Coastal Engineering 1980

Directional wave data obtained simultaneously at two measurement sites is used to confirm the constancy, and therefore the validity, of Snell's laws for wave packets. It is found that the wave packets refract according to Snell's law with the geometric ǵroup velocity whereas the wavelets within a packet refract according to Snell's law with phase velocity.

An expression for the ray curvature of a wave packet is derived which is suitable for use in wave prediction programs. The ray curvature of the wave packet is found to vanish if the packet direction becomes either perpendicular or parallel to the wave speed contours, assuming the wavelet direction is not parallel to the contours. This means that as a hydron (wave packet) moves into shoaling water refraction tends eventually to turn the hydron so that it is directed either perpendicular or parallel to the shoreline. The first case is similar to monochromatic waves. For parallel water depth contours, it is the result for hydrons which begin in deep water if the angle of incidence is between 0° and 74.8° with respect to the contour normal. However, for deep water angles of incidence equal to or greater than 74.8° the hydrons are turned and move parallel to shore in water of intermediate depth. The packet ray curvature approaches infinity as the wavelet direction, but not the hydron direction, becomes parallel to the wave speed contours. The result is total reflection of the waves. Total reflection occurs if a hydron is moving into deeper water and its initial direction exceeds a critical angle. At the reflection point the hydron direction becomes perpendicular to the water depth contours. Further, the hydron velocity goes to zero, which is consistent with a particle concept. As in quantum mechanics, the wave-particle duality is encountered.

Cokelet's numerical non-linear theory for progressive, periodic gravity waves is applied to the two-dimensional shoaling of finite amplitude waves on a beach up to breaking. The shoaling curves so obtained are compared with existing shoaling curves calculated from different finite amplitude wave theories, and with existing experimental data. It was found that the shoaling curves calculated from Cokelet's theory predict higher wave height ratios than other curves. The agreement between the present curves and the experimental results is good except near the breakpoint, where the wave height of the present curves is larger than the experimental wave height.

A least squares method to separate the incident and reflected spectra from the measured co-existing spectra is presented. This method requires a simultaneous measurement of the waves at three positions in the flume which are in reasonable proximity to each other and are on a line parallel to the direction of wave propagation.

Experimental investigations have shown that there is good agreement between the incident spectra calculated by the least squares method and the incident spectra measured concurrently in a side channel.

Experimental and theoretical study to determine the applicability of linear wave theory for the description of the velocity field in irregular waves. A comparison between theory and measurement was executed both in frequency and in time domain. In frequency domain by means of the experimentally and theoretically determined frequency response functions of wave motion to orbital velocity, and in time domain by means of the measured and computed time records of the velocities. The time records for the velocities were computed from the measured waterlevel fluctuations by using the impuls response function method. The orbital velocities were measured contactless with laser-doppler equipment.

The first part of the paper deals with some aspects of wave generation by mechanical wave-generators, especially with hydraulic transfer functions for pusher movement of the paddle, and the influences of signal characteristics and analysis methods. In the second part, results of measurements of orbital velocities and pressures in irregular waves are presented, together with some results from theoretical simulation methods in the frequency and time domain, based on linear wave theory.

A method of evaluation of the incident and reflected wave spectra in laboratory experiments or field investigations, based on the analysis of wave records obtained with a three-gauge array, is presented.

Results of a laboratory investigation with a rubble-mound breakwater and with a special type of sea-wall (ARC system) are given to illustrate the applications of the method.

A phase lag phenomenon in which waves are delayed in transmission through a permeable breakwaters was considered in an approximate calculation method using the superposition principle of Sommerfeld. Experimental verifications were carried out for a semi-infinite permeable breakwater. In addition, a field observation of wave height distribution around a small detached breakwater is reported.

A model study of wave agitation in small craft harbours was performed using a square and a rectangular marina basin subjected to monochromatic waves. Wave agitation was measured in up to 273 points within the marina basin and overall wave energy levels were calculated from these measurements for 4 different wave periods, 6 different entrances and 5 different lengths of energy absorbing sections along the perimeter walls. These values were compared and found to correspond well with a rather simple theoretical expression.

The results presented are from a series of experiments of periodic waves approaching breaking on a gently sloping beach.

The recorded surface profiles are compared with a cnoidal theory taking into account the effect of the bottom slope. In both theory and experiments a skewness of the profile is observed. A fair agreement is found within certain limits of the wave height to water depth ratio and when the slope is sufficiently gentle. The change in water depth over a wave length must be sufficiently small.

The detailed analysis of the surface profiles including the skewness element shows good agreement with the cnoidal theory in cases where the wave height variation is as predicted by cnoidal wave shoaling.

The recorded surface profiles together with the recorded phase velocities are further used in computing the wave energy flux based on the theoretical relations from linear and cnoidal theories. Reasonable constancy is observed over the whole length covered by the experiments.

Finally the recorded wave set-down is compared with the results of linear and cnoidal theories. When approaching breaking neither of the theories can apparently predict the recorded water level changes.

A new wave tunnel is presented as has been recently built at the Delft Hydraulics Laboratory. Several design aspects of the wave tunnel will be discussed and special attention is drawn to the required force and power diagrams.

Measurements of surface elevations and three orthogonal subsurface velocity components have been performed from a platform in the southern North Sea, off the Dutch coast, in order to check linear spectral transfer functions relating subsurface velocities to surface elevations, to obtain information about the directional properties of the waves, and to investigate the velocity statistics. The data obtained as far do not cover a sufficiently wide range of conditions to permit general conclusions. Some preliminary results are presented in the paper.

A Catalogue listing 550 known sources around the world of instrumentally-measured wave data has been prepared by the Marine Information and Advisory Service under the auspices of the Intergovernmental Oceanographic Commission of UNESCO.

A Littoral Environment Observation (LEO) Program was established along the West Coast of the United States in 1968. This program provides for visual observations of waves and surf conditions to be made systematically on a daily basis. The data addressed in this report were collected at three LEO sites (as shown in Figure 1) at Pt. Mugu California, located 50 miles northwest of Los Angeles.

In order to evaluate the reliability of wave heights and periods collected using the LEO techniques, comparisons of visual observations and measured wave gage records were made.

The study revealed that individual visual observations of breaker height can deviate significantly from measured wave heights even when the gage wave heights had been corrected for shoaling effects. On the average the LEO observations gave a fair estimate of prevailing wave heights.

LEO estimates of wave period tended to overpredict the period of maximum energy density. It is presumed that this occurred because observers often fail to count smaller waves when making this measurement. Statistics of the gage measurements of wave height and LEO wave heights are reasonably close.

In attempting to specify criteria for the design of structures on coastal reefs, it was found that no adequate method existed to derive those criteria from the deep water wave conditions.

In order to fill the gap, a program of measurements and analysis was initiated at the University of Hawaii.

The program consisted of prototype and laboratory measurements. Great emphasis was placed on reliable field data, which were collected on Ala Moana Reef, in Honolulu.

Laboratory investigations on the behavior of waves on shallow reefs are subject to scale effects; verification from field observations is required to obtain reliable results. As a result of this study, a mathematical model was developed for the calculation of wave attenuation and wave set-up on a shallow reef, using the incident waves in the ocean as boundary conditions.

This paper discusses the general behavior of waves approaching a shallow reef and presents some essential characteristics of the mathematical model. The study is limited to waves approaching the shoreline at right angles.

The results of this study can be extended to breakwaters with wide, submerged berms.

This paper describes the investigation into a method how to adjust the proper longshore current in a wave basin. In this method the basin geometry and the proper recirculation flow (outside wave guides) are determined by minimising the circulation flow (between wave guides). Using one wave field and one uniform beach the length of the downstream wave guide wall, the distribution of the recirculation flow at the upstream wave guide wall and the recirculation flow were varied. The investigation shows that the adjustment of the longshore current has to be done carefully in order to get uniformity along the beach and the correct magnitude and distribution normal to the beach.

A detailed discussion is made on the dynamic characteristics of waves and wave-induced currents in the nearshore area by using the laboratory and field investigation data collected during the last few years. The main purposes of this paper are to get the insight on the precise mechanism of the nearshore dynamic phenomena and to evaluate critically the applicability of the various assumptions commonly applied by the previous researchers.

An experimental investigation is described of the velocity field in a steady, spilling-type breaker, generated on a steady current by a submerged hydrofoil. Velocities have been measured with a laser-doppler system, and analysed with respect to mean and rms-values as well as Reynolds stresses. The results indicate that the turbulent flow field downstream of the initiation of the separation at the surface resembles that in a turbulent wake.

Numerical computations of water waves deforming until an overhanging, incipient jet has formed near the crest are studied in detail. Velocity and acceleration plots lead to the identification of three regions in the water which appear to be significant in the approach to breaking. In particular there is a region with particle accelerations greater than the acceleration of gravity.

The internal velocity and pressure fields of quasi-steady spilling breaking waves have been investigated experimentally. The internal flow fields are shown to be in qualitative agreement with a model proposed by Peregrine and Svendsen (1978). Furthermore a quantitative comparison is made with non-breaking wave theories. Measurements of the pressure field are presented, and interpreted semi-quantitatively using the vertical momentum balance. Finally, it is shown how the integral properties can be obtained and analysed.

A realistic description of the kinematics of hurricane waves requires that the directional spectrum of the sea be known. Models for hindcasting the directional spectrum have existed for some time, but there has been a dearth of data available for checking the directional characteristics of the hindcasts. Hurricane Carmen in 1974 and hurricane Eloise in 1975 passed reasonably close to platforms in the Gulf of Mexico which were instrumented with wave staffs and electromagnetic current meters. The maximum recorded significant wave height was 29 feet. The simultaneous measurements of wave height and water particle velocity permitted estimates of the directional spectra to be made. The estimated directional spectra are complicated and often bimodal in frequency and direction. Swell from the center of the storm can propagate in directions over 90 degrees away from the direction of the shorter waves which are in local equilibrium with the wind. The hindcast model reproduces these directional features remarkably well. The measurements of wave kinematics also permitted tests of the accuracy of wave theories in high and confused storm waves. All of the unidirectional theories tested showed a bias toward overpredicting the velocity under the highest waves. However, the kinetic energy in the velocity components and the velocity probability distribution could be found to within a ten perceńt scatter using directional spectral concepts and linear wave theory.

This paper presents a method to statistically estimate the severest sea state (significant wave height) from the observed data. For the estimation of extreme significant wave height, a precise representation of the data by a certain probability function is highly desirable. Since we do not have any specific technique to meet this requirement, this situation seriously affects the reliability of the current method of predicting the severest sea condition. The author's method is to express asymptotically the cumulative distribution of the significant wave height as a combination of an exponential and power of the significant wave height. The parameters involved are determined numerically by a nonlinear minimization procedure. The method is applied to available significant wave height data measured in the North Sea, the Canadian coast, and the U.S. coast. The results of the analysis show that the data are well represented by the proposed method over the entire range of the cumulative distribution.

A method is proposed for predicting properties of dominant waves in the forward region of hurricanes where the waves are found to propagate predominatly in the direction of hurricane forward travel. An extended fetch concept is used in which each wave component is exposed to the action of wind over a fetch length that is determined by wave group speed, hurricane forward speed, and location with respect to eye. Maximum extended fetches are found to the right of the eye (with respect to direction of hurricane travel) in the northern hemisphere. The method correctly predicts dominant wave frequencies and significant wave heights. The prediction method utilizes recently developed concepts in wave generation and energy transfer among wave spectral components; the predicted values are compared favorably with observations

Surface elevation and velocity measurements in shallow water on beaches show large fluctuations known as surf beat in the long period range from approximately 20s to 2000s (Munk, 1949; Tucker, 1950). A laboratory study was conducted to determine if two shoaling primary waves of nearly equal frequency would generate two-dimensional surf beat at their difference frequency. The experiments, carried out in the Scripps Institution of Oceanography Hydraulics Laboratory 30 m glass walled wave channel, show that the beat frequency motion in the channel consists of the sum of a forced progressive wave and two free standing waves. The progressive wave is forced by the local nonlinear interaction of the primary waves and grows sharply in shallow water. One of the free standing waves is generated directly by the wavemaker. The data is consistent with the hypotheses that the second, much larger, free wave is generated in shallow water as the reflection of the long, forced progressive wave, leading to the observed standing wave surf beat pattern.

Linear and nonlinear sets of equations of long waves in the Lagrangian description are solved numerically to obtain run-up heights. Numerical results are compared with theoretical ones in case of simple topographies and the agreement is quite satisfactory. As a practical application, the computation is carried out for the Okkirai Bay in Japan. The computed run-up heighs agree fairly well with the recorded ones.

Simultaneous offshore and onshore wind measurements were made at stations ranging from Somalia, near the equator, to the Gulf of Alaska. Offshore data obtained from standard U.S. NOAA buoys, research platforms, and merchant ships were compared with data from coastal stations. The results indicated that, under the commonly observed speed of 5-6 m/s, land measurements of mean wind speed are only 63% of the offshore mean speed. Furthermore, it was found that only those stations located in the beach area that measure wind speed above both the internal boundary layer and the nocturnal inversion height represent offshore conditions. In order to correct land-measured wind data, a formula is developed and verified by all existing data sets. A simplified equation, i.e., ${\text{U}}_{\text{sea}}=3{\text{U}}_{\text{land}}^{2/3},$ is proposed for offshore applications. Criteria for in situ wind measurements near the coast are outlined. Data reduction procedures for inland stations are also provided.

Details are presented of a general numerical hydrodynamic model for the generation and propagation of tropical cyclone or hurricane storm surge. The model, known as SURGE, solves the two-dimensional depth-integrated form of the Long Wave Equations using an explicit finite difference procedure, with tropical cyclone surface wind and pressure forcing estimated from an adaption of available models based on U.S. hurricanes. Variations in tropical cyclone parameters as well as the physical characteristics of a coastal location such as bathymetry and details of capes, bays, reefs and islands are accommodated by the model. The accuracy and stability of the numerical solution have been confirmed by a comprehensive wave deformation analysis including quasi-non-linear effects and the open boundary problem has been overcome by the use of a Bathystrophic Storm Tide approximation to boundary water levels. A detailed sensitivity analysis has identified the principal surge generating parameters and the model has been checked against an historical tropical cyclone storm surge. SURGE has been used extensively in the northern Australian region and examples are presented.

For studying storm waves in coastal areas, usual waves theories are no more valid. The presented cnoïdal theory allows the modelling of these problems. Furthermore, thanks to its non-linear properties, it makes possible the simulation of many phenomena usually neglected.

A numerical model using this theory has been developped. it has been tested against analytical results and certain properties of non-linear waves experimentaly observed.

Finaly, the practical problems raised by the utilisation of this model for harbour agitation computations, have been solved.

In nature short period storm waves generate longer waves with periods corresponding to the wave group periods. The long waves are generally referred to as the wave set-down of water level. The set-down term is of second order in the height of the short waves. With firstorder reproduction of natural storm waves in the laboratory, the setdown bound to the wave groups is not reproduced. As a result, various free waves are generated, propagate towards the model and reflect from the boundaries. These so-called parasitic waves cause an exaggeration of long wave phenomena, such as harbour resonance and slow drift oscillations of moored ships.

The parasitic waves can be eliminated by means of compensating free waves imposed on the system by second-order paddle motion reproducing the natural set-down. The control signal for this motion has been calculated and checked by testing. The agreement between calculated and measured results is found to be good.

Further, an alternative method for reducing the parasitic wave problem is presented. Utilizing the shoaling properties of the various waves, the influence of parasitic waves can be diminished by generating the waves in somewhat deeper water before they propagate into the shallower model area.

An analysis is presented for the propagation of water waves past a submarine trench of irregular shape. Two dimensional, linearized potential flow is assumed. The fluid domain is divided into two regions along the mouth of the trench. Solutions in each region are expressed in terms of the unknown normal derivative of the potential function along this common boundary with the final solution obtained by matching. Reflection and transmission coefficients are found for various submarine geometries. The accuracy of the technique employed is demonstrated by comparing with previously published results for a rectangular trench. In addition, results from limited laboratory experiments were included for comparison. The result shows that for a particular flow configuration, there exists an infinite number of discrete wave frequencies at which waves are completely transmitted.

The applicability of a time-stepping approximate finite difference method is tested for the response of a plane incoming tsunami of small amplitude meeting an idealized island (see Fig 1). The resulting amplitudes are compared with the exact solution, which comes out of solving the linear shallow water wave equation for the area in question. Since this wave equation excludes dissipation (bottom friction) and the Coriolis force, these terms are omitted in the Boussinesq equations, formulated as mass and momentum conservation, which are the bases of the finite difference scheme. Grid size is 1 × 1 km. The incoming wave is time-harmonic with a period of T = 480 s; the (test) solution to the wave equation is thus a truly steady-state solution. The finite difference scheme, however, has a so-called “cold start” and so it is transient in principle. During a time corresponding to three periods, in which disturbances from the open boundaries still have only a small effect on the wave field near the island, the time-series of signals in selected points can define a steady response, though. Considering the inevitable shortcomings of a provisional study like the present, satisfactory agreement with the exact solution is met over the shoal in Fig 1. We have thus a promising starting point for more elaborate studies, comprising new filtering algorithms for the boundaries, tests with real transient input signals, and including non-linearity, bottom friction, and the Coriolis force.

The numerical scheme used is the so-called System 21, developed at the Danish Hydraulic Institute and placed at our disposal for the present study.

This paper first gives a brief review of the existing research works on the laws governing the dissipation of wave energy by turbulence. Starting from the general theory of turbulent motion and the writer's suggestion in regard to the mixing length of water particles in two-dimensional flow and making use of the principle of dimensional analysis and the trochidal wave theory, a formula has been derived to compute the mean dissipation per unit time and per unit horizontal area of wave energy due to turbulence. The formula takes the horizontal and vertical gradients of both the horizontal and vertical velocity fields into consideration. Coefficient in the formula has been determined through laboratory experiments.

To gain a better understanding of the cycles of shoreline changes on Seabrook Island, South Carolina and advise a private developer on how to deal with localized erosion problems, a detailed field survey and historical study were completed. The data base included historical charts dating from 1661, vertical aerial photographs from 1939, field surveys of beach profiles and nearshore bathymetry over a six-month period, and sediment cores through the entire Holocene section. Seabrook Island, less than 6 km in length, is bounded by tidal inlets with extensive seaward shoals. With a 2 m tidal range for the area, changing exposure and orientation of the shoals over time has had a profound effect on the adjacent shoreline of Seabrook Island. Historical evidence points to the importance of offshore shoals which act as natural breakwaters and sediment storage systems. At various times in recent history, these shoals have supplied sediment to Seabrook beaches by means of bypassing mechanisms around tidal inlets. On the other hand, migration of shoals has allowed excess wave energy to strike portions of the shore causing local erosion. Along a portion of the shoreline, short-term erosion is jeopardizing the development. Based on the present study, a set of “soft” engineering designs was proposed which attempt to manipulate offshore sand bodies in a way that will be beneficial to the development and preserve the inherent beauty of the shoreline. Remedial measures recommended for the developer included dredging new inlet channels and construction of a breakwater in the position of a former protective shoal.

Results of regional geological studies on the southeastern Australian coast and inner continental shelf suggest that broad relationships between nearshore sediments and morphologies are often the result of factors other than incident waves and wave-induced currents. Five main factors (including wave action) have been identified:

It is thought that these factors have controlled coastal evolution in the past and also influence present-day coastal changes. Identification of the role played by individual factors in specific areas provides valuable information on coastal sediment budgets.

Studies of physical processes in reef-lagoon systems continue to emphasize the importance of waves and wave-induced currents at the reef crest as agents of sediment transport to backreef environments. These across-the-reef currents are also largely responsible for driving backreef lagoon circulation. Rapid energy transformations associated with the process of wave breaking at the reef crest are responsible for strong reef-normal surge currents. Estimates of energy loss, as determined by wave height changes caused by wave breaking, can be as high as 70-80% for discontinuous reefs and >90% for continuous examples. The amount of energy loss is related to depth of water over the reef crest, a function of reef topography and tidal regime. Low-tide conditions promote the greatest incident wave modification and attenuation as a result of increased breaking-wave intensity. Under trade-wind conditions found in the Caribbean, surge currents of 50-80 cm/sec for durations of 2-6 sec are common in a low to moderate wave-energy setting (4-6 sec input waves, 40-50 cm average heights). Sediments through the sand sizes up to pebbles are easily transported lagoonward by these periodic bursts of energy.

The two-dimensional topography, developed on a sandy sea bed between surf base and the breaker zone, is computed using (i) sediment gain or loss per unit bed area = zero, (ii) simple models of sediment drift in terms of, firstly, simplified saltation under Stokesian waves, and secondly, frictional wave work on the sea bed, (iii) the drift tendency in direction of wave propogation being offset of the local sea bed gradient. An input contour line at surf base is assumed, across which the input wave train is propogated. Using standard wave refraction combined with (i) to (iii), above, an equilibrium topography is generated by iteration. Inshore of the breaker line, longshore currents generated by radiation stress are combined with the gradient effect to balance sediment drift, producing bar – trough topography.

Field experiments on the coast of Southeastern Australia, supplemented by systematic observations in a variety of environments in other parts of the world, indicate at least three quasi-discrete modes of subaerial beach cut, each of which is related to a distinct set of mechanisms. For any given set of incident wave conditions, the operation or non-operation of a particular mode of cutting depends on the morphodynamic state of the surf-zone and beach. Steep, reflective, beaches are susceptible to cut under moderate swell conditions by accentuated runup and berm overtopping associated with subharmonic resonance. Appreciably more energy is required to cut flat dissipative beaches. Cut of dissipative beaches involves high setup which oscillates at infragravity frequency and allows the bores of broken waves to penetrate to the backshore. Beach states intermediate between the reflective and dissipative extremes are subject to cut by both the modes just described as well as by scour in the embayments of topographically arrested rips which can cause significant localized erosion even when the coast regionally is accreting. Beaches which most commonly exhibit intermediate topographies are the least stable and most mobile.

The kinematics of incipient breakers were measured on various complex natural beaches. Water velocities were found to consistently lag behind the wave crest. This phase shift appears to be partly inherent in shoaling waves and partly a result of partial wave reflection. Phase shifts vary from 5 degrees through to quadrature. This variation probably depends to a large extent upon beach reflectivity and distance of the break point from the shoreline. Phase shifting also varies vertically beneath the wave crests from uniform distributions to those in which maximum shifts occur near the bed. There is a strong relationship between the nature of phase shifting, the morphodynamic condition and the breaker type. Surging waves were associated with large, and vertically uniform phase shifts. Waves towards the plunging and spilling end of the breaker type continuum occurred where phase shifts were significantly larger at lower depths than near the surface.

The breaker wave height required to produce a particular beach-surfzone morphology is examined for micro-tidal, medium to fine sand beaches. Waves >2.5m produce dissipative beach systems with wide surfzones and shore parallel bar/s and channel/s. Breakers between 1 and 2.5m result in rip circulation and associated rhythmic morphology (crescentic bars, rip channels, megacusps, etc). Low waves (<lm) form steep, barless reflective beaches with characteristic cusps/berm. To gauge the stability/mobility of each of these beach types the range of beach profile changes associated with each is presented, for both the time and space domain. Modally dissipative beaches where breakers consistently exceed 2.5m undergo minor changes in profile and are consequently stable both temporally and spatially. Modally rhythmic beaches have a variable moderate energy wave climate are highly unstable both over time and alongshore. Modally reflective beaches with their low waves are relatively stable. Beaches which experience a highly variable wave climate over time exhibit all three types and are consequently highly unstable. The environmental parameters useful for quantifying these beach types and associated profile changes, and the implications of these results are discussed.

A two-dimensional laboratory investigation of sediment transport, induced by shallow-water waves, showed that the sediment motion over suspension-dominant asymmetric ripples is closely related to the development of eroding beaches. High-speed motion picture analysis revealed that vortices, formed over this type of ripple, play a crucial role in transporting the sediment to the offshore region. A relation for net offshore sediment flux was formulated for sand 0.02 cm in diameter. A simple model for eroding beaches was proposed and its validity was checked by using two existing data sets for 0.02-cm sand beaches; the model could predict fairly well profile and shoreline changes in the early stages.

Nearshore circulation on a partially rocky shore at Haranomachi Beach, Fukushima Prefecture, Japan has been studied in terms of field observations and numerical experiments for a low energy wave regime and with a physical experiment for a high energy wave regime. No significant distinctions were found in current velocity and rip current spacing between rocky and sandy beaches for the low energy wave regime, however the positions of rip currents were affected by wave refraction from the offshore exposed rocky bottom. On the other hand, since the surf zone bed is largely occupied by an exposed rocky floor for the high energy wave regime, the circulation exhibited fairly irregular patterns, so that a rip current becomes difficult to define, however the positions of inflow across the breaker line were found to be coincident with wave convergence zone.

This paper presents observations of currents recorded in the swash zones of a number of morphologically different types of beaches in order to demonstrate the large variability in run-up patterns that exists primarily because of variability in beach face and surf zone configuration. Run-up spectra are shown for steep and flat beaches under low (<0.5m) and moderate (0.5-2.0m) wave energy. The longshore variability of run-up patterns on rhythmic beaches is also discussed. On reflective beaches run-up occurs only at incident wave frequency under low energy conditions and at both incident frequency and its first subharmonic under moderate energy. Low energy dissipative beaches exhibit a range of frequencies across the swash zone from incident through low frequency infragravity. As wave height increases on flat beaches, high frequency oscillations vanish leaving a concentration of energy at low infragravity frequencies. On more complex inshore rhythmic topographies under low to moderate energy conditions, alternating transverse bars and troughs give rise to a close spatial co-existence of zones of surging, reflective run-up and zones of over-running progressive bores of the type observed on flat profiles.

The on-offshore sediment transport due to waves on a sloping beach is studied by analyzing the laboratory test data on two-dimensional beach deformation. The net rates of sediment transport both inside and outside the breaker zone are evaluated from beach profile changes and are related to the nondimensional bottom shear stress or the Shields parameter. The importance of the critical shear stress and of asymmetrical to-and-fro water partical motion near the bottom is pointed out.

As part of the DUCK-X experiment at the CERC field research facility at Duck, North Carolina in September, 1978, suspended sediment measurements were made along the CERC pier. In situ bulk water samples were collected during a moderate northeast storm and two days later during post-storm wave conditions. Concentrations varied from approximately 0.01 g/l to over 10.0 g/l. Vertical arrays of suspended sediment samples indicated that concentration decreases rapidly up to two meters above the bed, then remains relatively constant, reflecting the nature of the suspension; intermittent suspension of sand near the bed, and continuous washload higher in the water column. Concentrations were at a maximum during storm conditions when measured values were 3 to 5 times higher than during non-storm conditions. The total load of sediment in a pier cross section during sampling periods in storm and post-storm conditions was calculated from arrays of 49 samples each. With H_1/3 exceeding 2.3 m and the surf zone width over 300 m during the storm, the total load of sediment in suspension was approximately 10 times higher than during post-storm conditions (H_1/3 = 1.2 m and surf zone width approximately 100 m). Estimates of the longshore flux of suspended sediment indicate that as much as 60 times more sediment was transported during storm than during post-storm conditions. Longshore transport of sediment measured from 5 cm above the bed to the surface reached the equivalent of 22,330 m³/day. This value corresponds very closely to longshore transport predicted from wave energy flux. During post-storm conditions, on the other hand, transport of suspended sediment accounts for less than one-third of the transport predicted from wave energy flux.

In this paper a model is presented to describe onshore-offshore sand transport in the surf zone. The model is based on the physical consideration that when the net transport attains a state of equilibrium, the power expended through gravitational force in suspending sand grains is balanced by that due to the uplifting force arising from the turbulence generated by breaking waves.

Two important parameters controlling sand transport are the dimensionless fall-time parameter and bottom slope. Using these parameters, the direction of onshore-offshore transport and the beach profile in the surf zone are expressed as$$({\text{H}}_0/{\text{L}}_{\text{0}})\tan \text{β/}\frac{{\text{w}}_{\text{s}}}{\text{gT}}\underset{>}{\overset{<}{=}}0.5\begin{array}{l}\text{(onshore transport; accretive profile)}\hfill \\ \text{(neutral; equilibrium profile)}\hfill \\ \text{(offshore transport; erosive profile)}\hfill \end{array}$$

In this paper, models of the distribution of net on-offshore sediment transport based on two-dimensional equilibrium beach profiles and an equation of continuity of sediment transport are proposed. Various parameters of net on-offshore sediment transport in those models are discussed. Furhter, the relative importance of bed load and suspended load in the two-dimensional beach deformation are examined by measuring both of them on model beach experiments.

Forcing functions and sediment response were measured during two comprehensive surf zone experiments. The experiments included simultaneous measurements of waves and currents, and the movement of sediment as bed and suspended load. The longshore transport of suspended load was found to be about 10 to 20% of the tracer-measured load. Results from tracer measurements of the longshore transport of bed load indicate that previous measurements may have misestimated the effective “tracer layer thickness,” and a more rigorous method is proposed.

The approach adopted in N.S.W. for investigating coastal processes leading to development of a numero-descriptive model for management purposes is outlined. The technique involves the formation of a regional coastal model and its adaptation to site specific cases. This site specific conceptual model is then tested and modified on the basis of theoretical calculation and field data collection. Two specific case histories are outlined.

Based on the wave pattern, the geographical location and the disposition of rivers, the littoral drift moves predominantly from NE to SW direction in section II as shown in Fig. 1. Seven rivers of rapid stream bring tremendous amount of sediments from the high mountain to the nearshore of this section in typhoon season (i.e. from June to September). But for the winter monsoon season, i.e. from October to the next April, the waves induced by NE monsoons migrate littoral drift from North toward South.

The mean sediment transport rate obtained by using six known longshore transport formulae, for which the input variables are determined consistently, is used as best estimate of the transport. A good comparison is obtained when this package deal approach is compared with a prototype situation where the transport rates are inferred from quarterly bathymetric surveys over two years. The accuracy of the input variables is reviewed theoretically and the results are used to perform a sensitivity analysis.

The now familiar equilibrium shape of bay sculptured by waves between headlands can indicate to man the direction he could follow in stabilizing shorelines. The characteristics of these crenulate or zeta shapes are known and can be applied in design or defining limits of erosion. Some natural settings are discussed which introduce difficulties in identifying the correct bay shapes for applying these tools. The application of headland control to specific cases of instability is presented. The final requirement is emphasised of aiding Nature to protect the coastline by the formation of the offshore bar and its subsequent return to the beach without concurrent downcoast drift. The method currently receiving widespread support of placing offshore breakwaters in close proximity to each other is discounted as a viable protective alternative.

Equilibrium beach profiles have been investigated in the laboratory for two beach materials, 0.22 mm marine sand and 1.55 mm crushed coal. Analysis of the results confirms that the dimensionless fall velocity H₀/Tw is an important parameter influencing both surf zone hydraulics and the form of the resulting equilibrium profile. Beach permeability also significantly influences the hydraulics within the beach face and it has been found that both H₀/Tw and the parameter w_f/w, the ratio of the fluidising velocity to the fall velocity, influence the form of the equilibrium profiles of permeable beaches.

Tests were carried out in the oscillating water tunnel to determine the bed-form lengths of sand ranging from 0.1 mm to 0.55 mm subjected to oscillatory motion of various orbital diameters ranging from 0.15 m to 1.5 m and of various periods ranging from 3 to 15 s. The relationship for the bed-form length is given in the accompanying graph in dimensionless form.

Shoreline development and shore-zone sediment transport on the Alaskan North Slope are dependent upon levels of wave energy, sea ice conditions, and the ice-sediment characteristics of eroding tundra cliffs. Considerable variation exists between the coastal processes and the shore-zone morphology of the Chukchi and Beaufort Sea beaches, (respectively west and east of Point Barrow). The supply of coarse sediments (sands or gravels) and the volumes of material eroded from tundra cliffs are a function of the initial character of the cliff sediments and of the ice content of the exposed cliffs. As cliff heights decrease, the ice content of the cliff increases, erosion rates increase but the sediment supply rates decrease. Wave-energy levels are relatively high and maintain a constant level on the Chukchi coast. The transport system on this coast is continuous and is augmented by storm events. On the Beaufort coast, energy levels are much lower, transport processes discontinuous, and storm events are therefore more significant. Sediments supplied to the coastal zone on the Chukchi coast are derived largely from the erosion of tundra cliffs and the barriers are continuous, linear, and stable. Rivers are the primary source of coastal sediments on the Beaufort coast and the more variable energy levels produce unstable barriers that are subject to aperiodic transport processes.

This paper presents a semi-empirical model for describing sediment dispersal on the central New South Wales (N.S.W.) continental shelf. Results from a program of field experiments identify wind speed and direction, wave height and frequency distribution of near-bottom currents as being the dominant factors influencing near-bottom current asymmetry on this shelf. A combination of theoretical prediction and field experiment has been used to define the seaward limits for onshore/offshore sediment exchange and the modes of sediment transport operating within this active zone.

The coast of western Louisiana is presently receiving a new influx of fine-grained sediment from the Atchafalaya River to the east, the first such sediment pulse in recorded history. The major effect of this sediment, which accumulates as fluid mud in the nearshore and at the shoreline, is to attenuate incoming wave energy, thus providing conditions favorable for further sedimentation. Examination of color infrared photography and comparison of observations from aerial overflights and information from ground reconnaissance undertaken periodically since 1969 indicate that mudflat sedimentation is increasing and appears to be moving to the west. When muds move ashore and begin to dewater after becoming “shore attached,” they gain strength rapidly and can resist subsequent fair-weather wave scour if their bulk density exceeds 1.20-1.25 g/cm³. An understanding of why and how these fluid muds accumulate and move subaqueously may provide us with the ability to predict areas of future erosion and accretion along the western Louisiana shoreline.

A field project was conducted to measure swash and surf characteristics and related processes on a beach with a high tide range and very low slope. Variables measured were beach waterlevels in the surf and swash zones, beach groundwater levels, and on-offshore and alongshore currents. A variety of deployment patterns and instrument combinations were used. Results show a nonlinear transfer of wave energy from high to low frequencies. This appears to have occurred because finite amplitude waves and bores caused an onshore mass flux which produced an increased local waterlevel. Periodically, this impounded water was released. Groundwater records indicate that low frequency waterlevel oscillations on the beach face were the dominant forcing function for oscillations of the beach watertable. A model is generated which adequately predicts some of the response characteristics of the groundwater table.

A field experiment was conducted by the Coastal Engineering Research Center (CERC) to develop correlations between wave characteristics and longshore sediment transport. The waves were measured by two near-bottom mounted pressure transducers and the average longshore sediment transport rates were determined from sequential volumetric surveys behínd an offshore breakwater which was regarded as a total trap. The data analyzed herein encompass a period of nine months during which a total accumulation of 675,000 m³ occurred as documented by eight surveys. Spectral analyses of the wave data were conducted and yielded one direction per frequency. The correlations include immersed weight sediment transport rate, I, versus (1) longshore component of wave energy flux at breaking, P_ls and (2) the onshore flux of the longshore component of wave-induced momentum, S_xy. The most widely used correlation constant, K, in the relationship I = KP_ls is 0.77. The best-fit values found from the data were K = 0.65 and 0.92 for linear and log best-fits, respectively, as based on the P_ls values directed toward the trap. The corresponding values of K_* (dimensional) relating I and S_xy are 4.98 m/s and 6.37 m/s, respectively. One feature of this type of trap is the potential for overtrapping if the waves are directed nearly normal to shore.

It is known that nearshore areas occupied by longshore bars constitute a zone of active migration of bottom deposit due to agitation by breaking waves and wave-induced on-/offshore currents and longshore currents. So far there is still a lack of actual data from the field itself concerning the magnitude and variability of single parameters involved in the stability and migration of longshore bar features.

This paper summarizes data collected from a comprehensive field study in the years from 1976 to 1979 when grain size distributions were obtained from a narrow grid of core samples and repeated soundings and continuous measurements of waves and wave-induced currents were carried out. With regard to the characteristics of different longshore bar feature relationships e. g. in between bottom gradients and mean grain sizes are analyzed. Furthermore distinct types of topographic response within the submarine belt occupied by longshore bars depending upon the variable intensity and position of breaking waves and the resulting magnitude and variability of wave-induced currents are pointed out and presented for discussion as a contribution towards a general understanding of longshore bar characteristics and changes.

Sedimentation may be an important problem when quantities of suspended material are carried into an enclosed harbor on a flooding tide. In order to forecast future maintenance costs, two methods for predicting the sedimentation rate prior to harbor construction are proposed: 1) a sedimentation tank to be placed at the proposed harbor site, and 2) a mathematical model which uses sediment and hydraulic data collected at the harbor site.

Certain considerations in the design phase of a project may effect a reduction in harbor sedimentation. If feasible, the harbor may be sited in a region where suspended sediment concentrations are low and sediment sizes (settling velocities) are small. Proximity to river sediment sources may be a factor. Conversely, a harbor site in a clear-water river adjacent to a sediment-laden estuary may be desirable if bedload transport during freshets would not be a problem. Settlement of suspended material may occur in the channel which connects an enclosed harbor basin with navigable waters. This material may subsequently be resuspended and carried into the basin thereby increasing the sedimentation rate. To reduce that rate the channel should be designed as short as possible. A sill in the channel may also be used to reduce initial excavation costs and the sedimentation rate. Flotation for vessels in the basin will be provided at all times, but movement into and out of the harbor will be reduced to times of higher water. In high latitude areas where harbor use is limited to periods when ice cover is absent, the sedimentation rate may be reduced using a channel closure structure during non-use periods. Winter sedimentation rates can be predicted using the mathematical model for summer conditions, and when ice thickness is known.

Field investigations on sand-transport by wind were carried out at German North-Sea coast. A special trap was constructed, which allows to measure bed load and suspended load seperated. In addition wind speed was measured up to 10 m over the bottom. The results of the field investigations were used to calibrate a transport-equation for sand-transport by wind.

Between mid 1974 and mid 1975,760,000 m³ of sand was dredged from the bed of the Tweed River for the purpose of nourishing cyclone damaged beaches of the Gold Coast (Queensland). A comprehensive field data programme was established in 1976 to record the changes in the hydraulic processes of the Tweed River brought about by the dredging. The field measurements demonstrated that the dredged area was being infilled with sediments of both marine and estuarine origin. The dredging increased tidal ranges throughout the lower estuary, the effect being more pronounced at low water.

Sediment bedload rates were estimated from detailed measurements of bedforms and used to calibrate a sediment transport formula. The formula was used in conjunction with a 1 Dim. numerical model of tidal hydraulics to simulate estuarine shoal dynamics by means of a simple sediment routing technique. The results showed that the dredging had altered the tidal hydrodynamics so as to enhance the ebb transport of sediment towards the dredged hole. In the long term it was found that the sediment transport switched to a weak net upstream movement of sediment. The detailed hydraulic mechanisms involved are discussed. The study demonstrates that the impact of dredging can be minimised by location upstream of the entrance plug of marine sand.

Current meter observations indicate that a trapped eddy with a highspeed outer limb is formed downcurrent of the Damietta Nile promontory. This eddy is instrumental in the formation of the highly mobile sand body that extends seaward from the Damietta mouth, out onto the shelf, and curves back toward the coast just east of the Suez Canal entrance. Orientation of sand waves along the sand belt mirrors the direction of current flow within the eddy and indicates that the zone of reattachment of the separation streamline is located to the east of the Suez Canal. Dissipation of this sand belt will likely result in increased coastal erosion locally.

Field observations indicate that the effect of dredge-induced resuspension on sediment transport within small estuaries is generally negligible in comparison to the transport induced by natural storm events. Data obtained in the Thames River, near New London, Connecticut show dredge-induced resuspension to be essentially a near field phenomenon. The resultant plume of material increases total suspended load in the river by approximately 25% but extends over less than 2.5% of the total estuarine area. In contrast storms are observed to increase total suspended load by a factor of three, influencing concentration levels throughout the estuary. These factors, in combination with the lower frequency of dredging vis-a-vis significant storm events, appear to effectively limit the influence of dredge-induced resuspension.

This paper describes experimental results on the in-line and lift forces acting on inclined circular piles which are placed in two different planes: (1) a vertical plane parallel to the direction of wave propagation; and (2) a vertical plane parallel to the wave crest.

The in-line and lift force formulas for an inclined pile are formulated by referring to the conventional Morison and lift force formulas, respectively. Stokes third order wave theory is used for the estimation of flow kinematics induced around a pile. Based on these formulas, the time-independent and time-dependent values of the drag, mass and lift coefficients are determined by using several methods. Further, the timedependent coefficients are expanded into Fourier series which consist of several significant components.

Reliability of these coefficient values are studied by examining the relative deviation of the predicted wave forces based on these coefficient values from the measured ones. The analysis finds that relative deviations of the in-line and lift forces exceed in many cases 15% and 100%, respectively, when the time-independent coefficients are used for the prediction of wave forces, but that they are reduced to 5% and 15%, respectively, when the time-dependent coefficients are used for it.

This study deals with the seepage effects experienced by a large, vertical, circular cylinder resting on a submerged bed of sand when planar water waves interact with it. Potential theory is used to describe the seepage flow field. The sea bottom pressure condition is determined from the water field velocity potential derived by MacCamy and Fuchs (1954) in the case of planar waves diffracted by a large impervious cylinder. Consideration is also given to cylinders with a thin circular base whose diameter exceeds that of the cylinder itself.

The problem formulation as well as the initiation of the analysis apply to the general case of a bed of sand with finite depth.

For the case of infinite depth of the porous medium, theoretical solutions for the seepage pressure are obtained in the form of infinite integrals. Theoretical solutions for the pressure along the cylinder circular base are then derived, leading by integration to closed form expressions for the wave-induced seepage uplift force and overturning moment exerted on the cylinder. These expressions for the force and moment, which are presented in non-dimensional form are shown to be universal functions of a unique variable. Graphs are provided so that very few computations are required to determine the uplift force and overturning moment exerted on a cylinder. A comparison with various approximate theories reveals the present theory to be the only one which gives reliable results in general.

The amplitude and phase angle of the oscillating wave-induced pressure along the cylinder base are determined numerically. Results for the pressure amplitude are presented as non-dimensional ratios to the amplitude of the pressure that would prevail if no cylinder were disturbing the wave field.

Expressions for the exit gradient around the cylinder base are also determined. Contours of the ratio of the exit gradient to the one that would prevail in the absence of a cylinder are presented.

Laboratory measurements of uplift pressure amplitudes on a circular cylinder show good agreement with theoretical calculations.

Stability analysis of homogeneous and inhomogeneous seabed foundations under attack by storm waves are made by calculating the wave induced effective stresses. Wave induced effective stress analysis of homogeneous seabed is made using the theory previously developed by the senior author which is based on the poro-elastic theory by Biot. Effective stresses in inhomogeneous seabeds induced by waves are calculated by approximating an inhomogeneous bed by many layers of homogeneous soils each of which has different geotechnical properties of soils. A good agreement is obtained between the theory and the pore pressure data in situ field measurements. For a given wave length, it is found that there exists a most unstable thickness of homogeneous seabed when the seabed thickness is one-fifth of the wave length. As a realistic example of an inhomogeneous bed, the effective stresses in a typical seabed formation at the Mississippi Delta area of the Gulf of Mexico under the attack of design storm waves are calculated. The numerical results indicate that the storm waves induce a continuous submarine landslide which extends as deep as 9 m from the mud line. Numerical calculations also indicate that such landslides and liquefaction of seabeds can be prevented by placing a layer of concrete blocks or rubbles on the top of the seabeds.

Wave impact pressures and forces on composite breakwaters have been measured in the laboratory. A solid wall breakwater and a perforated breakwater were instrumented with small pressure transducers in a study designed to estimate the relative effectiveness of perforated breakwaters in reducing impact loads caused by breaking waves.

Experimental results of maximum pressures and forces measured on the breakwater walls are presented as cumulative probability distributions. It is concluded that the perforated breakwater experiences significantly lower breaking wave loads although local impact pressures may be as high as those measured on the solid wall breakwater. Further studies are required on the perforated breakwater and alternative designs to determine the most suitable caisson type for the reduction of wave impact forces.

A field investigation programme on simultaneous wave force and water particle velocity measurements is decribed with reference to an inclined tubular member subjected to offshore wave kinematics. First measurements at supercritical Reynolds numbers indicate strong irregularities in successively taken pressure distributions on the circumference of the test section as well as in the velocity vectors.

The influence of superimposed tidal currents is obvious.

It is well known that the relative dynamic strength of unreinforced slender concrete units decreases as the size increases. Big units can resist relatively smaller movements than small units. When model tests of cover layer stability are performed the determination of the damage criterion that should be adopted must therefore be based on knowledge of the dynamic strength of the corresponding prototype units.

With the purpose of establishing a relation between the size and the dynamic strength of unreinforced units some full scale tests to destruction of 1.5 and 5.4 t units were performed. The set up and the procedure of the tests which simulates the impact from rocking of the units and from concrete pieces that are thrown against the units are designed to make a comparison between the behaviour of units of different sizes possible. The test method is described and proposed as a standard method.

The theoretical expression for the dynamic strength is compared with the test results and it is shown that if the units are allowed to move there is an upper limit for the size of unreinforced units where a balance between the hydraulic stability of the cover layer and the strength of the units exists. Different ways of improving the strength of the units are discussed on the basis of the results from tests with different types of concrete.

The tests included an investigation of the influence of reinforcement, and of different types of concrete and surface cracks on the performance of the units.

The stability of a rubble mound breakwater section, with 3 in 2 armour slope, was tested under random waves attack. Tests analysis shows that the equivalent wave height characterizing the spectrum to be used in a stability formula elaborated with regular waves (for instance the Hudson's formula) is the upper twentieth height of the distribution for a storm duration of 6 hours. An analytical expression of the damage evolution as function of time modulates this choice according to the storm duration. The same rubble mound breakwater was also tested under the action of regular breaking waves. The damage was expressed in terms of the four following parameters:

H₀ : wave height

T : wave period

D_p : water depth at the toe of the structure

D_b : breaker depth without the breakwater

For a given wave height, the most important damage occur when : $$\frac{{\text{D}}_{\text{p}}}{{\text{D}}_{\text{b}}}=1$$ In this case the design wave height must be increased by about 30 % when using a stability formula elaborated for non breaking waves.

Features in wave overtopping of two new types of seawalls designed to be built in considerably deep sea conditions are presented herein. One of those is the seawall of concrete caisson with a parapet wall and armor blocks on the top of the caisson, and another one is the seawall with a slitted box-type wave absorber.

The former type of seawall has successfully been constructed in the Japan Sea and the Seto Inland Sea and is also to be constructed at a site directly exposed to an open sea of the Pacific Ocean in 1980 and 1981. The latter type of seawall was proposed in 1977 after numerous experiments and has been under construction in the Port of Osaka since 1978.

The results of the experiments on the wave overtopping over the slit-type seawall were compared with the calculated results, obtained by an analysis in which the wave overtopping over a parapet wall was considered similar to the phenomenon of flow over sharp-edged weirs having time-dependent overflow-head. The calculated curves obtained are in good agreement with the experimental results.

The designs of these two types of seawall are also presented herein.

Designs of dikes and dunes according to current Dutch guidelines, based on a deterministic approach, are not consistent with probabilistic philosophy. This statement is amplified in the present paper as a pilot investigation; a rough outline for a probabilistic method of dune and dike computation is given. Numerical comparison of probabilistic and deterministic methods is hampered due to the fact that the results according to the deterministic approach depend on engineering instinct in the choice of boundary conditions and because the probabilistic approach is not as yet operational. Illustrative computations show differences of a factor 1000 in failure probability, starting from dimensioning according to the same standards, following deterministic guidelines.

The construction of New Oil Port in Dalian, C.P.R., was started from the end 1974 and completed in autumn 1976. In this paper a summary of the essential considerations in design and construction of this oil port, such as the planning of the pier, the determination of exciting forces (namely wave forces, forces due to earthguake, mooring line forces and berthing forces due to the impact of tanker on the fenders)on structures, the design of the large cylindrical cassion with a diameter of 9m and a height up to 19.7m and the construction of connecting bridges by two types, is presented.

In the summer of 1978, a siting/design investigation for dock structures (Marshall Islands Dock Project) was conducted at 15 atolls within the Marshall Islands group (see Figure 1). The Marshall Islands are within the U.S. Trust Territory of the Pacific Islands (TTPI), located in the North Pacific. The Marshall Islands Dock Project is part of the Capital Improvements Program currently underway in the Marshalls. The program, aimed towards making the Marshall Islands more self-sufficient in preparation for their independence in 1981, includes the construction of low cost dock structures for use by the design vessels described in this paper to load/unload agricultural products, supplies, and passengers. This study did not include the feasibility of this approach versus other alternative loading/unloading approaches.

Wave-transmission and mooring-force data of the Tethered-Float Breakwater and Pole-Tire Breakwater (PT-Breakwater) were compared, and the basic costs (without mooring system) of two equivalent breakwaters determined. It was found that, for short-fetch applications, the PT-Breakwater was an order of magnitude less costly than the Tethered-Float Breakwater. The PT-Breakwater is a more effective wave-energy filter than a Tethered-Float Breakwater of equal size. For open ocean conditions neither of these breakwaters has so far been proven to be economically feasible.

To study the main direction of littoral drift of sand near the Port of Oarai, field observations were made. Through the analyses of the results the following facts were obtained.

Various types of synthetic filter fabrics are available for geoteehnical applications. Especially in the field of coastal engineering a lot of experiences are generally known. Unfortunately technical recommendations and testing regulations for specific implimentations of geotextiles are not generally available and some actual examples of damage of coastal structures urgently require investigations on long-term resistance. A research program oriented towards the development of guidelines for testing geotextiles, the development of filtration rules and the clarification of long-term resistance of fabrics was carried out. This paper deals with testing procedures associatied with the estimation of the opening size and the permeability to water of fabrics. Results of investigations on long-term resistance are described and filtration rules for selecting a fabric according to the special requirements of the application are given.

For most of the needed studies for the design of Calais harbour enlargement works, the “Laboratoire National d'Hydraulique” chose to use numerical models. This approach includes the determination of currents around and insiae the new outer-haroour, just as the evaluation of the project sedimentologic impact and of the long-term evolution of a bank nameo “le Riaen de ia Rade", edging the access channel.

Current studies were performed using four nested bidimensionnal computer models fitted on field data and supplying in each point the depth-averaged velocity and the total water height. These four models are based on an implicite finite difference fractionnal step method. Besides for the very near field model the method is especially elaborated to enable the detailed reproduction of edoies and flow separations.

The sedimentological numerical study is based upon current models results : the bed-load transport is computed from the depth-averaged velocity and the water height previously determined using an empirical formula, and tne continuity equation applied to this load transport gives then the bed evolution. As soon as the depth variation is significant enough to react on the flow pattern, current fielos are readjusted by a simple method based on flow continuity equation.

This numerical model, applied to the near field, has given an evaluation of the sedimentological impact of the harbour enlargement project:

This paper describes the analytical and experimental studies on the behaviors of a ship subjected to a sheering flow induced around a rectangular solid-type marine structure, and also deals with ship-structure protective systems against ship impacts.

Large bridge piers, which are constructed in a narrow waterway with strong tidal currents, are treated herein as one of the typical solidtype marine structures.

The influence of an opposing current on highly non-linear transient breaking waves in deep water is described quantitatively from experiments. 3 new parameters that describe crest front steepness and wave asymmetry are introduced. Further, joint probability density distributions are obtained from an analysis of field data containing nearly 25000 storm waves. Thus, a tool is provided from which estimates for probabilities for occurrences of steep breaking waves in deep water, may be obtained.

Using salinity as an example of dissolved substances in estuarine waters it is shown how the long term trend of concentrations can be split up into a man-made and a climatic contribution. The understanding of long term mixing processes and adequate sampling techniques are essential for this purpose. The physical state of the estuary can be described in terms of 3 basic variables, the river discharge, the filtered water level and the filtered salinity. The river discharge represents the climatic fluctuations in the catchment area, and the filtered water level is a record of the large scale weather pattern over the adjacent ocean basin. Salinity trends which cannot be attributed to these two variables must originate from man-made actions, such as dredging or other engineering activities which change the geometry of an estuary.

Two models are used for the trend analysis, the simplest possible mixing equation (which always holds for a sufficiently long time scale), and a salt flux consideration.

A field investigation program on waves in the Weser Estuary, German Bight of the North Sea, was started to learn about the complex wave climate in this region. The comparison of results in the various locations shows that most of the wave energy is transferred from deep water across the reef region to the wadden area. The comparison of spectra in the different sites and the parametrization of these multipeak-spectra gives another feasibility to describe estuarine waves.

For many years stability theories have been used both to design inlets and to appraise the performance of them. There are a variety of approaches to the formulation of stability criteria ranging from the purely empirical (Stevenson, 1884 – cited by Bruun & Gerritsen, 1958; O'Brien, 1931; Bruun, 1977) to the generalised analytical (Escoffier, 1940; Bruun & Gerritsen, 1958; Keulegan, 1967; O'Brien and Dean, 1972).

In 1966 a seemingly small perturbation made to the inlet of Wallis Lake resulted in significant changes to the estuary. The direct application of existing stability theories was of marginal value in explaining these changes and predicting the stable regime that the estuary may ultimately reach. This paper highlights some of the limitations of existing stability theories, presents a new method of dynamic behavioural analysis, outlines the case study of an estuary to which existing stability theories could not be effectively applied but to which the behavioural analysis produced interesting results, and recommends the direction in which further research could yield beneficial results.

Fourteen tidal inlets within the lower Chesapeake Bay were studied to examine whether significant differences existed in their hydraulic behavior relative to the larger oceanic inlets hitherto studied. Measurements included simultaneous external and internal tides, gaging of discharge through a tidal cycle, measurements of inlet geometry, and basin area. The results indicate that: a.) smaller inlets (A_c < 100 m²) depart from the relationship between inlet throat area and tidal prism developed for oceanic inlets; b.) examination of inlet width versus depth indicates the departure from ocean inlet geometry occurs at A_c values between 100 and 500 m²; c.) the maximum velocity in smaller inlets is significantly less than oceanic inlets (~0.35 vs 1.0 m/s); d.) tidal phase lags and tidal range ratio were generally equal. However, for conditions of significant tide range reduction, the low water phase lags more closely approximated the tide range ratio.

Between October 1976 and July 1977 a northern rubble mound jetty was constructed at the mouth of the Hastings River, transforming the entrance from a single to a double jettied system. Prior to the jetty construction the entrance was characterised by the presence of a substantial swash bar (alternatively called an ebb delta marginal shoal) which was a continuous feature over 100 years of hydrographic survey records. However, construction of the northern jetty triggered an unprecedented onshore movement of the swash bar. This movement was well documented by a field monitoring programme incorporating hydrosurveys, aerial photographs, tidal gaugings, sediment sampling, float tracking and nearby wave rider buoy information.

A semi-quantitative model was developed to aid understanding and quantification of the macro sedimentary processes associated with this phenomenon. The model demonstrated that the sudden reduction of the swash bar was due to the disruption of a circulation of sand which had previously aided the dynamic stability of the bar. The quantitative predictions of the model agreed well with subsequent entrance behaviour. The philosophical development of the model and its findings are discussed in detail.

In the literature there is a general lack of attempts to quantify the sediment transport relationships between the gross morphologic features of tidal entrances. This paper presents a methodology for assessing the sedimentary process at tidal entrances.

The migratory pattern of a small coastal inlet was examined in terms of the factors generally acknowledged to control inlet behavior. That is, the tidal discharge which acts to flush the inlet and, on the other hand, the intrusive littoral materials depositing in the inlet environment. Specifically, a “flow conveyance index” was computed and compared to shoreline movements. The “flow conveyance index” was defined as the ratio of the mean distribution of the overall planform area of the throat of the inlet to the mean distribution of the planform areas of shoals within the throat of the inlet. High and low “flow conveyance index” values would correspond, respectively, to periods of relatively high and low inlet flushing conditions. A consistent pattern obtained from this analysis, wherein high and low index values corresponded with high and low shoreline movements. Additionally, the plot of rates of shore movements against rates of change of “flow conveyance index” was fitted with a simple linear regression line having a positive correlation coefficient of 0.85. Further analyses of the mean distribution of the shoals within the throat of the inlet demonstrated the cause of time-varying rates of movement of points along the spiriferous east shoreline of the inlet. Shoreline movement rates were plotted on a time-space plane and isolines of shore movement rates contoured. The result was a three-dimensional image of shore movement rates over time and distance. The position of the centroid of the inlet shoal distribution at different times was superimposed upon the three-dimensional image. This revealed that variations of shoreline movement rates along the shore at any point in time are dependent on the mean position of the inlet shoal distribution. Also, the direction of movement of the mean position of the inlet shoal distribution appeared to indicate the predominant direction of flushing action, that is, flood or ebb tides.

The discharges issued by OTEC plants, thermal power plants and other engineering devices, give rise to the transport of “foreign” properties and substances into the natural ocean environment. In order to predict the functioning of such structures and assess their environmental impact, physical modelling has already been utilized. Since the simultaneous fulfillment of both Reynolds and Froude criteria is impossible (in a conventional small scale model operating with the prototype fluid) in the models mentioned the transport phenomenon was reproduced on the basis of the densimetric Froude number (Fr) only, the influence of the Reynolds number (Re) being neglected. On the other hand, the identification of the scale of Fr (viz λ_Fr) with unity can lead to sub-stantial differences between the model and prototype values of Re. (Because λ_Fr = 1 yields λ_Re = λ_l^3/2 where λ_l is the linear model scale.) Yet many of the pertinent aspects of a turbulent diffusion (energy dissipation, thickness of mixing zones, separation processes, etc.) are strongly dependent on Re, and therefore an appreciable distortion of Re (λ_l^3/2 ≪ 1) can lead to some substantial errors with regard to the similarity of these aspects.

In the present study the mooring systems of four bulk carriers which were moored at a jetty located parallel to a navigable water were investigated with special regard to forces due to passing ships. The objective of this study was to verify in praxi the present knowledge of moored vessels berthed at more protected sites and to prove proposed models of forcing functions by passing ships as well as numerical models for the computation of ship mooring systems. For that purpose the mooring forces and also those data which characterized the properties of the mooring systems were recorded. On the basis of the also recorded wind and current data and the data of the passing ships with which the external forces could be estimated the mooring forces were computed. These computed forces are compared with the measured mooring forces.

A two dimensional numerical model has been developed which is capable of predicting the tidal water elevations, depth averaged velocity components and horizontal concentration distributions in narrow entranced harbours and marinas. Particular attention has been paid to the numerical treatment of the convective accelerations where, as a result of narrow harbour entrances and the general nature of planform geometries, the resulting highly non-uniform flow fields can readily lead to non-linear instabilities and unstable numerical solutions.

In order to check the validity of the numerical results, a comprehensive study was carried out to compare, with scaled laboratory model studies, the predicted tidal velocity fields and flushing characteristics for a number of rectangular harbours of constant planform area but different length to breadth ratios. The experimentally measured average per cycle exchange coefficients and the observed mean water level path-lines agreed reasonably well with the corresponding numerically predicted exchange coefficients and depth averaged velocity fields.

The results of both the numerical and laboratory model studies confirmed conclusively that the maximum gross flushing characteristics occurred within a rectangular harbour when the length to breadth ratio was close to unity. Also, further tests showed that the insertion of impermeable barriers as a possible means of increasing the flushing efficiency proved to be unsatisfactory.

Experience gathered during the last few years shows that a serious problem when fighting oil spills out in open waters, is the mixing of the oil into the sea by breaking waves. In this paper we propose a theoretical model that we believe represent a fruitful approach to the problem of determining the amount of oil mixed into the sea by breaking waves. Our model is based primarily on probabilistic methods, but with experimental observations and data as an essential foundation.

As already stated in the previous conference, the fresh-water flow which passes through a river mouth horizontally into the sea, exhibits a special characteristic due to the effect of buoyancy. Its dynamics belongs, essentially to the same category with the transonic flow in aerodynamics. The interfacial Froude number plays a dominant role in this case, as well as the Mach number does in the transonic gas flow. The supercritical zone, in which the interfacial Froude number exceeds unity, occupies the sea surface with some area, in response to a degree of the discharge amount of the fresh water. This zone begins at the river mouth and stretches in the offshore directions over the sea, accompanied with a lateral growth.

As is well known, on the other hand, supersonic zones are sometimes formed partially along an airfoil, or in a tube with a varying cross-section, if they are placed in a subsonic gas flow. Those two different phenomena have been proved to be identical dynamically with each other [KASHIWAMURA and YOSHIDA 1978], [KASHIWAMURA 1979]. There have been a great number of researches in order to obtain an analytical solution of the transonic flow, in the past several decades, but there seem still many difficulties to attain a complete solution, except some particular cases such as a stream-lined approximation of immersed bodies being possible.

Considering such circumstances, it may also be difficult for the present problem to be solved completely, although it has not been decided yet to be impossible. The present author describes the process of his efforts for obtaining an analytical solution and its results, from a view point of the inspection on an applicability of the hodograph method, and its modification to this problem. In spite of incompleteness, they provide us several findings which are useful to understand the dynamics of the outflow of the fresh water. In addition to those, a few examples of field data concerning the horizontal distribution of the interfacial Froude number around a river mouth, and some experimental results are presented.

The object of this case study was to predict the likely degree of pollution resulting from the discharge of heated water from a proposed LNG plant into the sea (Figure 1). The expected thermal loading was 40 m³/s at a temperature of 10°C above the natural ambient sea water temperature. The investigation was required to provide data for an ecological study to determine the possible impact of the plant on the coastal and marine environment.

Information on tide levels, tidal currents, salinity, sea temperature, wind strength and direction was obtained in a general survey programme which had already been commissioned. These data provided vital information on seasonal variations in marine conditions and further local information was obtained from short intensive hydrographic surveys. The data were analysed to yield a simplified description of the tidal and wind induced currents and suitable values of mixing parameters for use in two numerical models. The first dealt with the “near field” processes of the spread of a buoyant layer of heated water under the convecting influence of the tidal currents. The second model simulated the “far field” processes which give rise to a general increase in the temperature of the sea in the region.

The heat balance of a water body mainly depends upon the heat exchange processes at the water surface. An experimental method has been developed for determining the heat exchange, the exchange coefficient and the equilibrium temperature. The measuring equipment consists of two similar, well insulated pools which are exposed to the meteorological conditions of the Lower Weser River, Germany. The water temperature of the first pool (T₁) is artificially adjusted to the actual river temperature either by cooling or heating. The temperature of the second pool (T₂) is held constant above the temperature T₁. The difference in power inputs required W₂ − W₁ is equivalent to the net rate of heat exchange due to the increase of temperature to ΔT above the river temperature.

The transport of fine suspended sediment in a partly-mixed estuary has been simulated on a physical model of a schematic estuary reproducing the main geometrical and hydrodynamical characteristics of the Gironde Estuary (France). The natural sediment consisting of silt and clay is simulated using a light and fine material, gilsonite, and the flocculation processes in salt water and under turbulence induced by tioal currents have been reproduced by adding in salt water a flocculating salt solution (sodium pyrophosphate). Then the formation of the turbidity maximum surveyed in the field and its upstream-downstream migration in response to varying river discharge have been successfully simulated and the results of different series of tests lead to the following conclusions:

– flocculation processes – which are responsible of the variation of the settling velocity with salinity and turbulence-have to be reproduced to explain the formation of the turbidity maximum;

– after high river discharges the convergence of bottom residual currents (null point) due to the salinity intrusion creates a trap for suspended sediments supplied by the river flood which accumulate in the form of the turbidity maximum. Without salinity intrusion, a large amount of sediment would escape out of the estuary to the sea;

– during low river flows, a part of the suspended sediment migrates upstream but the amplitude of this migration is small compared with the displacement of the upstream limit of the salinity intrusion;

– the upstream migration of the turbidity maximum is increased when a transverse bottom morphology (existence of a deeper navigation channel) is represented.

Construction of the Jebel Ali Port complex, 35 km southwest of Dubai, in the United Arab Emirates, has included the disposal of 110 Million cubic metres of excavated spoil.

Disposal of dredged carbonaceous breccia raised particular problems due to the high proportion of fines generated and which, unless properly controlled, could cause wide scale environmental damage in the coastal zone. At the same time it was necessary that acceptable reclamation should be created. An extensive data collection exercise was carried out in order to monitor the geotechnical, hydraulic, meteorological, marine climate and marine biology aspects of the operation.

The project “MORAN” (Morphological Analyses of the North-Sea-Coast) is an extensive program in order to try and combine all knowledge of the morphologic behaviour of a transitional zone of 5 to 7 km width with weather, tide, current and wave data. The area to be considered is about 9000 km² size. The program started in 1979 and will probably continue until 1984.

Oil and gas pipelines from the North Sea have reached the northeast coast of Scotland from offshore production platforms. The pipelines date from 1973 to 1976. The environmental effects of these pipelines are compared as are the relationships between engineering work, environmental impact assessment and planning procedures. There is also a discussion of methods used to protect and restore these three landfall areas.

This study deals with the statistical properties of the group formation of random waves determined by the zero-up-cross method. Probability distributions about

This paper represents a comparative analysis of the occurrence of wave grouping in field storm waves and laboratory waves with similar power spectra and wave height distribution.

Two wave patterns – runs of waves and jumps in wave heights – which have significant influence on the impact on coastal structures were included in the analysis of storm wave records off the coasts of Cornwall, U.K. and Jutland, Denmark. Two different laboratory wave generator systems, based on random phase distribution of component waves, were used. Within the limitations given by the relatively small number of analysed records it is shown that wave group statistics can be satisfactorily reproduced by random phase generators that are not based on a limited number of component waves, but for example based on filtering of white noise. It is also shown that the statistics of large waves and wave groups containing large waves depend on whether the waves are defined from zero-upcrossings or zero-downcrossings. Although very similar seas were chosen for the analysis it was found that significant differences in the wave group statistics from the two locations existed. Also a considerable scatter in the wave group statistics throughout the storms was found.

A high level of integration of disciplines and use of a centralised computer data base and programming system were seen to offer advantages in a study of the marine and coastal environment of the Port Melbourne Authority. These goals were only partially attained but the effort was well worthwhile.

The paper describes an analytical approach to the problem of wave induced oscillations of a long ship in water with a depth which is only slightly larger than the draught of the ship. The problem is linearized (i.e. small amplitude motions and waves) and the water flow induced by the incident waves, and by the motion of the ship is determined. This also yields results for the forces in the equations of motion for the ship. These equations can be solved analytically, but the paper concentrates on giving numerical results for the solutions. Results are also given for the hydrodynamic masses and movements of inertia, and for the damping due to radiation of wave energy.

Possible contributing factors to the 1978 failure of the massive main breakwater at Sines, Portugal are presented in a selective summary of the report of the Port Sines Investigating Panel. A failure scenario involving the impact breakage of unreinforced concrete armor units is developed.

Measurements have been made of drag on naturally rippled sand beds in an oscillatory-flow water tunnel. A partition splits the tunnel into two parallel channels with equal cross sections and volume rates of flow, one with a smooth flat rigid bottom and the other containing the sand bed. Roughly, the difference in the two bottom drags, the one known, is equal to the difference in the net pressure forces on the water in the two channels, which is obtained from measurements of pressure differences across the partition at each end of the sand bed. Each experiment provides the drag, or average bottom stress, on the rippled sand bed as a function of the phase, θ, of the sinusoidal flow. From a first set of thirteen experiments with a medium sand, a stress coefficient, f(θ), is presented in three families of curves which explore the additional effects of flow velocity, ripple length, and deviations of the ripple profile from normal equilibrium. Average rates of energy dissipation are calculated. Results show f to be a complicated function of θ and other parameters. In particular, the instantaneous stress is not simply related to the instantaneous velocity. Some salient features of f(θ) are described, qualitatively, by a simple model.