Search

This paper is written in continuation of earlier published material (2, 4, 5) dealing with stability of tidal inlets on littoral drift shores. The experience available at that time was responsible for the introduction of two parameters: .vmean max/ defined as the mean max. velocity in the gorge at spring tide and the K/M-tot ratio (tidal prism at spring tide divided by material transport to the entrance from the adjoining shores) as the most pertinent parameters for description of overall stability. A more detailed justification for this choice is given in this paper, based on computation of the relative sediment transport at various tidal phases. Examples of earlier date (4) and twelve new examples from India are given.

This paper is a sequence to two papers, (1) and (2), previously read at Coastal Engineering Conferences. They presented a mathematical model for estimating displacements, velocities and accelerations in a downrushmg wave on a rubble mound breakwater slope. Verification by photographic recording of displacements involved some uncertainties. In the present paper are reported measurements of velocities, which gave much more definite data. The correlation with velocities calculated from the model is shown to be good.

The Canadian Organizing Committee, the Vancouver Executive Committee and the National Research Council of Canada have done a superb job in planning this conference and in carrying out the enormous amount of detail necessary for its realization. On behalf of the Coastal Engineering Research Council, the other participating organizations, and all of the attendees I thank most heartily all who participated in this work. I am personally most grateful to those representatives of the Canadian Committee who made the final selection of papers. I should explain at this point that a small papers Committee is appointed for each of these conferences to review the summaries submitted by the authors - but this screening is intended only to appraise their appropriateness for a coastal engineering audience - and to eliminate those few papers which are promotional "blurbs". It has not been a technical review such as is made for "refereed" technical and scientific journals. The number of papers submitted for this Conference passing this simple review far exceeded the reasonable limits of the program - and for a brief period the Papers Committee faced the new and distasteful task of selection among papers acceptable under past standards. However, the problem was handled by the Canadian Committee - applying a formula which seemed equitable and reasonable. I trust that those affected concur in this judgment.

The paper describes the works carried out to improve and stabilise the entrance to the Creek at Dubai. The Creek which is about eight miles long discharges through a heavily charged littoral zone m which large volumes of sand are transported across the entrance from west to east. The works were required urgently and this coupled with financial restrictions prevented a study of the problem on an hydraulic model or the collection of comprehensive site information before construction of the work commenced. In the event the works were carried out in stages - succeeding stages being planned and designed after the effects of the previous stages on the regime had been established. The paper presents the results which were achieved using the prototype as a model and traces the effect of each stage on the Creek and littoral regimes from the commencement of the works.

This paper describes the Earth Resources Technology Satellite (ERTS) placed in orbit in July 1972 and the ERTS simulation high altitude aircraft flights which have been flown for approximately one year. The ERTS satellite and simulation programs conducted by the National Aeronautics and Space Administration (NASA) have been developed to demonstrate the techniques for efficient management of the earth's resources. To achieve this objective the ERTS-A satellite provides for the repetitive acquisition of high resolution multispectral data of the earth's surface on a global basis. Two sensor systems have been selected for this purpose: a fourchannel multispectral scanner (MSS) subsystem for ERTS-A and a threecamera return beam vidicon (RBV) system. Systematic repeating earth coverage under nearly constant observation conditions is provided for maximum utility of the multispectral images collected by the ERTS satellite, which operates in a circular sun synchronous nearly polar orbit at an altitude of 494 nautical miles. It circles the earth every 103 minutes completing 14 orbits per day and views the entire earth in 18 days. The orbit has been selected so that the satellite ground trace repeats its earth coverage at the same local time every 18-day period within 20 nautical miles. A number of data output products are available from this satellite which include 70 mm products for precise location of topographic features, 9.5 inch positive or paper prints and also computer compatible tapes or punched cards. Also described are the results of the ERTS-A simulation flights flown at an altitude of 65,000 feet as related to coastal studies. Simulations of both the RBV and MSS in coastal areas are presented.

Physical processes in the ocean, adjacent and marginal seas are mainly of special interest for oceanography and related sciences, whilst the knowledge and the understanding of these processes in coastal areas, estuaries and tidal rivers is also of significant practical importance for coastal engineers. Just measurements and observations are not sufficient to obtain a comprehensive insight into these processes and to explain and to understand the spatial and temporal states and their variations. Hydrodynamical~numerical investigations are delivering a considerable assistance. Within this paper my remarks will be restricted to some examples of the numerical reproduction of physical processes in shallow - water areas: 1) Dynamics depending on tides and wind; 2) Horizontal dispersion of suspended matter„ In concluding this Paper I shall mention a special coastal model with a permanent refined grid-net, which is a part of the wel] « known North Sea model.

The wave program described in this paper is one intended to provide wave statistics by having our Los Angeles County life guards observe the wave heights, directions and periods. Mark-sense cards and high speed data processing equipment and computers are used to handle the volumes of statistics. While some scientists are planning very accurate, costly solutions to the problems of wave statistics, agencies are reluctant to venture into an expensive, elaborate wave surveillance program requiring a large quantity of personnel. I feel that neither the accuracy of present day design or construction methods warrant "split hair" accuracy in wave surveillance. The method described in this paper will provide a practical solution if the statistics are handled as follow 1. Wave statistics are gathered continuously over many years of time. 2. A standard is set to check the observed values. 3. Large rare damaging storm conditions will be developed by any reasonable means available until enough years of observation have passed to provide adequate statistics.

Beach erosion is one of the serious problem in Japan. As a countermeasure against beach erosion, many preventive works, such as sea walls and groins, have been constructed during the past 20 or more years. However, as the result of field investigations, it has become clear that sea walls and groins are not always effective on beach erosion prevention, and inversely, in some cases, they accelerate the beach erosion. Based on the above cognition, the author has proposed and tried to apply the detached breakwater system as a measure against beach erosion for the last 8 years. This is for the purpose of developing the sand deposition behind the breakwater. Therefore several experimental works of the detached breakwater system were carried out under the guidance of the present author, and most of these tests were successful. The design method of this system was composed by the author on the basis of the result of field investigations, which have been conducted for more than 8 years. The numerous construction works of detached breakwaters have been carried out in accordance with the design method proposed in this paper, and the effectiveness of detached breakwaters has been proved on the several coasts in Japan where severe beach erosion occurs.

This paper deals with the estimation of total wave force on a vertical circular cylindrical pile. Firstly, finite amplitude wave theories such as those of Stokes waves and cnoidal waves are recalculated by the Stokes second definition of wave celerity and the applicability of the theories for wave crest height above the still water level, wave celerity and horizontal water particle velocity is briefly discussed. Secondly, the drag and inertia coefficients are estimated respectively from the results of experiments for total wave force by the authors and by other researchers, based on the Morison wave force equation applying the theories and characteristics of the coefficients are considered in relation to the wave characteristics and pile dimension. Lastly, the applicability of the wave force equation proposed is investigated in comparison with experimental and theoretical results for time variation of total wave force and maximum total wave force.

A simple method is presented for estimating the relative compatibility of borrow material being considered for beach fill purposes. The method defines the "compatible" fraction of the material as that coarser portion with the same mean diameter (in "phi" measure) as the native material on the beach. A single graph is presented which allows determination of the number of units of borrow material required to obtain one unit of compatible material. Use of this method requires that the size distributions be reasonably represented by the "lognormal" relationship and also requires knowledge of the means of the native and borrow materials and the standard deviation of the borrow material (all in phi measure). This method overcomes shortcomings of the Krumbein-James method published in 1965. Several examples are presented illustrating the application of the method presented in this paper.

The wave-pressure formulas derived in our laboratory have been verified by the investigations of the slide of the vertical walls of composite-type breakwaters due to severe waves during heavy storms which have attacked numerous harbors in Japan since 1959. Some of the examples are shown in this paper.

In this study, frequency response and transfer function techniques are used together with cross-spectral and fast Fourier transform methods to determine the proper boundary values for computing the flow field of a coastal sea. Tide data containing considerable perturbations from swell and meteorological disturbances are analyzed. In computing the frequency response estimates, the effect of noise in the input is treated by a cancelling technique and by the choice of a reference station to evaluate the interdependencies among the other stations at the boundary. The usefulness of the network frequency response function is threefold: (1) future conditions can be simulated using observed water levels at any single location, (2) boundary information for models of different grid size can be obtained by interpolation, and (3) missing data at a given location can be estimated optimally using data at neighboring stations and the network response function. The paper discusses an example of such an application, the determination of a boundary of a two-dimensional model of Jamaica Bay, New York City, U.S.A.

In this paper the practical design of coastal mobile bed models is considered. The semi-theoretical approach expressed by the author in earlier publications (9,10,11,12) is extended and used to classify and design coastal models. Fixed bed coastal models are discussed first to form a basis for the argument. Subsequently, mobile bed models are classified according to criteria of dynamic similarity satisfied in their design and scale effects present in their operation. Basic scale laws are next derived for all classifications of coastal models. This is done for both inshore and offshore models, the distinction being brought about by adjusting the velocity scales for unidirectional (and long wave) motion. Time and sediment transport scales are next derived and some well known models are compared. The presence of bedform and model distortion is also treated. The work is compared with that of other authors.

For coastal engineering works, as for other structures, the designer must search for the economic optimum point. This point represents the minimum in the sum of direct cost and cost of possible future damage. By setting up functional representations of these costs the optimum can be obtained directly. This approach is illustrated by models developed independently in the Netherlands and in Canada. At this stage the output of the models may be denoted as the 'perfect knowledge' optimum, in the sense that parameters of the cost functions are assumed to be known with complete accuracy. In the 'real world' case, however, the estimated values of the parameters will be subject to considerable uncertainty. It is shown that because of this uncertainty the 'real world' design optimum will generally be shifted to give a structure larger than that indicated by the 'perfect knowledge' assumption. The novel contribution of the present paper consists of analyzing this shift to obtain simple expressions for the apparent overdesign due to uncertainty and for the resulting cost increase. An illustrative example is presented.

Coastal Engineering literature contains many references to coastal structures in the design or construction stage but few references to these same structures concerning their maintenance effectiveness subsequent to completion. This paper describes a successful long-term maintenance history of major coastal public structures in the State of California, U.S.A. It is concluded that proper design combined with prudent maintenance will result in effective coastal structures with long economic lifetimes.

In this paper, the effects of a storm surge that happened on the 16th-17th January 1973 in the harbour of Leixoes are analysed and described. These effects were of two types: - As the storm surge coincided with a spring tide and rough seas, severe damages occurred in the outer breakwater, mainly in its head. - Associated to the storm surge range phenomena happened in the nS 2 dock; these movements, acting on a ship berthed in a nodal zone, caused several breakings in the ropes and damages in harbour structures. The characteristics of the storm surge and of the waves are analysed. Their effects on the breakwater are described. By comparing the periods of long waves observed in the tide records with the resonance periods of the inner docks it was possible to conclude that the intensity of the range phenomena observed was due to a half wave length resonance. Having in mind the affinities with the phenomena referred to above, the effects of range action in an oil terminal and new damages in the outer breakwater, that occurred in January and February 1974 respectively, are also briefly examined.

The paper deals with two-dimensional tests on a scale model of a dolos breakwater. It is related with the construction of a large harbour at Sines for tankers with up to 1 million dwt, ore ships with up to 300,000 dwt, general cargo, etc. The main breakwater is design ed with 40 t dolos, in order to withstand waves with up to 1 1 m significant wave height(100 years return period). Considerations on wave data and on modelling the spectrum ( Pierson-Moskowitz ) precede the presentation of three sets of tests on LNEC's irregular wave flume. Main results are compared with those from regular wave tests. The most important conclusions are stressed: influence of pla_ cement on dolos damages, irrelevance of maintenance, importance of the singular zone of the dolos support base, disadjustment of Hudson's formula for calculation of dolos weight using H as significant wave height,and importance of individual movements for the risk of breaking of individual blocks.

In shoaling water on sloping beach, waves break by hydraulic instability due to the finiteness of water depth, so that frequency spectra of waves in surf zone must have any limiting form similar to the equilibrium spectrum given by Phillips(l958) In this paper, authors haze derived an equilibrium form of spectra for surf waves from the limiting wave condition at constant water depth by Miche(l944) and from breaking wave experiments on sloped bottom by Iversen(l952) The results arc compared with surf wave spectra obtained from field observations by means of stereo-type wave meter devised by the authors(1968). By means of this spectrum and by deep water wave spectra for various wind conditions, significant wave heights and optimum periods of limiting waves m surf ^one are calculated.

This paper deals with wave forces from short crested waves as compared with two dimensional waves. The investigation comprised measurements of wind wave forces on fixed pontoons in a model, and a comparison of wave crest characteristics of wind waves in model and prototype. The model tests showed that the wave crests have a marked influence on the wave forces. The investigation of model and prototype wave data showed that the crest characteristics of the model waves compared well with that of prototype sea.

A model of the estuary of the Columbia River was built and tested at the University of California, Berkeley, during the years 1932 to 1936, to study the effects of proposed changes in the navigation channels on the currents and sediment movement. The project was sponsored by the North Pacific Division of the Corps of Engineers, and the engineering results were reported at that time in internal memoranda. The basis for the selection of the scale ratios and other factors affecting the design of the model were reported in some detail (O'Brien, 1935), but only a brief note was published regarding the operation and the accuracy of the model (Johnson, 1948). In some respects this model is still unique, and a description of it may be of interest to the coastal engineers. This paper deals primarily with the model itself and not with the practical problems of channel maintenance and improvement, but some information regarding the regimen of the Columbia is necessary background for understanding the problems which were to be studied in the model. Figure 1 shows the configuration of the estuary, the jetties, and the ship channel. The river was then unregulated; the freshwater discharge exhibited an annual cycle with an average annual flow of 235,000 second feet, an average summer freshet discharge of 660,000 second-feet, and an average low-water flow of 70,000 second-feet. The tide shows a diurnal inequality, with the long run-out following higher high water; the diurnal range of tide is 8.5 feet, and the average range is 6.5 feet. Freshet flows affect the range and lag of tide in the river section above the estuary to such a degree that the published USC and GS Tide Tables were valid only for the months September through May and not for the freshet season. The range of tide is approximately constant from the ends of the jetties to Harrington Point; the lag over this reach is approximately two hours. At low river stages the tide is evident as far as Bonneville, 140 miles from the mouth; the tide wave progresses with steadily decreasing amplitude and there are no nodal points. The tidal prism varies both with range of tide and river stage; at low river stages, the prism corresponding to an 8 foot range is between 600,000 and 700,000 acre feet.

The theory of dimensions has been subject of considerable controversy and only in the last few decades has it been agreed that dimensional methods can serve as a powerful tool m experimental investigations of physical phenomena Its effectiveness becomes especially noticeable when the number of factors involved is large and the theoretical knowledge is insufficient However, like any other mathematical tool, the theory of dimensions can supply correct and useful results only if it is properly applied One example of improper application is the introduction of an exaggerated and sometimes simply of a nonexistent correlation between the experimental results The purpose of the present paper is to analyse these kinds of spurious correlation.

Information on extreme wave conditions is needed in the design of offshore structures. This paper present the results of calculations of the parameters in the 50-year storm; the work has been based on extreme wind data and on instrumental wave measurements. The results are complementary, and are combined in two maps, one of extreme wave height and the other of the corresponding wave period.

The general problem of single-impulse induced waves has been under experimental investigation by the author for several years The present paper is confined to a presentation of the wave modes which are to be expected for various permutations of displacement velocity and displacement length at the impulse source Other portions of the study will be published elsewhere It is clear that a number of geometric arrangements in the laboratory may be made to generate impulse waves, for example, sudden upthrust or downdrop of a block on the tank bottom analagous to block faulting on the sea-floor in nature, or a hinged flap moving on the bottom analagous to the undulatory bottom motion which may occur during seismic disturbances on the sea floor However, it is my opinion that the impulse generator which is most simple and most easily related to contemporary generalized theory, is a single piston thrust at one end of the wave tank which pushes the fluid down channel (See Figure 1) As an additional simplification, the investigation is carried out for the flat bottom, fixed depth case, relegating the effect of varying depth to a later study.

The Nagoya Storm-Tide-Preventing Breakwater is a large-scale Breakwater built as a link in the general Ise Bay Storm-Tide-Prevention Project. The entire length of this breakwater is about 8,250 meters, which extends from the mouth of the Nabeta River, transversing the northern part of Ise Bay, to the Chita town. (Pig. 4) The greater half of this breakwater was built on an extremely unstable foundation, the nature of ground being of soft clay stratum with a thickness of 10 m - JO m. The sand-drain method was adopted for improving the ground on which caissons were laid, forming a composite type section. For this reason, during the process of construction a close work control was maintained constantly by applying boring, observation on the sinking, pore water pressure and other conditions to ascertain whether the sinking by consolidation took place according to the calculations laid in the design specification. Based on the date obtained in this manner the speed of the work was regulated and the work was conducted under strict control of soil mechanics. The required volume of materials for the construction of the breakwater was so immense that a special care had to be given to ensure their smooth and efficient supply. And to speed up the work with a view to reducing the effects of wind and waves to a minimum, large machinery were employed. The present paper describes the engineering features of this great 8,250-meters breakwater project which was completed in a short period of 2 years and 8 months at a cost of 30 million dollars after overcoming numerous obstacles.

In the design of mobile bed coastal models it is inherently assumed that prototype beach processes may be modelled using lightweight sediment. At the Queen's University Coastal Engineering Research Laboratory, a long range project is currently in progress to determine scaling laws and scale effect for mobile bed coastal models. A large portion of this program is directly concerned with beach profiles and in this paper preliminary work is reported, in which a comparison is made between two dimensional laboratory beach profiles obtained from controlled "prototype", undistorted model and some distorted model tests.

This paper is concerned with the quantitative study of the geometrical asymmetry associated with shallow water oscillatory waves in the breaker zone. Three descriptions of wave asymmetry are defined and examined : (l) Wave vertical asymmetry i2^ Wave slope asymmetry and (3) Wave horizontal asymmetry The effects of shoaling, produced by beaches of different slope, on the wave asymmetry are examined. Six beach slopes in the range 1:4 to 1:18 were employed, and a quantitative correlation was found to exist between the wave slope asymmetry, wave horizontal asymmetry and the wave vertical asymmetry. An expression is given for the wave horizontal asymmetry based on the expression for the wave vertical asymmetry from the cnoidal wave theory. The theoretical study of wave slope asymmetry made by Biesel (1) and the results of the experimental work on the wave slope asymmetry in the present work are compared and gave a good agreement*

The characteristics of oscillatory boundary layer flow have been treated with keen interest during the last decade from the various aspects. Among the previous results the theoretical treatment by K. Kajiura must be the most important and fruitful one to advance in our knowledge on the present phenomena. On the other hand the senior author has had a real interest in the behaviour of sediment particles due to oscillatory fluid motion, and has conducted his systematic investigations on the sediment movement in nearshore area. The aim of this paper is to introduce some results of the recent investigations conducted at the Coastal Engineering Laboratory, University of Tokyo, with the intention of investigating the applicability of Kajiura's theory to the oscillatory flow in the vicinity of bottom with sand ripples.

The paper describes a study of density-currents in locks where there is a net inflow of water into the dock The velocity profiles occurring are different than might be expected by simply superimposing the net flow onto a normal density-current profile The differences are shown to be due to the non-uniform salinity profiles occurring in the docks and a semi-theoretical study is presented which illustrates the importance of this salinity profile The accretion in the docks is explained by the transport of material into the docks during the levelling period The quantitative agreement between estimates based on measurements during the levelling period and the dredged quantities from the dock are good The locking operation is also shown to be an important factor in certain cases An attempt to describe the flow of silt into the dock using the onedimensional diffusion equation has shown that allowance must be made for the pick up of silt off the bed of the lock and the settling of silt (as the velocities drop) if quantitative agreement is to be obtained.

Measurements of drift were made in a wind and wave facility at different elevations below the mean water level. The drift profiles were obtained for reference wind speeds, Ur = 3.1, 5.7 and 9.6 m/sec. The measurement technique involved tracing the movement of small paper discs which were soaked in water to become neutrally buoyant at the elevation of release. A logarithmic drift profile is proposed. The water shear velocity, U*w, predicts a surface stress, TS = pw U*S, in agreement with that obtained from the wind shear velocity, Ts = Pa U*li where pa and pw refer to air and water densities, respectively. The influence of wind on phase speeds of waves was investigated by solving the first order perturbation problem of the coupled shear flows in air and water. The air velocity profile was described by a logarithmic distribution and the drift profile was described by the proposed drift profile. Adequate agreement is found between the calculated and measured phase speed using Doppler radar in the wave number range 1.9 - 10 cm-1. In the wave number range 0.05 - 0.5 cm-1, measurements of phase speeds were obtained by using two wave gages. The waves were mechanically generated without wind and the wave gages were spaced to obtain coherent signals. The wind was then allowed to blow over the waves and the distance between wave gages was increased to maintain coherence. The wave length and frequency were obtained from the distance between the gages and from the generator frequency, respectively. The measured phase speeds were found to increase with wind speed consistent with theoretical computations.

An annotated bibliography on groins, compiled by Balsillie and Bruno (1972J, has provided the background for this paper. A review of functional design criteria is presented including groin length, height, spacing, permeability-adjustability, and orientation. A discussion of coastal processes and their relationship to groin design and effectiveness is" also given.

The western coast of Taiwan has been accumulated to vast area of tidal flats by the sediment transported from numerous torential streams According to the aerial photographs, 53,800 hectares of tidal land are worth being reclaimed However, this coast suffers from waves generated by winter monsoons as well as waves and swells caused by typhoons in the summer Studies on the historical processes and future development of the shoreline are of great significance The ancient topographical data in An-Ping and Tseng-Pa areas as well as recent coastal line variations of Tseng-Pa and Yulm are reported in this paper, also the general features of waves along this coast are described The future of the coast is predicted as a conclusion.

In this paper the author describes an experimental attempt to prevent the rapid blocking of a harbor entrance caused by littoral drift in the summer period. This work was conducted at "Seppu", a fishing harbor constructed on a sandy beach in Hokkaido, Japan. This investigation was originally sponsored by the Harbor Section of the Hokkaido Prefectural Office One of the top priority objectives, at that time, was to determine the efficiency of two jetties constructed on the updrift side for the purpose of countering the sand drift. Detailed observations including preliminary model experiments, were made from 1961 to I963 on the general aspects (ie condition and phenomena) of the coast in question. Meteorological data were also compiled together with investigations as set forth by the government. Based on the above, the author finally suggested the utilization of natural forces ie waves, offshore currents etc, by constructing an offshore breakwater to curb the blockage of the harbor mouth. This idea was shown to be adequate at least qualitatively by model experiment with the exception of the troublesome time scale problem. These findings, however, have not been adopted as yet for actual improvement of the harbor at present.

The New England Division of the United States Army Corps of Engineers has created and improved many harbors along the New England coast for the benefit of commercial fishing and recreational boating fleets A harbor, to be effective, must provide a protected area for boats and it must have a safe access, that is, a protected and stabilized tidal inlet A coastal inlet has been defined as a waterway connecting a bay, lagoon or similar body of water with a larger body of water The major engineering problems encountered in the development of harbors have involved stabilization of these inlets The problems have been caused by excessive littoral drift resulting from erosion of the shorefront adjacent to the inlets by wave attack Planning, designing, constructing, and modifying these inlets under very dynamic conditions is complex and difficult Each inlet is unique This paper discusses very briefly some of the problems encountered.

Sediment transport In the vicinity of inlets and coastal regions depends on the combined bottom shear stresses due to both currents and waves. The modeling of the movement of bedload is controlled by the Proude law, bottom shear stress, wave steepness, and friction factor. Assuming Einstein's theory of bedload function can be applied to this study, an analysis was performed after conducting experiments in the flume and model basin. A series of results obtained from the flume tests is to Insure the relationship between the fluid characteristic and the movement of bedload. The final results concerning the longshore sediment transport appeared satisfactory with the estimated curves. The bottom configurations in the Inlet after each test were also shown satisfactorily similar. The sedimentologlcal time scale for the three bed materials were not In satisfactory agreement, however, more discussion of the results was presented in this paper.

In the stabilization of gullies, small overflow dams are used to retain silt and to control the stream grade. These dams are simple drop structures similar to those used in irrigation canals. In this paper the development of rules for the proportioning of such dams is described in terms of the hydraulic requirements for structure performance. The formulas included in the design rules are presented graphically for convenience in application. These rules are based on the accumulated experience of engineers in irrigation and soil conservation work and on the results of a series of laboratory test programs.

Since more than a century some features of the Dutch beach have been measured systematically* Some characteristics of the coast, which could be derived from these valuable series of data, are discussed in this paper. Since 1963 a new and largely extended program of measurements has been established, that will produce, every year, more than one million of numbers. It is hardly possible to handle such a huge quantity of data in the conventional manner; mechanical handling by means of modern computers becomes necessary. A short description is given how this is done and how it will perhaps be done in the near future.

Prototype data from 24 wave stations on and around the tidal flats south of the Elbe estuary enable us to elaborate special shallow water wave characteristics, concerning the variations and correlations of heights, periods, lengths and velocities. This paper deals with some interesting aspects from the engineer's point of view. It turns out that the steepness factor — or H L —^o- of breaking waves is much smaller than of nong- T^ breaking waves and that steepness is no suitable parameter to describe a natural wave spectrum in shallow waters. On the tidal flats the maximum wave heights only depend on the depth of water, not on the steepness. Moreover the possible wave height proves to become much higher than theoretically predicted, especially in depths of water less than 2 m.

The paper describes tests carried out m the laboratory and in the field in an attempt to discover whether a field of artificial seaweed placed offshore can promote an onshore transport of bed material and hence a build-up of beach levels. Tests in a wave tank showed that beach levels could be built up in this way - the effect of the seaweed being to increase the net drift of bed water m the direction of wave propagation i.e. towards the shore. The field trials were not as conclusive as was hoped, but nevertheless some build-up of beach levels did take place at a time when erosion of the beach due to many storms might have been anticipated. A simple hydrodynamic model is proposed to represent the effect of artificial seaweed on gravity waves. The model predicts increased wave attenuation and increased shoreward mass-transport consistent with the experimental results.

The height of sea water level in front of a coastal structure changes by the astronomical tide, the meteorological effect and the short period wave. From three histograms of the astronomical tide, meteorological tide and wave height, the probable level of wave crest in the coast will be estimated by the method presented in this paper.

The paper discusses firstly mathematical problems on the numerical calculation of storm surges. The partial differential equations of motion adopted here take into account the Coriolis force and the nonlinear terms such as the inertial terms and a quadratic form of bottom friction. As a result, special care must be taken in order to obtain stable forms of finite-difference equations. It is shown that inadequate forms accumulate errors to cause divergence of the step by step calculations. A set of stable forms of the finite-difference equations of motion and continuity has been derived. Sometimes, it is convenient to divide the numerical integration region into two or more sub-regions, the mesh-dimensions of which are not equal. A method is described to calculate both regions by one procedure. Japan coasts were frequently damaged by severe storm surges (Typhoon Tides). To protect the metropolitan area from storm surges, a proposal has been made to construct a dike across Tokyo Bay. A numerical calculation has been made by means of IBM 7090 to estimate for several opening width of the proposed dike its effects on the reduction of surges. Interactions between daily tides (astronomical tide) and surges are also discussed.

This paper summarizes the results of a continuing study at the hydraulic laboratory at the University of California at Berkeley on this subject, which is supported by the Coastal Engineering Research Center (CERC) and which has resulted over the years in the Theses of Huon ti (1954), M. Manohar (1955), G. Kalkanis (1957, 1963), M. M. Abou-Seida (1965), M. M. Das (1968) and is at this time being continued by T. C. Mac Donald. All these researchers have greatly contributed to the success of this work while the author was mostly responsible for the continuity of the study. The aim of the study was to see if it is possible to establish for the description and prediction of sediment transport by waves a general system of approach similar to that which the author published in 1950 under the title '.'The Bed-Load Function for Sediment Transport in Open Channel Flows". ( It was hoped at the time that many of the basic steps of such a description may at least be similar to those used for uni-directional flow. It became apparent that such similarities of approach were quite feasible; but another difficulty became apparent from the beginning. While in the uni-directional flow many details of the flow, such as velocity distributions, boundary layers and turbulence had been, studied and described previously, such knowledge was almost entirely lacking for wave motion. The first part of the study consisted entirely of hydraulic measurements and of their analysis. In order to determine the necessary scope of such hydraulic studies, the analogy with sediment transport in uni-directional flow was used. Some of the principles governing uni-directional flow transport are: 1. Sediment motion can be divided into bed-load motion or surface creep and suspension. 2. While moving as bed load, the particle weight is to a large part transmitted directly to the nonmoving bed, not to the flow. 3. The rate of bed-load motion is defined by the equilibrium exchange of sediment between the bed-load and the nonmoving bed. 4. This equilibrium gives a direct relationship between the sediment rate and the flow conditions near the bed, including the turbulence. 5. The flow condition near the bed can be predicted for a uni-directional boundary layer as a function of the bed shear and the bed roughness, only.

The seas in front of China coast such as Yellow Sea, East China Sea and Taiwan Straits are all located on continental shelf. In consequence, waves approaching these coasts are generated in shallow water area in comparsion with wave length. The authors has developed tangible calculation procedures for evaluating the wave features in such areas in stationary or moving fetches (l). However, the basical formulas of calculation are derived from experimental data of Bretschneider and Thijsse. In order to investigate the generating process of shallow water wind waves and obtain more detailed informations for correcting calculation criteria, a series of experiments have been performed at a wind tunnel of 75 meters in length. Various investigations on the relationships between waves and wind as well as water depth ar4 to be submitted in this paper. In addition, the situation of wind wave coexistance with regular wave is studied from experiments, because it resembles the superposition of refracted and local wind waves on the western coast of Taiwan.

An experimental deep water wave recording station has been operated in Lake Ontario, Canada, from 1969 to 1971. The station included a triangular array with four wave sensors and a stable platform. The aim of the study was to obtain a better understanding of the usually rather vaguely defined wavelength parameter of a wind-generated sea and to record the direction of wave propagation directly in the wave generation field. The station has also been used to test newly developed wave sensors, or to check and calibrate some of the existing wave recording systems, including staff gauges, pressure cells and accelerometers. The paper describes briefly the mooring system of the floating stable platform and the triangular array. A comparison is made between various wave recorders, mainly by using spectral analysis, and some results of the wavelength and wave direction study are discussed.

Wind-wave characteristics were recorded in the laboratory for the primary purposes of (a) analysis of the probability distribution of wave height and wave period with wind speed, water depth, and fetch length as major parameters, and (b) comparison of the test results with existing theory and empirical formulae. An important aspect of this study was to test the validity of the Tucker and Draper method (Draper, 1966) for the presentation of ocean wave data as applicable to wave-data analysis for simulated wind waves. It was interesting to note that some corrections were necessary when the method proposed by Draper at the 10th Coastal Engineering Conference was used for analyzing waves generated in the laboratory. Approximately a positive 20% correction was necessary for this study in which the wave spectra distribution is of very narrow range, the wave width parametere = V1-(T /T ) varles from 0.25 to 0.50, where Tc and T2 represent crest wave period ana zero-crossing wave period, respectively. However, only a negative 5% correction was necessary when the method was used to analyze sea waves (e = 0 73 to 0 76) measured off the shoreline near Look Laboratory Therefore, it was concluded that the Tucker and Draper Method is quite feasible for engineering purposes in analyzing wind-waves having a spectral width parameter of 0.60 to 0.75 The experimental data were compared with those wave heights predicted by the Darbyshire formulas (Francis, 1959) developed for ocean waves. A significant correction factor was necessary for laboratory waves produced by low-speed wi nds. The "fetch graph" was prepared and compared with those developed theoretically by Hino (1966) and empirically by Ijima and Tang (1966) at the 10th Conference on Coastal Engineering, Tokyo, Japan Comparison was also made with the previous empirical formulae by Bretschneider (1951, 1957), Sverdrup and Munk (1947), and Wilson (1961,1962). The experimental results compared well with the Hino theory for both wave heights and wave periods, and fairly well with Bretschneider's fetch graph for wave heights The difference in the comparison of wave data with other investigators is illustrated in this paper. It is recommended that further study be made with emphasis on (a) theoretical and experimental studies of wind-wave characteristics on pre-existing waves, particularly moving storms, (b) wave-energy spectra involving stochastic characteristics and extreme values of wind waves

This paper is concerned with the study of wave pressures exerted upon breakwaters of the vertical type from overtopping waves• The formulae for maximum wave pressure upon vertical walls and the wave crest elevation for overtopping waves are suggested by the author. The phase interval method for the maximum wave pressure is also given.

The rubble-mound seawalls, groins, breakwaters and ripraps around oceanfall pipelines are still the most common type of shore-protection structures currently in use. Major reasons include: easiness to construct and repair, flexible with respect to settlement, favorable wave-energy dissipation, fitness for any water depth and any foundation, and because of its economical nature if rubble-stones are readily available. However, the importance of a filter system in the stability of such structures must be emphasized. More recently, the submerged rubble-mound structures have become very popular due to aesthetic reasons. A filter system is considered a must to protect such a structure against erosion as a result of wave overtopping. Following a brief review of the problems, general discussions are made of the specific causes of failures including piping, overtopping, and nonstability. The physical factors that would affect the filter design are discussed in detail. Methods for design of filter system is presented including those applicable to the gradation of filter layers and to the plastic filters. The design procedure involves (a) making mechanical analysis of the backfill and base material, (b) estimating sizes of voids in the rubble-stones, (c) designing filter by Terzaghi criteria as revised by U.S. Army Waterways Experiment Station. A sample design of graded filter system behind rubble-mound seawalls is given. The procedure for the selection of plastic filters is also included. A comparison of the merits and demerits of these two types of filter systems will be made. This comparison will take into account the model test results conducted in the Look Laboratory. However, the readers are cautioned about the scale effects of the scour characteristics particularly on those tests with light-weight model sediments. This paper is intended as a general guideline for practicing engineers who will be responsible for design and construction of rubble-mound marine structures.

A new electrolytic turbulence transducer has been developed in order to measure the turbulent velocity fluctuation superposed on the oscillatory flow velocity The aim of the present paper is firstly to describe the outline of this transducer and secondly to introduce some of the experimental results The main items of the results are, l) the vertical distribution of turbulence intensity averaged over one wave cycle, where the turbulence is induced by ripples which appear on the movable bed of wave flume, and 2) the correlation between the turbulence intensity and the characteristics of sediment particles at the same level such as their fall velocity and sediment concentration.

This is a note paper of experiment in an air-water experimental waterway. Two cases of the uniform depth of water 50 cm and of the uniform depth of water 15 cm are examined. The boundary condition for air flow is not changed. In a condition of almost the same discharge of air flow on the water surface, the development of wind waves is investigated. The properties of wind waves are slightly different in each case, but the analysis of physical mechanism of the development suggests that almost the same mechanism is active throughout both cases. Stillmore the portion of tangential stress, which is apparently transfered to wave momentum, is numerically obtained, and it is not so different in both cases of depth of water.

In order to establish the mechanics of sand transport in an air or water stream, the mechanics of saltation of sand grains should first be considered In sand storms, most of the saltating sand grains on a granular bed have successively continued the saltation motion In this paper, such a saltation motion is defined as successive saltation A theoretical approach to the saltation of a single sand grain on a fixed granular bed is proposed on the basis of the equations of motion for the saltation and the dynamic characteristics of collision between a saltating sand grain and bed sand grains Some experiments of the successive saltation of a single sand gram on a fixed granular bed were carried out to compare with the theoretical relationships It was verified from the comparison that the theoretical relationships of the height and distance of saltation of a sand gram are in fairly good agreement m substance with the results of experiment.