Coastal Engineering 1984

Results of a WAVE-FOLLOWER EXPERIMENT are presented, in which a moving current meter entrained in the crest of a steep Stokes wave and a moving high-speed film camera follows the wave with its non-linear phase velocity. Measurements of wave particle velocities are then obtained both in non-breaking steep wave crests, and in breaking waves. The breaking waves in deep water conditions are obtained by the application of a non-linear sweep frequency modulation technique, and the Stokes wave becomes unstable due to interaction of 43 wave components focused into one single point in space and time, KJELDSEN 1982.

The result of this interaction is a large freak wave, breaking as a plunging breaker in deep water. Measured crest particle velocities obtained with the current meter exceeded the phase velocity of this wave with 36 %. Digitalisation of the high-speed film showed that particle velocities at the very tip of the plunging jet obtained the value 2.65 times the linear phase velocity. These results are then compared with predictions obtained from numerical simulations by LONGUET-HIGGINS & COKELET 1976 and VINJE & BREVIG 1980.

Breaking wave heights measured in both field and random wave laboratory experiments are examined. The dependence of breaker height and breaker depth on beach slope and deep water steepness is presented. The results are compared with the design curves of the Shore Protection Manual (SPM) and the predictions of the random wave model by Goda (1975). The comparisons indicate that the significant breaker height, based on Goda’s model, is slightly conservative for the experimental cases; but the maximum breaker heights are reasonably predicted by the model. The design procedures in the SPM are based on a monochromatic wave breaking, and appear overly conservative, particularly for low wave steepness (less than 0.01) which occur frequently on the West Coast of the United States. The use of the Rayleigh distribution to predict wave height statistics is tested with random wave data for both deep and shallow water regions.

The on-offshore and the vertical components u, w of the velocity in a surf zone on a uniformly sloping beach in a wave tank were measured simultaneously with a laser-doppler velocimeter under two conditions. The time variation of the Reynolds stress -u' w' during one wave period is discussed. The Reynolds stress behaves as that in the oscillatory pipe flow does. The magnitude of the terms including the Reynolds stress terms in the on-offshore momentum equation is estimated. The Reynolds stress terms does not play any important role in the on-offshore momentum transfer during one wave period in the surf zone.

A theoretical two-dimensional model for wave heights and set-up in a surf zone is described and compared to measurements. The integral wave properties energy flux E_f, and radiation stress S_xx are determined from crude approximations of the actual flow in surf zone waves. Some physical aspects of the outer region are discussed and found to agree with our knowledge of the waves seawards and shorewards of this region.

Measurements of surface elevations and internal velocities have been conducted in a natural surf zone. The results were used to investigate the quantitative performance of linear theory in predicting the wave kinematics from the surface elevations. It appears that linear theory systematically overpredicts the horizontal velocities by 20% in the frequency range around the peak, where the coherence with the surface motion is high, by 15% at 2 times the peak frequency, changing in an underprediction of 15% at higher frequencies. In these higher frequency ranges the rate of turbulent energy induced by breaking, contributes to the variance, so that the ratio of measured to theoretical r.m.s. fluctuation shows a trend of 25% theoretical overprediction at negligible turbulent energy rates to 5% underprediction at high turbulent energy rates. Furthermore the results were used to investigate the linear prediction of radiation stress and the effect of directionality on the radiation stress. Prediction of the radiation stress by unidirectional, linear theory gives an overestimation of 50% at negligible turbulent energy rates to 35% at high energy rates, which percentages reduce to 45% and 25% when the effect of shortcrestedness is taken into account.

Based on the observation that a shallow water breaking wave propagating over a region of uniform depth will reform and stabilize after some distance, an intuitive expression for the rate of energy dissipation is developed. Using linear wave theory and the energy balance equation, analytical solutions for monochromatic waves breaking on a flat shelf, plane slope, and "equilibrium" beach profile are presented and compared to laboratory data from Horikawa and Kuo (1966) with favorable results. Set-down/up in the mean water level, bottom friction losses, and bottom profiles of arbitrary shape are then introduced and the equations solved numerically. The model is calibrated and verified to laboratory data with very good results for wave decay for a wide range of beach slopes and incident conditions, but not so favorable for set-up. A test run on a prototype scale profile containing two bar and trough systems demonstrates the model’s ability to describe the shoaling, breaking, and wave reformation process commonly observed in nature. Bottom friction is found to play a negligible role in wave decay in the surf zone when compared to shoaling and breaking.

Initial efforts to numerically simulate surf zone waves by using a modified form of the nonlinear shallow water equations are described. Turbulence generated at the front of the moving bore-like wave spreads vertically downward to significantly alter the velocity profile and hence the horizontal momentum flux. This influence of turbulence is incorporated into the momentum balance equation through a momentum correction coefficient, α which is prescribed based in part upon the theoretical α (x) distribution beneath stationary hydraulic jumps. The numerical results show that with a suitably chosen α(x) distribution, the equations not only dissipate energy as the waves propagate, but also that the wave shape stabilizes as a realistic profile rather than progressively steepening as when the nonlinear shallow water equations are employed. Further research is needed to theoretically determine the appropriate α(x,t) distribution.

The objective of this paper is to propose a new approach based on the direction of the typhoon track for determing the probability of occurrence of extremal tides due to storm surges, as well as their return period. The study includes the effects of periods in tidal data and of tidal variation stemming from extensive reclamation along coasts on the fitness of the extremal data to probability density functions. The method is justified by application to an analysis of the probability of occurrence of storm surges in Osaka bay.

To investigate the transient characteristics of the tsunami-induced oscillations, records of tsunami caused by the Off-Miyagi earthquake in June, 1978 were analysed on the basis of theories on stationary and nonstationary stochastic processes. The stationary spectra show the average feature of the phenomenon. Discrepancies, however, are recognized between the first half oscillations and the second half oscillations during the tsunamis. Besides, the energy densities of non-stationary spectra do not always indicate stationary value at the periods which correspond to the predominant ones of the stationary spectra. These suggest that tsunami-induced oscillations are translative.

A computer intensive statistical procedure known as the bootstrap has been used to estimate the error in coastal stage-frequency relationships due to uncertainties in hurricane meteorological distributions. These stage-frequency relationships are developed through the use of a joint probability method, so that the probability of a storm event is the product of the probabilities of the individual independent components which comprise that storm event. The bootstrap technique provides an estimate of the error of the stage-frequency by determining the variation possible in each component’s probability distribution. This variability is due to the construction of the distribution from a finite set of historical events. An example of the bootstrap is given and stage-frequency results and error estimates typical of a coastal region are shown.

The numerical simulation of storm surges in shallow bays is investigated by multi-level models such as the 2-level and FE-FD models which are used to consider the velocity profiles in wind-induced currents. These models were applied to hindcast the storm surge caused by Typhoon 7916 in Osaka Bay with the result that the water surface elevations and currents induced by the storm surge were successfully simulated.

In the present paper a vertically integrated coastal zone numerical model has been described for the simulation of the surges generated by the tropical storms striking the Bangladesh coast. The model is fully nonlinear and uses a conditionally stable explicit finite-difference scheme for solving the relevant equations of motion. In this model the analysis area extends from 87°E to 93°E along the south coast of Bangladesh and there are three open-sea boundaries situated along 87°E, 93°E and 19°N. The model utilises a curvilinear boundary treatment to represent the coastline and uses a non-uniform off-shore grid spacing adjacent to the coastal boundary. This allows an increased resolution near the Bangladesh coast.

Using a forcing wind-stress distribution representative of the 1970 Chittagong cyclone, we compare the model predicted surges with the observed sea-surface elevations along the Bangladesh coast. The predicted peak surge elevation above mean sea level compares well with the observed values at Chittagong port. A comparison of the results has also been made with those obtained from the corresponding model having uniform off-shore grid spacing.

This paper presents the results of a study on the frequency of occurrence of storm surge levels in the river Scheldt at Antwerp, related to the design of a storm surge barrier and the evaluation of the dike safety in the Scheldt basin.

The basic principles of the extreme value distribution methods, the joint probability methods and simulation models are examined.

A new technique, based upon the simulation of storms by variables characterizing the resulting surge is proposed.

Results are compared with those of other methods.

This report will update the coastal zone practitioner on the National Flood Insurance Program (NFIP) as it affects the implementation of manmade changes along the coastline.

It is our intent to place in proper perspective this fast-changing and often difficult to interpret national program. Readers will achieve an overall understanding of the NFIP on the coast, and will be in a position to apply the program’s requirements in their efforts.

We will begin with a history of the application of the NFIP to the coastal zone. The history of the problems encountered will lead into current regulations, methodologies, and the changes the Federal Emergency Management Agency plans for the future.

The Great Barrier Reef Region which constitutes the north-eastern continental shelf waters of Australia, is an area that is subject to both large astronomical tides and the passage of tropical cyclones (hurricanes). One section of this area, centred on Mackay, is characterised by particularly high tides, with a springs range of order 10 metres. Numerical hydrodynamic modelling is used in the present study to: (a) simulate the M₂ tide to investigate possible effects of the reef barrier on tidal amplification; (b) simulate the passage of a tropical cyclone across the continental shelf; (c) investigate the effect and consequences of non-linear surge/tide interactions. The recent discovery of a major shipping route through the reef in this area and the continuing development of natural resources makes a much more detailed understanding of the region’s hydrodynamics essential for coastal engineering.

Hurricane Alicia moved inland over the Texas coast during the night of August 17, 1983 creating waves and surges in the Gulf of Mexico and adjacent bays. Waves eroded beaches and dunes and surges overtopped low-lying areas of barrier islands and inland areas adjacent to the bays behind the barriers. A three-day survey of field evidence of water levels and flow directions was carried out one week after the storm. Physical evidence, such as the elevation of debris lines, water marks in buildings and debris caught on fences was used along with additional data from tide gages operating in the area to estimate the maximum flood levels and flow directions associated with the storm. Before and after aerial photography was used to obtain data on beach recession, retreat of the vegetation line behind the beach and extent of oyerwash deposits. The evidence gathered shows that the barrier islands were overtopped from front-to-back in some areas and from back-to-front in other areas with quite different results. There was little or no beach erosion to the left of the storm as it came ashore; however, serious beach erosion occurred for 18 miles (29.0 km) to the right of the storm and there was significant erosion for 55 miles (88.5 km) to the right of the storm. Maximum water levels in the Gulf, including the effects of normal tides and storm effects, were 9 to 11 feet (2.74 to 3.35 m) and maximum water levels along the nothern portion of Galveston Bay were 11 to 14 feet (3.35 to 4.27 m).

Wave measurement using subsurface pressure gage has many advantages, especially in coastal waters. However, there are some disadvantages associated with indirect measurement of surface waves. This paper deals with the problems in the recovery of surface waves from the subsurface pressure measurement. Two problems are examined: more exact recovery of the surface waves from subsurface pressure signal and a simple real time recovery of surface waves from the pressure record.

The commonly used linear transformation from the subsurface pressure to surface elevation is evaluated and possible sources of error are examined. The effect of nonlinearity and effect of current are shown to be small in the intermediate water depth. For the case of shallow water where effects of nonlinearity and current are not negligible, a method of proper recovery of surface waves from the combination of pressure and current measurements is given.

A simple method to recover the time series surface waves from subsurface record is proposed which enables speedy near real-time recovery of surface waves from pressure measurement using a microprocessor.

Shallow water wave theory shows that estimates of directional wave climate may be obtained from the measurement of near-bottom pressure and horizontal velocity components. Recent developments in low powered sensors and high density data loggers, incorporated into a bottom-mounted directional wave recorder, make the collection of directional shallow water wave data possible on a routine basis. The instrument is compact, robust, reliable and easily manageable from small craft, providing deployment capacities of up to four months. Analysis methods have been developed which provide for conversion of the recorded data to useful, convenient information.

Methods for estimating wave overtopping of coastal structures are reviewed and compared with the very limited available data and with each other. The different methods yield results which can vary more than an order-of-magnitude. For vertical seawalls, the U.S. Army Engineer Shore Protection Manual method estimates more overtopping than Goda’s method except in very shallow water. For sloped structures, the Shore Protection Manual method usually estimates less overtopping than Battjes’ method and Owen’s method. However, data for adequately evaluating how well these methods predict overtopping has not been published.

Run-up of periodic waves on gentle or non-uniform slopes is discussed. Breaking condition and run-up height of non-breaking waves are derived by the use of the linear long wave theory in the Lagrangian description. As to the breaking waves, the width of swash zone and the run-up height are obtained for relatively gentle slopes (less than 1/30), on dividing the transformation of waves into dissipation and swash processes. The formula obtained here agrees with experimental data better than Hunt’s formula does. The same procedure is applied to non-uniform slopes and is found to give better results than Saville’s composite slope method.

The effect of sample size on confidence band in predicting the extreme wave height is related to the return period and the duration of the sample record length. An estimate of errors resulting from various methods of data acquisition is given. The uncertainties corresponding to various number of years of observation and various measurement errors are analyzed for various return intervals. It is shown that data accuracy and record length are equally important in long term wave predictions. At the present time, the determination of extreme event benefits more from relatively less accurate long-term hindcast calculation rather than short-term high quality measurements. In the long run, a long-term accurate measurement program is imperative if more definite descriptions of extreme events are sought.

We propose the use of a generalized representation for acquiring a design wave spectrum. The generalized form, free from any predetermined coefficients and exponents, requires only significant wave height and average wave period as input for practical applications. The usefulness of this representation has been demonstrated with over 2000 measured deep-water wave spectra recorded from NOMAD buoys in the Great Lakes during 1981.

The spatial variability of the nearshore wave field is examined in terms of the coherence functions found between five closely spaced wave gages moored off the North Carolina coast in 17 meters depth. Coherence was found to rapidly decrease as the separation distance increased, particularly in the along-crest direction. This effect is expressed as nondimensional coherence contours which can be used to provide an estimate of the wave coherence expected between two spatial positions.

Field measurements of narrow-band incident wind waves and the resulting run-up were made photographically at two different natural sand beaches along San Francisco Bay. The run-up spectra derived from the field-measured time series show some energy at the incident-wave peak frequency, with the predominant run-up spectral energy concentrated in frequency bands below the incident-wave peak frequency. Observations of the swash time series recorded at both beaches indicate that the low-frequency run-up is generated on the beach face by the interaction between the run-up and backwash during the swash cycle.

Coherence analyses indicate that the offshore incident waves and run-up on the beach are not linearly correlated but that the run-up is correlated in the alongshore direction. The slopes of the log-log run-up spectra computed over the frequency band of the incident waves are all approximately -3. Statistical hypothesis tests were used to compare the empirical run-up cumulative distribution functions with both normal and Rayleigh distribution functions.

This paper discusses the probability distributions of irregular wave run-up height and period on gentle slopes.

Assuming that the long period component appeared on the run-up oscillation corresponds to the incident envelope wave period, a nonlinear model to estimate the probability distributions of run-up heights and periods is proposed.

Laboratory experiments on gentle slopes of 1/15,1/30 and 1/40, and field measurements on a natural sandy beach with swash slopes of 1/6 to 1/14 were performed to examine the proposed model. The proposed model is shown to agree with the experiments.

Making the assumptions that solitons are one of the most elementary excitation in random nonlinear waves in shallow water and that the waves have a coherent dynamic structure of solitons, we attempt to describe the swell-like waves theoretically by deriving the asymptotic multisoliton solution for the KdV equation. Formulations of the random wave profiles and internal properties are also made. We conclude from the comparisons between observed and theoretical results of the propagation characteristics of the swell-like random waves and their water particle velocities, that the waves in shallow water have a coherent dynamic structure of solitons and that the theoretical expression for the waves has practically sufficient accuracy in estimating their propagation.

The relationship between the directional spectrum and the cross-power spectra in an incident and reflected wave field differs from the situation with no reflected waves because the phase lag between the incident and reflected waves is not random. Extra terms, which may be called phase interaction terms, exist. Hence standard methods for estimating the directional spectrum are not applicable. In the present study, the MLM is modified for this situation and the method is termed the MMLM (Modified Maximum Likelihood Method).

The validity of the MMLM is examined by numerical simulation. The results indicate that the MMLM has a high resolution power. Formulas to determine the reflection coefficient are derived and their accuracy and suitability are examined.

Two analysis techniques for calculating directional wave spectra from measured pressure and biaxial current components were intercompared using data from the 25 October 1980 Atlantic Remote Sensing Land Ocean Experiment (ARSLOE) storm. The two methods are the conventional Fast Fourier Transform (FFT) method and a Maximum Entropy Method (MEM). The MEM is a nonlinear data adaptive method of spectral analysis which is capable of generating higher resolution spectral estimates from shorter data records than conventional FFT methods. The MEM has shown good agreement with the frequency and directional wave spectra calculated using conventional methods.

In order to attain a satisfactory reproduction in physical and numerical models of Nature’s sea states, much development of the description of these sea states has to take place. This paper gives a discussion (i) of the problems that can be considered as solved today, and (ii) of the problem areas where much research is still needed.

Firstly, the paper presents the basic definition of the directional spread of energy (for a given frequency) as derived from a field record. This definition is necessarily a statistical one and leads directly to the determination in practice of the directional spectrum.

Secondly, the parameterization of spectra is discussed and it is proposed to express one-dimensional storm spectra by means of the four parameter F.I .-spectrum, which is more manageable than the JONSWAP-spectrum.

Thirdly, it is concluded that the first order components of any spectrum have random phases.

This paper presents the results of a study on non-Gaussian characteristic of coastal waves. From the results of the statistical analysis of more than 500 records obtained in the growing stage of the storm, the parameters involved in the non-Gaussian probability distribution which are significant for predicting wave characteristics are clarified, and these parameters are expressed as a function of water depth and sea severity. The limiting sea severity below which the wind-generated coastal waves are considered to be Gaussian is obtained for a given water depth.

A parametric shallow-water spectral wave modeling technique is developed and is tested against extensive field measurements of wave height, period and spectral shape. The wave model considers wave growth and finite water depth mechanisms such as spectral wave shoaling, wave-bottom interactions, wave-wave interactions and wave breaking. The key to this approach is that the resulting wave conditions are provided by transformation mechanisms rather than transforming spectral components during wave propagation. Thus long-term wave hindcasts can be performed economically without the loss in accuracy.

The typhoon wave forecasting technique proposed by C.L. Bretschneider (1) is a good simple method. However, the measured maximum wave height at Nan-Wan Bay (at southern tip of Taiwan) of Ida typhoon is about twice of the hindcasted maximum wave height. In general, the hindcasted maximum typhoon wave height arrives earlier than the measured data for Bretschneider’s method as well as the other methods, such as Tang’s and Ijima’s methods. And as the typhoon is approaching the station, the hindcasted wave heights are smaller than the measured ones. On the contrary, as the typhoon is leaving the station, the hindcasted wave heights are greater than the measured heights. In order to improve these defects, the typhoon swell proposed by Liang (7) is superimposed upon the typhoon wind wave according to the energy conservation principle. The modified wave period is calculated by the energy-weighted method.

In this paper 8 typhoons are as examples to show that the new method has amended the above-mentioned defects.

Waves with exceptional height and periods caused severe damage along the coast of California in 1982-83. Because these large wave events coincided with a strong El Nino-Southern Oscillation (ENSO) climatic anomaly, which occurs 20-25 times per century, there was interest in determining if the extreme waves resulted from the ENSO or its related features. The meteorological setting featured a very large and intense low pressure zone over the north-central Pacific. Associated with this Pacific-wide pattern, a series of large mid-latitude storms developed at about weekly intervals and produced exceptionally long fetchs directed at the California Coast.

Two time series of extreme wave events, using buoy data after 1981 and hindcasts before, were used covering the period from 1900 to 1984. One series considered waves with significant heights greater than 3 m (10 ft) and the second for those greater than 6 m (20 ft.) These were compared with a time history of ENSOs for the same period. A strong association was established between northern hemisphere winters during ENSO years and large wave events in Southern California. Strong ENSO winters had the largest storm waves, moderate ENSOs less intense waves, and weak ENSOs tended not to have storm waves greater than the threshold value used in this study. The correlation between large waves and ENSO years is significant at the 1% level. The correlation between lack of large waves and non-ENSO years is significant at the 0.5% level.

Because of the great southerly extent of the most energetic storms, a large number of energetic wave trains approach the coast from the west, rather than the northwest, as previously assumed by many. ENSO winters are responsible for producing all of the wave events in this study with both heights greater than 6 m and periods of peak energy longer than 19 seconds.

Five out of nine eastern Pacific tropical storms making landfalls on California in the 85 year period occurred during the late northern summer of ENSO years.

This paper investigates the following characteristics of run-up of random waves on gentle slopes experimentally: (1) the run-up wave energy spectrum, (2) the ratio of the number of run-up waves to that of incident waves, (3) the relationship between the representative run-up height, the deep-water wave steepness and the beach slope, (4) the run length of run-up heights, and (5) the effect of wave grouping on representative run-up heights.

Main results are summarized in the chapter of conclusions.

Probability distributions theoretically derived for gaussian, stationary processes are applied here to the sequential behaviour of sea-states. This behaviour defined by the curve of evolution of significant wave-height, H_s(t), is characterized by variables such as: intensity of storm peaks,time between beginnings of storms, average duration of calms and storms, average number of consecutive storms, expected value of the extremal storm peak, etc.

The distributions obtained for these variables heve been tested with 5 years of wave data, recorded in the north coast of Spain. The agreement obtained is satisfactory in most cases, showing the validity of the approach and its applicability to situations in which only a limited amount of data is available. However, in cases where a large volume of data exists, empirically selected distributions could provide a marginally better fit.

North Sea wave records, obtained in conditions of active wave generation, have been analyzed with respect to the distribution of the length of wave groups. The results are compared to a theory by Kimura, in its orginal form as well as with the addition of a new spectral wave groupiness parameter, based on the theory of Gaussian processes. The results lend support to the validity of Kimura’s theory, this in turn implies further evidence that the phenomenon of wave groups in sea waves can by and large be explained, both qualitatively and quantitatively, in terms of the linear, random phase model for the wave motion, even in conditions of active wave generation.

A model describing the average rate of energy dissipation in random waves breaking in shallow water, published previously by the first author and Janssen (1978), has been applied to an extensive set of data for the purposes of calibration and verification. Both laboratory and field data were used, obtained on beaches with a more or less plane slope as well as on barred beaches, and for a wide range of wave conditions. Optimal values have been estimated for an adjustable breaking waveheight-coefficient in the model; these appear to vary slightly but systematically with the incident wave steepness, in a range which is physically realistic. A parameterization of this dependence allows the use of the model for prediction. Applied to the present data set, the correlation coefficient between measured and predicted rms wave heights is 0.98, with an rms normalized error of 6% and a bias which does not differ significantly from zero.

This paper inquires into the questions of how wave groups are related to the wave spectrum, and how they differ in sea versus swell. Some results are presented in the form of a wave group model for sea spectra and for swell spectra. The models were developed from statistical analysis of a large number of wave records and apply to deep water only.

A field measurement was conducted in order to clarify the swash motion on a natural beach. It is found on this particular beach, which had a rather steep foreshore slope, that cross spectra calculated between the surface elevations, onshore velocities and the swash agree very well with those given by linear long two-dimensional standing wave theory in the lower frequency region than a certain value. This finding together with the observed f^-4 (f; frequency) high frequency saturation in swash spectra encourages a partial reflection model to describe the fluid motion in the inner surf zone, including the swash. The model developed shows a good agreement with the observed results, in which being employed an analogy to regular waves for the criticality of wave reflection. This model makes it possible to predict the swash spectrum for a given incident wave spectra and a given beach profile, as far as wave breaking takes place on a foreshore slope.

The identification of wave groups in wave records is sought in terms of the classical linear analysis techniques in the frequency and time domains. Unwrapping and detrending of the phase spectrum identifies apparent order where none is assumed in the Gaussian random wave model. Similarly unexpected order is observed in the tail of the correlogram of both the wave record and the Rice envelope function. These aspects are strongly suggestive of wave grouping.

Extensive field observations of swash on natural beaches are used to relate the magnitudes of swash oscillations to incident wave conditions and the beach slope. Swash fluctuations at wind wave frequencies (defined here as f > .05 Hz) appear to be "saturated". As in laboratory experiments with monochromatic waves, wave breaking prevents the magnitudes of swash oscillations at incident wave frequencies from increasing past a certain level which depends on the beach slope. All data sets considered support this conclusion. In contrast, the magnitude of swash oscillations at surf beat frequencies (defined as f < .05 Hz) varies between data sets. Possible reasons for the discrepancy are discussed. Despite their differences, all data sets show that motions at surf beat frequencies dominate the swash spectrum on dissipative beaches. As in previous studies, the frequencies of spectral hills and valleys in the spectra of surf zone sensors suggests that a significant fraction of the surf beat energy is contained in motions which are standing in the cross-shore direction. Preliminary analysis indicates that shoreward propagating surf beat is coupled to incident wave groups.

A laboratory study was conducted to measure the amplitudes of long waves in shallow water as induced by wave grouping. In a 55 m long wave channel with a plane beach at the end, two primary waves of nearly equal frequency were generated. Due to a sophisticated control of the wave paddle — including second order wave generation as well as active wave absorption at the paddle face — the wave action at the difference frequency was limited to an incident forced wave, propagating at the group velocity, and a reflected free wave generated in the surf zone. For the incident forced — or bound — wave, also known as set-down, the experimental results show good agreement with the existing theory. Furthermore, the experiments confirm qualitatively a theoretical model by Symonds et al. (1982) explaining two-dimensional surf beat as a result of the time-varying breakpoint of the incident primary waves.

In this paper, under the condition of waves in front of a breakwater being not broken, studies were made on the characteristcs of probability distribution of waves and wave pressures, the regularity of the spectral component attenuation with depth and the constitution of the high frequency band of wave pressure spectrum.

The distributions of wave heights in front of a vertical breakwater, the range of wave pressure fluctuation at different subsurface levels, and the wave periods have shown that they are practically invariable with depth and can be determined theoretically. The spectral constitution of wave pressure field and the regularity of attenuation of spectral components were analyzed at the vertical breakwater, and a new expression describing the equilibrium range of wave pressure spectrum was obtained.

The potential error of estimating the small pressure gradient under a directional wave field through the subtraction or comparison of relatively large total-head signals from adjacent pressure transducers in an array is avoided through the use of differential pressure transducers which measure directly the pressure gradients. A device which utilizes four differential pressure tranducers placed orthogonally about one absolute pressure transducer, (the "DPG"), was developed and field-tested at the U.S. Army Corps of Engineers Coastal Engineering Research Center Field Research Facility, Duck, North Carolina. The first five directional Fourier coefficients of the directional ocean spectra were developed from the DPG data, and although no other in situ directional wave monitors were available for comparison, the directional peak determined from the DPG agreed well with simultaneous High Frequency (HF) radar data. The DPG instrument is about one-half the size and less than one-sixth the weight of conventional pressure sensor arrays. The field establishment of the orientation of directional-measuring instruments is also discussed.

Two methods of numerically simulating random seas, given a target power spectrum, are discussed. Wave group statistics, such as the mean length of runs of high waves, produced by the different simulation schemes are compared. For a large number of spectral components, no significant differences are found in the wave group statistics produced by the two simulation techniques. Using the simulation techniques, it is shown that ocean gravity wave group statistics are not inconsistent with an underlying wave field composed of linearly superposed random waves. The majority of the field data examined were collected in 9-10 m depth, significant wave heights ranged from about 20 to 200 cm, and the spectral shapes ranged from fairly narrow to broad. For the 9-10 m depth data, observed mean run length, variance of run length, and the probabilities of runs of a given number of high waves were statistically consistent with the linear simulations. In contrast to the apparent linear behavior in 9-10 m depth, waves in 2-3 m depth showed substantial departures from the linear simulations.

Long waves of small amplitudes can excite harbour oscillations as well as the motion of floating structures or vessels. Field data from the Weser Estuary, German Bight of the North Sea were analysed with respect to waves with periods greater than 8 s. After preprocessing of the mostly noisy data records, special analysis incorporated the reconstruction of incorrectly recorded frequency components below .03 Hz and bivariate distributions of heights and periods. Results suggest that long wave activity increases towards the inner estuary. Grouping properties are dependent on wind direction and on directionality of the sea state. Further investigations and model studies for the response of travelling vessels to this wave climate are recommended.

Group bounded long waves which appear as a set-down under a group of high waves and a set-up in between groups are well described for constant water depth. However, their propagation into shallow water and their interaction with the constituent wave groups are not well understood and theoretically described yet. Therefore, model investigations were carried out to study shoaling properties of these second order waves in terms of amplitudes and phases. The tests give a good insight into the phenomenon and suggest distinct shoaling properties. Moreover, experimental results provide a valuable basis for future theoretical considerations.

A simple open boundary condition for limiting the computational domain in tidal simulations is presented. In modeling the impact of proposed coastal projects with a limited-area model, problems due to undesired reflection of gravity waves at open boundaries often occur. The boundary condition presented herein eliminates these problems in many instances and can be easily incorporated into a wide variety of models. The adapted procedure permits representation of appropriate forcing conditions while allowing propagation of internally-generated disturbances out of the open boundaries. Applications to real world engineering problems are presented.

Although many field experiments have shown that surf beat motion, with periods longer than incident wave periods, becomes the dominant feature of the nearshore velocity field as the shoreline is approached, the nature of this motion is still not fully understood. This paper describes a field experiment on a sheltered beach which was designed to distinguish between long wave motion directly forced by the incident wave envelope (as suggested by Longuet-Higgins and Stewart, 1962), and wave motion which is only weakly coupled to the local incident waves and therefore essentially free.

The results for on/offshore flows show that low frequency surf beat (frequency less than 0.03 Hz) is strongly correlated with the wave envelope, suggesting the dominance of forced wave motion at these frequencies. In a higher frequency band, between 0.06 and 0.095 Hz, the correlation is generally much lower, suggesting that free wave motion, possibly subharmonic edge waves, is significant in this band.

The longshore flows are much more weakly correlated to the envelope of either the longshore or on/offshore components of the orbital velocity. This is consistent with previous observations that edge wave motion dominates the longshore surf beat motion.

The development of MThw on the German North Sea coast is probably related to the development of the climate. Other important contributing factors are discussed. For the last 20 years a relatively steep rise of MThw level is recognizable. An even steeper rise as a result of climate changes appears possible within the next 100 years. With regard to the great importance for coastal engineering, the necessity of attentive observation and international cooperation among different scientific disciplines is stressed.

The likely effects of short-crested (sc) breaking waves on ships and structures are summarised in the case of the simplest non-trivial sc sea at medium/high crossing angle. Typical experimental data of sc breaking wave-height and sc water particle speeds are given at model-scale.

The mild-slope wave equation is derived by demanding minimum in total wave energy.

By demanding conservation of wave energy, two different functionals for the finite element solution of the mild-slope wave equation are constructed. The first functional is based on a finite/infinite element formulation, and the second one is based on a hybrid finite element formulation. Both functionals are constructed in a straight-forward way that leads to a better physical understanding of the functionals and a full understanding of each separate part of them.

A new method for computing the unsteady motion of a water surface, including the overturning of water waves as they break, has been developed. It is based on a Cauchy thoerem boundary integral for the evaluation of multiple time derivatives of the surface motion. The numerical implementation of the method is efficient, accurate and stable.

Explicit formulae are provided for wave problems covered by linear wave theory. Two goals are pursued. The first is to provide a faster and more flexible tool than usual wave tables. The second is to provide explicit, analytical solutions to problems that have so far demanded time consuming numerical integrations. As an example we solve the problem of wave height variation due to refraction, shoaling and energy dissipation over a soft mud bottom. The obtained explicit solutions are accurate enough for practical purposes and require very little computational effort, in fact they will enable the engineer to solve many wave problems with a handheld calculator. Another advantage of analytical solutions is that they are always much more instructive than numerical results.

The parabolic approximation is developed to study the combined refraction/diffraction of weakly nonlinear shallow water waves. Two methods of approach are taken. In the first method Boussinesq equations are used to derive evolution equations for spectral wave components in a slowly varying two-dimensional domain. The second method modifies the equation of Kadomtsev & Petviashvili to include varying depth in two dimensions. Comparisons are made between present numerical results, experimental data and previous numerical calculations.

From limited experimental evidence, shoaling monochromatic waves seem to possess certain similarities. Specifically, the harmonic composition follows the trend of solitary or cnoidal waves, and the phase difference of harmonics vary with water depth monotonically. Based on the above observation a similarity model is constructed to study the asymmetric properties of shoaling waves. The implication of wave asymmetry on wave breaking is discussed.

The solitary wave is first established in this paper by extending the series solution of periodic gravity wave as the wavelength approaches to infinite. Then, the highest gravity wave of permanent type in finite.depth of water is immediately analyzed. The maximum ratio of wave height to water depth is obtained as 0.854654..., and the angle at the crest for the considered highest wave is estimated to be 90°.

A method of calculation of the combined effects of wave refraction, diffraction and reflection in harbours of arbitrary shape and non-uniform water depth, subject to periodic or random waves is presented. Examples of application are given and practical aspects on the wave spectrum discretisation are considered.

Modifications of surface gravity waves and opposing nonuniform currents due to their interaction in coastal waters were experimentally and theoretically investigated. The flow field is modelled as a steady turbulent jet heads directly into the surface waves. Experimental results show that the net waves momentum flux is decreased as waves propagate into the jet which gives rise to mean water set-up towards the jet source. Opposing waves increase the spreading rate of the jet and causes vertical upwelling of the mean flow, near the bottom, towards the free surface. Theoretical predictions of the increase of the jet spreading rate and wave set-up agree with the experimental data. Wave-current interaction modifies significantly waves bottom flow pattern by focusing ambient nearshore waters on the jet outlet.

The applicability of a hybrid finite element model for the calculation of combined diffraction-refraction of small time-harmonic water waves is demonstrated. The model is valid for arbitrary water depths and wave lengths, i.e. it is based on intermediate depth theory (IDT). The model includes arbitrarily varying partial reflection along the boundaries. Superposition of waves (to simulate a spectrum approach) with different incident directions is demonstrated, and CPU-times and core memory requirements are given.

The model is verified and documented with respect to sensitivity of the model parameters in detailed tables, using the classical Homma island on a parabolic shoal. The wave period is here chosen in such a way that a small number of elements (larger than 500 and less than 2,000) is enough to get an accurate solution.

For a new simple, but realistic harbour geometry many detailed and accurate graphical results are given. The wave period (T = 9 sec.) is here chosen so that it is representative for natural wind waves, and the size of the harbour is selected, so that the model gets a fairly large number of elements (of the order 10,000).

The complete set of equations for the refraction of small surface gravity waves on large-scale currents over a gradually varying sea bed is derived and presented. Wave lengths, direction of propagation and wave heights are all determined along the so-called wave rays as solutions to ordinary, first-order differential equations.

Dissipation due to bed friction in the combined current wave motion is included. The ray tracing method is used in an example. A method for the calculation of current depth refraction of weakly non-linear waves is proposed.

A numerical model for refraction of linear and cnoidal waves over an arbitrary bottom is presented. The model, which is based on the ray theory of refraction (11), utilizes linear theory in deep and intermediate water and cnoidal theory in shallow water. The model permits one to determine nearshore wave properties using a nonlinear wave theory. Nearshore wave properties such as wave height, celerity, and wave angle determined using the linear-cnoidal refraction model may vary considerably from those determined using a linear refraction model. In general, cnoidal waves refract less, travel faster, and shoal higher than linear waves. This result can have a considerable effect on coastal engineering design, particularly in the areas of coastal structure design and longshore transport computations.

The transformation and the breaking of waves affected by an opposing current on the sloping sea bed were discussed. It was found that the characteristics of wave transformation before breaking point can be determined by the deep water wave steepness and the dimensionless unit width discharge. Concerning the wave decaying due to breaking, the characteristics of the change in the wave height depend only on the slope of the sea bed.

Fourth order solutions of Stokes wave on a uniform current were calculated based on the first and second definition of the wave celerity, respectively. The theoretical solutions for wave transformation by the energy flux method were presented. Comparisons between the theoretical solutions and the experimental results gave the criteria of the applicability of our solutions corresponding to the dimensionless unit width discharge. In the calculation of energy flux, it was pointed out that the change in the mean level of the free surface should be taken into account. It was made clear that the change in the mean level of the free surface can be evaluated by Bernoulli’s equation, and the energy flux in which the change in the mean level of the free surface was taken into account was proposed.

The criteria of breaking corresponding to the dimensionless unit width discharge were clarified, experimentally.

Measurements have been made with a laser doppler anemometer of the time-mean velocity of the fluid close to the bed in a wave flume. Both a rough bed, consisting of gravel of median diameter 11 mm, and a smooth bed were investigated. With the rough bed the time-mean velocity at a given height was found to be strongly dependent on position relative to prominent roughness elements. At one point the time-mean drift at a given height might be in the direction of wave propagation while, at another, in the opposite direction. Significant variation in time-mean drift with horizontal position was observed at all values of Reynolds number tested. The effect of bed roughness on the average value of the time-mean velocity at a given height was found to be most marked at low Reynolds numbers: the maximum near bed value with this gravel bed was about 3 times that for a smooth bed at the lowest Reynolds numbers tested. At the highest Reynolds numbers there was no clear difference between the rough and smooth bed values even though the boundary layer over the rough bed was fully turbulent whereas that over the smooth bed was laminar. However, at these high Reynolds numbers both the rough and the smooth beds showed a reduction in drift velocity below that predicted by Longuet-Higgins (9) because of the increased importance of higher harmonics in the flow.

In this paper, starting from the Prandtl hypothesis a three-dimensional numerical bottom boundary layer model has been developed, which allows to calculate bottom friction by a combination of waves and currents. The model has been compared with two-dimensional analytical computations which gave similar results.

The bottom friction values found are comparable to the ones, found by Lundgren (1972), however in the most relevant cases somewhat less. Furthermore in the two-dimensional case the model has been compared with measurements of Bakker and Van Doom (1978).

With respect to the oscillatory motion, still some minor deviations occur between theory and measurements, due to deficiencies of the Prandtl theory.

Both the effects of refraction and diffraction may be efficiently modeled in wave propagation models by introduction of the parabolic approximation. The performance of the model CREDIZ, which is based on this parabolic approximation, was investigated in three verification studies. Two of these studies concern laboratory situations, i.e. one having a simple geometry and one having a more complicated geometry. The third study concerns a field situation, i.e. a shoal dominated area in an estuary mouth. It is found that despite the schematization to monochromatic, nearly linear wave propagation, the model CREDIZ performs remarkably well for engineering purposes.

A new wave equation has been derived for the full nonlinear dispersive waves propagating over an arbitrarily shaped sea bed. The method of the derivation of the equation uses a conformal mapping technique by which the original domain can be transformed onto a domain with a uniform depth to make the basic equation easily integrable vertically. By taking an inverse Fourier transform, the velocity potential obtained by the integration can be expressed in the form which can construct the exact wave equation from the water surface boundary conditions. An algorithm for the numerical integration of the equation is presented with some examples of the solution.

The paper reports the current progress in developping a finite element method for the shallow water equations. Some recent developments as the implementation of a semi implicit scheme or the use of an incident wave condition are described. Different realistic applications are presented concerning tidal and storm surge simulations.

Further positive results on appropriate scaling of movable-bed models support an analytical expression developed in 1983. That development examined a simple parameter for a profile view of nearshore sedimentation, making a distinction between small and large situations by the incorporated threshold of sand motion. The resulting scale laws proved fairly consistent with various empirical results, including those, by E. Noda and P. Vellinga.

The focus in this paper is on full utilization of 25 available tests of profile development in large wave tanks. Seven published small tests are found to be notably accurate as unintended models of various large tests, giving support to the new scale law. Also, the occurrence of shore erosion or accretion in all large tests is seen to be in accordance with the basic sedimentation parameter.

A numerical model is presented for calculating beach profile development due to offshore sediment transport and tested with laboratory and field data. The model allows variable wave conditions, water level fluctuations due to tide and storm surge, arbitrary bathymetry, and arbitrary sediment size. The agreement between calculated and measured beach profile erosion is good.

A field study was conducted on the North Coast of the Gulf of St. Lawrence in Eastern Canada to evaluate sediment transport processes in a coastal area that would be affected by the modification of river regimes for hydropower production. Radioactive tracers were used to evaluate the mobility of coastal sediments. Three injections were carried out using Neodynium 147 (half-life 11.1 days), at 450, 550 and 2200 m. from the shoreline at depths from 3 to 10 m. The high sensitivity of the detection system allowed to monitor the study area for 44 days. The tagged sediments responded to waves and tidal currents and were sensitive to minor changes. Comparison of the patterns of evolution of the three injections permitted to evaluate the relative mobility of bottom sediments as a function of water depth and distance from shore. Bedload transport rates were calculated but they are related to specific events such as storms within the Gulf of St. Lawrence more than to steady state conditions.

Using those results which were judged to be reasonable among various experiments, an equation predicting the threshold shear velocity on a wet sand surface was obtained. Then, based on a literature survey, results from fundamental experiments, and information obtained from a series of field observation carried out by the authors, a hypothesis to explain the blown sand phenomena on a wet sand surface was developed. Experiments with a well-sorted sand having a median diameter of 0.3 mm showed that the prediction was valid if the water content of the sand layer was less than 8%.

The potential for longshore sediment transport (LST) is estimated from a three-year set of directional wave data measured off Haifa, Israel. The resulting annual cycle of LST, together with an analysis of the wave and shore characteristics, suggests a wave-induced sediment transport mechanism with a uni-directional annual transport that gradually decreases along the transport path from the source (Nile delta) to sink (Haifa Bay). Existing estimates of the rates of transport of Nile sediment are in good agreement with this result.

The long assumed uniform movement of sand along the coast produced by wave action can be disputed when the interaction of storm sequences and swell is considered. Storm waves form a protective bar, which essentially puts material back into circulation for the oblique swell to work upon. The resulting longshore transport is swift whilst the bar exists but decreases to negligible proportions once it is denuded and the normal swell-built beach profile recurs. This impulsive drift has many implications for engineers and geomorphologists and to researchers attempting to predict annual rates of transport.

When water flows over a stationary bed the fluid motion is retarded by both skin friction and local pressure gradient foces related to the roughness of the bed. At higher flow stages, Hanes and Bowen have suggested a model for bedload transport which is based upon the dynamics of collisional grain flows following Bagnold. In such a collision dominated flow, it appears that the resistance of a fixed bed to the same overlying flow. This result is consistent with the dynamics of rapid granular-fluid flows. Refs.

Beach cusps with a longshore spacing of 20 to 150 cm have been built by the continuous action of incident waves on a steep laboratory beach. In the formation stage of beach cusps, all bed materials on the beach moved shoreward. The backwash vortex, which was found first by Matsunaga and Honji (16,18) on a laboratory beach, gave a good explanation of the shoreward movement of bed materials. Beach cusps formed when the value of a dimensionless parameter $H_b{}^2{L}_b/h_b{}^{2}L,$ , which controls swash motion on a steep beach, became larger than 1.12; H_b, is the height of the breaking wave, L_b its wavelength, h_b the water depth at the breaking point and L the horizontal distance from the shoreline for still water level to the breaking point. The observational spacing of beach cusps formed regularly were in quite good agreement with half a wavelength of the zero-mode subharmonic edge wave generated on a sloping flat beach. As a result of this study, the contribution of edge waves on cusp formation becomes more undoubted.

Time and spatial variations of sediment concentration of both bed load and suspended load in the process of two-dimensional beach deformation were investigated experimentally. At the same time, the relation between the velocities of water-particle and sediment migration was analyzed theoretically. By using those results, a net rate of on-offshore sediment transport in the process of two-dimensional model beach deformation ${\overline{q}}_f$ was calculated on the basis of sediment flux. It is found that ${\overline{q}}_f$ coincides fairly well with the net rate of on-offshore sediment transport calculated from the change of water depth.

This paper presents an attempt towards the determination of the geometric distortion for beach mobile bed models. At first, a derivation of a scaling law for modelling equilibrium beach profiles is given, based on Valembois’ (1961) work. Further, an experimental verification of some criteria presented in literature for the reproduction of beach profiles in coastal mobile bed models (e.g. Noda, 1971; Yalin, 1971 and Vellinga, 1982) is carried out, leading to a comparison with the criterion developed herewith.

Model experiments were undertaken in a two-dimensional wave flume with regular waves in an attempt to verify the validity of the four similarity criteria for the reproduction of beach profiles.

For fine sand as model material, the experimental results proved valid the modified criterion based on Valembois (1961), among all criteria used.

The use of this similarity criterion showed that the beach profiles were correctly reproduced in the model. The use of cellulose acetate as model material did not give good results, and none of the similarity criteria used were verified. The use of this lightweight material should be avoided for modelling beach processes.

Further testing with finer sand is recommended to analyse the influence of the dimensionless fall time parameter (Dean, 1973) and to confirm its use for the prediction of equilibrium beach profiles.

A computational framework is presented to evaluate the stability of two inlets connecting the same bay to the ocean. It is assumed that both inlets are scoured in alluvial material. The main ingredients in the stability analysis are the closure surface and the equilibrium stress surface. The closure surface of an inlet is defined as the relation between the tidal maximum of the bottom stess and the cross-sectional areas of both inlets. The equilibrium stress surface of an inlet is the relation between the tidal maximum of the bottom stress and the cross-sectional area of that inlet at the time the inlet is in equilibrium with its hydraulic environment. The method is applied to Pass Cavallo and the entrance to the Matagorda Shipping channel further referred to as Matagorda Inlet. Both inlets connect Matagorda bay to the Gulf of Mexico.

A field exercise was performed on a high-energy beach east of the Sunday's River in Algoa Bay on the east coast of the Republic of South Africa in the latter half of April 1983. Recorded data include nearly continuous wave data at 7 stations within the breaker zone with simultaneous waverider recordings in a water depth of 10 m, suspended sediment data gathered by means of 'bamboo' poles and instantaneous bottle samplers, daily topographical measurements of the beach and inshore area, data on rip current intensity and spacing for a 10 km coastal strip, more than 3,000 bottom sediment sample analyses and visual observations of wave height and longshore current velocity at hourly intervals through the recording period. Analysis of the data has been completed and interpretation and correlation of various measured phenomena are underway. A second exercise was performed in August 1984, when the emphasis was on nearshore circulation patterns.

This paper presents a scale-model relationship for the similarity between large and small scale-models in two-dimensional equilibrium beach profiles. Taking large scale-models using large scale equipment as prototypes, the experimental scale of a medium-sized model was gradually varied keeping the grain size ratio of model to prototype constant. A similarity-comparison between large and small scale beach profiles is made by considering the degree of experimental errors. Judgement results are graphically shown, and a scale-model relationship is proposed. It is found that the scale-model relationship proposed agrees with the ones derived from the empirical formulae expressing the properties of beach profiles. Additionally, the applicability of this scale-model relationship to the reproduction test of natural beaches is examined.

This paper intends to clarify why and how such a huge tombolo having a surface area of 1,700,000 m² has been formed at the west coast of Iwojima for relatively short period of 33 years after 1945.

Analyses are performed on various data obtained through literature survey and field measurements to determine the growth rate of tombolo and variation rate of shore and sea floor surrounding the island. Model tests are also made on the formation of tombolo.

The followings are the conclusions derived through the analyses:

1. Source of the sediments is the one produced at the northern part of island where sea floor has been lifting at a rate exceeding 30 cm per year.
2. Waves with dominant direction of N to NE which appear in fall and winter erode the northern coast and currents induced by these waves carry these sediments southward along both coasts of the island.
3. Waves with dominant direction of S to SE which appear in summer and their induced currents carry the sediments northward along both coasts of the island.

Observation of the two-dimensional breaking of random waves on a beach suggests that under conditions of active surf an important mechanism in the process of offshore sediment transport is the transport by the undertow or return flow, induced by the breaking of waves. It is found that a model incorporating this mechanism exclusively is able to describe the local sediment transport and the resulting bottom variation of a beach under random wave attack to a first approximation. A laboratory verification is made based on measurements of both the dynamics of the water motion and the bottom profile. Finally, a realistic equilibrium state is shown to result from the model.

A compound mathematical model (COMOR) for the simulation of morphological changes in the coastal area is being developed. The model is very flexible; it can be composed according to the specific demands of the problem which is considered. So far the model is being applied in the advisory practice to predict initial morphological changes. Recent experiences have shown that the model is quite useful, although at present the knowledge of the individual coastal processes and their interactions is still insufficient to utilize it optimally. However, it is foreseen that in the near future such mathematical models will become a powerful tool in coastal engineering.

An energetics-based longshore sediment transport model is developed which takes the form of a modification to the wave power equation. Instead of being constant, the wave power coefficient is a function of the breaker angle and the ratio of the orbital velocity magnitude and the sediment fall velocity. This modification extends the range of application of the wave power equation to include both field and laboratory conditions.

An important component of beach nourishment design is to assess the compatibility of the borrow material with the native beach sediment. One avenue to judge the “success” of a project is the amount of fill retained over a specific period of time after fill placement. Presumably, if the fill material placed on the eroded beach is compatible with the energy of the coastal processes, it will be resorted along the profile but be retained within acceptable limits in the vicinity of the project area.

At present the selection of suitable borrow material is based only on theoretical criterion. Specifically, the Fill Factor and Renourishment Factor are based on models developed by Krumbein (1956), Krumbein and James (1965), James (1974), Dean (1974), James (1975) and Hobson (1977). These methods of judging borrow area suitability have not been fully tested in the field and the Shore Protection Manual (U.S. Army, 1977) warns that they should only be used as a general indication of possible fill behavior.

A review of monitoring reports on selected recent beach restoration and sand by-pass projects revealed a lack of standardization on data collection and analysis. Little evaluation of the actual behavior of fill material on the nourished beach had been carried out. To assess the suitability of the fill material, projects with adequate data were investigated and the short (one year) and long term (two to three years) behavior of actual fill data was described. Detailed collection of native sediment before nourishment, representative borrow material at time of placement and samples at specific times after fill placement were used to determine the redistribution of fill grain size characteristics and determine the accuracy of the present beach fill models.

It was found that present models do not take into account non-normal grain size distributions found at the projects studied or CaCO shell material. A safety factor assuming loss of fine material from the borrow should be used with the Adjusted Shore Protection Manual Fill Factor Method to give more accurate results. The delta variable in the Renourishment Factor was found to vary between projects and should be calculated for each project. At the present time use of the entire grain size distribution is necessary to understand the sediment redistribution after fill placement.

Natural beaches exhibit an equilibrium profile that is planar nearshore and non-planar, concave-up offshore. The longshore current on these Dean equilibrium beaches is shown to depend on the location of the intersection between the planar and non-planar profiles and on the dimensionless mixing strength parameter if the eddy viscosity coefficient is linearly dependent on the distance offshore. The effect of the profile intersection on the longshore sediment transport rate is demonstrated for two energetics based sediment transport models; viz. the Bagnold and energetics stress models.

Time scales of nearshore profile change are examined using a unique set of highly accurate surveys collected over a 3 ½ year period at CERC's Field Research Facility. The data are analyzed in terms of the formation and movement of the nearshore bars and with empirical eigenfunctions. The largest and most rapid changes in the profiles occurred during storms. The inner bar (depth of -0.6 to 1.5 m, 1.6 to 4.5 ft) moved offshore during even minor storms and recovered relatively quickly. The outer bar (depth of 3 to 4 m, 9 to 13 ft) formed during the largest storms and recovery was considerably slower, requiring six months or longer. The eigenvector analysis confirmed the importance of storms but identified a seasonal shift of material from the beach and inner bar to the offshore.

The paper outlines the results of comprehensive beach surveys carried out over more than 20 years showing the effects of seawalls, groynes and beach nourishment on the beaches of the beach resort city of Gold Coast, Australia. Beach profile changes and, in particular, quantification of the overall extent of accretion and erosion resulting from groynes which interrupt the longshore movement of sand are outlined. The paper confirms the already known principles of behaviour of these coastal works and documents clearly the full detrimental impact that inappropriate structures can have on a natural sand beach system.

Methods and procedures for the assignment of the pro rata share of damages caused by rising water and high winds arising from natural weather phenomena were virtually non-existent following Hurricane Frederic in 1979. Damages to beach front structures were often assumed to be caused by high water. Frederic marked the first natural weather disaster to strike a heavily populated area since the formation of the National Flood Insurance Program in 1970. The damages caused by the winds and rising water from Hurricane Frederic, therefore, created an economic incentive to attempt to distinguish between wind and rising water contributions. This paper presents a method and outlines procedures followed in damage assessments following Hurricane Frederic in an effort to minimize the difficulties insurance carriers and adjustors may have following future similar phenomena. It may, additionally, serve to promote improved design and/or building codes where such phenomena are probable.

The objective of the work presented herein is to quantitize dune erosion as a function of the awash mechanics. In order to achieve this aim, a numerical model is developed which solves the one dimensional continuity and momentum equations for depth and velocity of the swash at the face of the dune. These parameters are then used as input to the dune erosion model which predicts the e::tent of toe retreat of the dune as a function of time. Since the model is formulated in real time, both short and long term events may be simulated. This is particularly important in terms of understanding the short term event in which the dune and beach face do not achieve an equilibrium profile.

The details of a new oscillatory flow tunnel at Scripps Institution of Oceanography are discussed. The flow tunnel has a large cross-section and large water excursion distance. The piston motion is programmable. The test bed can be tilted. These, and other aspects, make the facility useful to a wide variety of oscillatory flow sediment transport experiments.

A 4-year set of beach and offshore profiles, measured at monthly intervals, is evaluated to determine the effect of wind-wave forcing and long period (1 year or greater) lake-level variation on beach profile change in the "tideless" Great Lakes. This evaluation indicates two distinct regions of change in the beach and nearshore area of these profiles. The beach-berm region responds directly to lake-level modulation of wind-wave forcing. This response occurs on two time scales (seasonal and long period), but always in direct relation to mean lake-level variation. The inner-bar actively changes under the influence of wind-waves, but appears to lack a well-defined seasonal pattern. Empirical eigenfunction analysis is applied to these data in order to statistically quantify the significance of these observed changes. This analysis provides confirmation of a hypothesized long-period (years) variation of the beach and berm in direct response to lake-level variation.

A numerical model is developed and applied to estimate the frequency distribution of severe erosion events. The proposed method is an extension of existing Monte Carlo storm surge simulation models. Hurricane and tropical storm meteorological parameters are randomly selected to generate a series of synthetic storms; the storm surge for each storm is estimated using a Bathystrophic storm surge model. The storm surge hydrograph is then used as input to a numerical erosion simulation model which determines beach profile response for each storm based on wave energy dissipation per unit volume as a general erosion forcing mechanism. Five 100-year random simulations are performed from which the return periods of storm surge and erosion,i.e. volume eroded and dune recession, are estimated.

The Nile littoral cell is an impressive example of the effect of dams on coastal erosion. The Nile littoral cell is located in the southeastern Mediterranean Sea and extends 700 km from Alexandria, Egypt in the south to Akko, Israel in the north. Until 1964, the major sediment source of the littoral cell was the Nile River. Construction of the High Aswan Dam, which began filling in 1964, has resulted in a near absence of Nile River flow into the Mediterranean and a corresponding complete loss of the Nile River as a source of nutrients to coastal waters, and as an active sediment source for the delta and the coastline of the Nile littoral cell. As a result, the Nile Delta is now subject to severe erosion in a number of localities. Refs.

In analysing measured sediment concentration distributions the effect of the non-uniformity of the bottom material is frequently not taken fully into account. Examples of calculations are given to clarify the grading effect on the parameters that determine the concentration distribution (e.g. diffusion coefficient distribution). Results of a preliminary test series indicate that the particle size affects the diffusion coefficient involved. [ε (sediment) = β ε (fluid); β size dependent].

Wildwood Harbor and Chagrin River are two areas on Lake Erie at which intensive boating activities occur throughout the recreational months of April through October. At Wildwood Harbor an enclosed basin exists with a relatively open mouth which allows excessive wave activity to enter. At Chagrin River a major project was recently completed to stabilize the river entrance which had experienced substantial shoaling, and to help prevent winter ice blockage; however, significant reflected waves resulted from this construction affecting navigation. Physical models were constructed of both sites to simulate present conditions, and to evaluate solution alternatives. This paper discusses the model construction, studies conducted with them, and alternatives that were evolved to solve the problems.

The coastal processes affecting Bethany Beach, Delaware were studied and the short-term and long-term trends in coastal changes were determined in order to develop recommendations for protecting Bethany against coastal erosion. Although erosion has long been considered a serious problem at Bethany Beach, the shoreline has not changed significantly since the groins were constructed nearly fifty years ago. Historical aerial photographs show that the groins accumulated sediment, thereby widening the beach. Examination of survey data revealed that substantial changes in beach sand volume occurred during the year, but the annual change in volume was very small. Considerable changes in elevation were observed in depths previously thought to be below the depth of closure. These and other aspects of the study are discussed in the paper. Refs.

In order to assess the technical feasibility of a long term maintenance dredging plan at Oregon Inlet, a simple procedure was devised to evaluate the capabilities of existing ocean going hopper dredges to maintain an ocean entrance channel in an inlet environment characterized by wave climate and resulting influx of littoral material as severe as any Atlantic coast location. The dredging analysis procedure described in this paper was used to evaluate dredge plant capabilities under the operational constraints imposed by depth limitations resulting from the continuous influx of sediment into the project channel, the wave climate, and dredging production capacity in terms of actual hopper capacity and cycle times for different disposal schemes. The shoaling and dredging simulation procedure is described interms of its application to the proposed navigation project at Oregon Inlet, NC.

Local morphological changes beneath pipelines originating from hydraulic conditions show variations which are on a relatively small scale compared to the water depth. A numerical model to compute these very local hydraulic conditions is essential for the study of scour problems as for example can occur with a submarine pipeline. A detailed computation of bed shear and turbulence characteristics is provided by the model presented in this paper. It has been used to obtain the sediment transport capacity along the bed near a pipeline. Although the bed shear is the leading parameter for the sediment transport a combination of the latter with an empirical bed load formula seems to result in a rather rigid schematization of the complex sediment transport for the presented examples of local scour. The computed bed changes include ripple development.

A very wide variety of conceptual models has been used to explain the movement of sediment in the nearshore region. While there is general agreement that the incident waves are primarily responsible for the mobilisation of sediment, many processes have been proposed as the transport agents, for example, wave drift velocities, wave assymetry, longshore and rip currents,undertow, the downslope component of gravity. As it is currently difficult to make reliable point measurements of sediment transport, many of these ideas can not be tested directly. However, in many cases, detailed measurements of the velocity field in the water can be used to examineat least the relative importance of these possible processes. The situation is complicated by the lack ofaccepted formulae for sediment transport. The result isthat the velocity measurements are also being used to examine the ‘reasonability’ of the various formulations.

Mechanism of scour in front of breakwaters by standing waves in two and three dimensions has been studied theoretically and experimentally to clarify the experimental conditions by which the prototype behavior could be best reproduced in laboratory. The phenomenal reproduction of scour in laboratory is satisfactory if some conditions on the characteristics of waves and bed materials are fulfilled. This enables experimental approach to find out the optimum protection methods against scour in front of breakwaters.

This paper presents a numerical model for predicting the change of bottom topography caused by coastal structures placed on a sandy beach. The model consists of three sub-models of wave transformation by varying topography and coastal structures, nearshore current and change of bottom topography. The computation of nearshore current patterns induced by the presence of a detached breakwater shows qualitative agreement with the experiment. The effects of wave and structure characteristics on current pattern and topographical change are investigated by consideration of model computation with several configurations of coastal structures such as detached breakwaters or groins. The main conclusions are that the model produces the general features of erosion and deposition caused by coastal structures and that drastic change of current pattern and bottom topography occur when reflected waves from the structures cover a large area.

An extensive investigation of tide and storm surge measurements in the coastal waters of the southeastern North Sea (German Bight) is now being concluded, giving new hints to tidal behaviour in a complex area, consisting of extended tidal flats, interrupted by islands, sand banks, estuaries and gullies. The analysis was promoted by the "German Coastal Engineering Board" (KFKI) and will be the basis of further investigations of the storm surge conditions in tidal estuaries.

Field studies were conducted in November 1979 to measure suspended sand transport on Twin Harbor Beach, Washington U.S.A. This beach has an average slope of 0.02 and is composed of well-sorted sand with a mean diameter of 0.21mm. The significant height of breaking swells approaching the beach at small angles can be estimated from variance spectra of water level by 4.36 ${\sigma }_n$ . In the surf zone significant wave heights are linearly related to the local mean water depth by $\gamma ={\text{H}}_{\text{s}}/h=\mathrm{0.45.}$ Variance, ${\sigma }_n^2$ in the gravity wave band (0.048 to 1.0 Hz) is proportional to water depth squared. Low-frequency variance (less than 0.048 Hz) although not systematically related to water depth, is usually largest in the inner surf zone where breakers are small.

Sand suspension is correlated with strong offshore flows that recur at about one-fifth the incident wave frequency. Vertical mixing of sand in the water column by these water motions rather than turbulence generated by shear at the bed associated with individual wave oscillations is a key mechanism in sand transport on dissipative beaches.

The largest sediment loads occur in the inner surf zone where lowfrequency motions dominate the breakers. Maximum longshore transport rates, however, were measured in the middle of the surf zone because of the higher longshore current speeds there. The suspended load probably accounts for as much as 45 percent of the litoral drift on a dissipative beach exposed to moderately-high swells approaching the shore at small angles.

The suspended sediment distribution and longshore sediment transport characteristics at Leadbetter Beach, Santa Barbara, California were investigated using a series of miniature optical backscatter sensors which can measure particle concentrations as high as 180 gm/l and have 10 Hz frequency response. Vertical arrays of sensors were maintained at up to four positions across the surf zone during 7-25 February 1980 and were operated concurrently with pressure sensors and current meters. Data were collected on a daily basis over 2-4 hour periods.

The data were analyzed to reveal concentration profiles of suspended sediment, the average suspended sediment loads, and the longshore particle flux in relation to varying wave conditions. Results show that sediment transport occurs as individual suspension events related to incident wave motions and infragravity motion oscillations within the surf zone; suspended sediment concentration decreases approximately logarithimically away from the seabed; the maximum values of longshore transport rates occur in the mid-surf zone; and the measured suspended sediment longshore transport rate is equal to the total longshore transport rate as predicted by existing transport equations.

This paper is concerned with wave-induced seabed forcing functions and sediment responses on the Australian South East Continental Shelf. The transfer of surface displacement energy to near-bed oscillatory water movement energy is examined with respect to linear and second order wave theories. Seabed sediment responses are examined by comparing field bedform size data to laboratory data with a view to determining characteristic spectral parameters that may be applied with existing theories to predict sediment responses under natural wave spectra. A rippled bed incipient motion criterion incorporating the contribution to boundary shear stress made by the presence of bedforms as well as particle size is developed empirically from field data using dimensional analysis techniques.

The Danish Natural Gas and Oil Transmission system included the landing of a 30 ft gas pipeline and a 20 ft Oil pipeline in a common shore approach at the Danish ft Sea Coast. The two pipes were pulled ashore in a common pre-dredged trench into a sheet piled cofferdam across the beach. After termination of the pulls and backlaying the trench was left for natural backfilling. The backfilling was monitored for one year together with the environmental conditions. This paper discusses the monitoring program and resulting data, including site conditions, environmental conditions, wind measurements, wave measurements, calculation of longshore transport, and related subjects.

Field campaigns were conducted in 1981 and 1982/83 on the Dutch coast near Egmond. Measurements were made of surface elevations, water velocities and sediment concentrations in 3 to 8 surf zone locations and 2 to 5 offshore locations simultaneously. A total of 50 measurement series was obtained under a variety of weather conditions, resulting in offshore wave heights of 0.2 to 4.6 m. A description is given of the field set-up, the instruments and measurements, and the collected data. The quality of the various measurement systems and the data produced has been investigated extensively by intercomparison of instruments and devices in the field. The results are reported here.

Both the concentration of suspended-load and the current velocity have been measured continuously in the surf zone. In order to measure the concentration of the suspended-load in the surf zone, a optical densitometer has been developed. The current velocity was measured by means of electromagnetic current meters. According to data analyses, the mean concentration of the suspended-load is high in the final breaking zone and in the breaker zone. In the final breaking zone, the concentration fluctuates with the period of the incident waves. On the other hand, it fluctuates with the period longer than 40 seconds in the breaker zone and it becomes high when the current is offshoreward. The directions of the net transport of the suspended-load in the middle layer in and near the surf zone are offshoreward.

A method is presented for predicting shoaling in dredged channels and basins where deposition of finer sediment fractions carried in suspension by tidal currents occurs.

The method is based on the analysis of hydrographic surveys of different dates, which show the hydrographic evolution of dredged areas located in the site or in its vicinity. It can also be applied to experimental dredged pits.

Results obtained from the analysis of surveys are worked out by using mathematical expressions deduced from a simplified hypothesis, empirically based. Parameters are determined which can be used to predict shoaling either when new dredgings are made or when previously dredged sites are deepened.

The three most common survey techniques used to measure nearshore profiles are (1) conventional boat-sonic depth sounder; (2) hydrostatic pressure profiler; and (3) the self powered Coastal Research Amphibious Buggy (CRAB). Theory of operation and methodology used for each technique are summarized and evaluated. Three separate field tests using survey data from each technique are evaluated for system repeatability. Data reduction, sea surface correction, and filtering methods for boat-depth sounder survey data are examined.

The longshore variability of wave run-up from a natural beach is examined using data from a large field experiment at the Field Research Facility in Duck, North Carolina, in October, 1982. Two particular runs were selected for intensive analysis. These were chosen to represent a dissipative and a reflective surf zone condition, so have I ribarren numbers 0.97 and 1.81 respectively. The dissipative data run showed much more uniform statistics in the longshore than did the reflective run. Also, the dissipative run was dominated by the infragravity band energy while the reflective run was dominated by the incident band. Selection of several important frequency bands for frequency-domain EOF analysis showed that the lower frequency peaks appeared to be associated with leaky modes (very long longshore wavelengths) and the pier had little influence. On the other hand, higher frequencies were clearly influenced by the pier in both amplitude and phase. An interesting subharmonic peak from the reflective run appeared to be a low (but not zero) mode standing edge wave.

A new technique, time exposure photography, is introduced. It allows the quick determination of longshore variability such as would be produced by a dominant standing edge wave. It can also be used to image offshore bathymetry and sand bar systems.

In October, 1982, a multi-agency nearshore processes experiment was conducted at Duck, NC to measure the nearshore morphological response to storm-induced waves and currents. The experimental setting for a series of companion papers is described, as are the oceanographic and meteorological characteristics of the storms. Rapid changes to the nearshore bar system occurred during the early stages of the first storm, and the bar developed a pronounced crescentic configuration during subsequent periods of high waves. Much of this activity is attributed to the effects of infragravity waves having periods greater than 30 seconds.

The safe entry during storms to the fishing harbour at Wheatley on Lake Erie was compromised by breaking waves at the harbour entrance. These waves approach the entrance from a narrow easterly sector due to storm tracks, fetch limitations, and refraction. Using a physical model, a small offshore breakwater was selected as the best solution to eliminate the breaking waves. During the six years since construction, the breakwater has performed satisfactorily and has had a negligible effect on the littoral processes as determined from regular bathymetric surveys.

Flow data were obtained in the surf zone across a barred profile during a storm. RMS cross-shore velocities due to waves in the infragravity band (wave periods greater than 20 s) had maxima in excess of 0.5 m/s over the bar crest. For comparison to measured spectra, synthetic spectra of cross-shore flow were computed using measured nearshore profiles. The synthetic spectra were calculated assuming a white runup spectrum of mode-4 edge waves of unit amplitude, although the results would be essentially the same for standing waves or any edge-wave mode above 2. The structure, in the infragravity band, of these synthetic spectra corresponded reasonably well with the structure of the measured spectra. Total variances of measured cross-shore flow within the infragravity band were nondimensionalized by dividing by total infragravity variances of synthetic spectra. These nondimensional variances were independent of distance offshore and increased with the square of the breaker height. Thus, cross-shore flow due to infragravity waves can be estimated with knowledge of the nearshore profile and incident wave conditions.

Engineering projects on the continental shelf off Sydney, Australia, have stimulated investigation into the sediment transport system of the shelf. Investigation activities associated with these projects have included: definition of sea bed morphology, sediment distribution and bedform characteristics; monitoring of steady and wave induced currents; wind data collection; suspended sediment sampling; bottom camera sediment movement investigations and analytical studies of sediment reaction to sea bed forcing functions. Sea bed velocity exceedence relationships for both wave oscillations and steady currents have been determined at depths of 24 m, 60 m and 80 m. Thresholds of sediment movement have been defined. Relative sediment transport computations have been undertaken and studies of suspended sediment concentration profiles are in progress so that absolute transport rates can be determined. The prevailing conditions, which include a mainly south bound current, are seldom sufficient to induce entrainment of shelf sediments. Transport events mainly result from major storms in the Tasman Sea which produce both high energy waves and north bound currents. Although these events are rare and short lived, the combined wave and current shear produced at the sea bed during the events gives rise to entrainment conditions which result in their dominance of the shelf sediment transport system.

A field experiment has been carried out to test the hypothesis that infragravity and lower frequency waves influence patterns of erosion and deposition on the beach foreshore. The data show coherent fluctuations in the foreshore sediment level which can be related to low frequency wave motions. The fluctuations have heights of up to 6 cm with typical time scales of 8 to 10 minute periods. They can be characterized in two ways: by the progression of the fluctuation up the foreshore slope (landward), and by the decrease in the root-mean-square (RMS) height of the fluctuations as they progress landward.

Analysis of runup time series obtained by time-lapse photography concurrent with the sediment level measurements reveals long-period waves of undetermined origin which are positively correlated with the sediment level fluctuations. This strongly suggests that the waves are responsible for forcing the sediment level fluctuations.

Field measurements of suspended sediment-transport were made across a dissipative surf zone during a storm. A correlation between high suspended mass in the water column and periods of onshore flow caused a net onshore transport of suspended sediment even though the mean near-bottom flow was directed offshore. The observed onshore migration of a nearshore bar was predicted by gradients in the cross-shore suspended-sediment transport.

Foreshore sediment level and sediment size were monitored as part of an extensive nearshore processes experiment - DUCK 82. Changes in foreshore texture were compared with computed values of onshore transported material based on current measurements from the surf zone and sediment transport theory (Bagnold, 1963, 1966). Preliminary results indicate reasonable agreement between predicted size of sediment transported onshore and beach texture changes. It is also demonstrated that coarse sediment may move onshore while finer material may simultaneously move offshore.

Physical parameters controlling the development of tombolo behind offshore breakwaters are clarified on the basis of the results obtained by laboratory tests. Especially, the depositional effects are evaluated by taking a permeable type structure into account. They are wave characteristics, sediment size, the water depth where the structures are to be placed and its dimension. The amount of sand deposition behind the structures is presented by non-dimensional parameters such as the relative distances from the initial shoreline to the structure and to the breaking point of waves, the ratio of the gap width to the wave length in deep water and the ratio of the length of the offshore breakwater to the wave length in deep water.

This paper reports on model experiments and up to 20 years of practice in nature with a permeable groyne system, consisting of single or double permeable rows of wooden piles perpendicular to the beach, without bottom protection. This system costs only 10 to 25% of the impermeable stone groynes which have for centuries been used in the Netherlands.

Model experiments confirm that wave-induced currents in the protected areas are reduced to 65%, and tidal currents even to 50%, depending on the pile screen configuration. Prototype measurements could not lead to straightforward conclusions with statistical significance: the effect of the pile screens on beach evolution is partly merged into natural fluctuations and trends. Wooden pile screens do not prevent the shoreward motion of tidal channels, which can cause washing out of piles. Furthermore, constructional failures, which in the future can be avoided, at some places resulted in negative experience. It is concluded that permeable pile screens deserve serious consideration as a first flexible and cheap phase in combating coastal erosion. Its application however should be based on a thorough analysis of the local coastal current climate.

The choice of a dumping area for dredged materials must be carried out taking into account the general movement of sediments in order to evaluate the risk they represent for the zone itself, the harbourworks and the coastal area.

The use of radioactive tracers allows to study, in situ, transfer properties under tidal currents of fine sediments resuspended during the release, the distribution over the sea-bed of coarse particles and their future evolution due to currents and waves.

In this way, parameters such as transport axis, mean velocity, dispersion, dilution and bed-load transport rates are determined.

Four experiments which took place at OCTEVILLE, ANTIFER (FRANCE), SINGAPORE and ZEEBRUGGE (BELGIUM) during the ten past years illustrate the method.

The wave-driven movement of sand across the alignment of a proposed navigation channel was investigated using radioactive chromium-51 labelled tracer sand. The mean particle velocity and thickness of the mobile layer were determined over a two-month period, and an annual infill rate estimated.

Wave height and period were measured concurrently. Despite two storms, during which near-bed oscillating velocities of 1.5 m s^-1 were calculated,the sand transport at 10 m (BMWL) appears to occur within the wave boundary layer. Onshore transport in the direction of wave propagation, due to mass transport velocity and wave asymmetry effects, was easily identified.

Tidal currents up to 1.2 m s^-1 (at 3 m above bed) had less than the expected effect on the tracer dispersion pattern.

A new method for continuously recording sediment concerttrations with high accuracy has been developed. It is proposed to apply the method for In-situ measurements in connection with investigations of tidal control and sediment transport induced by shipping traffic.

The operating principle is as follows: at the measurement location, sediment laden water is continuously sucked-in by means of a pump and is forced under pressure into a hydrocyclone ( solid bowl centrifuge ) through a delivery pipe of varying length. Here the extracted sediment flux (particle size = 5 μm) is delivered by the shortest route to a settling tank and continuously weighed under water (wet-weighing). Following calculation and appropriate adjustment to the sample discharge ( Q ) the weight increase for selected time intervals ( ΔG (Δt)) yields the mean concentration for the time interval ($\overline{\text{c}}$ (Δt)) in weight / unit volume ( mg/1 ) (direct measurement, calibration not required ).

Details and experiences of the 3 major development stages will be described. A fully-automatic instrument for continuously measuring nonsteady sediment movement is now available. The instrument may be installed above as well as below water as desired.

Prototype experiments on rip currents and sediment transport around structures were conducted at two fishery harbors on microtidal high energy beaches facing the Pacific Ocean. The purpose of the experiments was to examine the performance and mechanism of rip current barrier structures on harbor shoaling. Based on the results of five experiments, the wave breaker heights during which varied from 1.1 m to 3.0 m, it is concluded that shore-parallel rip current barriers are effective if their length is greater than the surf zone width and if they are located outside the surf zone. When the above conditions are satisfied, the rip current barrier is a cost-effective measure against shoaling of small craft harbors.

Large breakwaters and groins are being constructed at Oarai Harbor, Japan. As a result the beach is significantly deforming. The first part of this paper documents past and recent shoreline change at Oarai. The general characteristics of the offshore waves, breaking waves, and longshore current pattern are described and used to explain qualitative features of the observed shoreline change. The second part presents results of numerical simulations of shoreline change at the site which occurred over different time periods. The model includes three sources of wave diffraction, a rigorous formulation of the seawall boundary condition, and sand bypassing at groins. The modeling of historical shoreline change was reasonably successful. As an exercise in investigating problems associated with prediction, the model was used to forecast the shoreline position at the site five years from now. The prediction of the wave history was the main problem encountered. A simple intuitive method was devised to estimate the probable range in variation of the wave history, and the results are discussed in connection with the shoreline forecast.

In the present study, two-dimensional laboratory experiments were performed to investigate the sediment transport due to waves on a fixed sloping beach. Polystyrene particles and glass balls were used as tracers to determine the mass transport velocity near the bottom and the net transport velocity of sediment moving on an impermeable slope. Relationships between the mass transport velocity of water and the net sediment transport velocity are investigated experimentally. The mechanism of two-dimensional beach deformation from an initial uniform slope toward an equilibrium profile due to bed-load movement is discussed on the basis of spatial distributions of the net sediment transport velocity. In addition, some results of experiments using a movable bed are presented to confirm the validity of a beach deformation model derived from the discussion of the tracer experiments.

The paper discribes the littoral drift along the Eastfrisian Islands. The inlets between the islands are crossed by offshore bars which migrate round the deep channel of the inlet northwards on a bow. Their point of approaching the next island scatters. That causes periods of accretion during the approach of the bars on the beach and of erosion in certain beach sections without bar approach and sand supply.

When an offshore bar approaches a beach it moves a swash channel ahead as a rule. This causes a rising beach erosion by currents and wave wash and hinders the settling of the bar on that beach section. This paper reports a field study on influencing the migration of a bar by building a sand dam through such a swash channel. It was intended of feed the eroded section of the beach by the steered approach of the bar. The accretion by the desired approach of the bar on the eroded beach section was higher than expected and measured more than 270 m³/m.

Analyses were performed on a 6$\frac{1}{2}$ year time series of daily wave data, daily beach state data and monthly beach and surf zone profile data. Beach state changes, which involve the relatively rapid redistribution of sediment already stored locally, are predictable in terms of Dean’s (3) simple parameter Ω = H_b, /(w_s T) where H_b, is breaker height, w_s is sediment fall velocity and T is wave period. Each of the six beach states has a different equilibrium range of Ω values and the direction of change (erosion or accretion) depends on the departure from the equilibrium association. Empirical eigenvector analyses performed on the profile data permitted separation of different response components. The lower order vectors expressing the grosser aspects of the profile features such as beach volume and surf zone gradient displayed maximum variance at periods in excess of 2 years whereas much shorter response times characterized the higher order components such as bar-trough shapes and asymmetries. We infer that the fast response, and more predictable, components of beach and surf zone change largely involve smaller scale sediment exchanges between the beach and surf zone whereas the slower responses are related to larger scale exchanges between the surf zone and the inner continental shelf.

The study of beach morphology, for example, its changes with wave and tide conditions, is facilitated by the development of simple numerical values which characterize the morphology. Multivariate (EOF) analysis of topographic contour data is a means for determining important morphologic components which vary independently. If these components correspond to familiar shoreline features the researcher considers important, then the development of each component can be quantified by its significance, or weighting, in each sample. Alternatively, the components may be complicated and not useful in quantifying beach morphology. A study of these morphologic components, however, can provide insights into the dynamics of the beach system.

If multivariate analysis produces complicated components, an alternative approach, of subjectively identifying shoreline characteristics of interest, can be taken. The characteristics may be the same as those frequently used in past studies, such as beach slope or sand volume. It is likely, though, that EOF analysis of topographic data will suggest more sophisticated characteristics which should be used. Some of these, for example, mean shoreline position or amplitude of a rhythmic shoreline, may be easily quantified, whereas, others such as longshore position of rhythmic features or cusp width relative to embayment width, may be more difficult to quantify.

Both of these analysis approaches were applied to beach survey data obtained over a period of ten months (including the El Niño winter of 1982/83) on Siletz Spit, Oregon. The shoreline was rhythmic with an 800-850 m wavelength throughout the duration of the study. Rhythmic topography has been associated with significant past beach and dune erosion at this site. Hence, it is of interest to describe the beach morphology quantitatively, and relate three dimensional beach changes to wave and tide conditions.

Field observations and EOF analysis determined three important characteristics of shoreline morphology: overall accretion/erosion of the shoreline, amplitude of the rhythmic topography, and longshore position of the rhythmic features. EOF analysis was not able to separate these three morphologic components. They were quantified, respectively, by mean distance offshore to a specified contour, the standard deviation of a contour about that distance, and the weights of the first eigenvector calculated by EOF analysis of topographic contour data normalized to the same mean and standard deviation.

Mean shoreline position was shown to move onshore with increasing wave height, as expected. Rhythmicity amplitude varied inversely with the wave height, but there is evidence to believe this is not the case for all winters on Siletz Spit. Rhythmic topography formed and increased in amplitude under depositional conditions during the ten months of this field study. Due to differences between the rates of change of mean shoreline position (up to 5 m/2 wks) and of rhythmicity amplitude (up to 10 m/2 wks), rhythmic topography should be able to develop under erosional conditions as well.

In many beach systems, EOF analysis of topographic contour data should not be expected to produce simple morphologic components which correspond to familiar shoreline features. EOF analysis can be an aid in furthering one’s understanding of the dynamics of a beach system and can be a useful guide in subjectively identifying important shoreline characteristics. In some instances, EOF analysis of a modified data set may allow one to quantify one or more of these characteristics.

Prediction of depositional patterns in estuaries is one of the primary concerns to coastal engineers planning major hydraulic works. For a well-mixed estuary where suspended load is the dominant transport mode, we propose to use the divergence of the distribution of the net suspended load to predict the depositional patterns. The method is applied to Hangzhou Bay, and the results agree well qualitatively with measured results while quantitatively they are also of the right order of magnitude.

A description is given of laboratory experiments on uniform longshore currents and the comparison of the data with longshore current profiles predicted by a mathematical model. For the mathematical model it is assumed that longshore current generation takes place between the plunge line and the shoreline (instead of shoreward of the breaker line) and Battjes’ (2,3) lateral friction model is applied. Good agreement between theory and laboratory data is achieved with realistic values of the bottom roughness.

A nearshore current modeling system has been assembled which consists of a shallow water directional spectral wave model, an algorithm to convert directional spectral output from the wave model to radiation stress components and a current model to calculate nearshore wave-driven currents from the radiation stress field.

Wave-driven longshore currents have been hindcast at a coastal site for two wave conditions during a northeaster type storm off Cape Hatteras in October 1982. For one event, when local winds were strong, the calculated longshore current is only a fraction of what was measured. This discrepancy is attributed to a non-wave-driven component of flow which was present but not represented in the model. During the other event, winds were low and long period swell was present. In this case, the calculated and measured longshore flow agree well.

Both measured and calculated shore normal profiles of longshore current in each case show a generally uniform structure across the surf zone. This is in contrast to theoretical profiles based on monochromatic waves which show a maximum in longshore flow near the breaker line.

On the basis of many pairs of simultaneous measurements of wind speed onshore, U_LAND, and offshore, U_SEA, in areas ranging from Somalia, near the equator, to the Gulf of Alaska, and under conditions ranging from breeze to hurricane, it was found that for operational use U_SEA = 3.93 ${\text{U}}_{\text{LAND}}^{1/2}$ for U_LAND < 10 m S^-1 (or 20 kt); and U_SEA = 1.24 U_LAND for U_LAND ≤10ms^-1 . These formulas were developed mainly from theoretical considerations and were verified by field measurements.

Field measurements of steady current profiles under the influence of waves are described, including a technique for obtaining an extra independant estimate of the friction velocity. Field and laboratory measurements are analysed for the effect on apparent bed roughness by superimposing waves on a current. Finally the applicability of the eddy viscosity concept to combined flows is examined. The conclusion is that in general, different eddy viscosities must be applied to different flow components.

It is well known that on a three-dimensional beach large volumes of water carried shorewards by the breakers feed longshore currents, which eventually escape back through the breaker line, often as rip currents.

In a steady two-dimensional situation, however, the mass flux represented by (among other things) the surface roller in the breakers returns as a seaward current close to the bottom. This current is called the undertow.

In this paper theoretical results for the undertow are compared with the results of recent laboratory experiments.

Field measurements using electronmagnetic flowmeters on two natural beaches are presented. Mean flows are compared to theory. The horizontal and vertical structure are discussed.

Characteristics of the oscillatory boundary layer flow above rippled beds were investigated through experiments and numerical calculations. Experiments were conducted in an oscillatory flow tunnel. Velocities above symmetric and asymmetric ripples were measured with split-hot-film sensors under conditions of both sinusoidal and asymmetric oscillations. The stress field in the boundary layer was evaluated based on the distributions of the measured velocity and Reynolds stress. Relations between vortex formation and turbulence were examined, and effects of the asymmetry of oscillatory main flow and of ripple form on the velocity field were discussed. Numerical calculations were carried out by integrating the Navier-Stokes equations with an implicit finite difference scheme. Formation of a lee vortex above ripples was simulated in the calculations. The bottom shear stress and the energy dissipation rate were estimated based on the results of the experiments and calculations.

Different syphon type suspended load probes were used together with a newly developed ‘carousel’ sampler for measurements of the instantaneous sediment concentration in turbulent oscillatory flow over a sand bed. Shields parameters were well above the rippled/flat bed transition region, resulting in intense sediment transport over a flat bed. The measurements were performed at different levels in a large oscillating water tunnel. They showed some characteristic features of the temporal concentration variation and of the variation with height of the mean concentration. Also a pronounced effect of the orientation of the suction tube relative to the flow was observed.

A series of mobile bed model tests of a prototype circular sand island was performed to determine scale effects. It was found that scale effect was largely a function of mobility number with some secondary effects of Reynolds number, bedform and critical profile depth. It was concluded that a model series using prototype sand grain size is necessary at this time to effect successful extrapolation to prototype.

An analysis of 17 tropical cyclone impacts along barrier islands in the Gulf of Mexico has led to the following conclusions: 1) tropical cyclones are the primary mechanism of barrier island overwash and breaching, 2) landward-directed and seaward-directed overwash flow can breach barrier islands, 3) storm track orientation to the shoreline controls the direction of barrier island breaching, 4) shore-normal and right-oblique hurricane impacts breach barrier islands by landward-directed overwash flow, and 5) left-oblique hurricane impacts breach barrier islands by seaward-directed overwash flow.

In order to cope with such environmental problems as shoreline change and diffusion of discharged warm water and contaminations in the surf zone, it is necessary to predict velocity vector field due to nearshore currents accurately.

The present study is aimed at establishing a mathematical model applicable to the prediction of nearshore currents on actual coasts which have complicated bottom configurations. First, to investigate the mechanism of nearshore current generation hydraulic experiments were carried out. By the experiment it was made clear that the generation of a longshore current depends mainly upon a difference in mean water level in the longshore direction. After investigating estimation of radiation stress terms on the basis of the information obtained from the basic experiments a mathematical model of nearshore currents was developed and validity of the model was verified by both hydraulic model tests and field survey.

A second-order closure model of turbulent transport and recent model applications to some problems of practical importance in coastal engineering are presented. Particular examples considered are the turbulent wave boundary layer under a linear and a cnoidal wave; current-wave interaction within the bottom boundary layer; mixed layer dynamics; wind-driven currents in a channel. Comparisons are made between the computed results and field/laboratory data.

This study presents a new mathematical method calculating the water particle velocity in the wave-current co-existing systems. A boundary layer thickness Δ_w in the co-existing system is expected to be variable with the water particle velocity ratio of wave component to current component. In this method, the boundary layer equation is solved as a free boundary problem by treating Δ_w as an unknown boundary value. Several characteristics of the turbulent boundary layer such as the friction factor, friction velocity, boundary layer thickness, etc. are calculated by this method and the effect of the wave-current velocity ratio on them is discussed. Furthermore, the velocity reduction of the current due to wave superimposing is investigated.

In addition, near-bottom velocities are measured by a laser-doppler velocimeter in the pure current, the pure wave and the wave-current co-existing fields. These results are compared with calculated ones by this mathematical method.

The paper gives details of a study to refine and further develop a two-diirensional depth average numerical model to predict more accurately the eddy shedding features often observed in the lees of headlands. Details are given of the application of the model to Rattray Island, just east of Bowen, North Queensland, Australia, where the strong tidal currents flowing past the island give rise to separation and hydrodynamic circulation in the lee of the island.

In the governing differential equations used to predict the secondary circulation, particular emphasis has been placed on the representation of the shear stresses associated with the free shear lateral mixing layer in the downstream wake of the headland. Use of an experimentally determined lateral velocity distribution in the shear layer, together with an eddy viscosity approach, have led to the use of a relatively simple turbulence model, including both free shear layer and bed generated turbulence. A comparison of the numerically predicted velocities with corresponding field measured results around Rattray Island has shown an encouraging agreement, although there were some differences. The main difference between both sets of results was that the vorticity strength of the secondary circulation predicted in the numerical model was noticeably less than that measured in the field.

Any numerical solution of the convective transport equation in an Eulerian framework will exhibit inherent numerical dispersion and solution oscillations. The magnitude of such numerical errors is often so severe as to destroy the value of many computed solutions. A successful and economical algorithm for the convective transport equation in one spatial dimension has been published recently by one of the authors (RJS), in which an exact solution is achieved by means of a moving coordinate system. The present study describes the extension of this work to the more important and challenging two-dimensional case.

This paper discusses the need to incorporate a reliability analysis in the design procedures for rubble mound breakwaters. Such an analysis is defined and a suggested approach is outlined. Failure mechanisms are analysed and categorized in Damage Event Trees. The probability of failure is computed using a level III simulation method to include time and cumulative effects and to account for skewed probability distributions. Typical outputs of the computer program are shown and compared with results according to traditional design approaches. The paper concludes that there is a definite need to include reliability analysis in the design procedures for larger breakwaters and such an analysis must consider the accuracy of design parameters and methods.

A number of studies have been undertaken recently to select optimum methods for rehabilitating damaged breakwaters in the Mediterranean and in the Atlantic Ocean. This paper outlines the approach to these studies and discusses the relative merits of the various concepts considered for repairing the damaged structures. Based on case studies of two projects, the paper also shows how the principle concepts have been successfully applied.

In setting-up a breakwater test in a laboratory flume, the conventional practice is to scale geometrically the armour units, underlayer rocks and core material based on the Proude scaling criteria. However, because some of the properties of the water are not scaled for a model test, the Reynolds scaling law is violated. This can result in improper water flow distribution through the model breakwater. To investigate this problem, a series of tests were performed with a model breakwater in which the permeability (and porosity) of the core was varied over a wide range, and the hydraulic response and breakage of the armour units were measured. It was found that the overall stability of the breakwater could be drastically affected if the flow in the core is scaled incorrectly.

Photogrammetry has been applied as a technique to monitor the stability of dolosse on the Manasquan Inlet, New Jersey jetties. These jetties were rehabilitated between 1979 and 1982 with 16-ton steel-reinforced dolosse. The jetties have been exposed to a number of storms since 1982, including a design-level storm in March 1984. The photogrammetric measurements have provided a detailed record of the magnitude and direction of dolos movements in response to these storm events. Standard leveling techniques have been used to check the accuracy of the elevation data derived from photogrammetry. This paper describes the methods used in this monitoring effort and the results obtained from the photogrammetric measurements. Also presented are data on the structural integrity of the steelreinforced dolosse.

Limited data are presented for the ship-wave attenuation of a prototype concrete pontoon floating breakwater. Results are compared with wave attenuation performance of a breakwater of identical crosssection and similar anchoring configuration as predicted by model tests using monochromatic waves. Field test procedures and limitations are described.

A preliminary assessment of wave energy conversion by means of the Stellenbosch Wave Energy Converter (SWEC) has indicated the viability of this system as a supplementary source of electric power.

In order to refine the preliminary estimates of the cost of power delivered, detailed design of a 770 MW (rated output) installation at a site 60 km north of Cape Town has been undertaken.

This paper describes the power conversion characteristics of the SWEC at the proposed site, structural design of the collector arms and generating tower for both mass gravity or piled solutions, a construction scenario involving a casting harbour in nearby Saldanha Bay and the towing and placement of 53 m long precast modules, and finally an assessment of the environmental impact of the proposed 40 km array on the adjacent coastline.

The proposed system is found to be both technically and economically feasible and offers a useful contribution towards future electric power supply.

A rational design procedure for rubblemound breakwater protection which will ensure both the structural integrity and hydraulic stability of individual concrete armour units and the overall armour system is presented. The procedure involves new experimental techniques for measuring strains in model concrete armour units in a hydraulic model of a breakwater subjected to simulated prototype wave attack and analytical techniques for determining equivalent prototype loads on units. Selected design loads are used to define the resultant stress distribution to allow the designer to take the necessary measures to ensure the structural performance of the unit in a breakwater environment.

The reliability of rubble mound breakwaters depends on the hydraulic stability and the mechanical strength of the armour units. The paper deals with the important aspect of fatigue related to the strength of concrete armour units.

Results showing significant fatigue from impact tests with Dolosse made of unreinforced and steel fibre reinforced flyash concrete are presented. Moreover universal graphs for fatigue in armour units made of conventional unreinforced concrete exposed to impact load and pulsating load are presented. The effect of fibre reinforcement and the implementation of fatigue in a stochastic design process are discussed.

As part of a program to study the hydraulics of wave attack on rubble mound breakwaters tests were made on model armour units in a steady flow through a layer laid on a slope. The flow angle has little effect on stability for dolosse or rock layers. The head drop at failure across each type of layer is similar but the dolosse layer is more permeable and fails as a whole. There was no viscous scale effect. These results and earlier tests in oscillating flow suggest a ‘reservoir’ effect is important in the stability in steep waves.

The objective of the present research project is to give new practical design formulae for rubble mound slopes under random wave attack. The study is based upon a series of model tests. More than two hundred tests have been performed in order to vary systematically all the relevant variables. The main shortcomings in Hudson-type formulae have been solved as a result of the present series of investigations. Stability formulae are given which include the influence of wave period, number of waves, armour grading, spectrum shape, groupiness of waves and the permeability of the core.

Coastal engineers have long relied upon bathymetric surveys to determine the extent of underwater damage to jetties and breakwaters. Though such surveys supply important information about variations in water depth around structures, they alone do not show in sufficient detail the nature of the material on the structure, the extent of subbottom features, or the nature of the subbottom upon which the structure sits. However, by conducting bathymetric surveys in conjunction with other remote-sensing techniques and diving observations, it is possible to obtain more complete knowledge of the subaqueous condition of coastal structures.

During the summer of 1983 and the spring and summer of 1984, we conducted side scan sonar and shallow subbottom surveys in conjunction with bathymetric and diving surveys along three northern California coastal structures to determine the condition of the structures before extensive damage occurred. Then, we evaluated the applicability of the data collection techniques for condition surveys in general.

Two of the structures surveyed are the parallel jetties that protect the entrance to Humboldt Bay, California, and the third structure is the outer breakwater at Crescent City, California. Bathymetric records and sonographs from Humboldt Bay show deep holes along much of the inside of the south jetty and off the heads of both jetties. The subbottom record from inside Humboldt Bay shows a subsurface fault, the extension of which would run under the south jetty.

Sonographs from Crescent City show significant bedrock outcrops throughout the area outside the breakwater, making it difficult in places to identify the toe of the structure. The subbottom record shows that pockets of sand exist amidst the bedrock, but they are generally less than 2 m (6 ft) in thickness.

We found that the side scan sonar is an excellent tool for defining the toe of the structure; also, when waves are low, it can be useful in determining armor types and the slope of structures Our subbottom system provided information on fault and bedrock locations; however, other systems need to be tested to see if any of them can locate buried armor near the structures.

Predictions of the dynamic response of a floating breakwater obtained from a frequency domain analysis are compared with full-scale field measurements. Those parameters prominently affecting accurate response predictions are identified and discussed.

During the spring of 1982 a new container terminal was under construction at the Port of Haina, Dominican Republic. Changes in design conditions due to damages to the protective breakwaters at the port entrance required modifications to the design of slope protection under the pier. The stabilization of the rubble slope was, in fact, a stop gap measure in that repairs would be instituted on the breakwaters in the near future.

Due to a lack of suitable stone, the location of structural elements already in place and severe time constraints, an asphalt coating over relatively light weight rubble was selected to armor the slopes under the pier. The asphalt coating was prepared in a locally available batching plant and placed on-site using a crane equipped with a 4 cubic yard bucket. As a result of the use of the asphalt coating, construction delays were minimized and adequate slope protection was provided for the container pier without extensive design modifications.

The purpose of this paper is to discuss the advantages and disadvantages of the use of asphalt in the construction of shore protection facilities in the context of the site specific application at the Port of Haina.

An inspection survey of the Reef Runway Wave Protective Structure at the Honolulu International Airport was accomplished in 1982 to access the performance of the dolos and rock armored structure to date. The inspection showed the structure to be performing adequately considering that the design wave conditions were experienced.

Steel cylinders were submerged on a platform in the South Pass region of the Gulf of Mexico for one year to accumulate biofouling for later laboratory testing to determine wave force transfer coefficients. They were positioned at −55, −140, and −190 feet below the still water surface. Laboratory tests comprised steady tow up to Reynolds number cd 7x10⁵, and periodic waves up to Reynolds number of 1.6x10⁵ and Keulegan-Carpenter number up to 25. The force transfer coefficients for the −55 cylinder were about equal to those for a sand roughened cylinder with relative cylinder roughness, ε/D, of .03, where ε is the height of the equivalent sand roughness size and D is the smooth cylinder diameter. The drag coefficient for very high Keulegan-Carpenter number, or steady tow, is about 1.0 if the effective cylinder diameter is taken into account, for the rougher cylinders.

Fatigue damage to marine pipelines subjected to wave forces is evaluated using time-domain and frequency-domain methods. Spectral techniques are applied to North Sea, Gulf of Mexico and offshore Atlantic Canada wave conditions. Time-domain analysis is applied to wave conditions in the Canadian North Atlantic Ocean.

The frequency-domain analysis is performed using spectral and probabilistic techniques suggested by L. Borgman {?.). The pipeline dynamic characteristics are described by classical analytical descriptions. The time-domain analysis computes time histories of wave force loading on the submerged pipeline from actual wave records. The traditional Morison wave force equation is used to obtain the time history of the loading on the pipeline. Empirically determined wave spectra are shown not to produce as good a correlation with the deterministic results as the actual wave spectra.

Free spanning submarine pipelines subjected to cyclic surface wave loading accumulate strength reductions leading to failure from material fatigue. The Palmgren-Miner rule for the linear accumulation of fatigue damage is applied to evaluate the time to failure. The American Welding Society X-X stress accumulation curve is applied.

The results of the deterministic analysis were compared with those of the more efficient spectral analysis. It is shown that comparable results can be obtained from the spectral analysis provided the actual spectra of the water surface elevation is employed in the spectral analysis.

The design scheme of the Zeebrugge Outer Harbour, Belgium, consists of two breakwaters protruding into the sea as far as 1,750 m beyond the existing môle or 3,000 m out from the coastline. The west outer breakwater is 4,280 m long, the east breakwater runs 4,030 m out from the sea-wall. The east outer harbour will accommodate terminals for liquid bulk products such as LNG. The west outer harbour will provide space to install two harbour basins to suit general cargo, hazardous cargo, container and ferry traffic.

In the paper emphasis is put on the use of sand in the design of the breakwaters, firstly as part of the foundation by replacing the little resistant top layers by dumped sand, and secondly as part of the core, by dumping sand above the original sea-bottom. In as far as proposed criteria were not fulfilled, the dumped sand had to be compacted. Two methods are discussed : compaction by vibrating needles and compaction using explosives.

An extensive program of stability experiments in a highly detailed three-dimensional model has recently been completed to define a reconstruction technique for a damaged breakwater (Lillevang, Raichlen, Cox, and Behnke, 1984). Tests were conducted with both regular waves and irregular waves from various directions incident upon the breakwater. In comparison of the results of the regular wave tests to those of the irregular wave tests, a relation appeared to exist between breakwater damage and the accumulated energy to which the structure had been exposed. The energy delivered per wave is defined, as an approximation, as relating to the product of H² and L, where H is the significant height of a train of irregular waves and L is the wave length at a selected depth, calculated according to small amplitude wave theory using a wave period corresponding to the peak energy of the spectrum. As applied in regular wave testing, H is the uniform wave height and L is that associated with the period of the simple wave train. The damage in the model due to regular waves and that caused by irregular waves has been related through the use of the cumulative wave energy contained in those waves which have an energy greater than a threshold value for the breakwater.

Ten years after it was completed, and intact as originally built, West Breakwater at Diablo Canyon on the central coast of California was severely damaged during a wave storm in January 1981. The paper describes uncommonly detailed site investigations that followed and the development of a large three-dimensional hydraulic model for discovering the specific mechanism that precipitated the damage, and then for verification of the effectiveness of concepts for rebuilding the breakwater to resist greater storm events than had been used for the original design. Unique procedures for modelling contorted terrain, for producing reflection-corrected irregular wave systems, for eliminating abnormal waves at the start and at the end of test runs are discussed. The tested final concept for reconstruction is described and surveyed results of closely packed Tribar armoring, as reconstructed in 1983-84, are illustrated.

The authors conclude that investigations of problems involving wave attack on the termini of rubble mound breakwaters should always be undertaken with the aid of three-dimensional physical modelling unless owner and engineer are in a position knowingly to take large risks. Further, that physical modelling at suitably large scale is virtually mandated if the submerged terrain at a site is not regular.

A theoretical analysis using an integral equation derived for the unknown horizontal velocity component in a pervious wall is proposed for estimating the reflection and transmission coefficients of upright structures for wave dissipation, and various factors related to wave and structural conditions having influences on the wave dissipating characteristics are investigated for a breakwater with pervious vertical walls at both seaward and landward sides,

In two-dimensional experiments, the theoretical results are in. good agreement with experimental data with respect to reflection and transmission coefficients, and therefore, the wave dissipating characteristics of upright structures for wave dissipation can be explained by the integral equation method theory,.

Southern California was subjected to a series of severe winter storms in 198 3 that caused record damages to the coast. In the aftermath of the storms, emergency repairs were made and new designs were developed that responded to the severe conditions. These designs were often considerably more conservative than those previously undertaken. Agencies, owners, and engineers were compelled to use both higher design criteria and longer recurrence intervals to account for the wave characteristics and water levels that caused damages along the coast. This paper briefly discusses the unusual circumstances of the storm conditions and the associated damages. The primary purpose of the paper is to present new data that incorporates the effects of the 1983 winter storms to estimate the change in perception of what the wave climate and design criteria may be in this highly developed coastline. The results indicate that the design wave height for a given recurrence interval has increased approximately 26 percent, the wave periods are longer than previously used, and the severe storms tend to coincide with the extreme water levels. The engineer should consider the impacts of the 1983 winter storms in future designs. Despite the record damages, many structures survived. Merely using the highest water elevations and most severe waves of record may not be the most prudent design criteria. The concept of project life and economics must be employed to develop a design.

A simulation method is presented to improve small craft harbour design by studying the behaviour of moored vessels in small craft harbours, using physical modelling in medium size wave basins, available at most laboratories. Instead of carrying the study in an agitation model with noored vessel models and built in a large wave basin at a large geometric scale, it is performed in two consecutive models of different scales, in a medium size basin. Transfer functions of vessel movements and mooring and fender forces are determined in the first model, for representative types of vessels moored alternately at a solitary berth, under simulated inside harbour conditions and for various sea states and directions. Near berth wave spectra are obtained in the second (agitation) model for sea states covering the local climate. Integration of the wave spectra with the transfer functions leads to response spectra of vessel movements and forces. Finally, maximum movements and forces are determined from the response spectra and are used together with limiting criteria and the long term wave statistics to choose the optimum configuration of: harbour layout, types of berth structures and mooring and fendering systems.

The hydrodynamic force acting on a circular cylinder in a wavecurrent co-existing field and its generating mechanism are discussed. This study focuses on the asymmetries of both the water particle movement and the resultant vortex property with respect to the cylinder, which produce inherent characteristics in the hydrodynamic forces in the wave-current co-existing field.

First of all, the vortex property around a circular cylinder in the wave-adverse current co-existing field has been examined by flow visualization tests. It has been found that the vortex property depends on the flow characteristics around the trough phase when the wave-current composite velocity becomes maximum and can be represented with a newly proposed K.C. number for the co-existing field.

Secondly, the characteristics of the in-line force has been made clear by evaluating the drag coefficient and the mass coefficient in the expanded Morison’s equation for the co-existing field. These coefficients can be well arranged by ${\left(K,C\right)}_2^{*}$, which is one of the newly proposed K.C. numbers, and their characteristics coincide with the existing results in the wave only field. The in-line hydrodynamic force in the co-existing field can be explained sufficiently by considering the vortex property in the same manner as clarified in the wave only field.

Thirdly, the characteristics of the transverse force (lift force) are discussed in connection with the vortex properties. It has also been found that the fluctuating frequency of the lift force is synchronized with the loading wave frequency.

A series of study on wave power extractors which may utilize a part of the coastal structures has been performed by the group of faculties of Muroran Institute of Technology since 1978. Three kinds of extractor belonging to the so-called fixed type had been developed and studied in the laboratory. They are the air chamber with flap, the wave turbine system and the pendulor system. The last two systems have been subsequently studied at the field test plant constructed at Port Muroran. The study shows that the pendulor system brings an excellent power conversion efficiency.

This paper presents some results of simultaneous full-scale wave kinematic and local force measurements (field and laboratory) on a slender, vertical cylindrical pile (test-section) under shallow water conditions. The usual application of Morison’s equation is taken under critical consideration due to the real flow regime near the surf zone. The data were analyzed in the time domain as well as in the amplitude and frequency domain. Two estimation methods for force coefficients were tested and compared.

A horizontal plate laid on water surface to reduce the wave motion is proved to be effective theoretically and verified by model tests done at Tainan Hydraulics Laboratory. This principle has been put into practice on the northern coast of Taiwan for protecting a nuclear power plant cooling water intake against intruding waves.

The design and construction of wave prevention works of such type are described succinctly in the paper. Also the effect of wave diminishing has been affirmed by measuring the respective waves heights outside and inside of the wave pressing plate.

The existing breakwater at Civitavecchia Harbour, Italy, will be extended with a part of caissons. In order to investigate wave forces for this caisson, the Ministero del Lavori Public! commissioned the Delft Hydraulics Laboratory to perform a model investigation on the proposed extension. In the first part of the study quasi-static wave forces on the entire caisson were measured by means of a force measuring frame. In the second part wave impacts were recorded by pressure cells at 22 positions of the caisson.

The investigation contained two main items which are discussed in this paper:

- Comparison of quasi-static wave forces with maximum forces by wave impacts.

- Comparison of forces and impacts for a circular caisson with those measured for a square caisson.

The authors developed the numerical method to calculate the wave height distribution around a pair of breakwaters with arbitrary shape of the edge. The effect of the resonators equipped in the breakwaters on the diffracted wave height is simulated by using this method. Simulated results show that the resonators have remarkable effect to reduce wave heights in a harbor. However, in the experiments, resonators are not so effective as predicted by the theory.

This paper has dealt with the dynamic response of offshore structures to the ocean waves. In order to establish the calculation scheme for offshore structures, the methods of transfer matrices and of structural-property matrices have been introduced and applied to the analysis of dynamic response of pile structures. The validity of these calculation methods have been verified by the experiments in the laboratory.

Field measurements of the receding salt wedge were made at the mouth of the Ishikari River in October 1981. The gradually growing interfacial waves and the diffusion pattern of salinity are visualized by the Ultrasonic Method. The evolution mechanisms of waves are analysed in detail by calculating the power spectra of wave records. It is pointed out that the wave breaking, the wave-eddy interaction and the nonlinearity of waves are factors dominating the evolution. The nonlinear property of interfacial waves is studied further by watertank experiments.

Cohesive sediment related problems in estuaries include shoaling in navigable waterways and water pollution. A two-dimensional, depthaveraged, finite element cohesive sediment transport model, CSTM-H, has been developed and may be used to assist in predicting the fate of sorbed pollutants and the frequency and quantity of dredging required to maintain navigable depths. Algorithms which describe the transport processes of redispersion, resuspenslon, dispersive transport, settling, deposition, bed formation and bed consolidation are incorporated in CSTM-H.

The Galerkin weighted residual method is used to solve the advection-dispersion equation with appropriate source/sink terms at each time step for the nodal suspended sediment concentrations. The model yields stable and converging solutions. Verification was carried out against a series of erosion-deposition experiments in the laboratory using kaolinite and a natural mud as sediment. A model application under prototype conditions is described.

In commission of the Dutch Government (Ministry of Public Works), the Delft Hydraulics Laboratory carries out a long term research programme on the water quantity and water quality of the Rhine-Meuse estuary.

The researchprogramme has to provide the necessary hydraulic data as Input for a management decision-making process. The programme is based on an "integrated approach philosophy" with respect to the various subjects to be studied and the research tools to be used (data from nature, hydraulic model, mathematical models and fundamental research). The paper presents the essentials and backgrounds of the research programme and discusses some first results.

A detailed study of the historical development of Moriches Inlet, Long Island (New York), was completed to determine the morphodynamic interaction of tidally influenced processes and the effects of man-made alterations on the inlet channel and affiliated flood and ebbtidal deltas. The south shore of Long Island in the vicinity of Moriches Inlet is a microtidal, wave-dominated (mixed-energy) environment. Characteristic of this setting, the inlet bisects a low-lying barrier island backed by an open bay and has a prominent flood-tidal delta.

In this study, bathymetric charts of the inlet, bay, and barrier nearshore zones were contoured for analysis. Using a polar planimeter, the areas between isobaths from mean high water to the bottom surface were measured. This information was used to determine the volumetric distribution of sediment and water in the system. In addition, harmonic analysis was applied on digitized bay-tide records to ascertain the relationships of the semidiurnal overtide constituents. From the results, mean rise/fall duration differences, related to the conservation of mass, were calculated.

The results of the quantitative spatial analysis indicate that Moriches Inlet was flood-dominant from breach in 1931 until closure in 1951. After reopening in 1953, the inlet became ebb-dominant as a result of inlet stabilization and extensive dredge-and-spoil operations in the inlet and bay. Good correlations exist between net sedimentation in the inlet with (1) bay-surface area change, (2) water storage capabilities of the flood-tidal delta, and (3) the cross-sectional area of the inlet. The relationship among these variables suggests that there is a system-wide response to the change in the hydrodynamics caused by man-made alterations, resulting in ebb dominance.

The East Friesian Islands are located on a high energy shoreline. The average deepwater significant wave height exceeds 1.0 m and the spring tidal range varies from 2.7 to 2.9 m. A large easterly net longshore transport rate has caused eastward growth of the barrier islands. Reclamation of tidal flats has significantly reduced the backbarrier area and has resulted in a decrease in the ratio of inlet width to barrier island length from 42% to 16% during the past 300 years.

The headwaters of the major channel dissecting the tidal flats erode in an eastward direction in response to tidal and wave driven currents, wave suspension, and eastward barrier island elongation. Consequently, the drainage systems of most of the inlets are highly asymmetric with 70-80% of the tidal prism coming from the east. This pattern results in a hooked main channel. The location of the channel at the inlet throat is controlled by the westward ebb flow in the main channel, the inertia of ebb flow in the tributary creeks, eastward longshore sediment transport, and the regional stratigraphy.

The position and orientation of the main ebb channel controls the symmetry of the ebb-tidal delta about the inlet shoreline. This, in turn, affects the location of swash bar attachment to the beach and overall trends of erosion and deposition along the downdrift barrier.

The transverse structure of the residual transport of water, salt and suspended sediment in the upper reaches of the Tamar Estuary is investigated. Data were obtained at three cross-sections for spring and neap tides. The transport for each variable is analyzed in terms of the governing physical processes.

The mixing of dissolved material discharged from the Windscale nuclear re-processing plant is examined. The first phase involves a numerical modelling study of large-scale long-term mixing over the entire Continental Shelf. The second phase involves a similar modelling study of near-source mixing processes over a region some 100 km square immediately adjacent to the discharge position. In this latter phase, reproduction of instantaneous peak concentrations is required.

The first phase of this simulation has been successfully completed while the second phase is presently being considered. Ironically, it is shown that this second phase poses far more difficult modelling problems and hence the accuracy of simulation attained in the first phase may not be reproduced. The contrasts in these two modelling approaches are examined and their varying complexities explained.

This paper presents a one-dimensional dynamic water-quality model suitable for long-term application to estuaries. The computation techniques used in the model are very simple, but very good results have been obtained both for theoretical test cases and from applications to estuaries when compared with prototype measurements.

He propose a model for the two-layer, mean transport within a branched, recirculating fjord system. The recirculation is parameterized in terms of efflux/reflux coefficients at distinct mixing zones. The mass fluxes and efflux/reflux coefficients are determined from long-term salinity and current meter observations. The model provides a way to predict the mean concentrations of pollutants introduced within the system. An application to Puget Sound shows that different discharge sites markedly affect the concentrations landward of the sites themselves.

The disposal of sewage effluent into coastal waters for dilution and final disposal requires an effective mixing of sewage with the seawater in order to achieve the necessary or demanded reduction of bacterial population. Most of the design parameters originate from work done on ocean outfalls. RAWN et al. (I960) developped curves from field data for the determination of initial dilution in a waste issuing from a horizontal port. ABRAHAM (1963) extended these curves to show that the dilution is a function of the depth of discharge port, the diameter of the discharge orifice D and the FROUDE number F.

The question, to which extent this calculation method is also valid for outfalls in shallow water regions, is still open. In connection with the actual design of a diffuser in shallow coastal water the method of ABRAHAM was applied together with a new method derived by BERGEN (1980) which is based upon experiments which were carried out in the Leichtweiss- Institute at semi-technical scale. After the diffuser had been taken into operation by means of in-situ measurements the demanded dilution could be checked and herewith also the reliability of the applied design method for practical use.

To maintain the depth of the deepwater channel of the Elbe-Waterway extensive dredging has to be done permanently. Dumping should be optimized, choosing sites near the dredging area but with a small risk of recirculation of the dumped material. In order to estimate this risk field measurements with current meters and radioactive tracer tests in field and model were carried out.

At the Delft Hydraulics Laboratory the hydraulic model of the Rhine- Meuse estuary has been rebuilt and extended after being destroyed by fire in 1979. The new model has been operational since the summer of 1982 for water quantity and water quality research. The present paper deals with the calibration and adjustment procedures for this hydraulic model. Successively the (physical) backgrounds for the calibrationprocess, the techniques used for provision of boundary conditions and the procedures for adjusting flows and salinity distribution are discussed. Finally, the results of calibration and verification and the experiences gained on the employed techniques will be analysed.

A variety of different lateral mixing models have been employed in the equation of motion for determining wave-induced longshore currents. The equation of motion is cast into a general form which enables a comparison of the various models. Analytic solutions for longshore currents are developed for seven different mixing models. A nonplanar beach profile is employed because it has been found to be representative of many beaches and it allows for a distinction between offshore and depth scaling of eddies. The seven different mixing models include models which vary monotonically with horizontal distance offshore and models which change form at the breaker line. Numerical results indicate that the longshore current profile is rather insensitive to the form of the mixing model for nonplanar beach profiles.

During the last three decades several field and laboratory investigations have been conducted in which the waves generated by a wide variety of vessels have been measured. There is a need to synthesize the data published from these studies and to develop general ship wave prediction methods for designers. To complete this task some additional ship wave data must be collected. This paper initiates the effort to develop these prediction methods. A summary and critique of available data are given. Then, the appropriate portion of these data is employed to develop a ship wave height predictor model that gives the maximum ship wave height as a function of ship speed and displacement, water depth, and distance from the sailing line. This is an interim model that is quite applicable but can be improved pending additional data. Finally, planned future efforts to further develop design wave prediction methods are discussed.

Basic knowledge of a ship’s vertical motions in waves of different angles of approach is an essential requirement in the formulation of allowance criteria on which to base harbour accessibility under extreme wave conditions.

A comprehensive series of scale model tests are being undertaken to establish minimum underkeel clearance for given channel depths and sea states using two models representing typical 150 000 and 270 000 dwt bulk carriers.

The characteristics of ship-generated waves in shallow water and the motions of moored small vessel induced by the ship waves were investigated in a wide range of water-depth and ship-length Froude Numbers.

The maximum heights and periods of ship waves were obtained as functions of Froude Number. The relationships between maximum angular and translatory displacements of moored vessel and the maximum ship waves were determined.