sea bottom. The model uses third-order Stokes wave theory in relatively deep water and second-order cnoidal wave theory in relatively shallow water. It can also be run using combinations of lower-order wave theories, including a pure linear wave mode. The problem of the connection of Stokes and cnoidal theories is investigated, and it is found that the use of second-order rather than first-order cnoidal theory greatly reduces the connection discontinuity. Calculations are compared with physical model measurements of the height and direction of waves passing over an elliptical shoal. The finite-amplitude wave model gives better qualitative and quantitative agreement with the measurements than the linear model.

A numerical model to compute to a high degree of accuracy nonlinear wave-wave interactions of wind generated waves supplemented with formulations of wind generation and white-capping, has been used to estimate qualitatively and quantitatively the effect of these physical processes on the directional response of waves in a turning wind field. After a sudden shift in wind direction the wave spectrum develops a secondary peak in the new wind direction. The initial peak of the spectrum either merges fairly quickly with this new peak or it slowly disappears, depending on the magnitude of the directional wind shift. The turning of the mean wave direction towards the new wind direction is caused by wind generation. The processes of nonlinear wave-wave interactions and white-capping tend to slow down the turning rate induced by the wind generation. The net turning rate of the mean wave direction in the model is twice as slow as in observations acquired in the central and southern North Sea.

Investigations are presented, on some effects of nonlinearity in the motion of shallowa water wave spectra. The waves were generated, mechanically in a laboratory wave flume with fixed bottom. Essential differences with the linear dispersion relation are found, showing vanishing dispersivity of higher frequency spectral components in strongly nonlinear spectra. The mean frequency increases with decreasing water depth. The relation of the peak frequency to the mean frequency varied in the experiments from 0.9 to 0.5, for deep to shallow water wave spectra respectively.

A method is described for the computation of the two-dimensional unsteady motion of a solitary wave passing over submerged breakwaters. Far from the breakwater the fluid is assumed static and the sea bed is level. The fluid motion is assumed to be irrotational, incompressible and inviscid. The exact boundary conditions at the free surface and the impermeable bed are satisfied. Laplace’s equation for the velocity potential is solved using a boundary integral method.

Numerical results are reported which show the variety of ways in which solitary waves are distorted when they encounter submerged breakwaters.

The influence of wind on nearshore breaking waves was investigated in a laboratory wave tank. Breaker location, geometry, and type depended upon the wind acting on the wave as it broke. Onshore winds tended to cause waves to break earlier, in deeper water, and to spill: offshore winds tended to cause waves to break later, in shallower water, and to plunge. A change in wind direction from offshore to onshore increased the surf zone width by up to 100%. Wind’s effect was greatest for waves which were near the transition between breaker types in the absence of wind. For onshore winds, it was observed that microscale breaking can initiate spilling breaking by providing a perturbation on the crest of the underlying wave as it shoals.

Large-scale physical model test measurements of wave run-up are compared with wave run-up prediction derived from the Shore Protection Manual (SPM). Noteworthy discrepancies between the results of these two methods have been identified that include substantial overestimation of wave run-up elevations using the SPM approach, and computation of roughness coefficient values that vary as a function of wave steepness. The slope armors tested in the study at model scales of 1:3 and 1:4 include linked concrete matting and overlapped gravel-filled fabric bags.

The probability distribution of the maximum run of irregular wave height is introduced theoretically. Probability distributions for the 2nd maximum, 3rd maximum and further maximum runs are also introduced. Their statistical properties, including the means and their confidence regions, are applied to the verification of experiments with irregular waves in the realization of a "severe sea state" in the test.

The Labrador Sea Extreme Waves Experiment (LEWEX), is an international basic research programme concerned with full-scale measurements, analysis, modelling and simulation in test basins of 3-dimensional seas. The research is carried out in order to assess the significance of 3-dimensional sea states in engineering applications. The first phase of the programme full scale wave measurements in the North Atlantic Ocean was performed at a site and time that had a high probability of encountering severe sea states.

The present publication shows examples of measured bi-modal directional sea spectra obtained with the WAVESCAN buoy and directional sea spectra measured with an airborne Synthetic Aperture Radar (SAR). Directional spectra of gravity waves are obtained with the SAR both in open waters and below an ice cover. Further work is needed in order to verify SAR-measurements with in-situ observations. In-situ measured directional spectra are also compared with hindcast spectra from the 3G-WAM model. Hindcast significant wave heights were found to be lower than the in-situ measurements.

When a water wave breaks, it undergoes a complicated interchange of total, depth integrated horizontal momentum between that part due to the velocity field and the part that can be assigned to the pressure distribution beneath the surface. This partition of total momentum for a strong, plunging breaker is described by a relatively crude model in which the horizontal velocity profile (over the vertical) is schematized in two layers and the pressure distribution is related to a hydrostatic distribution for the given water depth. An example calculation at four locations across the breaking transition region on a plane beach is utilized to demonstrate the principles of the model. The limitations of the approach which assumes momentum conservation in a reference frame moving with the wave celerity defined at the wave crest are presented, but await verification. The ultimate goal is a relatively simple model to predict the transition width of breaking waves (spillers, plungers and intermediate types) for plain and bar-trough beaches.

A model of the response of the direction of the waves to changing winds is presented. First the theoretical results that associate an average direction of energy propagation to every wave component is introduced. From this model, numerical results are presented both by simulations of ideal wind veering situations and compared with field data taken from pitch and roll buoys.

The problem of combined cross-shore and longshore currents generated by waves in and around a surf zone is considered in its full three-dimensional formulation. The equations for the two current components are decoupled and it is found that for a cylindrical coast with no longshore variations the longshore current variation with depth and distance from the shoreline satisfies a Poisson equation. This equation is solved by a perturbation method and it is shown that the longshore velocities are always larger than the velocities found by classical theory. In the simple uncoupled case, the full 3-D current profile is constructed by combining the results with cross – shore velocities determined in previous publications. Also, the total velocities are larger than velocities found from simple depth averaged models.

Viscous grain-grain interaction is an important aspect of the dynamics of oscillating sheetflow. This interaction between sand grains has been investigated qualitatively in a pulsating water tunnel. Furthermore, experiments concerning the interaction between neutrally buoyant spheres in a Couette flow have been carried out at a scale of 100:1 in a new developed ring shear apparatus, called "Carrousel."

With respect to the dynamics of sheetflow, in-situ measuring devices for the sand concentration in the sheetflow ("Harp") and the bed load ("Swan") has been developed; some preliminary results are shown.

For sand grains, the intrusion depth of sheetflow appears to be of the order of several mm. On high speed video recordings no lateral mixing between grain layers can be observed; for this some physical explanation is given. This supports the modelling of the sheetflow mechanism as moving grain layers.

A brief account is given of theory and experiments for water wave focussing. The theory uses weakly nonlinear wave modulation theory, that is the nonlinear Schrödinger equation, summarises earlier theoretical papers and augments them with numerical results. Experiments were performed to compare with theory. The limited comparison shown here indicates that the theory gives satisfactory results even for waves close to breaking. Both the numerical and experimental results indicate the importance of linear diffraction when waves are focussed. The relevance of diffraction is easily assessed, and is likely to dominate in many coastal examples of weak focussing.

Characteristics of mean velocity and turbulence properties in oscillatory bottom boundary layers are investigated with low-Reynolds number turbulence model. Since this model is capable to describe the flow field close to the bottom, special attentions are paid on the characteristics of the viscous sublayer. Several interesting results, which coincide with or differ from existing knowledge on steady bottom boundary layers, are presented in paticular on the mean velocity profile, turbulent viscosity coefficient and growth of the viscous sublayer.

The assessment of design parameters has a fundamental importance for port planning and design of coastal structures. Special emphasis has to be put on the importance of the occurrence of abnormal storms. The authors’ experience from investigations of port projects has revealed that on many sites it is storms with unusual tracks or otherwise unusual behaviour that are determinant for the design events. This experience is documented by two case stories. The importance of unusual weather systems is discussed and statistical methods for investigation of such phenomena are discussed.

The paper gives the results of an extensive series of hydraulic model tests carried out in a random wave flume, in order to study the effects on wave overtopping of the main geometric parameters of a typical rubble mound breakwater with crown wall. The results have been compared with those from other studies and analyzed with different methods. Generalized design diagrams and formulae for the prediction of overtopping discharges are finally given for a large number of popular breakwater configurations.

Wave reflections at and within a coastal harbour may make a significant contribution to wave disturbance in the harbour. Reflected waves may lead to danger to vessels navigating close to structures, and may reduce the availability of berths within the harbour. Wave reflections may also increase local scour or general reduction in sea bed levels.

In the design of breakwaters, sea walls, and coastal revetments, it is therefore important to estimate and compare the reflection performance of alternative structure types. In the use of numerical models of wave motion within harbours, it is essential to define realistically the reflection properties of each boundary. This paper presents results from a study of the reflection performance of a wide range of structures used in coastal and harbour engineering.

Results from an extensive series of laboratory tests of irregular wave overtopping for a number of seawall and seawall/revetment configurations is presented. Data for 13 configurations has been collected and grouped into 7 data sets representing relatively similar geometrical characteristics. All data sets showed an approximately exponential relationship between the overtopping rate and a dimensionless freeboard parameter which is the ratio of the seawall freeboard to the local wave severity. This finding logically led to the development of three progressively more complex overtopping models. The models provide a relatively simple way to estimate overtopping rates and an objective way to evaluate the hydraulic performance of seawalls/revetments. Advantages and disadvantages of the models are discussed and their ability to predict overtopping rates is compared.

By invoking the assumption that in the surf zone, random waves behave as a collection of individual regular waves, two closed-form solutions for the probability density function of wave height on planar beaches are derived. The first uses shallow water linear theory for wave shoaling, assumes a uniform incipient condition, and prescribes breaking with a regular wave model that includes both bottom slope and wave steepness effects on the rate of decay. In the second model, the shallow water assumption is removed, and a distribution in wave period (incipient condition) is included. Preliminary results indicate that the models exhibit much of the behavior noted for random wave transformation reported in the literature, including bottom slope and wave steepness effects on the shape of the probability density function.

Design wave heights were estimated from measured data using a virtually continuous data set consisting of 8 years of waverider data. Evidence is given which shows that waveriders tend to malfunction during storms. Special care was taken to select independant and identically distributed samples from the data before fitting a number of probability distributions to the selected wave heights. Bootstrap techniques were used to select the models that give the best fit to the data as well as to determine the confidence bands for the predicted design wave heights. It is shown that once the model for the long term distribution of wave height is chosen, relatively narrow confidence bands can be obtained for the most probable value of up to the 100 year return period wave if maximum use is made of the available data. Uncertainty about the selection of the model and the representativeness of the measurements however reduces the usefulness of these confidence bands. A plea is also made in the paper to stop using the concept of a wave with a certain recurrence interval but rather to specify a wave with a given risk of being exceeded within the design life of the structure.

In order to establish a sound basis for the methodology deployed for the generation of realistic waves under laboratory conditions, a comparison is presented between numerical and physical realizations derived from the Random Phase and the Random Complex Spectrum method for wave synthesis. The comparisons are made in terms of 12 critical wave parameters, including three wave grouping parameters. The results indicate that, for the physical realizations of the limited conditions tested, the two methods give compatible results which fall within the expected band of variability. All physical waves undergo some evolutionary change during propagation which affects predominantly the spectral characteristics. For physical waves produced by the Random Phase method, this change increases the variability of some wave parameters. A sample analysis of one case, applying second order wave and wave generation theory to a numerical simulation, suggests that certain differences between numerical and physical simulations can be explained by non-linear wave theory.

This paper presents a summary of carefully conducted laboratory experiments on sediment response and resulting wave attenuation for waves, periodic as well as simulating a wave spectrum, propagating over an 18-m-long bottom section covered by a 10-cm-thick layer of 0.2-mm-diameter quartz sand. The results for wave-generated bedform geometry as well as the equivalent Nikuradse roughness are obtained. The results show that the sediment response to the agitation of a wave spectrum may be approximately described by the sediment response to an equivalent periodic wave having the same root-mean-square near-bottom orbital velocity and excursion amplitude as the spectral wave. This equivalent wave, defined by the near-bottom characteristics of the spectral wave, is identical to that derived by Madsen et al. (1988) in the context of dissipation within the wave boundary layer. Although limited by the range of experimental conditions achieved in this study, the results obtained here and in the companion paper suggest a predictive methodology for the evaluation of spectral wave attenuation from knowledge of sediment and wave characteristics.

We intend to present a brief description of the fundamen tals of a barotropic version of the 3D numerical model of the Institut für Meereskunde-Hamburg altogether with some results concerning the application of the model to the simulation of tidal currents in the Spanish atlantlc waters.

Waves breaking on various slopes in a wave flume are examined. Plunging and spilling breakers are considered. The parametric results show the consistency of the measurement and the independence of scale. A method is given for predicting the maximum breaking height for a wave of known period in a known depth. The velocity is measured to the crest of the wave and comparisions with numerical and analytical solutions demonstrate the shortcomings of many of the established methods of predicting wave kinematics.

A methodology based on linear theory is presented for analyzing wave groups from a random sea representation in the complex plane. A wave height function [H(t)], a local frequency function, [Ω(t)] , and an orbital velocity function [V(t)] are defined from the Hilbert transform of the sea surface elevation. Envelopes computed by the Hilbert transform are compared with the SIWEH. A three axes representation of the mean lengths of runs of waves is employed to compare the lengths of runs computed by the discrete wave method with runs computed by the Hilbert transform method.

A statistically-rational method of extreme wave data analysis is presented. A combination of the Fisher-Tippett type I and the four Weibull distributions is proposed as the candidates of distribution functions. The least square method is used for data fitting. The best plotting position formula for each function is determined by the Monte Carlo method with 10,000 simulations per sample size.

Confidence intervals of estimated extreme wave heights for given return periods are evaluated by simulations and expressed in the form of empirical formulas, for both the cases when the true distribution is known and unknown. An example of extreme wave data analysis is given.

The unsteady characteristics of flow around a vertical circular cylinder in a typical wave, under which the lift force acting on it is very stable and has a frequency which is twice that of the incident wave, have been investigated experimentally. The relationship between the fluctuating flow velocities near the boundary layer separation points and the lift force acting on a sectional part of the cylinder has been understood quantitatively. To clarify the region where the appearance of stable lift force occurs, the long time records of lift forces acting on vertical cylinders in waves are also performed.

A steady-state spectral model is presented. This model produces a solution equivalent to a full time-stepping spectral model, but at much reduced computational times. Comparisons shown here demonstrate that the spectral model provides a good representation of shallow-water wave propagation phenomena and that wind effects can significantly influence near-coast wave conditions.

A review of unidimensional numerical random sea simulators is provided, centering the attention on the measurement of distortions introduced by the different simulation techniques. Simulators by wave superposition are analyzed, with the conclusion being that they generate significant distortions on the realizations when the number of simulated points are larger than two times the number of wave components. Composed simulators are proposed for the purpose of generating long non-periodic realizations using FFT algorithms.

In order to qualify simulators, a justification, based on physical properties of random waves, is given to use m₀, m₁, Q_e and m₂ as the best spectral parameters to characterize processes. Mean values and variabilities of wave heights and periods are controlled by these parameters. A new robust technique is developed to estimate the parameters of an AR(p) model corresponding to a given target spectrum, Sη ( f ). MA(q) and ARMA(p,q) approximations are studied. The source of pseudo-random numbers to generate the input white noise has a critical impact on the statistical properties of the output.

The state of the art of ocean energy recovery activity in the United States is described. The technologies discussed in the paper include extraction of wave, tidal, ocean thermal and ocean current energy. This status report is intended to provide a description of the various ocean energy technologies and an assessment of potential benefits that might be expected and potential problems that might be encountered.

Short and Long Wave data recorded in Bilbao Harbour ( Spain ) have been analyzed in order to study water movements at the inner basins under storms conditions . Some of the trends obtained in prototype have been correlated with model test (regular long wave and irregular short waves ) .

This harbour has been chosen for this research on the one hand because of tha availability of the physical model and on thge other hand because of the means provided by the Bilbao Port Authority.

The wave setup for a given wave spectrum was re-evaluated with the radiation stress term including the low-frequency terms. This setup which is referred to here as "dynamic wave setup", was compared with the steady setup, which is generated by including only the non-periodic radiation stress terms.

The results of the study showed that the dynamic wave setup is greater than the steady wave setup, sometimes almost double its value. Therefore, the dynamic wave setup is important for engineering applications, particularly in the study of storm surges and coastal engineering problems.

The two projects (LUBIATOWO 79 and LUBIATOWO 86) were aimed at study pore pressure behaviour in natural sand bed in the coastal zone of the Baltic sea under the action of storm waves. During both projects, the wave induced pore pressures at the various levels in the sea bed were measured. The collected data were used to verify the applicability of the various theoretical approaches. In the conclusion, the range of the application of the particular analytical method is given.

An effort to empirically assess the slope of the equilibrium range in a wind-wave frequency spectrum with a large number of data recorded in the Great Lakes did not serve to clarify the uncertainty between a -4 or a -5 frequency exponent representation. The uncertainty is further compounded by indications that the slope is not necessarily unique, it tends to vary with wave momentum. For sufficiently well-developed wind waves the exponent appears to cluster between -3 and -4. For practical applications the f^-4 equilibrium range is perhaps an effective approximation. What the correct slope is for the equilibrium range, or even whether or not a unique slope exists, remains elusive and has yet to be satisfactorily substantiated.

Two dimensional generation of surf beats by incident wave groups is examined theoretically. An inhomogeneous wave equation describes the amplitude of the surf beat wave. The forcing function is the modulation of the radiation stress. The short waves are amplitude modulated both outside and inside the surf zone causing the long wave generation to continue right to the shore line. Resonant generation as shallow water is approached is included. The analytical solution is evaluated numerically and shows a highly complicated amplitude variation of the surf beat depending on the parameters of the problem.

A semi-empirical theory is formulated to predict wave reflection and transmission at a porous breakwater of rectangular cross section for normally incident solitary waves. The solution is based on the linearized form of the governing equations and on equivalent linearization of the friction loss in the porous structure.

Experimental results of transmission coefficients are presented for a large range of incident wave amplitudes, with several gravel sizes, water depths and breakwater geometries.

Experimental and theoretical results are compared and evaluated; the comparison shows satisfactory agreement for the transmission coefficient.

A knowledge of bed shear stress induced by waves is required to understand dynamic processes of nearshore morphologies as a results of sediment transport. However, the information on the stress is still incomplete due to lack of measured data. The study analyzes the unsteady horizontally averaged shear stresses measured over mobile beds in a water tunnel. It is found from the analysis that the presence of the third and fifth harmonics in the shear stress is in good agreement with the measured concentration of suspended sediments.

A spectral wave model based on a numerical solution of the Radiative Transfer Equation is used to create a synthetic data base on wave conditions within hurricanes. The results indicate that both the velocity of forward movement and maximum wind velocity within the storm play an important role in determining both the magnitude of the waves generated and also the spatial distribution of these waves. An equivalent fetch for hurricane wave generation which is a function of these two parameters is proposed. This concept, together with the standard JONSWAP fetch limited growth relationships, provide a simple means for estimating wave conditions within hurricanes.

This paper presents a numerical model of nearshore currents due to irregular waves. The radiation stress is estimated by a current-depth refraction model for irregular waves, in which the energy dissipation due to wave breaking is modeled through the use of a saturated frequency spectrum in shallow water. The model is in reasonable agreement with measured wave height, mean water level variation and observed nearshore current patterns. Next, the model is applied to the computation of wave transformation and nearshore currents on a uniformly sloping beach and on model topographies with complicated contour lines. Comparison with the results based on a regular wave model shows that wave irregularity has a smoothing effect on cross-shore distributions of wave height, mean water level variation and longshore currents, but that it does not have much effect on nearshore current patterns.

An original mathematical formulation for suspended sediments in a two-dimensional wave boundary layer is presented. The model accounts for non-immediate adaptation of sediments to the hydrodinamic conditions, and allows to include the effect of sorting of the different diameters considered.

The mathematical model is numerically solved through a finite difference scheme.

It is suitable that results compare favourably with experimental data by Staub et alii.

Measurements are presented of the conditions for the initial motion of sediment under combined steady and oscillatory flow. The measurements were made in a steady flow flume with an oscillating tray set into its bed. The direction of oscillation of the tray was at right angles to the axis of the steady flow flume. Four different grades of sand were tested.

It is found that the critical condition for the initiation of motion is reasonably represented by a critical value of the vector sum of the component shear stresses assuming no nonlinear interaction between the steady and oscillatory flows. The resultant bed shear stress was also calculated with the aid of several combined wave-current models. The results of these various approaches are compared with Shields curve.

For the planning and design of harbor and coastal Engineering, most important affected factors are waves and Littoral drift.

This research deals with analysis of the measured waves and the budget of the beach material whether it is deposited or scoured in the North-western coast of Taiwan; and the relationship between wave energy and littoral transport rate. For processing this research the field Survey wave measurement, sand sampling, and echo sounding is necessitated. The objective of this research is to establish the model of waves and littoral transport budget. Therefore, the results of this research are planned to submit to the planning and design of harbor and coastal engineering works of the Taiwan west sandy coast.

A numerical model for predicting the swash oscillation on a beach is described and compared with field data on wave setup and swash statistics on a moderately steep beach with a nearshore bar.

This paper presents results of two field experiments performed using portable traps to obtain point measurements of the longshore sand transport rate in the surf zone. The magnitude of the transport rate per unit width of surf zone is found to depend on the product of the local wave height and mean longshore current speed, but correlation is much improved by including two correction terms, one accounting for local wave energy dissipation and the other for the fluctuation in the longshore current. The field transport rates are also found to be compatible with laboratory rates obtained under combined unidirectional and oscillatory flow. Total transport rates previously reported for this experiment program are revised with recently determined sand trapping efficiencies.

Quantitative procedures provide the eroded dune geometries expected during an extreme storm on U.S. Atlantic and Gulf coasts. A criterion for either duneface retreat or dune removal is based on measured erosion cross sections in many cases where the pre-storm dune proved to be a durable barrier to wave effects. After that decision, the eroded profile is constructed using specified planar segments cut into or across the existing dune. This empirical treatment appears appropriately detailed for assessing hazards due to the 100-year event considered within the U.S. National Flood Insurance Program, and an example assessment is outlined. Additional discussion addresses other site-specific factors possibly affecting dune erosion, along with another potential application for this simplified methodology.

In this paper, we proposed a method of calculation to predict quantitatively the on-offshore sand movement and the wave deformation on a wave-current coexistent system by assuming a river mouth. And the calculated results were compared with the experimental data obtained for the coexistent system in a twodimensional wave tank. The distribution of wave height on the breaker zone was analyzed by use of BORE MODEL. It was required for the calculation of the sand transport rate. The model was established on the assumption that the value of energy loss in a breaking wave was equivalent to that of bore. The wave height distribution on the offshore side of breaking point was presumed employing the third order approximate solution of Stokian wave on the coexistent system. The breaking point was obtained by use of Miche's criteria equation. The local sand transport rate could be calculated by use of POWER MODEL. The predominant direction of sand drift was recognized using relations for judgement which were derived from the experimental results. The transformation of sea bottom and river one was estimated on the basis of the calculated distributions of the wave height and the sand transport rate. The results obtained by this analytical method agreed well with the experimental results.

The paper, based on the macroscopic analysis of the sediment movement, deals with the movable-bed model experiments of the coast under the combined action of the wave and tidal current. By these experiments we mainly desire to solve the problem of the way how to regulate the outer sandbar, including the rational trend of the guide dike, its length and the expected siltation amount in the navigation channel.

Quantities of sand transported along beaches are generally related to the "longshore component of wave power", P_l, through the proportionality I_s = KP_l where I_s is the immersed-weight sand transport rate and K is a dimensionless proportionality factor. A more-generally applicable relationship is that of Bagnold, ${\text{I}}_{\text{s}}={\text{K}}^{\text{'}}{(\text{ECn})}_{\text{b}}{\overline{\text{v}}}_{\text{l}}/{\text{u}}_{\text{m}}$ where (ECn)_b is the energy flux or total power of the breaking waves, ${\overline{\text{v}}}_{\text{l}}$ is the longshore current, u_m is the mean orbital velocity under the waves, and K' is another dimensionless coefficient. It is apparent that sediment transport rates on beaches should depend on environmental factors such as the grain diameter or settling velocity, and possibly on factors such as the beach slope or wave steepness. However, examinations of such dependencies for K and K' within the field data are hampered by problems with large random scatter within any one data set, and by systematic differences between separate studies which have employed diverse measurement techniques. Examinations of the field data for K and K' variations indicate that meaningful dependencies on sediment grain diameters and other factors cannot be established with confidence in the sand-size range. Limited data available from gravel beaches support the expected decreases in K and K' with increasing grain sizes. These data are too few in numbers to establish firm trends, but do suggest that future investigations to establish dependencies on environmental factors would be most profitably undertaken on gravel beaches. The measurements collected in recent years from sand beaches suggest revisions in average K and K' coefficients to be used in transport evaluations, but such revisions must be coordinated such that K/K’ = 2.7 so as to maintain agreement with the longshore current data.

Beach profiles have been being measured every day on sandy beach at the Hazaki Oceanographical Research Facility, facing to the Pacific Ocean. Based on the data obtained during the period from March 12, 1986 to September 11, the relation between the daily changes of shoreline position and energy flux of incident waves is analyzed. A tentative predictive model of the short-term shoreline changes is proposed. A combination of this model and the one-line theory is examined.

Three case studies are described in which long-term shoreline response was simulated using a numerical model. One project was along Kachemak Bay, Alaska and involved evaluation of design alternatives that included a detached breakwater, beach fill, and a revetment. The second project was on the north New Jersey coast and characterized by a long seawall and numerous groins. The third project was a model test of shoreline change behind three detached breakwaters Lake Erie. The shoreline response model used, called GENESIS, is demonstrated to have applicability to a wide range of commonly encountered shore protection situations.

To select a material for the top layer of the soour protection in the vicinity of a large-scale offshore structure, it is required to know when the material starts to move as a result of waves and currents. But, inception of the motion of sand particles in a region, where diffraction wave superimposes on incident wave and the water particles depict a resulting orbit of ellipse, differs from that calculated by formulae established in the two dimensional wave field.

This paper reveals the discrepancy in calculation when the conventional formulae were used and the data obtained by model experiment. It makes reference, also, to a possible method for a more accurate evaluation of the inception of motion.

An empirically based engineering numerical model is presented for simulating beach profile change in the surf zone produced by waveinduced cross-shore sand transport. The model simulates the dynamics of macroscale profile change, such as the growth and movement of berms and breakpoint bars. Model development was founded on two data sets from large wave tank experiments consisting of 42 cases with different incident wave conditions, median grain size, and initial beach shape. Model predictions are tested with field data, and reasonable agreement is found.

Local scour depth around a pile due to waves only is small, but under waves and weak currents combined it became large. If the flow velocity increases, the maximum scour depth increases and may approach to that by running water. In the processes of the scouring, Kármán vortex play an important role in deciding characteristics of a scour hole. In the case of the horseshoe vortex predominant, the maximum scour depth is found at the upstream end of a pile, but in the coupled field of waves and currents, the initial scouring position is a little apart from a pile in the offshore side and make an angle of about 45 degree in the shoreward direction. This depends on a vortex shedding from a pile. By using light weight aggregate, the effect of ripples on local scour depth is made clear.

In the last two years a whole of studies was realized in order to determine precise solutions to the regeneration of Villajoyosa's beach, in the Spanish mediterranean coast. Investigations were carried out to the surrounding coastal areas based in field investigations and laboratory analyses of the beaches materials.

The surrounding coastal area of the Segura's River mouth has registered in the last years many erosion problems. It is one of the biggest coastal conjunct in the Spanish mediterranean coast. A whole of studies was carried out to determine littoral and coastal processes in this area.

The study of sand mineralogy and grain rounding can help answer many questions of immediate concern to coastal engineers or to broader issues of beach preservation. The heavy-mineral contents of sands, together with statistical techniques such as factor analysis, can be used to delineate sediment sources, trace transport paths, and map out patterns of mixing during sediment dispersal. Variations in the degree of grain rounding can similarly be used to trace sand movements, or to obtain additional information concerning the history of the sediment particles.

The techniques of studying sand mineralogies and grain rounding, and the types of problems they can address, are illustrated by research on the Oregon coast. Heavy mineral compositions of Oregon beach sands are the products of mixing contributions from four sources; the Columbia River on the north, the smaller rivers draining the Coast Range, the Umpqua River on the southern Oregon coast, and the Klamath Mountains of southern Oregon and northern California. Numerous headlands now prevent the longshore transport and mixing of sands from these multiple sources. The beach-sand compositions instead reflect along-coast mixing during Pleistocene lowered sea levels when blockage by headlands was absent. At that time there was a net littoral sand transport to the north, evident from the dispersal of Klamath-derived sands. With a rise in sea level and accompanying migrations of the beaches, headlands eventually interrupted the along-coast mixing of nearshore sands. Therefore, the north to south variation in compositions of beach sands is in part a relict pattern inherited from mixing during lowered sea levels. This has been modified during the past several thousand years by some additions of sand to the beaches from sea-cliff erosion and from rivers. However, studies of sediment mineralogy and grain rounding indicate that sands derived from most rivers draining the Coast Range are presently trapped in estuaries and so are not significant sources of beach sand. The Columbia River now supplies sand to Oregon beaches only to the first headland, Tillamook Head. At that headland there is a marked change in mineralogy and grain rounding with angular, recently supplied Columbia River sand to the north and rounded relict sand to the south.

To investigate the reliability of a sandy soil layer in an ocean wave environment a liquefaction model is used in conjunction with a first order reliability method. Thus, sensitivity indices of the soil-water system with respoect to the uncertain strength and input variables are computed, and the relative importance of the various factors defining the problem can be determined. The relationship of this approach with more conventional design methods (deterministic models, risk models) is discussed along with the range of applicability of the different safety measurements.

Tests have been performed on a vertical pile subject to current only and to a combination of current with normal waves and current with breaking waves. The scour around the pile produced by current only is decreased by normal short waves superimposed upon that current and increased when breaking waves are superimposed upon the current. After analysis of the velocity profiles in the undisturbed area upstream of the pile and next to the pile, the following explanation is found for this phenomenon. When normal short waves are superimposed upon a current, the bottom shear stress of the combination of current with waves is increased more in the undisturbed area than next to the pile in the scour area. This results in a decrease of the scour around the pile. Due to the large values of the orbital velocity under breaking waves this effect is reversed for the combination of a current with breaking and relatively long waves. This results in an increase of the scour around the pile.

In this paper an improved bulk formulation for the longshore sediment transport rate is presented. It is based on a simplified hydrodynamic analysis of surf zone flow and supplemented by an exhaustive dimensional analysis. The proposed model includes the effect of the surf zone dynamic state (e.g. variation of longshore sand transport, II, with breaker type) and it is now being used in the one- and two-line shoreline evolution models developed by the Maritime Engineering Laboratory in Barcelona.

The longshore current and longshore sediment transport distributions are described across an equilibrium beach profile comprised of an intersecting planar foreshore and a concave-up profile. Such a profile shape avoids the singularity associated with the infinite-slope at the shoreline described by traditional equilibrium profile forms and allows prediction of beach processes at and above the shoreline. The mathematical expressions which describe the distributions are simplified and can be more readily applied relative to expressions previously presented in the literature. The findings are in general agreement with similar previous analytic studies and indicate that the current and transport maxima are generally located at about the intersection of the planar and concave-up portions of the profile.

Pocket beach is a usual method to restore an eroded or regressive: coast without natural sand supply. Nowadays, there are more than 40 of these beaGhes on. the Spanish coasts and a lot of them all over the world.

This paper deals with the design parameters of pocket beaches, based on the analysis of data collected from 24 existing beaches on the Mediterranean coast of Spain. Fourteen of these beaches have been studied in detail; nine of them located on the Alboran Sea and. the other five on the coast of Cataluña. Data from 10 additional beaches have also been considered.

Different parameters such as structural design, location of breakwaters, beach planform, beach profile, wave conditions at the site and sedimentary conditions have been analyzed. A mathematical model has been used for the study of the shoreline equilibrium planform.

Practical coastal criteria-design considerations have been drawn from the observed behaviour of the aforementioned beaches.

The modern technique of Coastal Engineering has enabled the succesful modification of the environment, the recuperation and the stabilization of those sandy areas which due to human action, were in a process of regression and erosion. This work developes a mathematical and numerical model to adjust and analyze the variations between the dissipative profiles and the reflectives ones. The research also emphasizes the enveloping profile to calculate the stable behaviour of the beach.

An experimental study is conducted in order to identify the major physical processes leading to the breakout of half-buried submarine pipelines from the seafloor under ocean wave action. Both the hydrodynamic loading on the exposed surface of the pipe, as well as the resulting displacement history of the pipe, were recorded and analyzed in order to identify the critical pipe-soil-wave conditions for the detachment of the pipe from the seabed. The paper also examines the balance of the pipe under the combined lift and drag loading from the water wave. An experimental breakout force-time power law is obtained and compared to available theoretical breakout models.

Wave tank experiments were conducted to investigate the response of a perched beach profile to storm wave attack. Irregular waves having a JONSWAP spectrum were used for all of the test runs. Beach profile erosion was measured initially for a 1:20 slope nourished profile without a toe structure in place. This established base test profiles for comparison with subsequent erosion profiles with a toe structure or sill in place. The subsequent tests with a sill were conducted with the sill placed at a range of depths along the nourished profile slope.

Each of the test conditions was subjected to erosive wave attack for 42 hours with periodic interruptions for measurement of resulting beach profiles. Test results are presented and interpreted to evaluate the effect of the sill structure on beach profile response and the effectiveness of the structure in retaining the beach. Scaling of the results to prototype conditions is also discussed.

An attempt is made to determine beach profile response due to the presence of a vertical seawall placed in various cross-shore positions, and to examine the differences between natural beaches and seawall-backed beaches in response to normally incident wave attack. The investigation was mainly restricted to two-dimensional profile response under erosive wave conditions, with beach recovery response monitored to a limited extent. Spatial and temporal profile response was investigated by examining time-series profile configuration, volumetric changes, sediment transport patterns, and quasiequilibrium profile configuration. Additionally, dominant profile features such as the break point and reflection bars (as well as scour at the toe of the seawall-backed profiles) were observed and quantified.

Bailard’s (1981) model of combined-flow, total-load sediment transport was used to calculate sediment flux at 8-m depth on a wave-dominated shoreface during fairweather and during a storm. Waves were skewed onshore during fairweather, however it was the reversing tidal current that controlled predicted transport direction. Transport direction during the early phase of the storm was also controlled by the mean flow, this time a wind-driven jetlike flow with an offshore component. As the storm progressed, waves became more organized and highly skewed, and by the end of the storm, predicted sediment transport was turned onshore by the shoreward-skewed waves against the mean flow. Measurements of changes in relative bed elevation at the 8-m depth site were used to verify the transport predictions. A total of 6 cm of accretion occurred over H.5 days of low-energy flow. It was found that predicted onshore transport was strongly correlated with erosion at the 8-m depth site, and predicted offshore transport was strongly correlated with accretion. Five cm of scour occurred during the initial phase of the storm, followed by 15 cm of rapid accretion. Onset of accretion was coincident with the organization of surface waves into long-period swell, and the maximum accretion rate was coincident with the most highly-skewed waves.

Field investigations have shown that infragravity frequencies may dominate nearshore fluid motions (Bowen and Huntley, 1984). Theoretical studies have suggested that the modal structure of the infragravity field, including the degree of modal coupling, is important in generating complicated beach morphologies (Holman and Bowen, 1982) but previous analyses of field data have not provided a description of the infragravity field which is sufficiently detailed to assess the importance of these ideas.

In this paper we present a statistical method which, when applied to data from any large sensor array, provides the desired description of the infragravity field. The method is applied to data from the NSTS (Nearshore Sediment Transport Study) experiment. The variance of the observed velocity field is described by a set of free wave modes. The results indicate that a complicated infragravity field composed of both edge waves and leaky modes is present. The modes modelled are also found to be significantly coupled over a range of modal pairs and frequencies.

In the present paper results of experimental study of two-dimensional transformation of sandy beach under varying wave climates are presented. The varying wave climates were composed of different systems of regular waves exerted one after another on the model beach. Through experiments it was found that sandy beach transformation within surf zone could be expressed by the changes of characteristic point A and characteristic slope tan β, and that although the expression for beach erosion-accretion criteria is dimensionless, similitude scale effects should still be taken into consideration.

This paper presents a technique to reproduce, by a two-dimensional moveable-bed model, beach change due to the time-dependent storm waves which are generated by the passage of an atmospheric depression. In the model test, scaling conditions for sand grain-size, vertical and horizontal lengths, and wave height and period characteristics were established by applying the authors’ scale-model relationship which was reported; and wave duration time also was decided. A method of employing regular waves in the model to represent irregular waves in the field is proposed. From the results, it was shown that the model can reproduce well the beach change in the field using the regular waves having the mean wave properties in the irregular waves.

A method is presented and Illustrated with examples to establish appropriate storm damage reduction and recreational benefits from beach nourishment projects. Unlike previous methods, benefits to project adjacent areas are recognized due to sand transport out of the project area and deposition on adjacent beaches. Assuming homogeniety along the shoreline, the character of storm damage reduction and recreational benefit relationships are such that sand transported from a project area and deposited on adjacent beaches always results in an increase rather than a reduction in benefits. A central element in calculating storm damage reduction benefits is the establishment of a proportional damage curve for upland structures as a function of beach width and storm return period. To illustrate the method, limiting cases are presented in which (A) all sediment remains within the area placed, and (B) all sediment spreads out immediately over a long segment of shoreline. Using Monte Carlo simulation to represent the random character of the storms, the method is applied to 15 realistic cases with varying project lengths, representative wave heights, added beach widths and interest rates. The present worth storm damage reduction and recreational benefits are calculated to demonstrate the effects of the various parameters. It is found that for short project lengths and relatively large wave heights, the benefits from project adjacent areas exceed those in the project area where the sand is placed. Although no littoral control structures, such as jetties are included in the present application, the method could be extended readily to include their effects.

The influence of coastal structures on a discharged flow and a depositional pattern of discharged sediment from a river are investigated experimentally. It is found that a pair of offshore detached breakwaters, as well as a pair of jetties, had a little influence on them. The offshore detached breakwater has also a function to prevent rivermouth from filling up with depositional sediment by waves. A numerical procedure for the prediction of depositional pattern of discharged sediment is developed based on the experimental results. The proposed numerical procedure is shown to reproduce depositional patterns around a rivermouth without structures and a jetty-protected rivermouth satisfactorily. However, the flow pattern around the offshore detached breakwater-protected rivermouth can not be reproduced.

The effectiveness of a novel sand/gel composite system for the temporary stabilization of coastal dunes was demonstrated in wavetank and field testing. The composite consists of 97% beach sand and water, with a few percent of a biodegradable aqueous polymeric gel made from nontoxic ingredients. The gel binds the sand into a firm but resilient composite that is natural in appearance and resists erosion from waves and tides. The composite is applied by pneumatic gun to the front face of a dune to a few feet below the berm level for toe protection.

This paper describes the initial development and performance of the composite system in wavetank tests at the Oregon State University Wave Research Facility and field trials at Anastasia State Park, St. Augustine, Florida; Chuck’s Steak House, Melbourne Beach, Florida; and Ocean Dunes Condominiums, Fort Fisher, North Carolina.

The littoral drift model developed at DHI and ISVA, see Deigaard et al. (1986b) has been extended to include the effects of the irregularity of the waves, of a coastal current and a wind acting on the surf zone. Further, a mathematical model to simulate the near-shore current pattern along a barred coast with rip channels has been developed.

The influence on the littoral drift of the irregularity of waves, wind, coastal current, and rip channels is discussed. It is concluded that irregularity of waves and presence of rip channels must be considered while coastal current and wind action are of minor importance.

Field measurements performed on two Caribbean islands revealed that two-dimensional nearshore bottom morphology is well represented by Dean's (1977) model of the beach equilibrium profile, h = A x^m, where h is depth below mean water level at a distance x offshore and A is a scale factor. For the curvature, m, we obtained an average value of approximately m = 1/2 through least squares curve fitting of observed profile data, yielding a more concave and therefore steeper profile inshore than m = 2/3, the average previously reported by Dean for quartz sand beaches in the United States. Furthermore, an objective measure of beach steepness was found to be A^1/m, a quantity which utilizes both of Dean’s parameters and which may serve as a surrogate for the beach-face slope, tan β, on highly concave beaches. Reasonable correlations were found between A^1/m and the environmental parameter, ${{\text{H}}_{\text{b}}}^2/{\text{gDT}}^2$ , where H_b is breaker height, D is sediment grain size, T is wave period and g is gravitational acceleration. Improved prediction of Caribbean beach slopes and beach equilibrium profiles is an important practical result.

The result of a theoretical approach shows that the beach profile characteristics is governed by a modified Iribarren number which includes the effects among the factors of initial beach slope, wave angle and wave steepness. A series of experiments are conducted in a three-dimensional movable bed model on the conditions of two different initial beach slopes, two incident wave angles as well as several erosive wave steepnesses. The relative importance of each factor involved in the parameter is discussed. It is shown that the modified Iribarren number is effective in the analysis, of beach profile characteristics under the action of inclined waves. The empirical relationships between beach profile changes and the modified Iribarren number are proposed on the basis of experimental results.

Laboratory experiments using a fiber-optic LDV system and a small pressure transducer have been made to reveal detailed characteristics of the velocity field in the surf zone and its relationship to the sediment suspension with special reference to the three-dimensional large scale eddies referred to as "obliquely descending eddies", the existence of which was recently revealed by Nadaoka (1986). A conditional sampling technique has been used to find that the obliquely descending eddies bring highly intermittent intensive turbulence to the bottom with the large onshoreward momentum at the upper layer of the water and thus essentially characterize the turbulent flow field in the surf zone. Visual observation and concentration measurements, especially a coherence analysis of two data sets of concentration close to the bottom, have shown that the sediment suspension is mostly governed by such large scale eddies in a wide extent of the surf zone; i.e., the eddies hit the bottom and then lift up the sediment into suspension, yielding the spot-like sediment cloud in accordance with the three-dimensional eddy structure.

The water particle velocity,the pressure fluctuation and suspended sediment concentration near the bottom were measured in the surf zone. Data were obtained on the mean sediment concentration, phase lag between onshore velocity and suspended sediment concentration. The near-bottom velocity distributions under finite amplitude waves were calculated on the basis of the turbulent boundary layer theory by using time-independent/dependent eddy viscosities and Prandtl mixing length theory. The concentrations at reference level were estimated from the Kalkanis’ theory using the velocity value at the top of a sand particle and the distributions of suspended sediment concentration were calculated on the basis of the turbulent diffusion theory by using time-independent/dependent diffusion coefficients. The computed mean values of the suspended sediment concentration agree with those observed by Noda, the authors and Nielsen and those measured by Deigaard et al.. The computed phase lag agrees well with observed by the authors.

Seymour and King (1982) evaluated eight models for predicting cross-shore transport using beach profile data from the Torrey Pines experiment of the Nearshore Sediment Transport Study (NSTS). None of the models showed useful skill in predicting the sense, or direction, of transport. Three more data sets were acquired under NSTS and have been used in the present work to re-evaluate the original four models as well as another six not previously tested. The three new data sets include two nominally plane West Coast beaches and a barred beach on the Atlantic coast, each under a variety of wave conditions. Six of the models evaluated claimed a capability to predict the sense of the cross-shore transport, two predicted the beach slope as a result of cross-shore movement, and two gave detail predictions of changes to the beach profile position and shape.

The performance of the six models predicting direction of transport ranged from a skill factor of 0.49 (less than chance) to only 0.68. Five of the models required large changes to their calibration factor (usually based upon laboratory data) in order to have approximately the same skill in predicting erosion or accretion. One of the slope models was validated and the other gave no useful results. One of the two generalized models gave interesting results in predicting the time history of profile changes on the plane beaches for which it was developed. The other general model was not evaluated because it exhibited the lowest skill in predicting direction of transport.

A semi-analytical model of 3D nearshore currents and sediment transport is presented. It describes the tidal motion, the waves, the surfzone currents and the sediment transport in complex coastal areas.

The results of a first application, to a well-documented case at the Dutch coast, indicate the potential and the shortcomings of the model. The latter are analysed and suggestions for improvement are given.

The semiempirical theory of turbulent diffusion may be used as a mathematical tool for description of suspended sediment mechanics. The Author’s solutions, with their exponential vertical profiles of sediment concentration, are presented in various ranges of time, space, and external factors. The inherent concept of eddy diffusivity K is shown to be ambiguous and incoherent. Therefore it is purposeless to investigate thoroughly the vertical profiles and other details of K. Accordingly, the Author makes use of his own and alien laboratory and field findings to propose such estimates of K under regular waves and currents which are not continuous functions of the vertical coordinate but instead are locally averaged over depth layers. These estimates become more complex in real coastal zones due to the randomness of waves and currents, wave breaking, three-dimensionality and nonstationarity of nearbed turbulence, a variety of interactions, and other sources of sediment dispersion. Hence gross estimates of averaged K seem even more appropriate; some formulae are put forward. The vertical profiles of sediment concentration are presented herein along with examples of sediment transport rates measured in nearshore zones.

In order to estimate erosion of sand beaches attacked by storm surges, experiments at prototype scale are necessary, since small scale models do not reproduce physical processes in the surf zone.

The present study describes the influence of erosion volume on crossshore sediment movement during the development of beach profile. The discussion includes parameters which affect the erosion volume and the accuracy of assessment.

Recent progress in the quantitative modelling of the undertow has stimulated the modelling of cross-shore sediment transport. More so than before it seems now possible to attempt the dynamic modelling of beach profile development. Also, integration of dynamic cross-shore sediment transport formulations in horizontally two-dimensional models for watermotion and sediment transport has recently been suggested. This seems to be a first step of integrating depth-averaged 2DH-modelling with 2DV-profile-modelling. Here an overview is given of these developments and the understanding gained sofar of the several current systems and the induced sediment transport and morphology that are found in the situation of random waves normally and obliquely incident on beaches which vary not or only slowly alongshore.

This paper describes characteristics of sand ripples and sand transport mechanism in regular and irregular oscillatory flows on the basis of detailed laboratory measurements. A set of empirical relations were proposed to evaluate the sand ripple geometry as well as the onset of the sheet flow transport. The applicability of the proposed relationships to the irregular wave conditions with prototype scales was confirmed with existing field data.

An extensive laboratory investigation into the behaviour of shingle beaches has been undertaken using a large random wave flume. The study utilised a lightweight material scaled to reproduce the correct permeability of the beach, and the correct threshold and relative magnitude of the onshore/offshore movement. Results are presented describing both the wave reflection characteristics of the beach and the probabilistic distribution of wave run-up crests on the foreshore. Where possible the laboratory results are validated against field data.

Pour series of tracer studies employing radioisotopic sand, tracked remotely from land, were carried out at the IBW PAN’s coastal research station at Lubiatowo. Incipient motion of single grains with velocity Vcr1 has agreed with Komar and Miller’s (1974) formula, and has been 5...8 times smaller than voro, the threshold velocity of water inducing bulk motion_of sediment. The ratio of average nearbed water velocity, $\overline{\text{v}}$ , to_the effective speed of tracer sand, in the inshore zone, ${\overline{\text{v}}}_{\text{s}}$ , is estimated about 100...1,000. The cross-shore sediment transport rates measured are ten times smaller than those predicted by Pruszak’s (1987) energetics formula, the discrepancy being due to the real field phenomena of mixing and overburdening in a thick bed layer. Our wave flume and wave tank studies with movable bed point to the importance of initial slope in shore evolution. The laboratory findings on bed variability are extended by our 1987 field data obtained with an ultrasonic setup. Intensive cyclic depth changes are acoorapanied by varying transport rates computed from continuity equation.

The bed load transport rate due to wave motion is measured in a wave flume. The modified stream function theory of the author (Tanaka (1988)) is applied to the formulation of the sediment transport rate in order to include the non-linearity. The proposed formula predicts well except near the surf zone where the effect of the acceleration plays an important role.

A new procedure for physical modelling of beach sedimentary processes is presented. It is shown that the modelling requirements proposed by Dean (1985) are necessary but not sufficient for dynamic similarity. Quantification of scale effects due to slope and relative grain size scaling conditions enables extrapolation of the physical model results to prototype situations. Selected examples of the application of the proposed model design are also given.

The effects of energy loss near the interface between the water and the sand bed on the wave-induced pore pressure are investigated by laboratory experiments. The interface between them includes the complicated factors: (1) roughness of seabed surface such as ripples; (2) boundary layer thickness in the sediment; (3) concentration of suspended sediments. These factors have been studied with respect to dimensionless parameters (e.g. Reynolds number, sediment Reynolds number, the ratio of orbital diameter to sand grain diameter, and Shields number), since many experimental formulas including these parameters have been proposed for predicting the geometry of roughness and the concentration of suspended sediments. The parameters described above are examined in relation to the damping characteristics of the wave-induced pore pressures. The transmissivity of pressure is constant until a critical value of the dimensionless parameters, and then decreases with increasing parameters. The critical values indicate the bed regime boundary of flat bed to ripple bed. Examinations of waveinduced pore pressure make it possible to predict the bed regime boundary.

Using a combination of laboratory, field, and numerical techniques, we have developed a methodology for predicting the extent of dune erosion due to a given set of wave conditions and the beach and dune morphology. A basic assumption in this model is that the volume eroded from the dune is a function of the swash acting on the dune. Because the model is built on this premise, it is necessary to look at the mechanics of two ongoing processes in the storm environment. The first is the relationship between the swash characteristics and the volume of material eroded from the dune face. The second is the relationship between the time history of the swash characteristics at the dune face and the statistics of the storm event, the significant wave height and wave period.

In this paper, we emphasize that there must exist a common mechanism governing ripple formation in the case of both waves where the acceleration effect exists, and unidirectional flow, where the acceleration effect is usually ignored. Using a light sediment with an immersed specific gravity of about 0.8, which is nearly one-half that of natural sand, a series of ripple formation experiments were performed in order to determine the formation criterion. Using the experimental data, along with data collected by other researchers the ripple-formation criterion was investigated in terms of the ratio of water particle orbital diameter to sediment grain diameter as an acceleration parameter, on the so-called Shields diagram. Emphasis is placed on the importance of this ratio in the criterion of ripple formation in relation to that by unidirectional flow.

At Oranjemund just north of the mouth of the Orange on the South-West African/Namibian coastline the Consolidated Diamond Mines (Pty) Limited (CDM) is mining for diamonds in the inshore area. They use an artificially-built seawall of sand to keep the sea out of the paddocks which are being stripped and mined at bedrock level, which is well below sea level. The seawall runs parallel to the original shoreline at a distance of up to 350 m offshore. The beach profile is correspondingly very steep and under most conditions offshore sediment losses occur, which are compensated for by artificial nourishment. During February 1987 offshore losses of about 120 m³ per running metre of seawall were recorded from above the waterline. In this paper a data set is presented to serve as a basis for the calibration of on-offshore sediment models and some simulations are reported on.

A mathematical model for sand-dike breach erosion is presented. The heart of the model is a modified Bagnold (1963) energetics-based sand transport conception combined with a simplified Galappatti and Vreugdenhil (1985) pick up mechanism for the suspended load. The model has been tested to three laboratory experiments. The agreement between model predictions and experimental results is surprisingly good. Prototype calculations are presented for the 73 m high sand-dike of a proposed pumped-storage plant in the Netherlands.

This paper examines the effects of random and deterministic cycling of wave direction on the updrift beach planform adjacent to a jetty. Results provided using a simplified numerical model cast in dimensionless form indicate the importance of the time series of wave direction in determining design jetty length for a given net sediment transport. Continuous cycling of wave direction leads to the expected analytical solution. Simplications in the numerical model used restrict the applications to small wave angles, no diffraction, no reflection of waves off structure, no refraction, and no sand bypassing at jetty. The concept can be extended to more sophisticated numerical models.

The rapid recession of the shingle bank of Hurst Beach (up to 3.5m/yr) makes it an excellent natural laboratory for the study of the factors which influence the stability of shingle beaches. Studies have included: the significance of long period, high energy, swell waves — the classification and quantification of overwash processes — run-up and seepage characteristics — the effect of settlement of the underlying strata — and the implications for practices in shingle nourishment. The studies have revealed the distinctive character of shingle beaches as compared with the more fully researched sand beaches. More detailed research on shingle beaches is justified particularly in relation to (i) the run-up characteristics including its interaction with swash cusps and (ii) the influence of the subsidiary sand fraction on the beach characteristics.

Beach changes around Tagonoura Port on the Fuji Coast were investigated by using the topographic survey data collected in the 15 years between 1968 and 1983. Temporal and spatial changes of the offshore distance from a reference point to certain contours were analyzed to elucidate the actual situation of topographic changes on the Fuji Coast, and the littoral transport rate on the downdrift coast of Tagonoura Port was found to be about 1.17x10⁵m³/yr on the average between 1973 and 1983. It is concluded that a large amount of sediment eroded from the downdrift beach of Tagonoura Port is carried away toword a zone deeper than 20m. A numerical model predicting three-dimensional beach changes was also developed, taking account of both the vertical distribution of littoral transport and the effect of the wave-dissipating breakwaters.

Sediment transport data from the field and laboratory tests are used to gain insight into two fundamental questions. Firstly: What is the relative importance of coexisting waves and currents for the resulting sediment transport? Secondly: Is the influence of grain size as strong as traditional models predict, or is it as weak as the empirical CERC-formula indicates?

Wave tank data reveal that the oscillatory velocity will in most cases determine the direction as well as the magnitude of the shore normal sediment transport, and wave flume data on shore normal transport as well as field data on littoral drift show weaker grain size dependance than traditional sediment transport models predict. It is suggested that wave dominance as well as weak grain size dependence are manifestations of the fact that the dominant transport mechanisms are often more organised than the diffusion process on which many traditional models are based.

Existing models for longshore sediment transport rate computations assume the sediment grain size and grain sizerelated parameters to be uniform in both the cross-shore and longshore directions. Field results from tideless beaches, which are briefly described in the paper, show that the latter change in both directions due to changing wave energylevels. The sensitivity analysis described in the paper shows that both longshore current and transport rate computations are sensitive to the cross-shore changes in grain size.Finally, a modified linearity coefficient for the wave power equation is proposed based upon the cross-shore distributions of grain size as found in nature.

Since the early 1960's, many seawalls against the beach erosion have been constructed in Japan, most of which were of vertical type. As a result, some of the seawalls even encouraged the beach erosion due to the reflected waves on the steep front of the seawalls. The author then proposed seawalls of new types with gentle front slope(l to 3) covered with armour units in 1981, and over one hundred fieldworks have successfully been carried out.

In 1985, the author proposed reforming the existing vertical type seawalls into the gentler front slope (1 to 5 or 6) seawalls. The laboratory test on the gentle slope seawall was made, and some experimental fieldworks were carried out. At this time, these new type gentler slope seawalls are successful.

Two and three dimensional laboratory studies have been carried out on the stability of a berm breakwater concept. The study has to some extent been general and to some extent been connected to a project study of the stability of a berm breakwater for the fishing port of Arviksand, Norway.

A mathematical model of flow on a sloping breakwater face is described and results of calculations compared with some experimental results to show how the model can be calibrated. Flow above the surface of the slope is represented by the shallow water wave equations solved by a finite difference method. Flow within the breakwater is calculated by one of two methods. A solution of the linear seepage flow equations, again using finite differences or a simplified model of inflow can be used. Experimental results for runup and reflection coefficient are from tests performed at HRL Wallingford.

Construction of detached breakwaters is one of the main countermeasures against beach erosion in Japan. The number of breakwaters has been rapidly increasing, with about 2500 constructed as of the end of 1981. This study aims at the investigation of the effect and stability of detached breakwaters along Japan’s coasts on the basis of survey of 1552 breakwaters constructed by the Ministry of Construction. The existing conditions of the dimensions of the detached breakwaters are statistically analyzed; the optimal dimensions for sand deposition behind a breakwater are proposed, and the critical conditions for advance of the shoreline facing an opening of breakwaters are investigated. Furthermore, the relations between the scattering rate of concrete blocks and various conditions such as bottom slope, the depth at the breakwater, the offshore distance of the breakwater and the weight of the blocks are studied. It is concluded that, in order to prevent scattering, the weight of the blocks should be at least 1.5 times heavier than that calculated from the Hudson formula.

To verify the effect of wave period on the motion of concrete blocks in rubble-mound breakwaters, simple physical models are employed and their motion is investigated by the numerical simulation. Finally, risk or reliability are calculated and the weight of concrete blocks for given physical condition is discussed by them.

The object of this present research is to study probabilistic design of armor blocks protecting composite breakwaters and to produce optimum design methodology for S-shaped breakwaters in terms of failure probability and construction cost. Failure probability in the vicinity of the still water level is greatest in the case of uniform sloped breakwaters. Therefore,S-shaped breakwaters of which the slope near the still water level is milder have a reduced risk of damage compared to uniform sloped ones. The optimum design index presents good economics and reliability in rubble-mound breakwater design.

Stability model tests and prototype breakage tests were done to provide data for the optimum design of dolos breakwater armouring.

Stability tests with irregular waves were done with dolosse with waist ratios of 0,33, 0,36, 0,38, 0,40 and 0,43 and breakwater slopes of 1:1,33, 1:1,5 and 1:2. All model dolosse had a mass of about 80 gr and were placed at a ‘normal’ density, Ø = 1,00. The results showed that regular waves with H_reg = 1,1 H_mo must be used to get similar damage. Also, a significant reduction in stability is evident for dolosse with larger waist-to-height ratios and for the shorter period waves (Figures 4 and 5),

Some 50 9 t dolosse, without reinforcing and with different types of simple rail reinforcing, were tested for breakage behaviour, using a specially developed cushioning device to closely represent breakwater conditions. The results showed that unreinforced dolosse can withstand falls up to 1,5 m, without breakage and X or double-V rail reinforced units about double this height.

The results of these tests, together with specific model tests, were used to design an effective protection for the Table Bay main breakwater. The tests indicated the use of 25 t dolosse (minimum) but, because of the shallow waterdepth, the toe dolosse of the repair slope were reinforced (double-V rail reinforcing), stabilized by 75 mm steel chains, and bitumen grout will be placed to reduce their movements.

All over the world shore-parallel constructions (seawalls; revetments; bulkheads) suffer from damage. It is argued that these constructions are in fact frequently built at places where they shouldn't.

A number of large scale tests on stability of rock slopes and gravel beaches is described and compared with small scale test results. The following topics are treated: the stability of a rock armour layer, the profile formation of a berm breakwater, the profile formation of gravel beaches, including ripple formation, and reflection and overtopping on rock slopes. The general conclusion is that scale effects could not be found.

Photogrammetry has been applied to make precise measurements of post-construction displacements of 38.2-metric ton (42-ton) dolosse on the outer breakwater at Crescent City, California. Data from two storm seasons are currently available from this monitoring program which was initiated in November 1986 and which is expected to continue at least through the next three winters. Supplemented by conventional land surveys, wave measurements, aerial inspections, and side scan sonar underwater imagery, observations from the photogrammetric monitoring have led to several preliminary conclusions regarding regions of relatively large dolos movement, dolos nesting, the dependency on breakwater slope of uprush or drawdown dominated armor unit movement, and the relative importance of armor unit movement and boundary conditions in dolos breakage. This paper describes the methods used for, and results obtained from, this monitoring effort along with the application of these results to a Corps study (Howell, 1988) Whose objective is to develop structural design criteria for the dolos concrete armor unit.

Analytical theory is derived for prediction of the wave force acting on a upright structure armored by concrete block mound of rectangular shape. The theoretical treatment starts from the linear long wave theory and the flow resistance in the mound is described by a linearized friction law. As a practical application of the theory, approximate method for the structure with sloping block mound is proposed. Experiments are conducted to verify the theory and approximate method.

A combination of a physical model and numerical models has been used in the design of a block revetment for the Danish North Sea coast. The wave pressure loading on the revetment during design conditions was investigated in a physical scale model. The measured wave pressures were used as a boundary condition for the numerical models. Solutions for the flow equations through the coverlayer, filter layer and subsoil were then obtained in the numerical models, taking into account the influence of turbulence. With these solutions the stability of the coverlayer and subsoil was evaluated. The paper presents a description of the various models and information about the design of the revetment.

Shock pressure phenomena due to breaking waves acting on sloping faces of sea dykes are focussed in this paper. The probability approach is pointed out and maximum shock pressure estimations are given for smooth and impermeable dyke slopes 1:4 and 1:6. An extension of the results to steeper and flatter slopes is proposed.

Results of full-scale stability tests on concrete block slope revetments are also reported in this paper. For various structural solutions with granular and geotextile filter layers stability numbers are recommended. Initial block lifting is explained physically by pressure measurements.

The full-scale experiments were carried out in the new research facility LARGE WAVE CHANNEL of the universities in Hannover and Braunschweig (Federal Republic of Germany).

The present paper describes a study carried out to investigate floating breakwater behavior in waves. Components of the study include a field survey of floating breakwaters in British Columbia, Canada, the development of a numerical model of breakwater behavior and the experimental testing of a particular breakwater design. The numerical model has been developed to provide breakwater motions, transmission coefficients and mooring forces. The model combines linear diffraction theory for obliquely incident waves, a mooring analysis, the inclusion of viscous damping coefficients obtained from experimental or field data, and the inclusion of drag and wave drift forces for use in the static analysis of the moorings. The experiments were carried out with normally incident regular waves of different heights and periods. Preliminary results indicate that the numerical model should prove to be a useful tool in floating breakwater design.

The characteristics of wave forces acting on a horizontal circular cylinder were investigated through numerical calculations as well as experimental findings. The laboratory data on wave forces were analyzed by the concept of wave force path and classified into two types. One is the circular type and the other one is the 8 – shaped type. In order to analyze the above phenomena, the discrete vortex method was applied with appropriate assumptions. The comparison between the numerically calculated results and laboratory data shows that the simulation model proposed in this paper seems to be favorable to predict the wave forces acting on a horizontal circular cylinder within a certain range of conditions.

The scattering of waves by a finite number of rows of circular cylinders is examined. Reflection and transmission coefficients are obtained and compared to Kakuno’s experimental data. Following Twersky (1962), the scattering from a single row of cylinders (or the single grating problem) is numerically solved. The wide-spacing approximation is used to find the effect of multiple gratings.

Several previous investigators have conducted experiments leading to expressions for predicting the transformation of waves passing through closely-spaced pile or large cylinder breakwaters. The present study extends the earlier experiments which used a single row of piles instead of a double row of piles forming a breakwater. The experiments using the double-pile breakwater were performed in the same facility as the experiments conducted on a single-pile breakwater and employed the same method of analysis for a more meaningful comparison.

The experiments consisted of allowing waves to pass through a pile array and measuring the incident and transmitted wave heights. The variables were: depth, period, diameter, monochromatic and random waves. The experimental matrix was three water depths, four wave periods, two pile diameters, two gap dimensions between piles and four random wave spectra: Darbyshire, I.T.T.C., Pierson- Moskowitz and JONSWAP, two pile diameters and two gap dimensions between piles.

The two-row breakwater had less wave transmission than the single-row breakwater, as expected. For a gap to a pile diameter ratio, or b/D = 0.2 (where b = gap spacing, D = pile diameter), the wave transmission was reduced by 15 percent, as compared with a single-row breakwater; for a gap ratio of b/D = 0.1, the wave transmission was reduced by 5 to 10 percent.

The horizontal forces, vertical forces and overturning moments exerted by waves on a fixed model of a 45" conical structure are presented. Irregular wave loading tests were conducted for a range of conditions described by base diameter on peak period wave length D/L_p from 0.31 to 1.76, water depth on peak period wave length h/L_p from 0.11 to 0.63, and significant wave height on peak period wave length H_m0/L_p up to 0.07.

Time series records, spectral densities and transfer functions for the irregular wave loading tests are used to illustrate the nonlinear nature of the measured wave loads. In most cases, similar trends in wave loading were observed for irregular and regular wave tests. For deep-water waves, the irregular and regular force measurements showed spectral peaks at the second harmonic of the wave frequency even though the waves themselves had relatively small second-order components. However, unlike the regular wave loading results, the fundamental spectral peak frequency for the irregular wave forces occurred at a frequency considerably lower than the peak frequency of the waves. Although linear diffraction theory provided a reasonable estimate of the wave forces for waves of low steepness, larger deviations were often present for higher wave steepness results. Comparison of theory and experiment for overturning moments was generally very poor for most wave conditions.

Under certain wave conditions, an immersed plate which is free to move horizontally produces what has already been called the oscillating water wall phenomenon. When this happens, the plate and the volume of fluid located under the plate move back and forth and then behave as a wave reflector. This type of breakwater was studied in a wave flume with monochromatic and irregular wave trains. Tests have provided a better understanding of the influence of certain parameters that define a plate and the hydraulic conditions under which the plate is used. Results show some interesting efficiencies and also transfert of the energy to harmonic frequencies.

Impacts, abrasion and physico-chemical weathering which sometimes result in rapid changes of armour shape and size can have disastrous consequences for armour stability. This paper draws together the background ideas and some new techniques which have been developed to tackle the prediction of weight loss and shape change of rock armourstone during the life of a coastal structure.

The framework proposed is to measure separately the wear resisting material properties of a rock type using a tumbling mill simulation of prototype block degradation. Time on the structure is then related to mill time by a factor which accounts for initial block size and the site specific environmental conditions. A field site in Scotland is used to demonstrate the new image analysis methods for measuring rounding of prototype blocks. The shape analysis results can also be used to calibrate the equivalent wear factor for conditions at that site. Discussion of this framework is extended to dynamically stable design concepts where abrasion losses are faster.

Preliminary flume testing in collaboration with H. R. Wallingford indicates that losses in stability due to rounding could be considerable.

Interaction of large amplitude wave with platforms or docks in a variable depth medium has been studied theoretically and numerically. The underside of the platform is equipped with energy absorbing linear spring in order to study the energy absorbing effect for reducing the uplift forces on the platform or dock.

The flow is assumed to be inviscid, irrotational without current. Laplace equation with full non-linear free surface equations are solved by isoparametric mapping technique. A Galerkin finite element model is used to model the transformed equations. The adaptive line SOR (Successive-Over-Relaxation) technique is used.

The results indicate that uplift wave forces on platforms or docks can be significantly reduced by very soft springs. Wave profile history confirms the manifested mechanism of energy absorption. The results also indicate that larger uplift forces are easier to be damped out by the prescribed energy absorbing mechanism than the smaller uplift forces.

This paper is to investigate both theoretically and experimentally the wave energy dissipation and air-pressure variation of a new type of breakwater having a pressurized air-chamber and two buoyancy tanks. The theoretical models are developed in this paper and they are shown to be in good agreement with experimental values. The new type of breakwater proposed in this paper is pointed out to attenuate the transmitted wave much better than the rectangular-shaped and concave-shaped breakwaters without the air-chamber.

This paper deals with a study on shock pressures, which occur on sloping seadykes and revetments due to breaking waves. Results from field measurements are presented with respect to peak pressure values as well as to characteristics of pressure-time histories.

A total of eleven new types of blocks are developed for this project. After performing a series of model tests for them and having a consideration of easy casting, two types of blocks are selected and presented here in this paper. They are named "Double U block" and "I block", respectively. The two have been compared with several existing types which have been widely used in Taiwan. It is shown that the Double U block is an excellent type of block with high stability and low reflection coefficient. The I block has an advantage of easy casting, although it is not outstanding in other characteristics.

There is a general lack of knowledge regarding the nature and magnitude of loads acting on armour units used for the protection of rubblemound coastal structures. Thus, a comprehensive design procedure incorporating both the hydraulic stability and the structural integrity of the armour units does not exist.

This paper presents the results of a detailed parametric study of the structural response of armour units to wave-induced loading in a physical breakwater model. The effect of the following design parameters is investigated: breakwater slope, armour unit location, wave period and wave height.

This research has made a number of significant contributions towards the development of a comprehensive design procedure for concrete armour units. It has identified a linear relationship between the wave-induced stress in the armour units and the incident wave height. In addition, it has shown that the conditional probability of waveinduced stress given wave height can be estimated by a log-normal distribution. Finally, a preliminary design chart has been developed which incorporates both the structural integrity and the hydraulic stability of the armour units.

This paper provides guidance for the design, fabrication, and installation of articulated concrete mat slope protection. Although articulated mat armor has been utilized for many years in low-energy wave environments, it has been extended recently to accommodate intermediate wave energies and severe ice loads. The development of the concept is discussed, after which hydraulic design considerations, material design considerations, and fabrication and installation techniques are presented. Prototype performance is reviewed. It is concluded that articulated concrete mat armor is capable of providing effective slope protection in intermediate-energy wave environments, and that additional research is required relating to hydraulic stability and failure modes under wave and ice loading.

The standard design for a rubble-mound breakwater as reported in recent text books and manuals has consisted of a core of rubble quarry-run that is protected from wave action by two layers of relatively large quarried stone or concrete units. Filter layers of intermediate size stone are recommended beneath the armour layer to prevent loss of the core material through the armour. The pioneering work of Hudson provides coefficients for a formula that allowed widespread use of this design concept throughout the world.

Damage of concrete armour units on a number of breakwaters around the world has brought into question the design methodology for these structures.

The interaction of waves with a rubblemound breakwater is a complex process typified by the random nature of the wave loadings and of the placement and orientation of the armour units.

The objective of this paper is to present the development of a more simplistic physical model for establishing a realistic upperbound for the forces occurring on concrete armour units, to more readily understand the response of the unit to various wave parameters, and to explore the effect of carrying out tests at different scales.

The results of these investigations demonstrate the applicability of employing simplified models to assist in understanding the response of armour in a breakwater and the consistency of the instrumentation at different scales.

Assessment of the characteristics of the wave force on the curtain-wall-type breakwater, due to obliquely incident waves, was conducted through numerical calculation, laboratory and field experiments. In the numerical calculations, the Boundary Integral Equation Method (BIEM) for obliquely incident waves was used. From the results of calculation and laboratory experiment, design graphs for estimating design wave force were established and the validity of the diagrams was verified through comparison with the results of laboratory and field experiments.

Several numerical models for estimating wave forces on dolosse are presented. These models are incorporated into a finite element method (FEM) analysis of a 42-ton unit. The results of the analysis permit identification of unit structural failure with respect to wave conditions.

Appropriately designed, constructed, and maintained rubble mound seawalls are an efficient and cost-effective means of protecting erodible sections of exposed coastline. This conclusion is supported by more than 25 years of satisfactory seawall performance along the Pacific Ocean coast of Santa Cruz County, California, U.S.A. Important factors in satisfactory seawall performance include a clear understanding of the oceanographic and geologic design parameters, a vigorous inspection program during construction, and continued observation and maintenance of the structures.

In this paper, studies on dynamic characteristics and responses under waves of caisson-type breakwaters by field and model testings as well as dynamic analyses are described. It is found that the gravity-type structure-foundation system can be simplified as a rigid body on a linear or non-linear elastic foundation for evaluating its dynamic characteristics and responses. The dynamic displacements of the caisson are found related to the wave heights, the water depth as well as the foundation soil properties.

Experimental measurements of hydrodynamic forces on a cubic block near the bottom under solitary waves were carried out. Horizontal and vertical forces were recorded and instantaneous and averaged values of hydrodynamic coefficients C_D, C_M and C_L for different boundary conditions, gap between block and bottom, e, and two or three-dimensional flow, were obtained. Horizontal and vertical forces were found to depend strongly on e/D, where D is the block side. Instantaneous values of hydrodynamic coefficients vary considerably during the wave passage and differ appreciably from the averaged coefficients.

The wave power extracting caisson breakwater can convert the wave energy into usable energy. The function and the stability of the caisson as a breakwater are investigated experimentally. It is found that wave reflection and wave transmission of the breakwater are relatively small and that the stability of the breakwater caisson against storm waves is high. The design method of the caisson is proposed considering the impact air pressure in the air chamber.

Mixing of thermal effluents, being discharged from thermal power plants on coastlines and which head into surface waves was investigated by analyzing extensive field and laboratory data on plume and ocean ambient conditions. Emphasis was given on the effect of waves and surf zone currents on the modifications of plume surface area and vertical temperature profile in the near-field area.

The results of this investigation showed that large opposing waves increase the plume surface area, in the vicinity of the outfall, for all cases of tide level and wave direction. Moreover, waves focused cold bottom currents on the discharge outlet and consequently the temperature of the released warm water was decreased at the surface and near the bottom. Wave-induced cross flows decreased the plume cumulative surface area which corresponded to fractional excess temperature ranging between 0.8 and 0.5 normalized values. This decrease was shown to be contingent that there is no interaction between the far-field and near-field plume waters. Gradient of wave momentum flux across surf zone was found to be necessary parameter to characterize the incident wave field.

This paper presents the results of stochastic analysis of offshore currents. The purpose of this study is to clarify the stochastic properties of offshore currents, and to develop a method to predict the magnitude of the extreme currents and their direction from measured data. Statistical analysis as well as spectral analysis are carried out on current velocities measured over a period of several months off Newfoundland, Canada. The effect of water depth on the statistical characteristics of current velocity is also clarified. The extreme current velocity expected to occur in 4- months and its direction are estimated by applying order statistics and the results are compared with the measured data.

The entrainment phenomena have been investigated across an interface between two-layered stratified flow induced by wind shear stress. The velocities of mean flow, turbulence and entrainment have been measured under three different conditions of water surface by using a wind-wave tank. When the entrainment velocity ue is expressed on the basis of the turbulent quantities at the interface, the turbulent entrainment coefficient $\text{E}(\equiv {\text{u}}_{\text{e}}/\text{u})$ is given by $\text{E}=\text{A}\cdot {(\text{ε}\text{gl}/{\text{u}}^2)}^{-3/2}$ ( A = 0.7). Here εg, u and 1 are the effective buoyancy, the turbulence intensity and the integral lengthscale of turbulence at the interface, respectively. This result coincides with the relationship of entrainment due to oscillating grid turbulence, in which the mean flow does not exist. When, for the practical purpose, the estimation of ue is made by using the mean velocity Um and the depth h of mixed layer, $${\text{E}}_{\text{m}}(\equiv {\text{u}}_{\text{e}}/{\text{U}}_{\text{m}})={\text{A}}_{\text{m}}\cdot {(\text{ε}{\text{gh/U}}_{\text{m}}2)}^{-3/2}$$ is derived from the transformation of $\text{E}\text{=}\text{A}\cdot {\text{(}\text{ε}{\text{gl/u}}^2\text{)}}^{-3/2}$ . There holds ${\text{A}}_{\text{m}}=\text{A}\cdot {\text{T}}_{\text{f}}$ between Am and Tf, Tf being a turbulence factor given by ${(\text{u}/{\text{U}}_{\text{m}})}^4\cdot {(1/\text{h})}^{-3/2}$ .It has been found that this relationship is also valid in various types of two-layered stratified flows as well as the wind-induced two-layered flows.

The effect of boundary conditions on numerical computations of stratified flow in coastal waters is examined. Clamped, free radiation and sponge layer conditions are implemented in a two-layer finite element model and the results of simple tests in a two-layer stratified basin are presented.

Bore front hydraulics are investigated in terms of Burgers equation to clarify the dynamics of a moving discontinuity in water flow. Burgers equation has been derived from the one dimensional open channel equation with the horizontal turbulent diffusion term. The derived equation system consists of Burgers with respect to dynamic characteristic and hyperbolic equation with respect to water surface elevation, which satisfys Jeffery-Vedernikov condition F_r = 2 through discontinuity. It has been verified from the experiments that the condition F_r = 2 is a good approximation of bore front dynamics. The numercal calulation method of Burgers equation employing Cole-Hopf transformation and QUICKEST algorithm was also proposed and confirmed its efficiency.

Cullera Bay is a neri tic ecosystem placed on the Spanish Mediterranean Littoral largely influencied by the Jucar River, that brings about lower salinities than sourrounding waters, and broad variations of its values. An extensive research, with 9 samplings throughout the year, was carried out, measuring both physical and chemical parameters, and the planktonic communities. The trophic status of the ecosystem, the spatial and temporal variations of the nutrients and the planktonic communities were studied, evaluating the influence of the river loads and the littoral dynamics. Some essential basis to allow a suitable emplacement of waste waters disposals along the Valencian littoral are set up in order to minimize the gradual eutrophication of this coast.

The flushing characteristics of a newly constructed marina were determined from a comprehensive field study which included a dye dilution experiment together with measurements of barotropic and baroclinic forcing parameters. The results to be presented show that the major exchange process in this particular marina is a baroclinic circulation, and that the exchange rate is controlled by the harbour entrance geometry.

The State of Hawaii's Ocean Science and Technology (HOST) Park, the U.S. Department of Energy (DOE), and the Pacific International Center for High Technology Research (PICHTR) sponsored the construction and installation of an expanded seawater supply system at the Natural Energy Laboratory of Hawaii (NELH). This effort included the installation of a 1.0m diameter high density polyethylene pipe capable of delivering 840 1/s of cold seawater, representing the longest (2,060m) large diameter pipe traversing the steepest slope ever spanned. Acceptance testing of the system was completed in June 1988 and the design service life is 10 years.

A time-dependent three-dimensional numerical model of coastal and estuarine circulation, which allows the use of generalized curvilinear grids to resolve the complex shoreline geometry and bathymetry, has been developed. Model formulation is briefly presented, followed by example model applications to such water bodies as Lake Okeechobee, James River and Chesapeake Bay.

Tidal wetland preservation, restoration and creation have become requisites for coastal development projects in the United States. A basic approach to design of tidal wetlands is presented, stressing cooperation between regulatory agencies, biologists, engineers, and developers. Basic principles of wetland functions are explained and presented as criteria for engineering design. A description of wetlands is given to identify biological features relevant to design. Also, some key features of tides are summarized as they affect wetland design. A numerical model was used to demonstrate how tidal wetlands may be designed to conform with criteria developed by the agencies and biologists. This approach has been used on wetland designs in California, but the approach may be applicable to other areas of the world.

Initial results are presented relating to an investigation of geomorphological parameters from 26 of a total of 28 tidal inlets and 11 coastal structures similar to inlets along the German Bight. The following parameters were investigated:

– tidal prism - inlet area relationship,

– cross-sectional form and depth,

– location of the channel within the cross-section,

– ebb tidal deltas and

– the structures of the back barrier regions.

The most important parameter governing the shaping process of these coastal structures is considered to be the tidal volume. The results of the investigations were compared with data from American publications. Despite the differences between the regions studied, in overall terms, surprizingly good agreement was obtained between the parameters investigated. Notable differences exist only in relation to the morphological structure of the back barrier regions (tidal flats, salt marshes, open water lagoons). In respect of the latter differences, a short account is given of the biological and climatological influencing factors.

In modeling studies the bottomstress parameter may not be taken as a constant for making predictions. This is particularly true when large changes are being made in the water bodies. Engineering judgement is than necessary as studies to a relation between the bottomstress parameter and tidal flow velocity are not conclusive.

In order to evaluate silt displacements and deposits in the outer part of the Loire Estuary over one year, a two-dimensional depth-integrated model of suspended sediment transport has been carried out. It takes into account transport and dispersion of suspended sediment by tidal currents, and processes of erosion, deposition and bed consolidation. Erosion laws and consolidation laws are specific of the Loire Estuary and come from laboratory experiments.

Representative tidal conditions and river Loire flowrates have been identified : results of the model for these typical cases will be tentatively extrapolated to a one year evolution.

Environmental assessment, engineering studies and designs were completed for a new 26.5 m³/s seawater intake system in the Persian Gulf. The original intake facility consisted of a curved, 60m breakwater with one end attached to the shoreline, a settling basin immediately adjacent to the shoreline and dredged to a maximum depth of approximately 5m, and a pumphouse structure located on shore such that the seaward wall formed one side of the settling basin. The facility located on an island in the Gulf, which served multiple seawater uses, had experienced both structural and operational problems, the latter consisting principally of excessive ingestion of sediment and seaweed. These factors plus the requirement for additional demands for seawater beyond plant capacity caused the owner to initiate a study of alternative intake systems, produce a design for the most effective solution and construct the new intake system.

In the beaches under study on the island of Grand Canary, we are identifying and measuring the intertidal annual cyclic processes of accretion and erosion, starting from the topographical movements of the strand.

These processes:

a) We are analyzing and interpreting these in the framework of the physical and geographical interdependences, and as responses to the more internal evolutions of the morphodynamics, in the sedimentary environments in question,

b) and permitting the definition and calculation of some indices of sedimentary gains and losses, of interest to coastal planning and management.

The submarine siphons with an overall length of almost 1300 meters and an ultimate capacity of 27 cubic meters (m³) per second (about 600 million gallons per day) will be a major element of the new wastewater conveyance and treatment system presently under construction in Athen, Greece. This will help alleviate the present condition where an average of more than 6 m³ per second (130 million gallons per day) of untreated domestic and industrial wastewater are discharged into the sea near Athens. Construction of the submarine siphon pipes started in late 1984 and was completed in early 1987.

Description of the data collection for and the design, manufacture and construction of these submarine siphons are presented in this paper.

The intent of this paper is to express the quantities of sand bypassed by a sand transfer facility and transported in the littoral drift at the South Lake Worth Inlet, Palm Beach County, Florida. Discussion on littoral transport volumes will include estimates of the annual average drift from 1948 to 1987, and discussions of sand bypassing quantities will include improvements in the estimation of pumping rates.

Eleven artificial headlands were constructed on the OhncKashima Beach facing the Pacific Ocean to prevent further extension of beach erosion and to form the dynamically stable beach. This paper summarizes the results of the follow-up study of the new works applied on the actual coast. Field investigations such as bottom sounding around headlands and aerial photographing were conducted. It was found that the periodic changes of the shoreline configuration correpsonding to seasonal change of the wave direction exist on this coast and these variations of the shoreline position can be reduced by the effect of these headlands.

A beach nourishment project was carried out at Atlantic City, NJ during the summer of 1986. One million cubic yards of sand was dredged from adjacent Absecon Inlet and placed over a 9000 foot long section of the beach. The authors monitored the fill for a period of eighteen months, including two winters, after placement of the fill.

This paper briefly summarizes the fill project and monitoring program. Key results of the monitoring program are presented and compared with results of the monitoring program for previous nourishment projects at the site in 1963 and 1970. Differences in the behavior of the 1986 fill vis-a-vis the 1963 and 1970 fills are discussed and possible reasons for these differences are given.

In order to investigate the effect of enchanced sea level rising (greenhouse effect), of sand mining in the North sea and the largescale effects of beach nourishment, the Rijkswaterstaat (Governmental Board for Ways, Waterways and Harbours) started the project "Coastal Genesis". This paper deals about research, carried out at the Delft University of Technology in the scope of this project.

The behaviour of the Holland coast at three timescales, i.e. 15 years, 1000 years and 6000 years is considered. Use is made of line models. New techniques are developed for finding the coastal constants of these models (the use of Kalman filtering) and for simulating the effect of sea level rise on coastal accretion and erosion. An extensive set of data on coastal topography, the JARKUS dataset is analyzed.

It is concluded that the effect of cross-shore transport becomes more and more dominant compared to the longshore transport when the time scale increases. A physical conception is displayed, which explains more or less the accretion of the Dutch coast between 4000 Before Christ and the Roman times, and the erosion later on.

High water levels on Lake Michigan during 1985 and 1986 created substantial erosion of the shoreline and reduced the size and recreational potential of many of the parks and beaches. To prevent further erosion, protect existing properties and structures, and to create and improve recreational areas along the Lake Michigan shoreline, four coastal engineering projects were designed and constructed during this time. Artificial beach units stabilized by offshore breakwaters were used as the main component of each project.

Physical hydraulic model studies were used to determine the orientation, size, and spacing of breakwaters and artificial beach units. Model predictions of beach profiles and plan shapes compare closely with prototype surveys. Surveys completed since construction demonstrate the stability of the beaches and support their use as effective, low maintenance shoreline protection.

Prototype experience has shown that these projects are extremely successful both in their ability to withstand storms on the Great Lakes and to attract people for recreational activities.

Steady erosion has occured on the beaches at Ostend, Belgium, especially on the section between the Casino and the Harbour Entrance. The gravel beach supported by a sandfill core has been proven to be a feasible and cost effective flood protection alternative, the first objective of the long term beach enhancement programme. Secondary goals are also met such as : new beach recreational facilities in safe conditions for the public ; the economic incentive for the needed redevelopment of this part of down-town Ostend and the beach front ; the conservation of the present sea-view from the promenade.

As shown in Fig.1 the main fairway of Port of Kaohsiung is running from north to south with a length of 12 kilometers. To the west, there is a sand bar served as a natural breakwater, the so called outer Breakwater, to provide the port and resident’s property the necessary safety and security. Recently, due to rapid growth of container traffic and bulk cargo transportation, Port of Kaohsiung has developed some parts of the outer breakwater near the 2nd Harbor Entrance as Container Terminal No.4 with seven 14-meter-deep, 320-meter-long container berths and about 100 hectares container yard on northern side, and coal Terminal with 16-meter-deep, 320-meter-long berth and a huge storage yard on southern side. Therefore, the shore protection along the area become more and more important year by year. So far, some 6-kilometer seawall and 20 groynes have built successively, and already played a very important role for the shore protection there.

The results of scale-model simulation of wave-induced hull motions of large bulk carriers under conditions representative of those for coastal ports are presented and discussed to illustrate their usefulness in studies aimed at evaluating the optimum depth requirements for port approach channels.

To investigate the dynamic behavior of a mooring buoy installed in an open shore, a simplified simulation model is developed, which consists of the surging and heaving motions of a mooring buoy.

A series of the model tests is performed to examine the reliability of the developed model. The model tests verify that the developed model can predict the dynamic motion of a mooring buoy satisfactorily.

Finally, simulation is made for the buoy installed in the west shore of Iwo-jima which failed during a stormy weather. This simulation indicates that the external loads enough to cause the failure has been loaded on the buoy at the moment of the failure.

This study aims at clarifying the effective method to set up the fish aggregation device (FAD) thrown down from a ship on the designed position most accurately. The numerical simulation technique is developed to analyzed the behavior of the settling FAD in consideration of the effect of vortices generated behind it. From the systematic calculations for the change of the initial condition on the posture of the FAD at throwing, the effective initial posture of the FAD which reduces the settled area on the sea floor most is investigated. Furthermore, the added-mass coefficient of the settling FAD is numerically analyzed from the kinetic energy of the fluid induced by the settling FAD. The FAD treated in this study is the structure to gather fishes.

The ship refuge inside a harbor in storm requires the analysis of moored ship motions along a quay wall. In this case the time domain analysis with the convolution integral method becomes effective. But the calculation accuracy is not enough and must be improved to analyze actual moored ship motions. In this paper some methods of the improvement are proposed and their efficiency is verified by comparing the calculation results with the experimental ones.

Fenders are to be selected taking into account two quite distinct functions they have to fulfill:

– During berthing manoeuvres fenders have to avoid damage to the ship and to the berthing structure;

– After ships are already berthed and moored, fenders have to keep them quiet during loading and unloading operations.

To fulfill the first function fenders have to be able, while deflecing, to absorb a very large amount of energy.

To fulfill the second function fenders need to be able, while recovering their form, to dissipate a large amount of energy. Besides, they have to contribute to reduce or to increase the natural period of oscillation of already moored ships, depending on their tendency to oscillate in phase or out of phase with waves reaching the berths.

The behavior of the model of a moored vessel in a harbor’s hydraulic model (Froude’s model) is studied, taking into account the difficulties arising from the fact that modelling a moored vessel requires to incorporate the Reynolds number. Experiments made with the model of a large grain carrier at a 1/175 scale are shown. The horizontal motions of this ship due to the waves were measured when it is moored in a zone in which the length scale along the vertical axis was modified (vertical distortion), and the influence of different depths on these motions was studied.

This study was performed in order to be able to use this ship model for the evaluation of different alternatives of harbor design, in the building of new facilities at a port placed in the Atlantic coast of Uruguay.

A two-dimensional wave prediction model suitable for use on personal computers is described. The model requires the twodimensional time-dependent wind field as input. Output consists of wave height, wave period, and wave direction estimates at all grid points on a computational grid representing an enclosed or semi-closed basin. Model predictions compare favorably with observations from a wave research tower in Lake Erie. A formula is provided to estimate how long a model simulation would take on a personal computer given the surface area of the computational domain, the grid size, and the computer clock speed.