Coastal Engineering 1998

A limited review of methodologies for design and prediction ofbeach nourishment performance is presented and some recent results of the evolution of the total plan area of a nourishment project on a long straight beach are examined. The emphasis is on rather simple approaches which may be more applicable for preliminary design and screening of candidate designs rather than final design. Most beach nourishment projects are placed at slopes that are steeper than equilibrium. Thus the project is initially out of equilibrium both in the planform and profile. The simple approaches represent the planform evolution and cross-shore processes separately. Planform evolution can be represented by the Pelnard Considere equation, which in addition to providing a basis for representing the performance of a particular design, also provides a good overall basis for understanding the behavior of beach nourishment projects. Several solutions of the Pelnard Considere equation are examined and some of the general results obtainable from this equation are presented and discussed. Particular results include the insensitivity ofevolution to storm sequence, the reduction of spreading “losses” due to refraction around a planform anomaly, relative insensitivity of planform evolution to wave direction for nourishment sand that is compatible with the native, and the effects of nourishing on beaches with sand coarser and finer than the native. Profile evolution is best modeled over short time scales when the profile is significantly out of equilibrium. Limited observations indicate that profile equilibration time scales associated with oversteepened nourished profiles are on the order of 5 years. Application of equilibrium beach profile methodology demonstrates the sensitivity of additional dry beach width to sand size. Recent results of the evolution of the total plan area of a beach nourishment project are presented. It is found that nourishment with sands coarser and finer than the native, results in total plan areas that increase and decrease, respectively, with time. Because the results obtained considering nourishment sands of a single size are unrealistic, a method is applied in which the nourishment sands are characterized by two sizes of different proportions. The results for this approach are more reasonable and consistent with expectations.

A brief review is given of the initial development of a model for the turbulence generated by a spilling breaker riding on an unsteady wave. The turbulent volume of water in a spiller is modelled as a thin layer. The basis for such a model comes from the analysis of the interaction between an air-water interface with patche of turbulence. Hence, the behaviour of a free surface which is affected by strong turbulence is being studied. We summarise some of the salient points of our work. These include a derivation of averaged boundary conditions which include mass and momentum flows in the surface layer and the transfer to the bulk liquid. A brief account is also given of the type of equations needed to represent the motion of the front edge of the breaker. Illustration of the method is only given in terms of the equations derived by integration from the equation of mass conservation. Finally, there is description of the various free surface regimes that occur and need to be considered in order to determine suitable closures for the averaged terms.

A breaking wave model is presented to simulate non-equilibrium evolution of turbulence with a time-dependent depth-integrated equation of turbulence intensity, which is to be coupled with nonlinear wave. As the crucial part of the modeling, a method to estimate the production rate of turbulent kinetic energy is developed. This method is based on the experimental observation of the pseudo-periodic generation of large-scale eddies near the wave crest of turbulent bore. As a demonstration to show the performance of the present model, numerical examples are given for regular and irregular waves on a slope and regular waves on a double step, indicating that this model can give favorable features of evolution of regular and irregular breaking waves and the production and diffusion of turbulent kinetic energy.

Numerical computations using a fully nonlinear potential flow solver are carried out on water of intermediate depth. Properties of single and multiple wave groups are examined on horizontal and sloping beaches. Comparisons are made with linear and weakly nonlinear theories. An important result is that the increase in wave amplitude due to wave shoaling is likely to be much less than the linear theory result for short steep wave groups because of the tendency for the group to spread.

A simple model is presented to compute the average rate of energy dissipation in irregular breaking waves. The average rate of energy dissipation rate is assumed to be proportional to the difference between the local mean energy flux and stable energy flux. The local fraction of breaking waves is determine from the derivation of Battjes and Janssen (1978). Root mean square wave height deformation is computed from the energy flux conservation. The model is validated using root mean square wave height data from small and large scale laboratory and field experiments. Total 144 wave height profiles are used in the calibration and verification of the model. Reasonable good agreement is obtained between the measured and computed root mean square wave heights. The root mean square relative error of the model is 10.2 %.

In this paper we shall study and model the nonlinear transformation offrequency wave spectra using two different types of stochastic models. The nonlinear processes considered include triad wave interaction and dissipation due to depth-induced wave breaking. The two stochastic models are the two-equation model proposed by Kofoed-Hansen and Rasmussen (1998) and the one-equation Lumped Triad Approximation (LTA) originally proposed by Eldeberky and Battjes (1995). Model results are compared with laboratory experiments and results obtained by the underlying deterministic time-domain Boussinesq model. The two stochastic models are found in good agreement with measurements of wave height (H_m0) and wave period (T₀₁). In case of wave transformation on a horizontal bottom, the LTA model fails as the rapid oscillations are neglected. The two-equation model predicts the energy transfer to sub-harmonics and non-resonant interaction excellently. In the inner surf zone and where the nonlinearity is strong, only the underlying deterministic model predicts the spectra and higher order wave statistics accurately.

The SWAN wave model for shallow water is used in three generation modes to show the differences in results between these modes and with observations in two real, rather field situations. These are situations of waves approaching two different sites in the Netherlands and Germany: one closed part of an estuary and one region between and beyond barrier islands with channels and tidal flats. The differences between the modes are significant (more than 25 % locally) in terms of significant wave height and mean wave period. These differences are ascribed, at least partially to the indirect effects of triad wave-wave interactions which shorten the wave period. The observations are located at positions where the differences between the modes are hardly significant.

Two sets of observations of wave transformation near two quasi one-dimensional coasts, from deep water (22 m) to shallow water (0.5 m) have been simulated with the third-generation spectral wave model SWAN. The first set of observations contains wind waves that are generated by a local storm off the North Sea coast of the Netherlands. The second set contains a mix of swell and local wind waves at the Pacific coast of Japan. Repeated computations without triad wave-wave interactions show that the inclusion of this process in the model is essential. A f ²-dependency of the depth-induced dissipation (rather than the conventional frequency independence in SWAN), causes too much energy dissipation in the high frequencies, shifting the mean frequency to too low values.

This paper presents a new and more accurate set of deterministic evolution equations for three-wave interactions involving fully dispersive, weakly nonlinear, irregular, unidirectional waves. The equations are derived directly from the Laplace equation with leading order nonlinearity in the surface boundary conditions. It is demonstrated that previous fully dispersive formulations from the literature have used an inconsistent linear relation between the velocity potential and the surface elevation. As a consequence these formulations are accurate only in shallow water, while nonlinear transfer of energy is significantly underestimated for larger wave numbers. In the present work we correct this inconsistency. In addition to the improved deterministic formulation, we present improved stochastic evolution equations in terms of the energy spectrum and the bispectrum for unidirectional waves.

The mean flow outside the surf zone can be unstable and form a train of submerged vortices, which migrate slowly in the offshore direction, as discovered by Matsunaga , Takehara & Awaya (1988, 1994). Li and Dalrymple (1998) conducted large scale experiments and a numerical study. They showed that two layers of vortices could exist over the water depth. Eddies near the water surface rotated in the opposite direction of eddies at mid-depth. For example, for the surface wave propagating to the right, the rotation direction of eddies near mid-depth was counterclockwise, while the rotation direction of eddies near surface was clockwise. The vortices decay offshore where there was no shear layers over water depth. Experimental and numerical studies show the velocity of long time scale vortical motion is uniform over water depth and is much slower than the undertow. A theoretical analysis showes that the stresses due to turbulence and wave serve as the source of the vorticity and this vortex train is formed by the shear instabilities of the mean flow in the cross-shore direction.

The Edgeworth expansion with the measured skewness and kurtosis is shown to be capable to describe the measured nonlinear distributions of the surface elevation and horizontal velocity in the shoaling and surf zones. The moments involved in the energetics-based model are expressed in terms of the skewness and kurtosis and shown to be in agreement with available data. Stokes wave theory is applied to obtain a relationship between skewness and kurtosis. The relationship is adjusted empirically because of the limitation of Stokes wave theory in the shoaling and surf zones. The relative simple relationship for the higher moments obtained here may be applied for cross-shore sediment transport analysis.

A general formalism for computing the nonlinear interactions between triads of coastally-trapped gravity and vorticity waves is developed. An analysis of the linearized problem reveals that gravity (or edge) waves and vorticity (or shear) waves exist as members of the same non-Sturm-Liouville eigenvalue problem, with unstable shear waves representing the complex eigenvalue portion of the resulting spectrum. Interaction equations derived here cover resonant interactions between three edge waves, three shear waves, or a shear wave and two edge waves. Numerical examples are shown for the case of three edge waves on a planar beach in the absence of a longshore current. It is found that edge waves can exchange significant amounts of energy over time scales on the order of ten wave periods, for realistic choices of edge wave parameters.

The effects of lateral mixing on the stability of longshore currents are examined. For the model problem originally considered by Bowen and Holman (1989), it is shown that the inclusion of lateral mixing changes the stability characteristics of the longshore current. In particular, it eliminates the low wavenumber cutoff predicted by the inviscid theory.

In the present paper we address the far-infragravity motion (0.001–0.01 Hz) associated with shear (or vorticity) waves over a fixed-bed, longshore nonuniform beach. The model equations are simplified forms of the fully nonlinear, depth-integrated, wave-averaged Reynolds equations, which are solved by the SHORECIRC numerical model. The currents are forced by stationary, monochromatic, incident short waves. The formation of flow instabilities depends on physical model parameters (e.g., bottom friction), the incident wave field, and the beach topography. The latter two effects are analysed here in the prediction of shear waves and unsteady rip-currents.

Most of the literature on edge waves is only concerned with edge-wave propagation over a bottom that is uniform in the propagation direction. There is still little knowledge of what happens when the bottom topography changes suddenly, as in the presence ofa cape, submarine valley or harbour.

This paper presents some results of our study on the wave motion in such places, where edge waves may be transmitted, reflected or radiated as free waves and thus may have an important role in determining the wave conditions in otherwise sheltered regions.

We send an edge wave along a coast with an alongshore uniform bottom profile and, at a given section change suddenly for another bottom profile. This study is carried out with a very simple model. The linearised shallow water equations are used in a wide channel with the simplest bottom profile that enables the existence of edge waves: a ledge close to the coast and a uniform depth offshore.

The paper describes results with a breaking wave model based on an extended set of Boussinesq equations. The wave breaking is described by accounting for the effect of vorticity generated by the breaking process. The vorticity field in the domain is obtained by solving the vorticity transport equation, which is based entirely on the Reynold's equations. In addition to the wave height decay and profile deformation predicted by earlier breaker models, the present model also provides information about the velocity profiles. The model results give good agreement with experimental data for wave height, setup and the velocity profiles. The crossshore variation of the radiation stress calculated from the model results gives a good representation of the results from experimental data.

This paper presents a numerical study of nearshore wave dynamics including the surf zone. Two different time-domain Boussinesq type formulations are applied for this purpose. The first model incoporates Padé [2,2] dispersion characteristics and lowest order nonlinearity. The second and more sophisticated model incorporates Padé [4,4] characteristics and higher-order nonlinearity in the dispersive terms. The models are validated on the shoaling and breaking of regular and irregular waves with and without an ambient current.

This paper describes the details of a 2D model of. waves and undertow in the surf zone. The model uses an assumed shape of the undertow velocity profile together with the wave energy equation, surface and near-bed shear stresses and the mass flux balance due to the wave drift, surface roller and undertow velocity to compute the cross-shore wave development, surface set-up/set-down and the vertical distribution ofthe undertow velocity at cross-shore sections. The numerical model has been tested against both laboratory and field data and produces good agreements.

Field measurements of undertow over longshore bars were conducted at Hazaki Oceanographical Research Station (HORS) on the Kashima coast of Japan facing the Pacific Ocean. The field measurements, other field measurements and large-scale experiments were compared with one-dimensional models for undertow; one of them was developed in this study. The comparisons showed that the present model well predicted the undertow velocities over longshore bars in the field, while a previous model calibrated with small-scale experiment data underestimated the velocities.

An undertow model calibrated for regular waves on plane beaches is applied to predict the irregular wave induced undertow for both plane and barred beaches and for both laboratory and field data sets. The model combines a logarithmic profile in the bottom boundary layer with a conventional parabolic profile in the interior. The height and period of the irregular waves are represented by the local root-mean-square wave height and spectral peak period, and the measured mean volume flux below trough level is used as input to the model. The model is capable of predicting the undertow profiles both inside and outside the surf zone, provided that the empirical coefficient associated with the mean bottom shear stress is adjusted at each measuring line. The model appears to give reasonable predictions of the bottom boundary layer thickness and shear velocity, although these predictions could not be verified due to a lack of data. To develop a predictive undertow model, a simple relationship with an adjustable coefficient is applied to predict the measured volume flux below trough level using the local wave height and water depth. The calibration coefficients involved in the predictive model are not universal among the lab and field conditions possibly due to the effects of wave directionality and longshore currents in the field measurements which are neglected in this paper.

In recent years fast ferries have been introduced on many ferry routes throughout the world. Particularly when operating in shallow waters and near the coast, the waves generated by these ferries give rise to conflicts with recreational use of beaches and coastal waters. Also the potential coastal erosion caused by a changed wave impact has been a matter of concern. The paper presents the results of studies carried out with the objective of providing an unbiased description of these wave phenomena, which has served as basis for a new legislation for regulation offast ferry operation. The coastal erosion potential was studied and sediment transport simulations showed that the longperiodic ship-generated waves give rise to beach accretion and steepening of the crossshore profile.

This paper deals with the analysis of wave propagation directions from wave climate measurements in field. A simple method is presented to analyse wave approach directions from signals of a current meter and a wave gauge in time domain. Results using this method of analyzation are demonstrated exemplarily with data from field monitoring.

Errors in parabolic equation models (PEM) for wave refraction and diffraction are investigated by examining the case of waves propagating over a planar bathymetry for which the analytical solution is well known. The models investigated are: i) lowest order parabolic approximation (Simple method), ii) Padé approximation and iii) Minimax approximation models.

Errors in wave heights, wave directions, radiation stresses and resulting longshore currents are investigated analytically and by numerical tests using the parabolic equation model MIKE 21 PMS. The results indicate that, while the predicted wave directions are generally accurate, the wave heights, radiation stresses and longshore currents can contain significant errors depending on the parabolic approximation used.

A numerical model for wave refraction and diffraction has been used to compute irregular waves. The model is based on the parabolic approximation, but, by combining with the perfect boundary condition, it is suitable for waves propagating with large incident angles. The irregular waves are modelled through linear superposition ofwave components. In order to apply the model to field cases, however, the numerical computations were carried out with one representative frequency while retaining spectral representation of the directionality of waves. This approximation has been examined by the laboratory conditions of Vincent & Briggs; The model’s performances in thefield cases were also investigated.

A method simply treating the governing equation for Z-D wave-motion is proposed in this paper. The Enter’s velocity in whole depth can be directly calculated with this method if the wave free surface is given. For the linear waves the wave surface is determined from given directional spectrum (Yu. et al. 1991) or other wave surfaces at near locations with an inversion method proposed in this paper. For the nonlinear waves the wave surface can be determined with the method proposed by Dommermuth and Yue (1987). These methods proposed by authors are tested and verified with numerical simulation, model test or field observation data.

The paper concerns the reflection performance of so-called ’sponge’ layers, which are used to model partially reflecting (porous) structures in a numerical model domain. Various compositions of sponge layers and their performance with respect to wave reflection, main direction of propagation, and directional spreading have been investigated. The numerical model used in this study was a finite difference model based on the time-dependent mild-slope equation. Comparisons are made with reflection measured in physical experiments with short-crested waves. The results obtained so far indicate that in several cases partial reflection of short crested waves can be described satisfactorily in numerical models by use of sponge layers.

A horizontally two-dimensional, time dependent numerical model for obliquely incident shallow water waves with arbitrary incident angles is developed to predict the temporal and spatial variations of the free surface elevations and fluid velocities on inclined coastal structures. As a first attempt, use is made of periodic lateral boundary conditions, which limits the computations to regular waves on the slope of alongshore uniformity. The numerical method and the seaward and landward boundary algorithms are fairly general and expected to be applicable to irregular waves as well. The computed results for plunging waves on a rough 1:3.5 slope with the incident angles in the range of 0° – 80° are presented.

A shallow-water flow solver with non-hydrostatic pressure in a coordinates has been developed to include effects due to the moving grid, referred to as the ALES approach. The formulation is outlined for 2D vertical plane problems and tested against experimental data for wave flows over plane beds, bars and trenches. Agreement with experiment is generally good and the importance of non-hydrostatic pressure and moving-grid terms is demonstrated.

In the present study, the transmission and reflection of long waves traveling through right-angled channel bends of constant depth and width are investigated by using numerical simulation based on the linear and nondispersive long wave equations. The present linear results are compared with the results obtained by Shi, Teng and Wu (1998) based on the weakly nonlinear and dispersive Boussinesq equations. The objective is to examine the difference between linear and nonlinear modeling of long waves propagating through curved channels.

The differences between the full and shallow-water wave theories for edge waves are reviewed. Detailed comparisons between the solutions of the second-order mass transport velocities within the laminar boundary layer obtained through the two theories are carried out for the first three edge-wave modes. The results clearly show that the error of the shallow-water approximation is larger as the mode number gels larger, and/or the beach slope gets steeper. It is also found that the magnitude ofshallow-water approximation error increases in the offshore direction first, then it decreases as the distance approaches further offshore due to the energy decay in that direction. The affecting area of the shallow water approximation is relatively larger for the longshore transport than for the cross-shore transport in higher-mode edge waves. The significant differences between the full and shallow water-wave solutions in the near shore region identified in the present study issue a warning to the modellers ofcoastal hydrodynamics and nearshore topography, who utilize the shallow water approximation.

Laboratory measurements of the instantaneous horizontal and vertical velocities induced by regular waves spilling on a rough, impermeable slope were analyzed to elucidate the nature of turbulence generated in the bottom boundary layer and by wave breaking. In the bottom boundary layer outside the surf zone, both the absolute shear stress |T'| and the turbulent kinetic energy k' exhibited intermittent behavior where the instantaneous values were often several times greater than the phase-averaged values. The motions occurred with the passing of each regular wave, however, and the phase-averaged values described the turbulent fluctuations reasonably well. A quadrant analysis showed that the turbulent velocities u' and w' were strongly correlated and oriented in either the first and third quadrants with u'w' > 0 during the acceleration phases or in the second and fourth quadrants with u'w' < 0 in the deceleration phase. The Reynolds stress contributions for this unsteady flow case depended strongly on the phase. Inside the surf zone, |T'| and k' were marked by intense, intermittent events which did not occur with the passing of each wave and which were roughly two orders of magnitude larger than the phase-averaged values. This intermittent motion extended into the wave bottom boundary layer. Near trough level, the intermittent events were phase-dependent, and the intense motion was primarily in the fourth quadrant. Near the bottom, the intermittent events were less phase- dependent. A preliminary analysis of the intensity and duration of the intermittent events indicated that coherent events occurred for about 10% of the record and accounted for approximately 50% of the motion, whereas intense events occurred for about 2% of the record and accounted for approximately 20% of the motion. These statistics clearly indicated that the intense, coherent events were intermittent and infrequent but contributed significantly to the magnitude of the absolute shear stress and turbulent kinetic energy.

A mechanical generation method of an asymmetric oscillatory flow has been proposed by the authors ( Tanaka et al., 1997, 1998 ), though, its applicability to an actual experiments has not been thoroughly examined yet. In the present study, laboratory experiments are carried out for an asymmetric oscillatory flow in a U-shaped oscillating tunnel to make comprehensive investigation on the validity of the generation method under both laminar and turbulent condition using air and water respectively as working fluid.

This paper presents a numerical solution for the bottom boundary layer (BBL) in the surf zone. The upper boundary of the BBL is determined through the solution of a breaking waves model. Different turbulence models have been tested to determine the distribution of turbulent kinetic energy, energy dissipation and eddy viscosity in the BBL. Finally, the vertical profiles of horizontal velocity can be found out through the solution of the governing equations of the BBL.

The WISE group is a group of investigators who have agreed to jointly (i) study the physical processes affecting waves in shallow water, (ii) develop numerical codes to explicitly represent these processes in operational models and (iii) verify these wave models in real coastal conditions. The group meets once per year in Europe or North America to discuss progress and coordinate future plans. Since the first meeting in 1993, interesting results have been obtained in all of the three aspects, including operational third-generation spectral wave models for shallow water (one of which has been released in public domain).

A long-term shallow water hindcast system for the evaluation of wave climate is applied to consecutive computation of nearshore waves over a period of 9 years from 1986 to 1994 at 6 wave measurement stations of the Pacific coast of Japan. The data of the wind fields was acquired from the ECMWF wind data sets. Comparison between hindcasts and measurements is made for wave climate represented by not only significant waves and mean wave direction but also frequency-integrated directional wave energy and directional spectrum in addition to time variation of significant waves and mean wave direction. The conclusion is that the newly-revised system is fairly useful for a reasonable and computationally efficient evaluation of the wave climate at the level of spectral representation.

The study aims at investigating the non-linear triad interaction process affecting shoaling surface gravity wave fields in shallow water areas. Attention is specifically paid to analyse the effects of these second-order non-linearities on the directional distribution of incident waves. A stochastic approach was chosen to model the triad interaction process. Three source terms have been implemented in the spectral wave model TOMAWAC developed at the Laboratoire National d’Hydraulique (LNH). The model results are compared to the laboratory data of Nwogu (1994).

The influence of reflection and dissipation on wave-induced mean magnitudes is studied. Starting from linear wave theory the second order quantities are derived in terms of transfer functions considering regular as well as irregular waves. It is shown that any reflective and dissipative natural or artificial structure such as a vegetation field, or an emerged or submerged breakwater, induces spatial variations of the mean quantities such as the mean water level, mass flux, energy flux or radiation stress. The evolution of these magnitudes is analogous to their behavior in the surf zone, showing wave damping and modulation. Compared with the experimental results, the models presented are able to reproduce wave height transformation as well as mean water level variations along the dissipative structures with reasonable accuracy.

A parabolic approximation of the mild slope equation was derived in terms of polar coordinates to describe waves diverging from a point source. Numerical solutions of the equation were used to extend the application of Green-function method to a wave field over arbitrary bathymetry. Validity of the equation obtained and usefulness of the numerical model were demon-strated through trial computations of wave diffraction, refraction and multiple reflection in model basins and in an actual harbor.

Wave induced pore pressure and instantaneous liquefaction are known to occur and cause loss of bearing capacity of sand. Wave bottom pressure $$\overline{p}$$ forms the boundary condition for the wave induced pore pressure. It is believed that not only variation of the pressure itself, but also the variations of its first and second order spatial derivative play an important role in the formation of liquefaction. An experimental and a preliminary numerical study on unidirectional water wave propagation over a bar are presented. Emphasis is placed upon investigation on the wave induced pressure gradient at the seabed. Single sinusoidal, two-component sinusoidal and five-component sinusoidal waves are investigated in a wave flume of constant water density ρ. Only the results for single sinusoidal waves are reported herein. The variation of the dimensionless pressure gradient $$C_p=\left(\partial \overline{p}/\partial x\right)/\left(\rho g\right)$$ was within ±0.4 for all experiments with a tendency of larger values for downslope gradients (negative values) than for upslope. (g is the acceleration gravity). The numerical results, based on the two-dimensional Green-Naghdi theory for fluid sheets – level II, compare well for sea bed pressures and gradients, but the sea surface does not fit the observations so well.

To improve the accuracy of depth-integrated models for water waves, it is important to express the vertical characteristic of wave motion properly. In the present study, a multi-level model for nonlinear dispersive water waves is derived, in which vertical profile of horizontal velocity is assumed to be a chain of quadratic portions. The properties of the model in dispersion relation and second order nonlinear interactions turned out to converge to that of the Stokes wave theory, with the increasing number of layers.

Local polynomial approximation models for water wave simulation are examined with the aim of improving accuracy and efficiency. Several potential improvements are considered. The first is based on a linearisation of the solution for Laplace’s equation and is shown to have good theoretical characteristics. However, it is found to have a fatal instability to high wavenumber bottom disturbances. The second method uses empirical collocation adjustment to provide better agreement with exact solutions for steady waves. This method provides significant improvements in accuracy for a given level of approximation and is recommended for future use.

Characteristics of periodic wave shoaling over a barred-beach are calculated in a fully nonlinear numerical wave tank. Variations of wave elevation, slopes, height, asymmetry, and celerity are discussed. Over and beyond the bar, classical highly nonlinear decomposition phenomena occur in a modulation region (MR); in shallower water, shoaling reoccurs. Depth inversion algorithms developed and calibrated for mild slopes are applied to the barred-beach. Expectedly, errors on depth prediction occur in the MR; suggestions for improvements are made.

Nonlinear mild-slope equations are a set of equations which were derived to analyze fully-nonlinear and fully-dispersive wave transformation. In the present study, it is shown that refraction-diffraction equations including the mild-slope equation, nonlinear shallow water equations and Boussinesq equations are derived as special cases of the nonlinear mild-slope equations. Then, a numerical model is developed for fully-nonlinear wave refraction and diffraction on the basis of the nonlinear mild-slope equations. The model is verified through comparison of numerical results with theoretical and experimental results. Finally, effect of nonlinearity on wave diffraction through a breakwater gap is discussed.

Two recent approaches for computing wave evolution over varying topography are presented: the high order Boussinesq model of Gobbi and Kirby (1998) and the local polynomial approximation (LPA) method of Kennedy and Fenton (1997). Both analytical results and numerical solutions of Gobbi and Kirby (1998) model and two variants of the LPA method are presented and compared with exact solutions and laboratory measurements of waves propagating over submerged features.

Evolution of periodically generated wave groups of different shapes that propagate over a sloping beach is studied experimentally and theoretically, by solving numerically the cubic Schrödinger equation. The agreements and disagreements between the experimental and the numerical results are discussed.

The instability of bichromatic wave train in water of intermediate depth is investigated by means of a perturbation method. The analytical solution, treated as the result of an initial value problem, yields the modulation and disintegration of the wave train, caused by the interaction of two incident waves of finite amplitude. A laboratory study was also conducted to measure the surface elevations of bichromatic waves generated by several types of compound sinusoidal signals. The calculation using the third-order finite-amplitude wave equation is carried out, and its prediction is compared with the measured data obtained under several experimental conditions.

Three-dimensional propagating nonlinear waves can be simulated with a timedomain numerical model based on a boundary integral equation method. For the simulation of nonlinear wave deformation by a shoal, a domain decomposition method is used to increase the efficiency of the model. Features and efficiency of the domain decomposition method are described and its application to the shoal problem is discussed.

Variability of spectral estimates is examined with respect to the nonlinearity of the wave field considered. Both measured field data and numerical simulations are used for checking the extent of variations, which are quantified as histograms that closely follow the chi-square distribution. An absolute assessment of the variations over the entire frequency band of a spectrum is also made and found to approach to a mean of 70% regardless of the frequency concerned. Finally, it is observed that a nonlinearly evolving wave field of initially constant spectral shape gradually assumes a spectral variability, which is characterized by the chi-square distribution. The last finding provides a clue for a possible cause of the variations observed in the estimates of spectra.

Experiments have been performed with regular deep-water waves propagating obliquely across a relatively narrow jet-type current. Measurements have been made of wave refraction using an 8-element wave array and 3d acoustic Doppler flowmeters. Results show that wave height and celerity follow the trends predicted by gradually-varied flow theory, but with wave height modulated by weak reflections as the waves pass across the jet. Direction of wave propagation is found to be sensitive to the presence of internal reflections from the shear layers.

This paper considers the interaction between two-dimensional random waves and a co-linear, depth-varying, current. Two rotational wave-current models, capable of incorporating the effects of a depth dependent vorticity distribution, are combined with a conservation equation describing the total energy flux. This provides new solutions capable of predicting the change in a wave spectrum due to the interaction with a current. Comparisons between these solutions and a new data set confirms that a successful wave-current model must incorporate both the Döppler shift associated with the surface current and the near-surface vorticity distribution. Typical design calculations, based on a uniform current approximation, commonly satisfy neither of these constraints. Accordingly, they are shown to provide a poor description of the laboratory data. Furthermore, the nature of the wave-current interaction, which is shown to be significantly larger than the nonlinear wave-wave interactions, involves both a currentinduced change in the wave motion and a wave-induced change in the current. While the former is reasonably well understood, the latter remains difficult to predict. Indeed, both parts of this overall interaction are shown to be strongly vorticity dependent.

The tailwater level is together with rainfall the most important input to flood modeling in coastal rivers. Thus, the need for an ocean-river interface which can provide tailwater levels for numerical models is obvious. The state of the art is however not very advanced. Detailed waterlevel profiles through the Brunswick River entrance from 500m inside the breakwaters to 150m outside during a wide range of weather conditions revealed that the wave setup through the zone of wave breaking is much smaller than what is being used by practicing modelers in Australia. Barometric effects of the order 1cm per hPa is only a minor part of the tidal anomalies, which range up to 0.8m 500m inside the breakwaters, and wind effects, although not modeled in detail, are estimated to be small on the fairly narrow continental shelf of South East Australia. Tidal anomalies of the order 0.5 to 0.7 metres have been observed in the absence of rainfall and strong local winds during Cyclone Roger in 1993. An offshore record indicated that a substantial fraction of this tidal anomaly (of the order 0.25m) also occurred in 25m of water offshore from the Tweed River on the border between New South Wales and Queensland. This indicates the presence of weather related oceanic forcing of a nature which is not understood in detail.

Measurements of mean velocity profiles in a wave-current flume have shown some features for which the mechanism is far from trivial. A 2DV model based on the so-called Generalized Lagrangian Mean formulation is developed to study the influence of waves on the mean motion, the mean horizontal velocity in particular. This influence can be split in two parts, viz. a direct effect of the waves via wave-induced driving forces and an indirect effect of waves via secondary circulations. To include both effects an existing 1DV model is extended by introducing lateral variations including side-wall boundary layers. Resulting formulations have been implemented in an existing 2DV non-hydrostatic numerical flow model. Computations for regular waves following and opposing a turbulent current have been carried out and compared with both experimental results and results from an existing numerical model.

Water wave breaking is of considerable importance in the transfer of momentum from the waves to currents. Near shore lines most of the water motions are dominated by breaking waves. Recent work on the generation of vorticity by breaking waves and bores in the surf zone on beaches within the shallow water approximation has shown that non-uniformity in the strength of bores is an important source of potential vorticity. This is illustrated by discussing the generation of longshore currents and illustrated with a numerical example of vorticity generation due to a non-uniform bed. These demonstrate that the horizontal excursion of vorticity transported by the incident waves may be a significant factor in interpreting velocity measurements at a fixed site.

A series of experiments on monochromatic waves being blocked by opposing currents are presented in this paper. A heirarchial pattern in the wave field characteristics was observed with increasing wave amplitude. A shoaling model using a bore dissipation formulation to simulate current limited breaking is compared with the data. It is observed that amplitude dispersion plays an important role in wave blocking and cannot be ignored. For the large amplitude waves side band instabilities radically affect the wave field and prevent wave blocking.

Based on theoretical considerations it is demonstrated that in the near-shore zone the tidal water level fluctuations are mainly caused by cross-shore volume fluxes. Phase differences between the tidal wave propagating on the shelf and in the shallow near-shore zone create cross-shore surface gradients which result in an onshore directed flow during rising water and an offshore directed flow during falling water. Observations of near bed velocities in the near-shore zone confirm the presence of these currents. It results in an anti clockwise rotating current vector at a water depth of about 10m . Comparisons of these observations with results obtained from a 1-DV flow model show that the tidal ellipses are not the result of Coriolis forces but are generated by the alternating cross-shore water fluxes due to the tide.

Coastal current in the nearshore zone is generated by both breaking waves inside the surf zone and by the wind over the extended area of the coastal and offshore zones. Wind-induced currents as well as wave-induced currents are characterized by strong shear flows and complicated turbulence flow fields. In order to develop mathematical models for these currents, it is essential to formulate wind and wave stresses acting on the sea surface. Unfortunately, there has been no reliable observation of current profile in the surf zone under the condition of strong wind. No extensive information on wind stresses inside the nearshore zone has been made available, primarily because of the challenge of recording these data without facilities such as observation pier or towers.

In this paper we conducted a continuous recording of nearshore current profile and wind stresses in/out the surf zone by using high frequency ADCP (Acoustic Doppler Current Profiler, 1200kHz) installed on the sea bottom under the observation pier of Ogata Wave Observatory, together with 3-component ultrasonic anemometer. This two and half months observation revealed part of the structure of nearshore currents and some characteristics of the wind drag coefficient in the nearshore zone.

A nearshore circulation modeling system has been applied to a closed wave basin with a longshore bar and two rip channels. The major characteristics of the flow pattern have been established by the model including the recirculation cells, the feeder currents and the bias of the rip current toward the center of the basin. Wave current interaction is established as one of the significant mechanisms in the flow. The parameters for the eddy viscosity and the bottom friction have been shown to influence the stability of the flow. The flow is generally fluctuating and large vortex systems are formed. The model results are compared with the experimental data matching magnitudes of mean velocities as well as trends of oscillations.

This paper presents a quasi-three dimensional numerical model of wave-induced current due to wave breaking so as to make it applicable to the coastal region with the coastal structures. First, applicability of the present model to undertow velocity and longshore current field was investigated. Secondly, laboratory tests were carried out to examine the characteristics of nearshore currents around the detached breakwater. Thirdly, nearshore currents around the breakwater were computed using the present numerical model. Finally, the results of computation were compared with those of laboratory tests and the applicability of the numerical model was discussed.

Wave-induced currents in a surf zone must be explained by the change of wave motion. The driving force for nearshore currents is the radiation stresses which are defined as the excess momentum flux due to wave motion. However, there is no model which can describe the three-dimensional structure of the nearshore currents. This study aims to develop a model of this kind, in which only wave motion is taken as the driving force to the currents. Governing equations are derived from the Navier-Stokes equations. This model is proved to reproduce the currents measured in the experiments.

Bothe two and three dimensional numerical simulation of wave fields around the submerged breakwater is carried out using the SOLA-SURF method. The results of the calculation are compared with the laboratory experiment. It is shown that the side wall boundary condition for the three dimensional calculation of the laboratory tank should be nonviscous(slip-type) to reproduce the experimental data. The calculation method is easily extendible to a field scale case.

The wave breaking and post-breaking wave deformation due to a submerged breakwater in a three-dimensional wave field have been investigated numerically and experimentally in this study. The calculated and measured results have revealed that the breaking limit and the breaker types are almost independent of the relative structure length W/L_i (0.5 ≤ W/L_i ≤ 2.5), and that the horizontal and vertical circulation flows are formed around the submerged breakwater. It is also found that the wave breaking in three-dimensional wave field is affected strongly by the wave refraction, different from the twodimensional case. The numerical calculation method based on a SOLA-VOF method has been developed and has reproduced well laboratory experiments in case of a weak breaker such as the Spilling breaker.

The paper uses the ’parameter map’ which has been developed under PROVERBS (Probabilistic Design Tools for Vertical Breakwaters) in the frame of the ongoing MAST III programme of the European Union (EU contract no. MAS3- CT95-0041) to classify the wave loading on monolithic coastal structures and to identify the conditions leading to wave impacts. Data from four different hydraulic model tests have been used to verify and extend the parameter map. As a result an updated version is proposed for further design purposes.

The present investigation reports synoptic measurements and analysis of particle accelerations and kinematics of plunging crests in deep water wave groups. The unexpected occurrence of unusully large waves has been documented on numerous occasions. While little is known about the statistics of these waves, even less is known of the dynamical conditions under which they occur. Nonlinear interactions among individual waves travelling within a group on an opposing current have been identified as an important mechanism in the formation of giant waves in deep waters in the ocean. In this study, the non-linear packet-focusing technique is used to generate steep, deep water plunging waves in two laboratory flumes. In one of these flumes the plunging breakers were generated on opposing currents. The kinematics of these waves are measured just up-wave of the onset of plunging, and these results are compared to those of a superposition model, a modified stretching model, and a model based on Stokes 3^rd order theory combined with a linear wave spectrum for an irregular sea on an opposing current, developed for the present study. The present model represents the velocity beneath the plunging breakers significantly better than the two other models.

In this paper, the VOF method for free surface flow is applied to simulate breaking waves incident on a submerged reef. An efficient numerical wave channel with two absorbing boundaries is developed. Corresponding boundary conditions are prescribed. Smagorinsky’s sub-grid scale model is incorporated to account for the sub-grid scale turbulence. Numerical results are compared with laboratory measurements.

Prediction of limiting wave heights in conditions of depth-induced breaking is subject to considerable uncertainties, yet the (local) wave height is probably the most important input variable in design of coastal, harbour or shoreline structures subject to wave action.

This paper presents selected results from laboratory experiments to measure depthlimited wave breaking over steep bed slopes (1:50, 30, 20, and 1:10) in fully random wave conditions. Experimental measurements are compared with predictions for H_ms, H_s and H_max under shoaling and breaking. The effects of shoaling and breaking on the wave height distributions are explored. An alternative empirical method to predict H_1/3 and H_max is suggested.

Wave discretization is a usual procedure in ocean engineering for the statistical analysis of wave records. Different criteria can be used for performing that discretization. The orbital criterion presents important advantages with respect to the zero-up-crossing criterion, more commonly used. These criteria provide significantly different statistical results, as shown when applied to wave records from the scalar Waverider buoy of Valencia, off the Mediterranean Spanish coast.

Field measurements highlighted enormous changes in the attenuation of waves propagating from offshore across the ebb delta on the shore face of the East Frisian island of Norderney. The application of mathematical wave model SWAN made evident that the migration of the ebb delta is the cause of these changes. The results are very important for coastal protection measures.

The wave-current interaction process in a one way coupled system for the Southern North Sea region was studied. To this end, a modified version of the third-generation spectral wave model WAM was run in a three level nested grid system, taking into account the hydrodynamic fields (coupled version) computed by a tide/surge model. The resolution in these three grids corresponds roughly to 35 km (coarse), 5 km (local) and 1 km (fine). Hydrodynamic information was only available at the resolution of the local grid. Results are compared with those of the same version without considering the interaction with tide and surges (uncoupled version). The emphasis is on the results from the local grid calculations. The sensitivity to the source of boundary conditions (coupled vs. uncoupled) and to the frequency of information exchange is investigated. Also the spectral evolution is studied.

Numerical results in the local grid are in good agreement with buoy data. The phase and amplitude of the modulations of wave period observed from the buoy data are quite well reproduced by the coupled version. The model results in the local grid did not show much sensitivity to the source of boundary condition information, nor were they very sensitive to the information update frequency of the hydrodynamic fields. The directional spectra computed in the coupled mode show a broader energy distribution and a more rapid growth. The fine grid results only differ marginally from the local grid results due to the limited resolution of the hydrodynamic fields used.

This paper presents probability density functions applicable to peaks, troughs and peak-to-trough excursions of coastal waves with finite water depth in closed form. It is found that for a non-Gaussian waves for which the skewness of the distribution is less than 1.2, the probability density function of peaks (and troughs) can be approximately represented by the Rayleigh distribution with a parameter which is a function of three parameters representing the non-Gaussian waves. The agreement between the probability density functions and the histograms constructed from data obtained by the Coastal Engineering Research Center is satisfactory.

We analyze annual variations and the long-term tendency of wave heights along the coast of Japan, based on observed data for more than 10 years. And we analyze the trend of wave heights over the last 10 years in the North Pacific with hindcast data. As a result of the analysis, the wave height has shown an increase trend at most stations along the Pacific coast of Japan. The average increase rate is 0.6cm/year. The estimated wave height by a wave model also shows an increased trend in the North Pacific Ocean. Since there is a correlation relation between 500hPa height anomaly at specific areas and the wave height anomaly at each station, an increase trend of wave height in the Northern Hemisphere is supposed to be related to the change in an atmospheric planetary wave pattern.

The aim of this paper is to summarise the main results obtained from wave data collected in the Portuguese west coast near Sines Harbour. In spite of special attention given to wave characteristics during storm occurrences, some considerations about mean wave regimen will be done.

A new method for the determination of short-term variability of some commonly used wave height and period parameters is presented. The new TFD method combines some previously available time and frequency domain approaches, optimizing their application and giving greater accuracy with easy implementation. Short-term variability predicted by the new TFD method is consistently higher than the one obtained with theoretical frequency domain expressions, and proves to be in very good agreement with sampling variability observed in Gaussian, non-periodic and non-deterministic random wave records generated with stable ARMA numerical simulators.

The relationship between sea state intensity, sea state duration and frequency is pursued in the context of wave data from five sites in U.S. waters. A rational methodology is presented for the interpolation and extrapolation of measured trends, based on extreme value series for intensity, given duration. The inevitable short duration data base problem is addressed by routine application of the triple annual maximum methodology. A format is suggested for IDF data preparation and presentation. Examples are given for wave climate data on the Pacific and Atlantic coasts of the United States.

Some coastal and offshore structures, e.g. offshore platforms and vertical wall breakwaters in deep water, are often designed according to a design individual wave height.

The conventional method for the determination of the design individual wave height is first to obtain the design significant wave height corresponding to a certain exceedence probability within a structure lifetime (encounter probability), based on the statistical analysis of long-term extreme significant wave height. Then the design individual wave height is calculated as the expected maximum individual wave height associated with the design significant wave height, with the assumption that the individual wave heights follow the Rayleigh distribution.

However, the exceedence probability of such a design individual wave height within the structure lifetime is unknown.

The paper presents a method for the determination of the design individual wave height corresponding to an exceedence probability within the structure lifetime, given the long-term extreme significant wave height. The method can also be applied for estimation of the number of relatively large waves for fatigue analysis of constructions.

The determination of the crest level is one of the most important points in the design of sloping coastal structures. The crest level of sloping coastal structures is governed by wave run-up and overtopping. Recent measurement results of run-up on prototype have indicated that wave run-up may be underpredicted by scale model tests. So full scale measurements of wave run-up is necessary. At the same time the overtopping discharge on a prototype breakwater will be measured. Within the MAST III - OPTICREST project, these measurements will be carried out at coastal structures at two locations: Zeebrugge (Belgium) and Petten (The Netherlands). The results obtained from these prototype measurements will be compared with those from scale model tests and will be used to calibrate numerical models. This paper also presents the contents of the OPTICREST project.

An experimental study was performed to measure the effects of depthlimited conditions on wave runup and reflection from coastal structures. The measurements are compared with existing empirical formulas. An existing model to predict wave runup is shown to overpredict the runup and a clear trend of increased wave runup in depth-limited conditions is shown. A new empirical model is presented that includes the effects of depth-limited conditions on wave runup. Existing models to predict wave reflection based on the surf similarity parameter are shown to fail to collapse the measured data onto a single line. A recently developed model based on a number of parameters is shown to accurately predict wave runup in cases where no wave breaking occurred before the structure. However, at the shallower water depths where wave breaking occurred seaward of the structure, the model underpredicted the reflection coefficient. This model was modified to increase its accuracy in depth-limited conditions based upon the laboratory results presented in this study.

Estimation of the run-up and overtopping rates corresponding to breakwaters is a critical aspect for designing. Although it is widely assumed that onshore winds significantly increase runup and overtopping, very few design rules and experimental data have been published to estimate the effects of wind on runup and overtopping. A conventional and several cuenco amortiguador breakwater cross sections were tested at the UPV wind and wave test facility using wind velocities up to 10 m/s. A neural network modeling using simulated annealing was developed to analyze the experimental results. A preliminary analysis of the results found that wave overtopping was sensitive to wind speed (U>0), while runup seems sensitive only to high wind speed (U> 8 m/s). The runup measurements using capacitance wave gauges placed along the slope are dependent on the distance from the theoretical profile; therefore, a pair of wave gauges placed at D_n50/3 and 2 D_n5o/3 were used to calculate the measured runup on the conventional breakwater. A significant discrepancy was found between the visual observations of runup on the conventional breakwater and the measured runup using the capacitance wave gauges; it seems that capacitance wave gauges underestimate the runup because of the alteration of the capacity of the water due to air intrusion during the breaking process.

A new absorbing multidirectional wavemaker is under development at the Danish Hydraulic Institute. In this process numerous aspects of the design and control of multielement wavemakers as well as the theory for wave generation and active absorption have been considered. This paper focuses on two specific and specialized points. First, the influence of finite segment width on the wave field generated is analysed for different types of paddle front. In this connection a new criterion for the truncation of directional spectra to be generated is suggested. Second, the appearance and reduction of aliasing problems for 3D active absorption is discussed. Aliasing appears due to the spatial sampling typically used for obtaining a hydrodynamic feedback in the absorption procedure.

The dual–mode snake–type directional random wave maker has been developed in order to reproduce double peak directional waves, long period waves and directional waves with oblique principal wave direction. Results from a series of wave generation tests demonstrate that the dual-mode generator system is suitable to reproduce the the target wave conditions with good accuracy.

The present paper concerns the nonlinear description of large waves in which the wave energy is spread in both the frequency and the directional domains. A new series of experimental observations are briefly described in which a large number of deep-water focused wave groups were generated in a large wave basin. For each combination of frequency bandwidth and directional spread the intensity of the wave, measured in terms of a linear amplitude sum, was varied from a near-linear condition to the limit of incipient wave breaking. Comparisons between this laboratory data and a new fully nonlinear, multi-directional, numerical model are used to validate the modelling procedure and highlight the importance of the directionality. In particular, the results show that for a given linear amplitude sum an increase in the directional spread leads to a reduction in the magnitude of the nonlinear wave-wave interactions. Conversely, the maximum nonlinear crest elevation, observed just prior to the onset of wave breaking, increases with the directional spread assuming the frequency bandwidth remains constant. From a practical perspective, the paper demonstrates that an accurate representation of an extreme ocean wave requires a model that incorporates nonlinearity, unsteadiness and directionality. The present model satisfies these requirements.

The nearshore potential vorticity balance of Bowen and Holman (1989) is expanded to include the forcing from wave group-induced radiation stresses. Model results suggest that the forcing from radiation stresses can drive oscillations in the longshore current that have a spatial structure similar to linear shear instabilities of the longshore current. In addition, the forced response is nearly resonant when the forcing has scales (k, σ) similar to the linearly most unstable mode. Thus, we suggest that the wave groups may provide an initial perturbation necessary for the generation of shear instabilities of longshore currents and enough forcing to overcome frictional damping.

Analysis of data from the SUPERDUCK (1986) field experiment reveals that wave groups were present on days when strong low frequency surf zone motion (shear waves) existed. In addition, some of these groups are shown to have periods and longshore spatial structures comparable to the observed shear wave motions suggesting that incident wave groups are present on this open coast with the required spatial and temporal structure to initiate the low frequency oscillations in the longshore current.

In connection with hydraulic studies of a new coastal resort development on the south-east coast of Bali in Indonesia, a three-dimensional (3D) physical model study was carried out. The study was aimed at the determination of the wave transformation over a shallow natural reef in front of the resort and for the design of the rubble mound revetments to be built for coastal protection. Due to the heavy wave breaking on the reef, physical model tests were the only viable avenue for obtaining a reliable design of the revetment structures located behind the shallow reef area. The stability of the armour layer as well as the overtopping of the revetments were equally important aspects of this part of the study, since not only should the resort be protected against storm waves, but visitors should also be able to comfortably visit the coastal areas during more normal wave conditions.

This paper mainly concerns the wave dynamics on the reef. Due to the limited water depth the wave conditions were dominated by heavy wave breaking and the associated release of the bound long-period wave components in the wave groups of the incident wave train. These long-period wave components caused a dynamic water level set-up with long-period variations in front of the revetments (surf beats). The depthlimited wave conditions on the reef and the dynamic water level set-up had major influence on the evolution of damage and overtopping of the revetments and made the design of the revetments particularly complex.

This paper addresses the influence of long waves on the design wave height of structures in shallow water. Wave heights, wave periods, depths of water at the structure, time of wave measurement, length of the wave-guides were all varied in 29 series of twodimensional hydraulic model tests. The results indicated that long wave activity is an important design parameter for breakwaters in shallow water. The wave height at breaking and long wave reflection from the structure are the primary parameters influencing long wave activity.

In this study the tsunami-wave run-up along the Alborán Seacoast (Spain) have been evaluated. An indirect statistical method has been used to estimate the tsunami risk along the southeastern Spanish coast. This method can be summarized as: (1) analysis of the global neotectonic setting, the geodynamic processes as well as seismicity of the region; (2) tsunami source model; (3) generation, propagation and run-up numerical models; and (4) the risk model. The purpose of this study is to establish tsunami-wave elevation at the shoreline versus the return period curves for different locations along the Alboran seacoast. It is concluded that, the tsunamis generated in the Alborán basin have a medium-to-low intensity, with the most important elevations in the Málaga, Adra and Melilla areas.

Field measurements of long-period wave have been preformed for the Gamcheon Harbor in Korea. A Galerkin finite element model based on the extended mild-slope equation has been developed for simulating harbor oscillation more accurately. Infinite and joint elements are introduced to accomodate radiation condition at infinity and matching conditions at harbor mouth for the consideration of the energy loss due to flow separation, respectively. Comparisons with the results obtained by hydraulic experiments by Lepelletier (1980) show that the present model gives fairly good results. Model results reveal that the influence of entrance loss at the harbor mouth is considerably significant. From the application to the Gamcheon Harbor it is seen that the computed resonant periods and amplification ratios well agree with the measured results. The entrance loss effects were found to be insignificant unless the incident wave height is large.

One of the major engineering problems for large harbors with container ship operation is the motion of moored ships due to long wave activity. In order that the wave-induced ship-motions may be effectively controlled, the response characteristics of the harbor basin due to incident waves must be accurately determined. This study focuses on the application of a computer model in the harbor resonance study in connection with modification of harbor basins. The computer model used is a finite element model with the mild-slope equations as the governing equations. Various boundary conditions are incorporated in the model: fully and partially reflecting boundaries, permeable boundary. Energy losses across the harbor entrance due to flow separation and frictional loss at the bottom are also incorporated in the model. Good comparison between the computer model results and the physical model data of the Los Angeles-Long Beach harbor basin has been obtained.

The computer model has been applied to the large scale harbor basin of Los Angeles & Long Beach Harbors. Effects on response characteristics due to incident wave system with and without breakwater at Pier J in Long Beach Harbor have been determined. The construction of the proposed breakwater outside Pier J in Long Beach Harbor appears to be effective in reducing the wave amplification for wave period less than 140 sec. The wave period associated with resonant peak has been shifted to 170 sec. or higher. With the advancement of computing power, it is found that computer model offers a very powerful alternative to physical model in the study of wave response characteristics. All the computation reported herein are done by Pentium 2-300 MHz personal computer.

A large resonator which has a similar size of the outer basin of a double-basin type harbor is designed by the Wave Filter Theory. This resonator aims to protect an inner basin from incoming very long waves which may cause long-period motions of moored ships at piers. Performance of the designed resonator is examined by the physical and numerical experiments. It was confirmed that the large resonator designed by the Wave Filter Theory is effective for protecting the inner basin from very long waves with a period of 30s or longer. However, the aspect ratio of the resonant basin should be nearly equal to 2:1 for the effective reduction as pointed out by Valembois(1953).

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.

For the basic design of Pusan New Harbor that will be the third largest container hub-port in the world, extensive wave measurements and wave propagation modeling were made. They are mainly for estimating shallow-water design wave height and determining breakwater alignment to acquire harbor tranquility. The directionality of short crested waves is proved to be very important when they propagate through the waterway. Bounded long-period waves with a small amplification were observed in the shallow water area, which might cause horizontal motions of the container ship moored at a berth aligned to the south. Modified and extended numerical wave models are found to be reasonably good at simulating the measured wave propagation phenomena. Hybrid modeling was made to evaluate harbor tranquility combining numerical and physical modeling results.

Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program.

Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.

Mathematical modelling of nearshore oceanographic conditions was carried out, in connection with a large industrial fishery harbour planned to be implemented in a coastal stretch protected by two reefal systems, on the western coast of Sri Lanka. MIKE 21, a two dimensional mathematical modelling system with a wide range of coastal engineering applications, and LITPACK, a one dimensional coastal processes modelling system, were extensively used in this study. The major features of modelling were the successful simulation of wave transmission over reefs and wave overtopping mass flux induced currents behind the innermost reef.

The validated model under existing conditions was used to optimise the harbour layout with safe navigational access, acceptable wave agitation within the basin and adequate sediment by-pass capacity at the entrance. The wave and other hydrodynamic parameters for the economical design of harbour breakwaters were also obtained. A well calibrated hydrodynamic model covering most of the western coast of Sri Lanka also evolved as a byproduct of this study.

Studies of flows near the coast from the viewpoint of coastal engineering have focused on tidal currents and nearshore currents that are generated by waves in breaker zones. However, on-site observations have shown that there also exist strong flows with long periods of several days. As these long-period flows have a high velocity even at deep water levels outside breaker zones,they are thought to play an important role in the offshore drift-sand phenomenon and in the convection and diffusion of floating larvae of marine organisms.Through analysis of observation date on wind velocity and flow velocity recorded around Tomakomai Harbor, the temporal and spatial characteristics of long-period velocity fluctuations of these flows were clarified.We confirmed the existence of and clarified the characteristics of long-period flow velocity fluctuations around Tomakomai Harbor that have a period of 3∼4 days and propagate in a westerly direction at a phase velocity of approximately 2.0km/h. These long-period flow velocity fluctuations can be estimated by the storm surge formula that assumes wind stress to be the external force and Coriolis force to be the restoring force.

Interaction of short waves modulation and long waves evolution is studied. Existence of free long waves is taken into account. Laboratory experiment and numerical simulation with coupled equations are performed. Mechanism of the modulation is discussed. The distance, below which the modulation may be neglected, is evaluated.

Field observations of low-frequency wave on natural beaches are carried out. The ratio of the wave height of low-frequency wave near the shoreline to the wind wave height at the offshore has positive correlation with the surf similarity parameter. Using the field data, a validation of a numerical model was made. The model includes basic mechanisms of low-frequency wave generation that low-frequency wave increases with shoaling of wind waves groups, they are released from wave groups due to wave breaking and wind wave period becomes longer due to run-up to the beach. The model results tend to be excessively computed against field data.

The present paper describes a numerical study of infragravity waves forced by obliquely-incident wave groups. In this study, the depthintegrated, shortwave-averaged nearshore circulation model SHORECIRC (Van Dongeren et al., 1994), which includes the quasi three-dimensional effects, is used. The governing equations that form the basis of the model, as well as the numerical model and the boundary conditions are described. The model is applied to the case of leaky infragravity waves. The magnitude of the quasi 3-D terms and their effect on the infragravity wave envelope is analyzed, and the velocity profiles of the infragravity waves are shown.

This paper presents a state-of-the-art numerical model for ship motion analyses along with an application of the model to a seiche problem in the Port of Long Beach, California. The practical uses of the model are emphasized along with a discussion of the efficacy of the modeling approach as a tool for decision-making.

In a temporary facility built within Buffington Harbour, it was proposed to operate two floating vessels as casinos. An extensive program of physical and numerical model investigations was undertaken to design a harbour and mooring layout that would ensure effective operation with minimal downtime for casino operations. Through a sophisticated model testing program, the motions of the floating vessels were established for different sea states. These motions were then used as inputs to a ship simulator where client representatives participated in the full scale simulations in order to select the sea states that would cause discomfort to clients.

Statistical wave forecasting methods have been applied because of their convenience. Most of them, however, include some drawbacks from the statistical or numerical viewpoints. In this paper, these drawbacks are discussed and a new statistical wave forecasting method utilizing the Kalman filter technique combined with Principal Component Analysis (PCA) is proposed in order to mitigate the drawbacks. The applicability and reliability of the proposed method is examined for five wave observation stations around Japan through simulations based on 5-years of wave data and weather charts.

A data assimilation method for state updating in a hydrodynamic model is presented. The method is based on the extended Kalman filter in which the error covariance matrix is approximated by a matrix of lower rank using a square-root factorisation (reduced rank square-root filter). Results from a test of the Kalman filter in a regional model of the North Sea and Baltic Sea are presented. In this respect, the influence of using nested hydrodynamic models together with data assimilation techniques is illustrated and discussed. The test reveals that assimilation of water level measurements from coastal stations significantly improves the model results.

The difference in reshaping of a traditional berm breakwater constructed of two stone classes and a more stable armoured type of berm breakwater with the largest berm stones used as an armour layer has been studied through physical model tests at the Danish Hydraulic Institute. A total of eight series of model tests were carried out in a wave flume with the aim of studying the effect of different armouring of the berm. The test results are described in the form of profile development, recession of the berm, waves generated by overtopping and wave reflection.

Further, four series of flume tests were carried out for studying the influence of the width of the stone gradation for the berm material and the permeability of the berm material. Two stone gradations and three permeabilities of the berm material were tested.

Finally, four test series were carried out for studying the influence of scour protection on the scouring in front of the berm breakwater and the behaviour of the berm breakwater.

Berm breakwaters have been designed and constructed in Iceland since 1983. Over twenty rubble mound structures of the berm type have been constructed so far, fourteen were new structures, whereas the remaining six were improvements or repairs of existing breakwaters. During 1998 two berm breakwaters are being extended. Further two structures will be built every year for the next 2-3 years.

Although some of the berm structures in Iceland have already experienced the design or near to design wave conditions, only minor profile changes have been observed. Valuable experience has, however, been learned from the inspection of the reshaped profile of one structure.

The initial idea of berm breakwaters was that they should be wide voluminous structures, built of two stone classes with a wide size gradation. The Icelandic type of berm breakwaters has however been developed into a less voluminous, more stable structure, where large emphasis is put on maximising the outcome of the armour stone quarry and utilising this to the benefit to the design.

An alternative berm type breakwater was proposed at the South Breakwater of the Typhoon Shelter at Hei Ling Chau, Hong Kong. The required berm width and the stone sizes were initially determined using a numerical model. The proposed berm breakwater was then tested using physical modelling approach. The testing programme made use of both two dimensional and three dimensional hydraulic model studies to assess the stability of the trunk and head sections respectively. Both tests confirmed that the proposed berm type breakwater would perform satisfactorily and the reshaped profiles would not encroach on the core material.

The paper describes laboratory tests on berm breakwaters in shallow water, e.g. in water depths where waves might break before they break on the breakwater. Analysis have been made of test results for breakwaters in shallow and deep waters and a unified design equation is presented for the berm recession of berm breakwaters in shallow and deep water.

This paper presents the design and economic analysis for two alternatives (soft-versus-hard) for shore protection of facilities at the US Navy’s Fleet Combat Training Center, Dam Neck, Virginia, USA. Three key factors are discussed that resulted in the selection of the soft alternative (dune construction and beach nourishment) which also included a buried seawall/revetment structure beneath the dune to provide a unique solution for shore protection. Construction was completed in the fall of 1996 and the results of the first year’s monitoring effort are presented. The advantages of the soft alternative are many (environmental, recreational, etc.) and may even include the economic advantage as demonstrated in this paper for one site on the Atlantic Ocean.

The nature of uncertainty in coastal engineering is discussed with reference to an empirical study of practising coastal engineers in the UK. This study provided evidence which indicates that a complex multi-disciplinary set of issues are taken into account in decision making only some of which are explicitly articulated. It is argued that current approaches to handling uncertainty based on reliability theory provide an important but incomplete perspective on a rich and complex topic. An approach to uncertainty modelling based on Interval Probability Theory is proposed. Process modelling is used to track the sources of uncertainty in analysis, design and decision making and to integrate different types of evidence. This approach to uncertainty analysis, which involves exploring and accounting for the sources and nature of uncertainty in decision making, is illustrated with reference to sea defence projects on the East Coast of the UK.

During seasonal storms, waves wash over the major peninsular sand spit protecting the Port of Walvis Bay. The possibility of breaching of the spit was assessed and conceptual measures were proposed to prevent breaching. Aeolian, longshore and cross-shore sand transport rates were computed. Modelling was done of beach profile changes during storms. It was found that the spit would probably not be breached during a single storm. Sand nourishment, methods to prevent erosion, and methods to induce accretion in vulnerable areas were considered to prevent breaching. A contingency plan was recommended involving the use of low-cost shore protection.

The paper deals with experimental and theoretical investigations of dynamics of a plate–fluid system. In experiments, a horizontal plate was suspended elastically in a wave flume and loaded with impact pressure forces resulting from growing water waves. The data obtained in experiments has revealed the essential role of the elasticity of the plate and its supports as well as the fluid compressibility in estimating the structure-fluid interactions. Therefore, in order to get a better insight into the problem considered, harmonic vibrations of an elastic band plate submerged in an infinite domain of compressible fluid have also been examined. The solution obtained and formulae derived enable to calculate the fluid pressure induced by the plate vibrations.

For violent wave impacts against sea walls and breakwaters Cooker and Peregrine (1990,1992) suggest the use of a pressure-impulse model. Here the model is used for three-dimensional examples.

Thyborøn, Denmark is placed at the entrance to a fjord system, which connects the North Sea with Kattegat. The inlet acts as a trap for the littoral transport from both sides. The adjacent barrier beaches suffer from severe erosion, which is alleviated by large structures and nourishment. The entrance was formed only 135 years ago and is still undergoing morphological changes. During its lifetime engineers have investigated various schemes for stabilising the shoreline – the most radical suggestion has been to close the entrance to avoid the ongoing loss of beach material. The present paper presents the major findings of a comprehensive study of the hydrographic and geological conditions, the coastal processes and the morphological evolution.

Hornbæk Harbour was built more than a hundred years ago on a sandy coast with predominant eastward longshore sediment transport. After construction of the harbour the littoral transport was disrupted leading to a large accretion of sand upstream of the harbour whereas lee-side erosion occurred downstream of the harbour. Soon problems were experienced due to sedimentation in the harbour entrance and in the beginning of the century a breakwater was constructed for blocking the sand transport. This breakwater was later extended and finally a lee-side breakwater was constructed.

Hornbæk harbour represents a classical case of the problems encountered when constructing a harbour on a coast with littoral drift. Only in recent years focus has been put on environmental issues and the present project shows a good example of remedial measures by involving a number of shore protection schemes.

The applied shore protection schemes consist of beach nourishment, beach dewatering and maintenance of shingle beaches along with extension and repair of existing slope protection. On completion of the project a monitoring programme has been started in order to track the development of the coastline in response to the beach nourishment scheme.

The establishment of breakwaters in Japanese ports has progressed in recent years and has greatly improved the calmness in the ports. However, the seawater exchange within and outside of the port has greatly decreased. In ports near urban areas, in particular, the inflow of domestic and industrial wastewater, and the accumulation of sludge are causing a variety of environmental problems. Therefore, it is necessary to solve two contradictory technical problems: improving seawater exchange while at the same time improving calmness in the port.

An armored caisson breakwater with intake holes has been developed to conduct external seawater into the port using wave energy. In this paper, the hydraulic characteristics and the practical design of this structure will be presented.

The use of different wave overtopping models has been analysed. These overtopping models were applied to vertical walls with different geometries built for the protection against storm surges in the harbour of Hamburg (Germany). A comparison of existing overtopping test data and results from specific hydraulic model tests for existing geometries in Hamburg was also performed. A simple design diagram to predict both the overtopping rate q and the required freeboard R_C is presented. Furthermore, a simple engineering approach is proposedfor the reduction of the horizontal wave load of the harbour walls due to wave overtopping. Finally, conclusions are drawn to come up with a "general overtopping formula" and further research work is outlined.

Quality assessment of dikes is being set up in the Netherlands. The existing placed block revetments are a part of this assessment. In cases where a routine assessment is insufficient to come to a definitive conclusion, legislation prescribes a more advanced assessment. In this paper, the possibilities of such an advanced assessment are investigated. Three locations were selectedfor this assessment. The paper describes the experiments, field tests and calculations performed and concludes with the results ofthe assessment. Permeability of filter layer and cover layer appears much lower than expected, which influences the possible failure mechanism. The residual strength of a clay layer of 0.8 m underneath the blocks appears to be limited.

The basic and detailed design of revetments and breakwaters in the Öresund Link were carried out by the Consultant, Carl Bro a/s⁴ for the Contractor, Öresund Marine Joint Venture, ÖMJV⁵, based on design requirements and additional background information given by the Owner, Öresundskonsortiet, ÖSK. Final design was to be approved by the Owner, but with the liability of the Consultant/Contractor and with due consideration to the contractors method of construction. As part of the design process and in order to fulfil given geometrical restrictions the design requirements where further elaborated based on results of physical model tests and desk studies of critical assumptions. Some of the aspects and considerations in that process are discussed below.

Within the scope of the research on the stability of open slope revetments, much knowledge has been developed about the stability of placed (pitched) stone revetments under wave load (CUR/TAW 1995) and stability of rock under wave and current load (CUR/CIRIA 1991).

Until recently, no or unsatisfactory design tools were available for a number of other (open) types of revetment and for other stability aspects. This is why the design methodology for placed block revetments has recently been extended in applicability by means of a number of desk-studies for other (open) revetments:

This paper aims at giving a summary of the increased knowledge, especially that concerning the design tools that have been made available. The details behind it can be found in (Pilarczyk et al 1998).

This paper describes the results of a nationwide inventory of the stability of existing placed block revetments in the Netherlands. The inventory is now complete at a basic level: the revetments have been tested using simple stability criteria. These criteria are described in this paper and the main results of the inventory are presented and discussed.

Wave diffraction around a large vertical circular bottom mounted cylinder is considered. Results from a 3D second-order numerical time domain Boundary Element Model, a 3D second-order semi-analytical frequency domain model and experiments are compared and show good agreement over a wide range of wave frequencies and wave steepnesses. In general the agreement between the calculated and experimental results is satisfactory even in some cases where second-order Stokes’ wave theory is not a priori expected to provide accurate results. The two numerical models have thus been validated against each other and validated against experiments. It is noted that the inclusion of second-order effects is important for the accurate estimation of run-up on a structure.

High-specific gravity (HSG) armor blocks have high stability for waves compared with the same size blocks made with normal concrete. Since an armor layer constructed with HSG armor blocks is thinner than the equivalent layer built with normal concrete, it is expected that it will produce significantly higher wave reflection. The goal of the present study is to investigate experimentally the effect of a double layer of HSG tetrapods (referred to as 2-tetrapod layer) on wave reflection. During the tests, regular waves were generated against a breakwater covered with the 2-tetrapod layer, and wave reflection was recorded for several layer thicknesses. Six sizes of tetrapod models were used ranging from 3.1 to 16.6 cm in vertical height, i.e., the 2-tetrapod layer thickness varied from 5.2 to 22.5 cm. Based on the laboratory test data, the effect of the layer thickness on wave reflection was examined using dimensionless factors derived from dimensional analysis. It was concluded that wave reflection increases as the specific gravity of armor blocks becomes larger, in a manner that depends on the deep water wave steepness.

The numerical wave flume VOFbreak² for simulation of wave interaction with a rubble mound breakwater is presented. The key innovations are a porous flow model and wave boundary conditions. The porous flow is implemented using a Forchheimer model. At the boundaries waves are generated using a combined wave generation-absorption technique and are absorped using a numerical sponge layer.

A nonlinear numerical model is developed for the interaction of waves with a pipeline covered with rubble. The wave field utilizes a fully nonlinear potential formulation while the porous medium is governed by modified Navier-Stokes equations. The model employs the BEM in the water column and the FEM in the rubble layer. Wave forces on the pipeline are calculated by integrating pressure around the pipeline perimeter. The numerical and experimental results for the wave kinematics in the pipeline vicinity are found to be in reasonable agreement. Numerical analyse indicate that the horizontal wave force is larger than the vertical force for all tested wave and rubble conditions. Forces increase with increasing wave height and decreasing depth. However, for the cases examined there is an intemediate water depth at h/L ≈ 1/6 for which the forces are largest. The armor stone size and rubble layer pososity have little influence on the magnitudes of the forces. The horizontal force is nearly independent of the depth of rubble cover over the pipeline. However, the vertical force increases significantly as the depth of cover decreases. Also, for partial pipeline cover, the maximum horizontal and vertical forces are more in phase, which combined with the larger vertical force, results in a substantially less stable condition.

This paper reports some of the results of a theoretical and experimental study of submerged, detached, segmented, trapezoidal rubble mound breakwaters. It focuses on the phenomenon of sea level set-up which occurs at these structures. A theoretical analysis is presented which gives an explanation for the occurrence of set-up and the experimental results so far confirm the proposed relationship, which is given by Equation 4. Various other checks are presented in the paper, such as a demonstration that the set-up can be eliminated by pumping out from behind the breakwater and the measurement of a net drift velocity offshore in the core of the breakwater.

It is well known that the littoral drift carries much sand into a sheltered area caused by the presence of coastal structures such as detached breakwaters. As a result, the shoreline in the sheltered area advances, whereas the shoreline of the neighboring coast recedes to balance a sand budget of the coast. An artificial island for storage of crude oil was constructed off the Kashiwabara coast, Shibushi, Kagoshima Prefecture, Japan since 1985. The island has a rectangular shape roughly 1.5 km long and 1.5 km wide. This paper describes coastal processes related to the construction of the artificial island, and proposes a new dredging and beach fill scheme including a groin to decrease the coastal erosion due to the sheltering effect by the artificial island.

The morphological aspects of the design of shore-parallel breakwaters are investigated through a series of tests using a two-dimensional (in the horizontal plane) morphological modelling system. The analysis focuses on the optimisation of the breakwater length and its distance to shore in order to achieve the desired type of response. The results obtained are compared to empirical formulas from the literature and observations from the field.

The application of shore parallel offshore breakwaters in coastal engineering is discussed. Four well-defined practical coastal engineering problems are the starting point of discussion. The possibilities of a new morphological model and a design support model are indicated.

The combined action of waves (incident and reflected) and the alongbreakwater current driven by wave energy dissipation inside an infinitely long porous breakwater under oblique wave attack (Baquerizo and Losada, 1998), is taken into account to study the formation of bars in front of the structure and the sediment transport at the toe of it. The main features of the bars are explained in terms of the incident wave characteristics, remarking the wave incidence angle dependence, and the structural and hydrodynamic properties of the breakwater. Results may explain the existence of erosion/deposition patterns at the toe of the structure.

This paper describes the experimental and theoretical analysis carried out to improve our knowledge of the stability of near-bed rubble-mound structures. Laboratory tests have been performed to improve the data base on the stability of this kind of structure. The experimental results are compared with the results of three different approaches to stability: dimensional analysis, Morison forces and forces derived from bed shear stresses. In all cases considered, the influence of the geometry of the structure has not been taken into account, and the characteristics of the flow around the structures have been obtained from linear wave theory. The analysis of the data shows that the mobility parameter, a non-dimensional form of the bed shear stress, gives the best representation of the damage in these structures. From the analysis it can also be concluded that inertia forces are not relevant in the representation of the damage using Morison forces. Based on these approaches, some formulations of damage are presented. These formulations indicate that, for the first stages of damage, damage varies almost linearly with force (Morison or bed shear stress).

100 Years of Experience In a High Energy Wave Climate

This paper uses the examples of Coffs Harbour breakwaters and the training wall head on the Richmond River at Ballina to outline some of the developments in coastal engineering design and construction over the last century. Most of the 63 major structures along the New South Wales (NSW) coastline are similar. Recent developments in data collection and analysis as well as the evolution of physical modelling techniques used for coastal structure design at the NSW Department of Public Works and Services’ Manly Hydraulics Laboratory (MHL) are discussed using these two projects. The use of computational models in conjunction with physical models and the introduction of new variables such as wave obliquity and groupiness into breakwater design are discussed. The need to evaluate the performance of artificial units such as Accropodes, concrete cubes and Hanbars for primary armour at breakwater heads due to restrictions on the availability of quarry armour and available construction techniques is briefly addressed.

Alderney is the northernmost of the Channel Islands, lying 13km off the Normandy coast. The main breakwater at Alderney, known as the Admiralty Breakwater, provides essential shelter to the commercial and fishing quays and swing moorings for fishing boats and visiting yachts. It also provides protection to the shoreline around Braye Bay.

Wave conditions at Alderney are frequently severe. In response to this severe wave attack the Admiralty Breakwater (constructed between 1847 and 1864) has required continual maintenance (costing £447,000 in 1998). Even with this level of investment, however, the long-term decay of the structure and occasional breaches continue.

This paper explores the history to the Admiralty Breakwater, why there is a need for works and how a range of disparate designs have evolved over time leading ultimately to a small number of viable solutions.

The trunk section of the south breakwater, at the entrance to the Port of Richards Bay, has suffered some damage since its construction which was completed in 1976. This paper briefly discusses the changes in the design conditions as a result of sand-trap dredging off the breakwater, the annual photographic monitoring results showing the excessive rates of damage, and the model testing of various repair options, using 20t and 30t dolosse. Both 2D flume and 3D basin model tests were carried out at various scales, with fixed and movable bed models. Finally the construction of the optimal repair, carried out in 1997/98, using a heavy duty mobile crane (with 48m boom reach) and DGPS positioning, is described.

The entrances to the six largest ports in South Africa are protected by rubble mound breakwaters, which have Dolos armouring. PORTNET, the national Port Authority, have commissioned the CSIR to conduct detailed monitoring of existing rubble mound breakwaters including records of the wave conditions to which they are subjected in service. This paper presents the image processing techniques used to monitor breakwater damage as well as the wave field causing the damage. Wider applications of these techniques have been commissioned during pipeline outfall construction as well as during the design & modelling stage of a proposed new harbour. The image processing techniques have been used to measure both breakwater settling and damage as well as moored ship motion for competing breakwater designs constructed as in scale models, of proposed harbours at the CSIR’s physical modelling facilities in Stellenbosch.. The image processing techniques developed by TECHTRIX International are reported here.

There have been several investigations on the stability of site specific single layer breakwaters, e.g. for Søvœt Fishing Port, Bratteland and Tørum (1971) and for Berlevaag Harbour, Kjelstrup (1977). However, despite the frequent use of the single layer design only little systematic investigations of the stability have been conducted until now. During the winter/spring 1997 a series of physical model tests have been conducted at SINTEF with focus on the hydraulic stability of the single layer rubble mound breakwater armour layer and the wave induced loading (Hald and Tørum (1997)). The present paper describes the results of these tests.

A slit caisson breakwater has now been under construction at Takamatsu Harbor, Kagawa Prefecture, Japan, as an amenity-oriented breakwater (that is, a human friendly breakwater opened for citizen). However, wave pressures and forces acting on the slit caisson have not been evaluated. Hydraulic experiments are carried out to examine the stability of the slit caisson breakwater and uplift forces on a upper board, and to investigate a desired type of upper board of the breakwater.

Since the work by Ahrens and McCartney (1975) and Bruun and Johannesson (1976), it has been accepted that, for given slope, unit type and damage level, the stability number, N_s, and the so called K_d factor depend on Iribarren number, I_r, and that the worst stable conditions are related to collapsing wave breakers. The plotted values of N_s and K_d from laboratory tests, as a function of I_r, show a large scatter. This scatter is larger for large values of I_r. It is shown here that the scatter almost disappears once the data are plotted against kh, or I_rt, using the total wave height at the toe of the structure instead of the incident wave height. The total wave height, H_t, results from the interaction of the incident and reflected wave trains on the slope and depends not only on the magnitude of the reflection coefficient but also on its phase.

In 1996, the U.S. Army Corps of Engineers, Waterways Experiment Station, Coastal and Hydraulics Laboratory in conjuction with Oregon State University and Concrete Technology Corporation, Tacoma WA, conducted the first structural response experiments of the new concrete armor unit, CORE-LOC^®. Large scale 32-kg and prototype 9.2-tonne core-loc units, were molded, cast, and fitted with surface-mounted strain gages. The units were subjected to repeated impact loads generated during drop tests. In addition to the CORE-LOC^® drop test, similiar tests were conducted on 26-kg and 10.9-tonne dolosse. The structural response to these loads were recorded and analyzed. Measured maximum tensile stresses in CORE-LOC^® were approximately half those in similiar size dolosse.

The newly completed fishing and recreational harbour at Port St Francis, on the south-east coast of South Africa, has a 220m outer rubble mound breakwater and an inner revetment, both protected by Core-loc® armour units. This paper briefly discusses the breakwater layout and armouring design, the effect of severe storm conditions during construction, and the performance of the Core-loc armouring, as based on the results of photographic monitoring, crane-and-ball profile surveys, visual observations and diver surveys below water.

The first project in which Core-Locs were used as the main breakwater armour unit, is a small craft harbour on the south east coast of South Africa named Port St Francis. The Core-Loc was selected based on economic advantages over other units. Stability of 15 t units was confirmed in a full three-dimensional model study. Construction ofthe harbour commenced in early 1996 and was successfully completed towards the end of 1997. Practical construction issues are discussed in detail. Core-Loc performance under construction stage storms was excellent and virtually no damage has taken place under design storm conditions subsequent to the completion ofthe structure.

An experiment is described consisting of seven relatively long-duration breakwater damage test series. The test series were conducted in a flume using irregular waves. New damage measurement techniques were developed and damage development data were acquired for breaking wave conditions. Wave height, wave period, water depth, storm duration, storm sequencing, and stone gradation were all varied systematically. The experiment yielded relationships for both temporal and spatial damage development. The relations by Melby and Kobayashi (1998a,b) for predicting temporal variations of mean damage with wave height and period varying with time in steps are shown to describe damage reasonably well (within one standard deviation) for new test series, although damage initiation is consistently underpredicted by more than a standard deviation. The prediction is shown to improve significantly if the initial profile adjustment is accounted for in the test series with relatively small cumulative damage.

To reduce the high expenses of armour layers for the protection of sandy beds in rivers and coastal areas around structures a so called geometrically open armouring, consisting of a single layer of large rocks, is often tried nowadays. In most models it is assumed that the mean flow (and shear stress) above the armour layer penetrates in the pores between the armour elements and that this penetrated flow is responsible for the erosion of the sand bed below the armour layer. However, the relatively thin armour layer these models predict does not always suffice for a safe armouring of the sand bed in practice. Measurements of the flow velocities in the pores between armour elements in a flume using the laser-Doppler technique suggest a completely different erosion mechanism. Erosion appears not to be caused by the mean pore flow. Instead small-scale locally generated velocity fluctuations in the pores lift the sand particles from the bed; large-scale fluctuations, due to large-scale turbulence in the main flow, transport the sand particles through the armour layer into the flow above.

This study complements the wave kinematical investigation on the performance of rubble mound breakwater under uni and multidirectional waves. The measurements of wave kinematics over the head and trunk sections were undertaken to achieve an improved understanding of the influence of wave directionality on the stability of armour layers. The directionality and magnitude of velocity vectors over the head and trunk sections under 3D waves were assessed by comparing them with the measurements under 2D waves. The sensitive zones of the initial damage in the head and trunk were evaluated by linking the velocity measurements with the stability formulas for armour stone movement.

This article presents a methodology for the design of breakwater dikes which includes wave estimation, evaluation of the runup at the dike, calculation of the dynamic and pseudohidrostatic forces operating on the crown wall and finally the estimation of the stability ofthe armour units in the main layer.

The methodology presented is a development of existing experience in the evaluation of the effects produced by regular or monochromatic waves on structures (stability of pieces, inducedforces andflow on the slope). This experience is extended to irregular or spectral waves via statistical distribution of waves, taking account of parameters such as root mean square or significant wave height, mean or peak period and water depth.

The application of the methodology described here has given satisfactory results compared with those of other methodologies and experimental data from various researchers.

A cost comparison have been made between various types of breakwaters for a fictitious situation in waterdepths to a local maximum of -15 m and an adopted sea climate. The comparison is based on optimal total project costs, being the sum of costs of construction and capitalized damage during the service period. For these selected conditions the caisson breakwater and the rubble mound type provided with a single concrete armour layer appear most attractive. Composite type of breakwaters seem advantageousfor water depths approximately below -20 m.

Following an old Italian tradition of prototype measurements of wave pressures at vertical breakwaters (Franco, 1994), a new twin recording station was set up and operated in 1992-1994 at Porto Torres (Sardinia, Italy) industrial harbour breakwater. In the framework of the MAST3-PROVERBS project an extensive analysis of the available data has been carried out.

Within the same project 2D model tests have also been performed in order to investigate the relation between pressure distribution and overall forces on and under both plain and perforated (multichamber) caissons. The results have been compared with the available design formulae like Goda’s (1985). Statistical distributions of the horizontal and uplift forces for both structure types have also been derived. The scope of the study has been to assess the reliability of the present design methods and to outline a more physically based approach especially for the perforated structure type.

The paper concerns horizontal wave forces on caisson breakwaters in multidirectional breaking seas. It is based on model tests performed in a 3D wave tank at Hydraulics and Coastal Engineering Laboratory, Aalborg University. The measured horizontal wave forces are compared to the Goda force. Good agreement with the Goda formula is found for waves not breaking directly on the structure, while increasing degree of breaking on the structure results in forces of up to 50 % higher than the Goda force. Furthermore, the reduction of the horizontal wave force on long structures due to the non full correlation of the wave pressure along the structure is investigated. A formula for the force reduction factor based on cross correlation coefficients is given as a function of the mean wave direction and the wave spreading.

Prototype tests, aiming to describe the dynamics of caisson breakwater oscillations, were carried out at Genoa Voltri and at Brindisi Punta Riso. The rigid body naturalfrequencies and modes of oscillation of the caissons were evaluated as well as the rate of damping. The effect of the longitudinal array structure, never tested in physical models, was found extremely relevant; the Mass Spring Dash-pot model for an isolated caisson of Oumeraci & Kortenhaus (1994) was then conveniently updated in order to represent an array structure, showingfinally good agreement with the recorded signals.

After presenting a summary offield survey-observed damage incurred over the past 20 years by caisson walls ofJapanese breakwaters, this study describes a series ofmodel experiments and three-dimensional FEM simulations performed to evaluate the dynamic response of a caisson wall subjected to breaking wave impulsive pressure. The important roles played by “elastic” and “inertia” soil pressures are subsequently clarified, and good agreement is obtained between measured and calculated results. The proposed calculation method, which applies the Goda pressure formulae in conjunction with the impulsive pressure coefficient α₁, is expected to provide a practical design method against impulsive pressures.

Submerged rubblemound breakwaters are becoming more popular as a potential alternative to coastal protection measures where a moderate degree of energy transmission is acceptable. Such situations include areas where vegetative shore protection is existing or proposed or in the event that an existing shore protection structure has become damaged or under designed and a method is needed to reduce the incident wave energy. Although there have been previous investigations on the performance of submerged rubblemound breakwaters, there are only a few design equations available to the design engineer. Those available are based on a limited range of input design variables and as a result are insufficient in some cases.

Physical model studies were performed at the Queen's University Coastal Engineering Research Laboratory (QUCERL) in Kingston, Canada to assess the performance of submerged rubblemound breakwaters under a wide range of design conditions in twodimensional (2-D) and three-dimensional (3-D) settings. The tests include a number of wide crested structures to provide data where previous investigations have not. The results show that the relative submergence, incident wave height and structure crest width are the most important design variables.

A number of potential design equations were evaluated by statistical analysis methods. The proposed design equation fits the 2-D test data well and provides moderate agreement with the 3-D test results. Although physical testing is suggested for all design applications due to the complexity of site specific considerations, the proposed equation does provide a good preliminary design tool for submerged rubblemound breakwaters.

The results are presented of 2DH numerical modelling of morphological effects of submerged breakwaters. In particular, segmented configurations are focussed upon, since segmented submerged breakwaters induce interesting and important current circulations in the horizontal plane.

In a previous study, a module that calculates a phase-averaged stationary wave field was used to compute wave forces. These forces were next used to calculate current patterns. In the present study, waves are introduced via a harmonic boundary condition in a phase-resolving module, based on the nonlinear shallow water equations. The advantage of this approach is that the current patterns are directly calculated, the disadvantage is that it requires more computation time.

The first results of morphodynamic computations with submerged breakwaters, in intra-wave mode, are promising. The most important mechanisms are reproduced rather well. Some of the shortcomings of the previous model study with a stationary wave model have been overcome. However, a lot of fine tuning still needs to be done.

The pressure distribution at permeable vertical walls is investigated within a comprehensive large-scale test programme considering experiments with a variation of wave parameters and structure porosities. Monochromatic non breaking and slightly breaking waves on such structures are examined and results are compared to the GODA formula for impermeable vertical walls and a modified GODA method which has been developed here for permeable walls. Two parameters involving the structure porosity are introduced to account for the nonlinear processes at permeable walls. Using these parameters new prediction formulae have been derived for the pressure distribution at the wall.

Recent research under PROVERBS has demonstrated that wave impact loads can cause damage or failure of caisson or blockwork breakwaters. Research studies of wave loadings, pulsating or impact, have generally used only 2 - dimensional wave flume experiments, and so most design methods are strongly biased towards 2-d.

This paper describes results from 3-dimensional wave basin tests by Universities of Naples, Sheffield, and HR Wallingford in the UK Coastal Research Facility (CRF). The aim of the study was to quantify effects on wave pressures or forces of oblique or short-crested wave conditions on simple vertical or composite breakwaters.

This analysis has focussed particularly on wave impact loadings as earlier 2-d tests at Wallingford showed them to be potentially severe for some combinations of foundation level and relative wave conditions. New reduction factors are presented.

This paper presents a comparison of measured and predicted wave forces on a vertical wave barrier, defined here as a thin impermeable vertical wall extending from above the water surface down to near mid-depth. Theoretical wave loads are computed using the eigenfunction expansion method. Measured wave loads are obtained from two sets of laboratory experiments, one conducted at the U.S. Naval Academy and the other conducted at the Oregon State University in a large wave flume. Results of this study suggest that the eigenfunction theory can predict wave loads to within 10% to 20% accuracy for a wide range of wave conditions, water depths, and wave barrier drafts.

This paper discusses the statistical distribution of wave impact forces on vertical wall structures. It describes new analysis carried out based on the distribution type to identify the parameter combinations that lead to wave impacts.

Comprehensive 2-dimensional random wave model tests were carried out to measure wave pressures on a range of structure types. Initial analysis of these tests showed that the Weibull distribution could be used to describe non-breaking wave forces.

For some structural configurations however the wave forces were found to give a poor fit with the Weibull distribution. These data had been excluded from the initial analysis. The new analysis described in this paper has resulted in a revised parameter map to summarise the risk of wave impact, derived from the full data set and based on the distribution type.

For the design ofvertical breakwaters, reliable predictions of the horizontal forces are required. Through physical modelling useful predictions can be made but, due to the very complex interaction between waves and structures, the derivation of reliable empirical relations based on such tests can still be rather difficult. Here, based on a large data-set from physical model tests, use is made of Neural Network modelling to predict horizontal forces on vertical structures. In addition, a method is developed to estimate the reliability-intervals around the predictions. The resulting tool is a complementary design-tool for predicting forces on vertical breakwaters and also a suitable tool for application in probabilistic design methods.

When calculating the stability of a breakwater foundation information on the pore pressures directly underneath the caisson in the bedding layer and in the sand layer is needed. In this paper easy to handle calculation techniques are presented to derive the pore pressures underneath the caisson. A quasi-stationary calculation technique has been verified for the situation of a caisson breakwater, by a hind cast of laboratory tests. The differences between the quasi-stationary calculations and the laboratory measurements appear to be small and can be explained by non-stationary effects. The pore pressure distribution in real cases may considerably deviate from the traditionally assumed triangular distribution, due to several effects. Non-stationary effects are only relevant if the rubble is relatively fine and wave impact occurs. The pore pressures in the sand layer have been studied by centrifuge tests. Two types of pore pressure development can be distinguished, the instantaneous pore pressures, which follow the wave action at sea and the residual pore pressures, which gradually develop under repetition of loading. The residual pore pressures may lead to liquefaction if silt or fine sand is present in the subsoil.

In the design ofcoastal structures, the choice of the safety levelfor which the structure has to be designed is a major problem. This is also the case for vertical breakwaters. This paper applies the concept of economic optimisation to derive the appropriate safety level and at the same time the optimal geometry. Application to a design case shows that it can be economically optimal not to distribute the acceptable failure probability equally over all failure modes, but rather let one or two failure modes determine the total probability of failure.

The paper presents a new system for implementation of target reliability in caisson breakwater designs by means ofpartial safety factors. The development of the system is explained, and tables of partial safety factors are presented for important overall stability failure modes related to caisson structures placed on bedding layers and high rubble moundfoundations with underlaying sand and clay subsoils.

A new submerged breakwater structure for shore protection is proposed and called the longitudinal reef system. It is efficient in dissipating wave energy by increasing wave heights at the front through wave refraction effect and by enhancing wave breaking. Comparison is made between the new longitudinal reef system and the conventional broad-crested reef system through model experiments and numerical computation. The superiority of the longitudinal system to the conventional system is confirmed through the comparison.

The concept of a horizontal perforated plate placed in water, with a method for implementing the concept in a real sea as a new type of reef breakwater, is proposed in thepresentpaper. The feasibility andsuperiority ofthe proposed breakwater in hydraulic characteristics in comparison with conventional reef breakwaters has been shown by theoretical and experimental study.

A submerged active breakwater consists of a large buoyant cylinder that is held horizontal beneath the free surface of the water, by a spring and damper restraint system. The cylinder will be forced to oscillate in a certain mode, in response to an incident wave train. If properly “tuned”, the cylinder can absorb a considerable fraction of the incident wave energy. Utilization of this concept may provide a number of potential benefits including; 1) a no loss to fish habitat; 2) a depth-independent materials cost; 3) a scheme easily adaptable to long term water level changes (such as those which occur naturally in the Great Lakes and those which are anticipated with sea level rise); and 4) the capability of adequately protecting a coastal area while maintaining boat access and water circulation. Knowledge of these devices however, is currently limited to performance in; 1) regular wave trains of narrow frequency bands, 2) zero angle of incidence between the wave crest and the structure, and 3) waves of small amplitude.

Research evaluating the performance of submerged active breakwaters was performed in a two-dimensional wave flume in the Queen’s University Coastal Engineering Research Laboratory (QUCERL). Both single cylinders and multi-cylinders placed in series were evaluated. Transmission coefficients in the range of 0.3 to 0.7 were measured over a broad range of conditions, indicating the possibility of these devices being used in prototype situations to achieve the benefits described above.

The stability of armor units for composite breakwaters was studied by two- and three-dimensional model tests and prototype failure analyses. The wave force on armor blocks was cleared for different relative mound depths and berm widths. The stable weight of armor blocks is proposed in which the block shape factor is used as a parameter. The necessary thickness of foot-protection blocks is formulated as a function of the relative mound depth for the breakwater trunk and head.

The hydraulic performance of an innovative structure based on the concept of a high mound composite breakwater has been investigated in large-scale hydraulic model tests in the Large Wave Flume (GWK) of the Coastal Research Center (FZK), Germany. The experimental results concerning wave breaking, wave transmission and wave reflection are presented.

The effectiveness of a second perforated barrier seaward of a solid wave barrier in significantly reducing wave reflections and simultaneously improving wave protection is demonstrated in the paper. The indicated optimum seaward wall porosities and overall widths can be readily incorporated into practical structural designs for small craft facilities in relatively sheltered waters with limited wave periods. Results of an extended laboratory testing program and specific application to a recently designed and constructed structure are presented.

A general expression for the overtopping discharge of a rubble mound breakwater has been derived utilising the general experience on this subject found in the bibliography and from the results of comprehensive series of model tests carried out at Danish Hydraulic Institute (DHI). The expression includes the important breakwater parameters (geometry of the breakwater profile) and the environmental parameters, and has been derived for applications with non-breaking waves in front of the structure. In research studies, model test series were carried out on pure rubble mound breakwater profiles with quarry rock as armour layer. Through results from projects carried out at DHI, the expression was extended to include different armour types and to describe the influence of a superstructure.

The aim has been to set-up a reliable expression, which is simple, general and easy to use. Previously, predictions of overtopping discharges have been based either on expressions including empirical constants for different shapes of the breakwater profile, on very complicated expressions or on diagrams giving the overtopping discharges as function of the layout of the breakwater profile and the environmental conditions.

The accurate estimation of wave overtopping quantity is of great importance for the design of seawalls to protect artificial islands constructed offshore. The estimation model for overtopping rate in multi-directional waves is proposed and it is experimentally verified. The numerical results demonstrate that the overtopping rate in multi-directional waves becomes smaller than in unidirectional waves when the incident principal wave angles are near to the normal to sea wall face. The result becomes reverse when the wave angle is more than 30°.

Major beach erosion has been occurring along the Nile Delta shoreline. The erosion is primarily caused by diminished sediment transport in the River Nile due to construction of the Aswan high dam.

Egyption and foreign experts have evaluated various shore protection methods since 1983.

A summary of alternative shore protection methods, including offshore breakwaters, beach sand replenishment, groins, inlet training jetties, etc. is presented.

This paper deals with two-dimensional hydrodynamical and morphological modelling of a large nontidal coastal area located at the German coast of the Baltic Sea. This work has been carried out in order to consider the morphological response of this region caused by climatological changes. The morphological processes in this region are mainly wave-dominated, hence a shallow water wave model was coupled with a vertical integrated flow model. Stationary simulations for waves, currents and sediment transport are carried out for a large range of meteorological situations, which were defined due to a statistical analysis of the output fields of a coupled ocean – atmosphere global circulation model. The wave parameters of this surface wave model are used as input to coastal area models.

The calculated morphological trends obtained for different meteorological situations show good agreement with the morphological changes observed in this area. By combining and weighting the individual situations the resulting flow field and sediment transport for known meteorological events can be found. The morphological sensitivity to climatological changes of the coastal area is investigated by applying this methodology to different climate scenarios.

For an efficient protection of the north coast of the Dutch Waddensea island Texel, a long dam was constructed in 1995. The position of this dam is on the southern swash platform of the ebb tidal delta of the Eijerlandse Gat: the tidal inlet between the two Waddensea islands Texel and Vlieland. The long dam changed the hydro-morphological conditions in this tidal inlet. The changes in the inlet’s morphology have been monitored through regular bathymetry surveys. This paper describes some of the most remarkable changes that occurred in the inlet after the construction of the long dam. The impact of the long dam on the inlet's morphology and the adjacent shoreline stability has been examined with the use of a medium-term morphodynamic model. From a comparison between the observed and predicted morphological changes it followed that the model was able to simulate the large scale morphological response of the inlet system. However, on a smaller scale there were still important discrepancies between the observations and the predictions.

The Atlantic Ocean coast of Uruguay extends from Punta del Este outer limit of the Rio de la Plata Estuary, to the Brazilian border, over 220 kms. This case study applies to a homogeneous coastal stretch of 80 kms long, north of Punta del Este. The main coastal features are three littoral lagoons, Jose Ignacio, Garzón and Rocha, whose mouths open and close by natural or antropic actions every year. The coastline is formed by 1-2 mm coarse sand on highly reflective beaches. Beach berm is overwashed by the SE storm waves. Landward there is a dune system. This beach-dune structure is approximately 100 m wide. At least three similar morphological structures may be landward identified, which were developed during a period of time when the sea level was about 5 m higher than today’s sea level (approximately 5000 years BP). ¹⁴C technique applied to chalk samples shows a relative decrease of the sea level in the last 5000 years. Furthermore, gravimetric data shows that there is an anomaly, which supports the existence of an isostatic rise of the continental shelf. As a result, the Atlantic Ocean Coast of Uruguay is prograding. The beach coarse material is provided by the wave action from the continental shelf, while the fine dune material seems to be obtained from the erosion of the land weathered granite.

The construction peculiarities of the new model of turbidimeter for measurement of instantaneous values of suspended sediment concentration are described in this paper. The presence of optic negative feed back is the basic feature ofthis turbidimeter, which allows to eliminate practically completely the temperature instability oflight source and of its electronic units. A new model ofturbidimeter has given a possibility to create a three-dimensional lattice for the investigations of suspended particle spatial shift. One turbidimeter of the lattice cell is recording continuously the background transparency ofexamined liquid in a real scale. It gives possibility ofcontinuous controlling not only ofthe light radiation flux attenuation by suspendedparticles but and ofa ratio between the lightflux absorption in researched water column with suspendedparticles and the lightflux absorption in "clean" water. During the field experiments with the help of turbidimeters new data about physical mechanisms of sediment suspension above a smooth and rippled bottom were received.

Suspended sediment flux and cross-shore beach deformation in the breaker zone are elucidated experimentally with the CRIEPI's irregular wave flumes of large and middle sizes. Effects of long waves on suspended sediment transport are also investigated with a new experimental system for correct reproduction of infragravity waves bounded by irregular wave groups. Based on the experimental results, the pick up rate from sea bed and convection and diffusion of suspended sediment are modelled, and a new numerical model is developed for cross-shore beach deformation due to irregular waves. This numerical model can well reproduce wave deformation, suspended concentration, undertow, sediment flux and beach topography change.

This paper reports on the results from a field test of the Bailard energetics sediment transport model. Model predictions agreed well with observed and measured volumetric change in the inner surf zone under erosional as well as accretionary conditions, occurring over a 72 h long storm event. The observed formation of a nearshore bar was reproduced by the model; bar formation was predicted to be due to a sediment transport convergence generated by seaward directed undertow and landward directed incident wave asymmetry.

A series of field experiments have been conducted to investigate small-scale sediment dynamics near the seabed in the nearshore region. The experiments took place at the U.S. Army Corps of Engineers Field Research Facility, in Duck, North Carolina, U.S.A., where the seabed typically consists of fine to medium sized sand. An array of instrumentation was deployed at various locations across the surf zone and nearshore region between depths ranging from 1 to 5 meters. Examples of suspended sediment measurements are presented along with examples of observed bedforms. We observed that the suspension of sand tends to occur at low frequencies that correspond to the time scale of wave groups. Small wave ripples are also found to evolve over similar time scales. We explore the linkages between the suspension of sediment and the evolution of small wave ripples, and show that the size of the ripples plays a significant role in determining the amount and distribution of suspended sediment.

In connection with the design of new marine facilities a hydraulic study was carried out at Pecém, NE Brazil The project comprised mathematical modeling of waves, nearshore hydrodynamics and sediment transport before and after the construction of the offshore harbor in front of Ponta do Pecém. The wave conditions are characterized by the simultaneous occurrence of sea and swell from different directions. The littoral current generated by the sea becomes detached at the headland. A shore-connected spit develops under these circumstances. During periods of predominant swell the spit erodes. The main impact of the harbor is a further reduction of the littoral drift W of the headland, which causes increased sediment accumulation immediately W of the headland and coastal erosion W of the city of Pecém.

One of the topics of the National Dutch research program COAST*2000 focuses on the long-term (50-100 years) and large-scale (1-100 km) morphological problems of the Dutch coast and the implications for coastal management. Examples of such problems are the effects of climate change and sea-level rise on a partly protected coastline, the long-term effects of on-going sand nourishments, the far-field effects of large-scale land reclamation and of the required sand-mining etc. Within this framework a pilot version of a conceptual model (the so-called PoNTos-model) has been developed, basically capable of simulating the morphological evolution of the Dutch coast at the above-mentioned spatial and temporal scales.

This present paper focuses on the theoretical background of the model. The results of a preliminary application of the model for the closed coastal section of the Dutch coast between Hoek van Holland and Den Helder are also presented.

The actual PONTos-model is based on the multi-layer concept, in which the crossshore profile is schematised as a number of mutually coupled layers, defined between fixed profile depths. These layers interact through cross-shore transport. In longshore direction the layers respond to gradients in the longshore transport generated at the profile regions they represent. The main input of the model, to be provided by the user, are the characteristics of the coastal stretch to be studied, including the initial positions of the various layers and offshore hydraulic conditions in terms of wave and tidal climate tables. On the basis of these data the yearly-averaged sediment transport pattern is computed and finally used for the assessment of the coastal evolution.

A simple method to parameterize beach erosion and accretion processes is presented. The parameterization is accomplished by combining important findings from two studies on the initiation of sediment movement, with near-bottom velocities estimated from nonlinear wave theory. This synthesis allows the development of a simple schematization or model based on only two variables that provides considerable insight on cross-shore sediment movement. Once calibrated, the model shows surprising skill (0.94) in predicting erosional or accretionary profile changes on sand beaches and is general enough to predict observed onshore movement of gravel during storms. If linear wave theory is used, the ability to discriminate between erosional and accretionary events declines.

Remotely-sensed images can provide synoptic or nearly synoptic data for large areas of the sea surface. Photographic and, more recently, radar measurement techniques can resolve the pattern of waves on the water surface and can provide a very dense sampling of kinematical variables of interest, ranging from a complete picture of the wave phase (in the case of single photographs) to horizontal velocity components at the water surface resulting from wind, tides, or waves (in the case of advanced radar techniques). When applied in the coastal zone, these images contain surface waves that are propagating over a complex bottom bathymetry and current field, and that are affected by a combination of shoaling, refraction, diffraction and nonlinear processes. This paper examines two methods to determine bathymetry from surface elevation information. The first is to examine the ability of linear dispersion relationship models to determine bathymetry, in cases with refraction and diffraction, and the second, based on lagged correlation method (and several images), is more generally useful for application.

The analysis of field observations of surf zone dynamics has revealed some ‘unexpected’ behaviour of the coastal system, generally referred to as ‘free behaviour’, which is behaviour that is unrelated to similar patterns in the external forcing. Present-day process-based modeling concepts are not capable to deal with these free modes of behaviour. In order to assess the validity of model-based predictions of bar dynamics, the relative importance of free behaviour versus forced response in the surf zone needs to be addressed. This work aims to contribute to the debate, by investigating the sensitivity of breaker bar behaviour to chronology effects from coastal profile modeling at a multiple-barred beach, with probabilistic forcing conditions. The results show chronology effects merely affect the predicted height of the bars, rather than their location which is remarkably consistent over the various runs. The latter observation has raised the question up to what extent predicted bar behaviour is controlled by model characteristics (concept, parameter settings), rather than system and forcing characteristics.

Restrictions imposed by the physical size of testing facilities has limited the range of trials undertaken on field instruments and little is known about interactions between the observed processes and large frames used to deploy equipment in the sea. Further, limited information on the physical processes from the field leads to ambiguity in interpretation of field data. This paper describes tests of the autonomous multi-sensor instrument STABLE, and process studies conducted in the Deltaflume (230 m long, 5 m wide and 7 m deep) of the Delft Hydraulics Laboratory. Regular and random waves with a specified time history and height up to 1.5 m, were used to test instrument performance and to examine sediment processes under waves on beds of medium (D₅₀ = 0.329 mm) and fine sand (D₅₀ = 0.162 mm). Selected results from studies of hydrodynamics, bedforms and suspended sediments are presented.

This paper presents the experimental results obtained at prototype scale in the Large Oscillating Water Tunnel (LOWT) facility of WL I Delft Hydraulics with graded sediment subjected to non-linear waves and linear waves plus current flows. The objective of this experiment is to increase our present understanding and physical insight of the basic mechanisms of bed-load and suspended load transport in oscillatory flow conditions when graded sediments are present in the bed. The sediment bed consists of a mixture of two well sorted sands (two fractions) that have been used before in the tunnel in order to make comparisons possible. Net sediment transport rates, time averaged suspended sediment profiles, time dependent concentrations in the suspension and sheet flow layers as well as time dependent velocity profiles are measured. Moreover, the sediment bed composition before and after each test is recorded in order to calculate the transport rate of each sediment fraction. Selected results are presented here. Full details are included in the data report (Hamm et al, 1998). The data will be used for the development of mathematical model formulations for graded sediment transport.

It is often assumed that in sheet flow conditions the transport rate in oscillatory flow behaves quasi-steady, i.e. showing a direct relation with the instantaneous flow velocity (e.g. Ribberink et ah, 1994). In this paper it will be shown that this assumption is not always valid.

Therefore a new semi-unsteady sand transport model is developed which takes into account phase-lag effects of the sediment on the net transport rate. In order to verify this new semi-unsteady model and two existing quasi-steady models, new experiments were performed in the Large Oscillating Water Tunnel (LOWT) of WL \ DELFT HYDRAULICS. Together with earlier experiments these measurements form a data set of net sand transport rates of uniform sand for three different grain sizes (D₅₀ = 0.13; 0.21 and 0.32 mm) in combined wave-current sheet flow conditions.

The verification shows that phase-lag effects become important for a combination of fine sand, large flow velocities and small wave periods. Under these conditions the quasi-steady models cannot predict the behaviour of the net transport rates correctly and the predictions of the new semi-unsteady model show much better agreement.

Sediment sorting processes (sorting on grain size and density) are the result of local hydrodynamic conditions. In this paper two measuring techniques are described which derive in situ time dependent and time averaged distributions of sediment sorted on grain size and density. The technique on measuring grain size of the sediment is described in more detail. The sediment distributions give information on the local hydrodynamic conditions on different time scales. Measurements from the field serve as a test case of describing the depth of closure from measurements of sediment composition.

When building a large scale land reclamation, the safest way is to shift the existing profile over the required distance of the reclamation project, up to a depth of say 20 m. This way the profile in cross-shore direction does not change and therefore also cross-shore sediment transports will be the same as before the land reclamation was made. A large disadvantage however is that a very large amount of material is needed for realising the reclamation. This makes the reclamation very costly.

To reduce the amount of material a cut profile can be applied. Above a certain depth (say CD -8 m) the cross-shore profile will be the same as the existing profile, but below this depth a relatively steep profile (say 1:50) is constructed. By doing this, material saving up to 40% can be achieved. A disadvantage of this cut profile is that a relatively steep profile has been made, which will effect the sediment transports. In this study the effect of a cut profile are investigated by using the numerical model UNIBEST-TC of DELFT HYDRAULICS for the computation of wave energy dissipation and cross-shore sediment transports. As an example the 'Plan Waterman', a plan for a land reclamation between Hook of Holland and Scheveningen, is used in this study. Various different cut profiles have been studied and it is found that especially relatively large waves, which break at the edge of the cut-off, have large influence on the cross-shore sediment transports. It is concluded, that the cut-off should at least be applied at CD-12 m if large changes in the coastal system are not desired.

The Distorted Ripple Train System, which is aimed to control the crossshore sediment transport, is proposed. The concept and basic functions of the artificial ripple system are introduced in the study and a detailed discussion is given on the determination of the optimum size of the individual ripple which enhance the effect of control.

This paper provides information on the effect of sediment (sand) composition on cross-shore sand transport and cross-shore bed profile evolution, based on computational results of a mathematical cross-shore profile model (CROSMOR) and data from flume and field experiments (Egmond beach, The Netherlands and Duck beach, USA). The model has also been applied to study longshore sand transport along a sand-gravel beach. Finally, the effect of sediment size on shoreface nourishment is discussed.

The physical principles, which govern the breaching process, are analysed. It will be shown that this process involves both geotechnical and hydraulic phenomena. The stability of the surface of the slope and the internal stability are studied. The theories are compared with results from a large-scale experimental programme. Results show that the propagation velocity of the breach is influenced by the permeability and that the resulting slope is gentler as the breach height increases. The breaching process can even become unstable which can lead to failure of a slope over a very large distance.

Macroscopic analysis based on the energy conservation on sea cliff erosion gives a dimensionless parameter including recession rate of the cliff, wave energy flux at the breaking point, Young’s modulus of rocks composing the cliff, and cliff height. This parameter was examined through field data on the Pukushima Coast where a series of soft rock cliffs extends about 50 km. The modulus was obtained by the measurement of the propagation velocity of elastic waves in the rocks and the energy flux was evaluated by the wave ray method. The long-term recession rate had been obtained from the aerial photographs. The recession rate is shown to be proportional to the wave energy flux and inversely proportional to Young’s modulus. These quantities prove that the dimensionless parameter has the constant value of 0.082.

The sand trapping trench for controlling wind-blown sand is proposed and general functioning, evaluation of sand trapping efficiency, process of trench development, and usage methods are descrived.

The MAST-III RTD project COAST3D started in October 1997. A consortium of 11 partners including hydraulic laboratories, universities and national regulatory authorities from five EU states (UK, Netherlands, France, Spain and Belgium) will undertake this three-and-a-half year project. The project will make field measurements of waves, currents, sediment transport and morphodynamics at two contrasting sites. The results will be used to valid existing morphodynamic computational models, and lead to coastal zone management tools.

An extension of the bedload model of Kaczmarek & Ostrowski (1996), taking account of suspended sediment, is proposed for the calculation of sediment transport features, such as the transport rate and thickness. The paper is focused on the transition region (named as a contact load layer) between the outer region (suspension layer) and the bedload layer within the proposed three-layer sediment transport model.

A computationally efficient, analytical model to determine net sediment transport rates in oscillatory flow is presented. The model is based on (approximate) analytical solutions to the IDV momentum and advection-diffusion equations and on the subsequent analytical integration of the sediment flux over time and depth. The model is validated against measurements of sediment concentrations and net transport rates performed in WL|DELFT HYDRAULICS’ Large Oscillating Water Tunnel (LOWT). Further, comparisons are made with the predictions of numerical IDV models and sediment transport formulae. The model gives accurate estimates of the net transport rates for medium sand. For finer sand, although qualitatively correct, the model fails to predict the strong offshore sediment transport rates at higher velocities, mainly due to limitations of the diffusion approach for the upward transport of sediment.

Most commonly, nearshore suspended sediment time series are characterized by distinct high concentration events. These events are coherent structures which should have lengths scales that are dependent on the length scale of the near bed turbulence. Possible generation mechanisms for coherent turbulent structures include bed shear, vortex shedding from bed forms, shear instabilities of oscillatory boundary layers, and surficial wave breaking. For turbulence mechanisms other than wave breaking, the characteristic length scale should be governed by the thickness of the bottom boundary layer. The objective of this investigation is to characterize the observed vertical length scales of suspended sediment plumes over the course of a single evolving storm and to compare these length scale estimates with the thickness of the displacement WBBL.

Field observations were made at Queensland Beach on the east coast of Nova Scotia in 1995. This steep planar beach faces a restricted opening, with incoming waves approaching normal to the shore and has a 1 m tidal range. The instruments were located in an intermediate water depth of 3.2 m where the median grain size was 0.02 cm. Sediment suspension was measured with a 2.25 MHz acoustic sounder looking downward and the bed geometry was measure with a rotary sonar.

Over the course of a relatively short lived storm event within a 24 hour period, the wave height ranged from .35 m to 1.4 m and the bed geometry underwent multiple transitions. During this event, the sediment suspension observations showed that while the the relatively infrequent large suspension events increase with increasing storm intensity, the mean suspension event length scale shows little variability. The suspended sediment length scales were compared with an estimate of the displacement thickness of the wave bottom boundary layer. Although the two estimates showed an order of magnitude agreement, the displacement thickness estimates increased slightly with increasing storm intensity. The rms deviation between the estimated boundary layer thickness and the mean length scale of the suspended sediment vertical excursion was 1.2 cm.

Near-bottom sediment suspension reacts to non-breaking random wave-induced velocity field showing a pulsating structure (high concentration discrete events) lagged with respect to the actual velocity field. A coefficient of variation, GF_Cfib, has been applied to low pass filtered concentration time series to characterise these pulses. The use of simple parameters based on the actual velocity field such as the shear stress (e.g. using the velocity squared) is not enough to fully explain the sediment response. To take into account the apparent relationship between groups and sediment pulses, several parameters characterising groupiness have been analysed: (i) the groupiness factor, GF, derived from SIWKEH; (ii) the mean run length, j₁, and mean total run, j₂, based on the use of the envelope; and (iii) the spectral correlation coefficient between successive waves, ρ. The best predictor for the pulsating structure of the sediment response was found to be GF, with a linear relationship for similar energetic wave states (u_*,rms/u_*,cr)² > 1), i.e. the larger the GF is, the larger GF_Cfil the will be. When the time lag in the sediment response is analysed, the parameters retaining information about the temporal structure of the groups such as j₁ or ρ are the only able to predict it. Thus, a linear relationship was found between the time lag and the mean run length and ρ, i.e. the longer the group is, the longer the lag in the sediment response will be.

Observations of vertical sediment flux and velocity structure are made under prototype scale waves in the Wave Research Flume at the National Research Council (NRC) in Ottawa. Observations were made under regular waves of 3.5 s period with heights ranging from 20 to 70 cm. Direct measurement of sediment flux is made possible using 1.1 MHz pulse-to-pulse coherent sonar which determines concentration from acoustic backscatter levels and velocity using acoustic Doppler. Operating over a 0.8 m range, velocity profiles with 1.4 cm range resolution and a 0.5 cm s^-1 vertical velocity accuracy can be made at a rate of 30 profiles per second. We find that there is an apparent balance between the mean downward flux of sediment and the upward flux due to turbulent motions. The component of (upward) vertical flux caused by wave action is small compared to the turbulent and mean components. Profiles of turbulence intensity are provided by the vertical velocity fluctuations, these profiles show a rapid rise to a peak value within 5 cm of the bottom and then a subsequent decrease. The (near bottom) peak value of root-mean-square vertical velocity fluctuations are equal to the friction velocity characteristic of the bottom boundary layer. The decrease in turbulence with height above the bottom, shows behavior consistent with the decrease in grid generated turbulence but appears sensitive to the length scales of the bed-forms rather than sand grain roughness.

Motivated by recent experimental results on wave, current and combined wave-current flows over an artificially rippled bed, the boundary resistance experienced by waves over two-dimensional bottom roughness elements is formulated in terms of a drag law. The resulting empirical relationship for the drag coefficient suggests a flow resistance that is similar in nature to one obtained from a constant, pseudo-laminar eddy viscosity model for the wave boundary layer flow. Analysis of available experimental data on energy dissipation for oscillatory flow over movable rippled beds leads to a constant eddy viscosity model for wave boundary layers above naturally rippled beds. The constant eddy viscosity model is modified to include a near-bottom linear transition to make it zero at the bed. This hybrid eddy viscosity model is shown to capture the essential features of wave boundary layer flows for the full range of bottom roughnesses encountered, i.e. from sand grains to ripples. Application of the hybrid model requires knowledge of the equivalent bottom roughness for which empirical expressions are derived. The implication of the results, obtained here for waves, for combined wavecurrent boundary layer flows suggests modifications of the Grant-Madsen model that greatly improve this model's ability to predict observed current velocity profiles over rippled bottoms in the presence of waves.

A shear plate has been developed to obtain direct measurements of bottom shear stress under non-breaking surface gravity waves on a movable sand bed. The shear plate provides a direct measurement of the bottom shear stress on a sand bend under complex flow conditions particularly over bottom roughnesses. It was designed for use under laboratory oscillatory flow conditions where the periods of motion range from 1.5 to 6 seconds and the range of shear forces are from 0.08 Nm^-2 to 84 Nm^-2. The spatially averaged bottom shear stress was determined and the quadratic drag law was used to convert measurements of bottom shear stress to values of wave friction factor. The apparent roughness of the bed was specified usingfour times the sum of the mean and standard deviation of the sediment profile on the shear plate. Values of wave friction factor compared well with both theory and data obtained through previous laboratory studies.

This paper evaluates a number of widely used predictive transport equations and the use of tracers and GPS in the measurement of longshore transport for the validation of such equations. It also addresses the inconsistencies which can sometimes be introduced as a result of these techniques. The analysis shows that most of the equations examined tend to over-predict the expected transport by a factor of 1.5 to 4. The use of tracers on macro-tidal coarse grained beaches is found to be a viable method for obtaining reliable transport rate measurements of which the confidence levels are expected to increase as present day calculation techniques are adapted for use on macro-tidal shingle and mixed beaches. DGPS appears to be an economical way of data collection but needs to be used with the highest possible accuracy level settings if it is to be used in quantifiable sediment transport calculations.

Motions of pebbles on an artificial pebble beach were measured by tracking tracers. After the beach profile reached equilibrium, pebbles moved mainly in the longshore direction parallel to the shore line under the condition of oblique wave incidence. Intensive motions of pebbles were observed in the swash zone and the maximum displacement reached 30m during one week. The authors proposed a numerical procedure for analyzing pebble motion. The motion of pebble up to the maximum wave set-up point can be predicted numerically when the time and spatial variation of water particle velocity and fluid force on pebbles are given.

This paper describes the latest revision of the Queen's University coastal morphology model ONELINE. The model provides practical and reliable full, timedependent simulations of shoreline change for coasts controlled by structures and complex boundary conditions. ONELINE calculates shoreline change due to longshore sediment differentials as well as on-offshore sediment movements. Model tests and case studies from around the world were conducted to test ONELINE's capabilities. Two case studies for Sea Isle City beach, New Jersey, and along the Nile Delta Coast in Egypt are discussed in this paper. Results are compared with observed field measurements to examine the model capabilities.

An algorithm for representing seasonal variations in shoreline position as caused by on-offshore sediment transport in a one-line model is presented. The study was based on an analysis of an 11-year long time series of waves and shoreline location obtained at Duck, North Carolina. Two different approaches were used: one was based on wave steepness and dimensionlessfa.il speed and the other on ratio of the maximum near-bottom orbital velocity to the critical velocity required to initiate sediment movement. Both applications showed that it is possible to reproduce the overall spatial and temporal behavior of seasonal cross-shore transport related shoreline variation using two simple one-line model compatible approaches. Preliminary calculations show that the method may be used for analyzing the seasonal behavior of a beach. At the same time, the impact of individual storms are not represented to any significant degree.

The measurement, monitoring and modelling of the impacts of a major sedimentary discharge to the highly dynamic coastline of southern Namibia is described. Some 27 million m³ of sediment will be discharged over a 5 year period as a result ofa novel diamond mining technique employing an inland dredger. The study demonstrates that mathematical modelling, supported by comprehensive monitoring information, constitutes an important tool for mining optimization and impact prediction and management.

It is shown that the two-dimensional flow field and the bottom configuration induced by a wave of small amplitude normally approaching a straigth beach may be unstable with respect to infinitesimal perturbations. The time development of the bottom perturbation leads to the formation of crescentic forms periodic in the longshore direction. The growth of the perturbation is due to a positive feedback mechanism, involving the incoming wave, synchronous edge waves and the bedforms. In particular the growth is related to the presence of steady currents caused by the interaction of the incoming wave with synchronous edge waves which in turn are excited by the incoming wave moving over the wavy bed. For natural beaches the model predicts two maxima in the amplification rate; the former is related to incoming waves of low-frequency, the latter to wind waves. Thus two bedforms of different wavelengths can coexist in the nearshore region, the longshore spacing of which is few hundreds and few decades of metres respectively. To illustrate the potential validity of the model, its results are compared with field data.

Simple theoretical models are presented to calculate the equilibrium profile shape under breaking and non-breaking waves. For the case of breaking waves the seaward transport in the undertow at equilibrium is locally balanced by a net vertical sedimentation so that no bottom changes occur. The parameterization of the water and sediment flux in the surf zone yields a power curve for the equilibrium profile with a power of 2/3. Three different models are developed to derive the profile shape under non-breaking waves, namely (1) a variational formulation where the wave energy dissipation in the bottom boundary layer is minimized over the part of the profile affected by non-breaking waves, (2) an integration of a small-scale sediment transport formula over a wave period where the slope conditions that yield zero net transport determine equilibrium, and (3) a conceptual formulation of mechanisms for onshore and offshore sediment transport where a balance between the mechanisms defines equilibrium conditions. All three models produce equilibrium profile shapes of power-type with the power typically in the range 0.15-0.30. Comparisons with laboratory and field data support the results obtained indicating different powers for the equilibrium profile shape in the surf zone and offshore zone.

The results of two sediment transport models based ore the sheet flow approach and the energetics approach are compared with experimental data of random waves over fine sand beaches in equilibrium in a wave flume. Two tests were conducted with a terraced profile (test 1) and a barred profile (test 2). The energetics-based model predicts the equilibrium profile better than the sheet flow model for both tests. However, the energetics model predicts offshore sediment transport and bar migration, whereas the sheet flow model predicts onshore sediment transport and bar migration. These models cannot predict zero net sediment transport rate on these equilibrium profiles with negligible profile changes, whereas the standard equilibrium profile cannot explain the existence of the terrace and bar.

The formulation ofIsobe and Horikawa (1982) is modified and adaptedfor use in a probabilistic cross-shore transport model (CROSMOR). Computed changes of wave height, peak near-bed orbital velocity and depth-averaged return flow are compared to laboratory measurements. A comparison is made between computed and measured bedprofile changesfor a large scale laboratory experiment.

A monitoring programme has been established for the 351km of the UK Southern North Sea Coast (between the Humber and Thames estuaries). This has produced over 3300 beach profiles captured to a clear specification at 1km intervals in summer and winter since 1991. The analysis of this data has been previously linked to specific flood defence and coastal protection engineering schemes. The first analysis on a region wide basis has now been undertaken to provide some strategic insight into how the coast is evolving on an Integrated Scale. The analysis provides quantification of the change at the coast, and demonstrates that simple analytical tools combined with geomorphological interpretation can provide meaningful information for coastal management.

We quantified the strengths and weaknesses of two sources of morphologic data available from Duck, NC, utilizing an objective definition of nearshore morphology (Gaussian curves added to a plane slope). Directly surveyed bathymetry provided the most complete estimate of the morphologic state of the nearshore bathymetry. That is, all of the parameters of the morphologic model could be estimated from these data. Oblique video images were used to estimate the position of inner bars. This information represented only a subset of the morphologic parameters defined in the morphologic model. However, the image data were collected frequently (daily) and, thus, resolved a wide range of temporal scales. Bar crest positions estimated from the video images were well correlated with estimates extracted from the bathymetric surveys (R² = 0.8). Differences between the two estimates of bar position depended on both wave height and on the bar amplitude.

A time-averaged model is developed to predict the cross-shore variations of the mean and standard deviation of the free surface elevation from outside the surf zone to the lower swash zone on beaches. This new model includes nonlinear correction terms in the cross-shore radiation stress and energy flux that become important in very shallow water. Empirical formulas are proposed for the skewness and kurtosis as well as the ratio of the root-mean-square wave height to the mean water depth which increases rapidly near the still water shoreline. The developed model is shown to be in agreement with three irregular wave tests on a 1:16 smooth impermeable slope and two tests of quasi-equilibrium terraced and barred beaches. The model can predict the observed large increase of wave setup near the still water shoreline. The developed model and empirical formulas will need to be verified using additional experiments.

Observations offoreshore morphologic change and swash flow velocities were made at Duck, NC in an effort to estimate cross-shore sediment flux magnitudes. The three-dimensional foreshore surface over an approximately 10 x 20m study area was determined repeatedly to roughly centimeter accuracy using a stereometric video method. Sediment flux magnitudes derived from the temporal gradient of these data showed erosion rates of over 25 cm/hr. Near-bed, cross-shore swash velocities were measured at multiple cross-shore locations using a separate video technique. Swash velocities estimated using this method were found to be consistent with current measurements obtained using acoustic Doppler and ducted impeller current meters. The swash zone profile observations and velocity estimates were used to test an energetics-based total load sediment transport model. Although the trends of both the model and the observations were qualitatively consistent, the magnitudes and positioning of observed sediment fluxes did not match the transport model predictions. This discrepancy implies that other factors, such as water depth variations, infiltration, or sediment advection, may be important.

This paper describes field measurements of near-surface hydraulic gradients within a sandy beach during individual swash cycles. We show several different types of behaviour which may have implications for swash zone sediment transport: (1) measurements of swash depth; (2) ‘unloading’ events with large upward-acting hydraulic gradients; (3) infiltration events with smaller downward-acting hydraulic gradients; (4) situations where the probes lower in the bed measure significantly lower heads than the probe at the surface, leading to strongly downward-acting hydraulic gradients; and (5) measurements in the capillary fringe. Large hydraulic gradients, which are more than sufficient to induce fluidisation, occur in the top 15 mm of the bed under swash and backwash. These large hydraulic gradients, which occur only in the very top section of the bed, may coincide with a significant depth of water (up to 40 mm), which suggests the potential for entrainment of the fluidised bed under backwash.

In order to understand the external and internal flow structures of broken waves on a sloping bottom, a special design of run-up gauge combined with LDV measuring system is used to detect the velocity fields of run-up and run-down in our experiments. According to the experimental results, it is found that the heights of run-up and run-down are mainly determined by incident wave steepness. The dimensionless heights of run-up, run-down and the related swash length for different wave breakers are also discussed respectively. In addition, the elaborate measurements of flow structures, turbulent intensity and Reynolds stress in swash zone are also analyzed in this paper.

Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1^st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2^nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.

A morphodynamic model is developed and analyzed to gain fundamental understanding on the basic physical mechanisms responsible for the characteristics of shoreface-connected sand ridges observed in some coastal seas. These alongshore rhythmic bedforms have a horizontal length-scale of order 10 km. It is found that the positive feedback between the topographic disturbances of a sloping bottom and the subsequent deflection of the mean coastal current is the main cause of the ridges. To be effective, this mechanism needs an averaged sediment transport mainly due to wave stirring during storms and an averaged current driven by pressure gradients rather than surface stresses. Even in the presence of significant tidal currents, their origin — related to the mean current instead of tidal oscillation — is essentialy different from that of tidal sand banks.

In this work we describe preliminary results from a newly developed aerial video system which can be used to rapidly (2-4 hours) and accurately (5 m resolution) sample the horizontal scales of sand bar morphology over several hundred km's of coastline. Observations from, for example, the North Carolina coastline on the central eastern seaboard of the U. S., indicate marked changes in the alongshore morphological patterns, which can be cyclic with lengths scales of 5-10 km's along one stretch of coast but adjacently the bars can be absent altogether. Other observations from the lower sloping west coast beaches of the U. S. Pacific Northwest show highly complex sand bar morphology which also exhibit marked alongshore variability. Along this coast the beach systems are not continuous and are separated by large headlands, and the morphology at any particular beach behaves independently from the bar morphology in adjacent compartments.

The temporal evolution of nearshore bar topography forced by incident, wind-generated waves is predicted by a two-dimensional (2D) model. Predictions are compared with observed bathymetry from Duck, North Carolina, USA, acquired by the Field Research Facility (FRF) of the US Corps of Engineers over a period of 17 years (1980 — 1997). The model simulations presented are seen to approximate well the formation of the most frequently-observed shore-parallel bars at Duck as well as dynamic changes in their pattern caused by storm waves and varying mean water level.

The closure concept is a fundamental cross-shore boundary condition for morphodynamics and other applications such as beach nourishment and sediment budgets. This paper examines closure at a range of scales, particularly from events up to years. At these scales, closure is primarily a function of direct external forcing (cross-shore redistribution of sediment by waves), indirect external forcing (sediment loss/gain by littoral transport and the resulting profile translation) and internal system dynamics (bar dynamics). Therefore, simple wave-based models such as Hallermeier (1981) cannot be expected to predict the actual closure, although they can predict distributional properties such as the limit. A general approach to develop more userorientated estimates of closure over a range of timescales is outlined based on equilibrium theory. This will include a user-defined depth change criterion as a function of timescale.

Morphological changes at the shoreface of the Ebro delta have been analysed with emphasis on the Trabucador barrier, using two types of approximations: (i) an aggregated-scale approach, i.e. by evaluating the depth of closure from comparison of beach profiles from a data set of 4 years and, (ii) a process-oriented one, where changes are analysed in terms of driving factors and resulting sediment transport from a small scale experiment. Results from the depth of closure analysis show that acting processes are restricted down to an average depth of 6.5 m, with an important spatial variability. A year with high energy contents gives same results than using the whole data set. A sedimentation of about 7 cm was detected during the small scale experiment at 8.5 m and 12.5 m depth under the passage of several storms. The analysed velocity field and sediment flux showed that onshore transport close to the bottom and offshore transport in the upper part prevailed under storms. These forcing conditions were similar to the registered in previous analysis although no morphological changes were previously detected. Results show that the depth of closure analysis is a good starter point to define morphological activity in the nearshore profile, but it has to be complemented with other type of approaches such us the process-oriented one to accurately define the limits for morphological activity.

Depth of closure has been identified and its characteristics investigated over larger temporal ( ≥ 25 years) and spatial ( < 100 kilometres) scales than previous research. In addition to the 'normal' shoreward closure produced by breaking waves and crossshore bar migration, at longer timescales ( ≥ 10 years) shoreface morphodynamics also produce significant profile changes. The shoreward closure is primarily controlled by wave breaking with a secondary control of bar morphodynamics. Shoreface changes are slow and steady and as timescale increases, so more profiles exhibit re-opening in depths typically greater than 10 metres. This is then usually followed by the re-closure of the profile on the middle/lower shoreface. Such phenomena have not been observed in past studies of this type and result from the large temporal and spatial extent of the data set used here. Over long time scales (≥ 10 years) such changes have a coastal engineering significance.

A method of analysis of depth of closure and bed variability is presented in the study. Statistical analysis of measurements showed standardized depths are gaussian random variables Repetitive measurements revealed peaked patterns of standard deviation of depth change and range between extreme measurements. They were approximated by a smooth functional type inform of a sum of exponential curves. The peaks were then associated with both the corresponding time scales and locations of bed features. The patterns can thus be used to identify segments of beach profiles controlled by events typical of given time scales The tail of the outermost peak was extrapolated to evaluate decadal depth of closure.

A 2D-horizontal sediment transport energetics model is developed in this work for the evaluation of the wave-induced sediment transport. The time dependent energy equation is incorporated into a nonlinear dispersive wave model in order to simulate breaking wave propagation in the surf zone. Total immersed weight transport is related, through an energetics approach, to the total dissipated fluid power. Both the dissipation due to bed friction and, inside the surf zone, due to the wave breaking are considered. The methodology is applied to predict the longshore transport rate and to simulate the coastline evolution in beach nourishment scenario assuming a trapezoidal beachfill.

Longshore sediment transport (LST) is ofprimary importance to long-term shoreline changes and must be accounted for in most coastal designs. Predicting LST has been hampered by the lack of direct measurements during storm conditions against which the models can be calibrated. The Sensor Insertion System (SIS) developed at the US Army Corps of Engineers (USACE) Field Research Facility provides a way to directly measure LST during storms. The SIS was operated during the growth, peak, and waning stages of three storms between April, 1997 and February, 1998 in which the waves reached a maximum individual height of 5.6m. In up to 14 cross-shore locations, concentration and velocity measurements were made throughout the water column. These measurements were compared to total transport models of USACE 1984, Kamphius 1991, Kraus, et al. 1988, Walton 1980, and the cross-shore distribution model of Bodge and Dean 1987. The results show the storm measurements had a consistent pattern; rapidly increasing to a peak rate, then gradually decreasing during the waning stages of each storm. Cross-shore distributions of longshore flux tended to peak over the offshore bar and at the beach where wave dissipation caused high suspended sediment concentrations. These peaks were not co-located with maximum longshore currents, which tended to peak at mid-surf. The comparisons show that the models would benefit from comparison to the storm measurements.

A model is presentedfor the dynamics ofthe mobile layer ofsediment on the sea bed under sheetflow conditions. The Karman-Polhausen method is used to determine the thickness ofthe mobile layer, the scalingfor velocity phase and amplitude, and the phase lead ofthe velocity at the bottom ofthe mobile layer. The model does not make use ofconstitutive equations such as those suggested by Bagnold (1956). Agreement between the predictions ofthe model and existing laboratory measurements is good.

This paper presents a numerical investigation of sediment transport under the combined effect ofwaves and current motion. Comparison of predictions to experimental measurements showed good agreement. The presence of a second peak over the decelerating andflow reversal was predicted by the numerical model due to the inclusion ofan extended bed reference concentration and a turbulence model that is able to predict a sudden increase of the turbulent properties of the flow over this stage. Evidence suggests that the second peak is caused by an inflection point in the velocity profile leading to high diffusivities near the wall.

The paper presents the results of a study dealing with the inclusion of wave randomness into a beach deformation and a sand transport model developed for the regular wave input. The effect of wave irregularity is considered by employing the significant wave characteristics method and a joint distribution of wave heights and wave periods. The theoretical framework and the practical method for obtaining the joint distribution together with its application procedure are presented. The validity of the random wave approach modelling is verified by applying it for two different models: a time-averaged beach deformation model and a time-dependent sand transport model. The time-averaged model is capable of computing the beach deformation profiles while the time-dependent turbulent sand transport model is capable of computing the total sand transport rate over the entire surf zone. The simulation results for both numerical models are compared with laboratory data in order to verify, analyze and discuss the validity of the random wave approach as presented.

Details are given herein of the development and application of a three dimensional layer integrated numerical model to predict geomorphological changes in estuarine and coastal waters. An Alternating Direction Implicit finite difference scheme has been usedfor solving the governing differential equations, which include the conservation of mass and momentum for flow, the transport equation for suspended sediment fluxes and mass conservation for bed level changes. Model predictions, have been compared to predictions using other existing models and against laboratory measurements. A series of experiments have been carried out for a laboratory model harbour, with the modelpredictions being compared to laboratory measurements.

Recentfield and laboratory research indicates the potential importance of complex wave spectra (combining swell and wind sea) in the design ofgravel beach recharge schemes. The paper discusses the research and introduces a swell wave atlas as an aid to understanding the occurrence probability ofcomplex wave conditions around England and Wales.

The nourishment of beaches is an environmentally friendly method of shore protection but the annual sand requirement may lead to substantial expenditure. Therefore the annual sand demand should be minimized. Factors which affect the sand demand along a sandy coastline in order retain the shoreline at a given position will be discussed. A wide normally dry beach on which waves can dissipate their energy at raised water levels without substantial reshaping of the underwater profile is desirable. Where such a beach cannot be created measures have to be taken to minimize sand losses from dunes during extreme events into the everyday surf zone. Furthermore the sand requirement for an open sand system, like the Island Sylt/North Sea, can be obtained by a reduction of the amount of sand from longshore transport which is carried over the ends of the island and is lost from the system.

The beach fill situation in five European countries is highlighted and discussed with respect to the general situation, project type and objectives, design and evaluation procedures, legal framework, and financial aspects. As expected, significant differences were found between the investigated countries. In general, the study shows that it would be very profitable for south European countries to learn about the Dutch and German practices, particularly regarding the long-term coastal management and the regular monitoring of the coastal morphology. On the other hand, recent Dutch experience has shown that their legal system is a bit too rigid leading to automatic local renourishments that are unnecessary to reach the global objective.

Since 1982, large-scale coastal protection works have taken place on the Danish North Sea coast. The subject of the first part ofthis paper is the coastal protection policy, the engineering approaches to erosion and flood control and the results achieved. An important tool for coastal protection has always been and still is nourishment. In the second part of the paper, the effect of the nourishment will be evaluated with focus on the positioning of the nourishment in the profile and on the use of coarse materials.

First results about the behaviour of the nourishment done at Zurriola beach, Vase Country, Spain, have been obtained, by means of the data acquired during 2 years monitoring. The general conclusion appoint to a good agreement with the previous physical model results: in spite of a small percentage of sand is lost, the beach is “self kept”. A rough evaluation of losses has been done, helping us to predict the future maintenance to do. The topography and bathymetry of the beach do not help to a easy modelling by means of mathematical models.

After having shortly discussed about the nourishment fundamentals, focussing the attention on the benefits and on the factors promoting the beach fills, some specific questions on fill design, on related processes and on the temporal aspects of such beachprotecting intervention were addressed and tentatively answered.

In the second part, the physical-model tool, as a way for answering to the suggested questions is presented and three different case studies are discussed.

Depth ofclosure is studied on a nourished beach in the light ofits autonomous behaviour over long temporal and large spatial scales. Long term data show that depth ofclosure is variable alongshore, being shallower to the west and deeper to the east. Following placement of a shore nourishment along the middle section of the coast, the spatial variation ofdepth ofclosure changes. Initially the depth ofclosure is shallowest where the fill was placed. With time after the placement of the fill, this effect diminishes. Depth of closure observed in this study is influenced by bar behaviour. The fill material affects the observed depths of closure by reducing offshore bar migration. Maximum depths of closure for any particular timescale observed in this study are well predicted by the Hallermeier (1981) formulation for the depth limit to the active profile. In conclusion, pre-flll observations and Hallermeier (1981) provide a useful limit to the observed post-fill depth of closure. Similar analysis ofother beach nourishmentprojects would be useful.

The behavior of Oregon Inlet, located north of Cape Hatteras, North Carolina, on the Pamlico Sound estuary, and its commercial, ecological, and recreational importance have been the subject of much study and controversy. The construction of a terminal groin on the southern shoulder of the inlet in 1990 served to heighten this interest. Both the U.S. Army Corps of Engineers (USACE) and the NC Department of Transportation (NCDOT) have maintained monitoring programs since that time to study the impact of the terminal groin on the morphology of the inlet and the adjacent shorelines. This paper utilizes data from the USACE and NCDOT programs to examine the relationship between the growth of the Bodie Island spit and the resulting bathymetric changes in the inlet. Data collected are compared with results from the literature.

The morphology of Oregon Inlet exhibited changes expected with the stabilization of a single shoulder of a tidal inlet. In contrast, the cross-sectional area of the channel at the minimum inlet width changed little. When analyzed in light of empirical equilibrium conditions reported in the literature, the results supported the conclusion that the inlet had achieved a new equilibrium configuration due to the presence of the terminal groin.

A predictive model of the three-dimensional development and deformation of a river mouth delta is developed. This model enables the prediction of not only the shoreline change but also the three-dimensional, long-term topographic changes around a river mouth, and offshore sand transport can be taken into account when the sea bottom slope exceeds a critical value given by the angle of repose of sand. Numerical simulation of three cases of initial beach slopes is carried out and compared. The calculated and actual beach changes measured around the Fuji and Tenryu River mouths are compared. It is concluded that calculated results can reproduce real phenomena measured around river mouths qualitatively.

The Fuji coast in Japan is one of the beach which is suffering from coastal erosion. One reason for erosion is seemed to be the offshore sediment transport through the submarine canyon in front of eroded area. The present paper concerns the field investigation in order to confirm the sediment transport into the submarine canyon with two new type tracers. One tracer is the artificial sand and gravel made of the hard plastic. The other is the tracer with an ultrasonic transmitter. These tracers are very effective for tracking the sediment.

The Perth metropolitan coastline is characterised by one of the strongest and most consistent sea breeze systems in the world. In contrast to the ‘classic’ sea breeze system, characterised by sea breezes blowing in the onshore direction, the sea breeze in Perth blows in a predominantly alongshore direction. Each year, around 200 sea breezes are experienced with an average wind speed of 5.7 m/s. Sea breezes in summer are stronger and more persistent than in winter. The importance of the sea breeze is clearly indicated by wind spectra showing significant spectral peaks at the diurnal frequency. The sea breeze system directly forces the incident wave field and induces a diurnal cycle of nearshore change by causing: (1) an increase in wave height; (2) a decrease in wave period; (3) an intensification of the nearshore currents; and (4) an increase in suspended sediment levels and suspended sediment transport. In addition, the seasonal variation in sea breeze activity, with frequent and strong sea breezes in summer and infrequent and weaker sea breezes in winter, is responsible for a seasonal change in the littoral drift direction. In summer, longshore sediment transport is towards the north and causes beaches located south of structures or headlands to widen considerably. In winter, when littoral drift is towards the south due to northwesterly storms, beaches located north of structures or headlands will become wider. It is further demonstrated that strong sea breeze activity is common along the entire Western Australian coastline, implying that the results obtained for the Perth metropolitan coastline can be applied to some extent to the entire state.

A distinct propagation of erosion and accretion waves was discovered along the Shizuoka and Shimizu coasts facing Suruga Bay in Japan. Their propagation velocities were 270m/yr and 250m/yr. "Hagoromo-no-matsu", a scenic beach famous in Japan, where, along the shoreline, people can see Mt. Fuji in the distance, sandy beaches and pine trees, will be eroded in two years, whereas it takes 30 years for longshore sand supply to reach this beach. Countermeasures must be taken, without relying on natural sand supply from the upcoast by longshore sand transport which will take for at least 30 years. Severe beach erosion began at the time of large-scale river bed excavation conducted before 1967 in the Abe River which is the source of littoral sand, and beach erosion has a propagation mode of erosion waves. Measures combining the construction of headlands to stabilize the natural sandy beach with beach nourishment should be taken immediately.

This paper describes the development of a solution to a large scale, long term erosion process along the Atlantic coast of eastern Ghana in West Africa. The understanding of the erosion process was developed through a combination ofgeomorphic investigations and numerical and physical modeling of coastal processes. Key aspects of the investigations are described in this paper. The performance of the adopted sea defence system, consisting of rubblemound structures and beach nourishment, was evaluated using the GENESIS and COSMOS numerical models ofshoreline change. The numerical models were also used to modify the sea defence system such that an acceptable level of downdrift impact was confined within the study area.

A simple morphological based index to determine beach vulnerability is proposed in this paper. The presented morphological vulnerability index (I_v) relates maximum annual volumetric difference and average beach volume for each particular site. High index values are representative of coastlines vulnerable to erosion.

After the index application to 15 Portuguese sites it was possible to determine empirical threshold values, defining limits between beach stages. Based on these limits the beaches can be classified as: robust beaches, for I_v < 0.35; fragile beaches, for 0.35 < I_v ≤ 0.9; and extremelyfragile beaches, for I_v > 0.9. The index validation tests against field observations and recent shoreline evolution gave good results, indicating that the I_v has a strong potential application to characterise medium to long-term beach evolution.

In this paper, the problem of (in)homogeneous data in coastal engineering applications is studied. Statistical analysis of coastal engineering data such as flood data, wind data, wave height data, etc., is essentially a problem of information scarcity. Records are usually too short to ensure reliable estimates of low exceedance probability quantiles in many practical problems. Determination of quantiles is needed for the design, construction and operation of hydraulic structures, insurance studies and protection of populated areas. To perform a frequency analysis of data from coastal engineering practice, the data first has to be tested for homogeneity. Non-homogeneous data may lead to wrong quantiles. A homogeneity test must be able to separate data sets that do not come from the same distribution. In this paper statistical and physical-based homogeneity tests will be presented.

A method is presented to obtain a first estimate of long-term bathymetric changes based on an initial transport field obtained from a 2DH process model. The results are compared with full morphodynamic simulations and measured bottom developments after extension of the harbour moles at Umuiden, the Netherlands.

A beach morphology monitoring program was initiated in the Columbia River littoral cell along the coasts of Oregon and Washington, USA, during the summer of 1997. The field program is designed to document short- to medium-term morphologic variability of the highenergy dissipative beaches within the littoral cell over a variety of spatial scales. Following the installation of a dense network of geodetic control monuments, a nested sampling scheme of cross-shore beach profiling, 3-dimensional beach surface mapping and shoreline reference feature surveying was devised. Monitoring is being conducted using RTK DGPS survey methods that combine both high accuracy and speed of measurement. Sampling methods resolve alongshore length scales of O(100 m) to O(100 km) and cross-shore length scales of O(1 m) to O(1 km). Long-term beach profile evolution, estimated via a comparison with surveys collected in the 1940s, feature regional variability. Some beach profiles revealed remarkably little change over the last 50 years. Although this study is in its infancy, large signals in both forcing and response have yielded exciting results. During the 1997/1998 winter, the littoral cell was influenced by one of the most significant El Niño events on record. Steeper than typical southerly wave angles forced alongshore sediment transport gradients that were evident in seasonal morphology on a regional scale. The morphologic data from the monitoring program are being integrated with other geophysical data sets to develop a conceptual model of the region and to begin shoreline change modeling to predict coastal evolution at a management scale (ie., decades and tens of kilometers). The magnitudes of both the environmental forcing and morphologic variability of the beaches along the Columbia River littoral cell are greater than the better understood, lower energy and more reflective beaches of, for example, Duck, North Carolina and the central Dutch coast (Holland). These differences in scale raise questions regarding the validity of directly applying morphologic change models developed from these coasts to the Columbia River littoral cell.

Tidal basins with a length of the order of 1/4 of a wave length of the dominant tide, susceptible to resonance, occur on many sites on the world. This paper will show, that these basins can become morphologically unstable. The most primitive schematization possible has been investigated: a prismatic channel, closed at one end. Under some circumstances (for which dimensionless criteria are given), small increments in depth intensify the vertical tidal amplitude at the landward side of the basin, which in turn triggers increased erosion of the basin. Knowledge on this subject can lead to redirect sand fluxes in the basin by taking small measures just in time. Starting from the assumption of a power-law sand transport formula, it is found, that for prismatic channels, morphodynamic instabilities occur when a small increment dh of depth generates a larger value² of Z₀/h, where Z₀ is the amplitude of the vertical tide at the landward end of the channel. This criterium can be translated in relative length of the basin and in bottom roughness (fig.2).

This paper introduces a process-based model for calculating the equilibrium cross-sectional area of a tidal inlet and temporal behavior of small perturbations in channel area from equilibrium. The model accounts for the dynamic balance between inlet ebb-tidal transport and longshore sand transport at the inlet entrance. Expressed in terms of a water discharge through the inlet and the gross longshore sand transport rate, the formulation can account for tidal, river, and wind-driven flows. The resultant predictive equation recovers the form of the well-known empirical formula A_E = CPⁿ, where A_E is the equilibrium (minimum) cross-sectional area, P is the tidal prism, and C and n are empirical coefficients. An explicit expression is obtained for C in terms of coastal sediment-transport processes, and the value of n derived is in the range found empirically. The process-based model qualitatively predicts the difference in trends in inlet crosssectional area on wave-sheltered and fully-exposed coasts. In time-dependent mode, the model reproduces qualitative behavior of the departure of the crosssectional area from equilibrium under perturbations in the driving forces of discharge and waves.

Hornafjordur is a tidal entrance on the south-east coast of Iceland, a shore with a heavy littoral drift. An extreme storm hit the coast in January 1990. It caused large shoaling to encroach upon the entrance channel from both sides, and a breakthrough occurred between the rock headland Hvanney and the South Barrier. The inlet was closed for several weeks.

A rubble mound shore protection was built on its west side in 1991 to restore the South Barrier. A curved breakwater of berm type was constructed during the summer 1995. Due to severe wave action and strong current a berm structure with toe protection was chosen.

The paper presents the experiences gained on the tidal inlet based on hydrodynamic and hydraulic models, both calibrated to the field data.

The navigation channel of Navia is designed applying a long-term evolution model oftidal inlets. Navia is a port located on the North coast ofSpain, and accessed by a narrow inlet, influenced by strong tidal currents, waves and a variable morphology. To define the design depth, the most important oceanographic processes are included in a probabilistic approach. The model allows comparing different scenarios, according to jetties length and maintenance dredging. In this way, optimum design represents a balance between capital costs and maintenance requirements. The long-term evolution model turns out to be an efficient tool for navigation channel design, and a must for optimum design.

The deepening of estuarine waterways enforces essential changes of mean tidal water level peaks and range. Legal requirements askfor their determination by preservation of evidence. A method has been established to evaluate these effects quantitatively by statistical tools for each measure, even in the case ofsubsequent deepenings.

Two tidal inlets with strikingly different physical characteristics have been investigated through an analysis of multi-year beach survey results and field investigations of the nearshore wave and current structure adjacent to the inlets. The survey results indicate that the downdrift shoreline adjacent to both inlets is dominated by persistent inlet directed currents, which run counter to the net sediment transport direction. The two wave and current studies differed in both their spatial and temporal resolution, requiring the use of separate analysis techniques to determine the forcing mechanisms responsible for the observed inlet directed currents. The two analysis techniques produced similar results which indicate that tidal-induced circulation generates the persistent nearshore current structure. Episodic wind-generated currents and nonlinear wave and current interactions were found to reach the same order of magnitude as the tide-induced currents, and could either enhance or reverse the observed nearshore current structure.