Coastal Engineering 1966

This paper describes a method of analysis of sea-wave records and ways of presentation of the results. The author hopes that standard techniques can be agreed amongst users of wave data, and puts forward this paper as a possible model.

Waves were recorded at Sekondi during 1958. The results of an analysis of these records is presented.

It is the aim of this paper to give theoretical derivations of the windwave characteristics from a viewpoint of fundamental mechanism of wind-wave generation.

A hypothesis is proposed as a basic principle of the air-sea interaction, which asserts the maximum ratio of the energy transfer from wind to wave to the energy dissipation within wind. As the theoretical consequences of the hypothesis combined with the recent theories on wind-wave spectra by Miles and Phillips, wind-wave characteristics such as the fetch graph, the roughness of the sea, the spectral peak frequency, the ratio of pressure contribution to total drag and the energy transfer from wind to wave are derived with remarkable agreements with experimental data.

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.

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 clarify the transformation process of ocean waves in shallow water, a series of wave observations were carried out along some coasts in Japan by photographing two or three convenient buoys aligned m the direction of the waves with two 16 urn cine-cameras. The equipment and methods used in observations and analyses are here described together with some of the results obtained. By examining the motion of the buoys off the coast at Shirahama it was found that the method of wave observation by means of anchored buoys was very useful in the case of comparatively long waves.

The paper concerns the characteristics of the correction factor which is introduced into the relationship between the water surface elevation of progressive waves and its corresponding fluctuation of underwater wave pressure.

As a result of extensive investigations conducted both in laboratory and field, it is verified that the correction factor is well expressed by a certain function of relative water depth. By using an empirical formula proposed in this paper the power spectrum of surface elevation and its significant wave height off the Ohita Coast are estimated from the record of underwater pressure fluctuation. The estimated values, generally speaking, have a satisfactory agreement with the actual ones determined from the records of surface water elevation.

In the last two decades the problem of wave height damping due to bottom friction has received increasing attention among near-shore oceanographers. This fact is reflected in the wealth of papers on the subject; the list of references given herein presents a minor selection only.

The purpose of this paper is to discover the mechanism of the laminar damping of oscillatory waves due to bottom friction with the aid of the theory of the laminar boundary layer due to waves and of the measurements of instantaneous shearing stresses exerted on a smooth bottom, resulting from wave motion and wave amplitude attenuation with distance. In a theoretical approach the effects of convective terms involved in the basic equations of laminar boundary layers developing both on the bottom and the side walls of a wave channel, are considered on the basis of an approximate solution of the equation, and a theory of the laminar damping of Airy waves is established. In experimental studies, furthermore, direct measurements of instantaneous stresses and observations of wave amplitude attenuation were performed, and the experimental results are compared with both the above theory and the linearized one.

Indentations of a shoreline or ups and downs of sea bottom form a small oscillating system of water. When the period of natural oscillation in it is near that of advancing sea waves a forced standing oscillation develops there, accompanied by an uneven mean surface level of second order. If the height of the sea waves varies slowly with time, the mean surface fluctuates with the period same as that of the envelope of the sea waves, and such fluctuation will be sent back offshore as a surf beat when it is released by breaking of the original sea waves. The generated long wave seems to be correlated positively or negatively with the envelope of the sea waves, depending on the topography of the basin and the period of the incident sea waves. A possibility of generation of similar long wave in front of a breakwater or a steep beach is also suggested.

The wave transformation inside surf zone is treated analytically in this paper under the several appropriate assumptions. The theoretical curves computed numerically have a consistant agreement with the experimental data in the case of wave transformation on a horizontal bottom. On the other hand, in the case of wave transformation on a uniformly sloping beach, the analytical treatment seems to be inadequate to clarify the actual phenomena. Besides them the numerous data on wave height attenuation and others are presented in the graphical forms.

Shock pressure due to breaking wave was studied experimentally and analytically for the case of two-dimensional regular oscillatory wave.

In the first part of this paper, important characteristics of shock pressures were described, which were obtained by using the newly designed pressure gauges of very high frequency responces ( 10 ∼ 10000 c/s ). And the following two points were mainly examined i) the detailed characteristics of pressure-time histories of shock pressures, and ii) the similarity of pressure-time histories observed simultaneously with two separated gauges.

In the second part of this paper, the dynamical models representing the generation mechanism of shock pressure were examined to explain the observed properties of shock pressures, in which the new air-cushion model extended from the original air-cushion model of Bagnold (1939) was included.

Under the assumption of small compression of the air cushion, the analytical solutions representing the pressure-time histories were obtained both for the original model of Bagnold (1939) and for the present new model. For the cases of relatively high-intensity shock pressures, the consistent results were obtained by analyzing the observed shock pressures by the new air-cushion model. The discussion of shock pressure due to finite compression of air cushion was also included.

A series of experiments were run in a two-dimensional wave channel to study solitary wave deformation on plane slopes ranging from horizontal to vertical. The test objectives included verification of deformation theories, delineation of the shoaling processes associated with various beach slopes, and examination of the limit-height-wave concept. The results showed that the deformation process can be classified as a function of the ratio of initial wave height to water depth and beach slope. The deformation theory for reflection from a vertical wall was verified, but the theory for low slopes was found to be only qualitatively accurate. Finally, a redefinition of the limit-height wave on sloping beaches is suggested.

Variations in wave characteristics for solitary waves in shoaling water are discussed. The transition of wave character from the solitary wave to the bore is basic to the understanding of the problem.

Experimental curves representing the transformation of wave height prior to breaking as well as the curves giving the breaker conditions are presented. Theories for the transformation of wave height after breaking and the prediction of the plunge point are presented and compared favorably with the laboratory measurements. Runup heights and wave quantities at the shoreline are measured to compare with the theory of a bore on a dry bed.

The shoaling enhancement of small-amplitude, dispersive wave trains traveling over uniform, impermeable slopes was observed in a specially-constructed wave channel, where the reproducible wave elevation measurement accuracy was about .0005-in. These observations substantially support the enhancement predicted from linear theory (conservation of energy flux) except in very shallow water and on very steep slopes, where accelerative effects become important.

On the hypothesis that small-amplitude runup theory might be similarly valid for periodic waves of finite height, provided that the positive incident wave amplitude Is replaced by the local crest height above still water, this theory was modified to include the effect of the superelevation under a wave crest due to profile asymmetry. The modified theory is shown to agree acceptably with runup observations of larger waves previously reported – both for breaking and non-breaking waves.

Because solutions to the modified theory cannot conveniently be obtained by manual calculation, a nomograph chart is included, from which runup predictions can be easily made, given only the wave height, period, and water depth a wavelength or so from shore, and the beach slope.

The experimental results of wave run-up and overtopping on coastal dikes with a steep seaside slope are presented. Wave run-up heights are calculated by regarding to the crest height of standing wave in none breaking zone and to the reflected bore height in breaking zone. The calculated values indicate good agreement with the experimental results. As for wave overtopping, the experimental results are mainly discussed with regard to the effect of wave breaker to overtopping phenomena.

This paper deals with the transient deformation of surges (bores) both theoretically and experimentally. Ideal surges in open channels would normally disperse into periodic waves and be transformed to the undular bore. A train of these dispersive waves may finally reach some stable form e.g. solitary or cnoidal waves.

In the transient process, with the development of the undulations, the height of the initial wave would not be constant as has been suggested by Keulegan-Patterson(1940), but would fluctuate in a complicated manner. The author indicates, theoretically, regions in which wave crests or troughs can exist and gives experimental criteria by which modes of breaking (spilling, surging or plunging) can be determined. He also believes that the curvature of the wave surface plays a leading role in the mechanism of dispersion and may act as a convective agent in the development of the undulation.

This paper presents a fundamental study of the dynamics of wind in the vicinity of progressive water waves. The normal pressure distribution and the structure of the velocity profile immediately above progressive water waves are investigated.

A wind-wave facility 115 feet long, 74½ inches high, and 35½ inches wide is used which is equipped with an oscillatmg-plate wave generator. Velocities up to 80 fps can be obtained at a nominal water depth of 3 feet.

An oscillating device (or wave follower) was designed and built, on which a pressure sensor could be mounted and could be held at a fixed distance (within ¼ inch) above progressive water waves at all times.

The results indicate that a pressure shift does exist as predicted by Miles [1957] within the assumptions of the theory. Furthermore, the results demonstrate clearly the importance of using a pressure sensor which follows the water surface in obtaining meaningful pressures at the air-water interface. Mean velocity profiles with and without mechanically generated waves were obtained. Contrary to what is normally assumed, the results indicate that the boundary layer in the vicinity of water waves is affected by the presence of waves.

The wave action due to a sudden impulse in a body of water was studied in a wave basin with beach in the laboratory. Waves were impulsively generated in the 90 ft. tank of water, 3 ft. deep, by the impact or sudden withdrawal of a paraboloidal plunger 14 ft. in diameter. The waves had a dominant height of 2 inches and period of 3 seconds, respectively, at a distance of 50 ft. from the plunger.

Such waves are scale representations of those generated by sudden impulses in the ocean, such as an underwater nuclear explosion, a sudden change in the ocean bed due to earthquakes, or the impact of a land slide. The waves produced by a downward impulse, or by an underwater explosion, form a dispersive system: whose properties are not constant as in a uniform progressive wave train. Wave periodicities, celerities and wave lengths increase with time of travel and wave heights decrease with travel distance. Theory has already been developed to predict the wave properties at a given travel time and distance for given source energy, displacement and travel path depth profile (Jordaan 1965). Measurements agree fairly well with predictions.

The process of sedimentation can be traced from its initiation as weathering of base rock, transport to the ocean by rivers, and its distribution by waves. The sediment supplied by a river is dependent upon catchment characteristics – topography, precipitation, vegetation and geology. The grading of this sediment can change over geologic time.

The transport of material by waves is an important aspect of this overall movement, to a destination of either coastal plain or offshore shoal. The persistent occurrence and direction of ocean swell make this wave domain the most important in this process. In enclosed seas littoral drift is effected by storm type waves, per medium of a different beach profile from that on oceanic margins.

Accepting that the wave climate has not changed significantly over geologic time, it is possible to picture the geomorphology of river and coastal plains to the present continental outline. The coastlines of Japan are examined in this paper with such an emphasis.

Lowland so formed is of extreme economic importance. In order to promote accretion of further areas on a large scale, the character of the sediment and of the natural forces available at any location must be considered. Suitable structures and their siting within natural shoreline features are discussed.

The conventional method of dealing with relationships between wave action and topographic response on a beach is to reduce the problem to a two-dimensional scheme that regards basic processes as taking place in a vertical plane normal to the shoreline. This scheme is valid only if the waves arrive at right angles to the shore and the nearshore contours are reasonably straight and parallel the beach. As these conditions are not realized in many cases another analytical method is necessary – one that recognizes effects of other than normal wave arrival and systematic patterns of diversification in nearshore topography. This study, based on a long period of field investigation on the Outer Banks, North Carolina, examines a three-dimensional approach. Observations from a long pier were used to explain nearshore topographic diversification and resulted in conclusions that were confirmed by subsequent field observation.

Validity of seven analytical formula as well as linear and non-linear multiple regressive schemes was tested using field data from the Outer Banks, North Carolina. Generally, agreement proved unsatisfactory. Field experiences indicate that the longshore current is a velocity field consisting of a multitude of velocity vectors whose basic pattern varies depending upon the regimes of wavecurrent topography interaction. The need to recognize topography as a responding variable as well as a process variable in the physical scheme of longshore current is emphasized.

This paper presents some results of experiment made to clarify the changes of shoreline taken place by the construction of offshore breakwater, the amount of sand deposits within the region sheltered by the breakwater and the sand movement at the sandy beach through the progress of beach deformation up to the accomplishment of the equilibrium profile. The initial profiles are made by the waves of two kinds of wave steepness δ₀ = 0.0192 and δ₀ = 0.0461 and the new equilibrium profile of sandy beach is formed by sending again the wave of the same steepness in the state of existence of offshore breakwater.

Based on the longitudinal variation series in various properties of beach sediments and topographic profiles along the southern coast of Ishikawa Prefecture, Japan, the prevailing direction and mechanism of littoral drift are discussed.

Port Hueneme Harbor, California, constructed in 1940, resulted in the average annual erosion of 1,200,000 cubic yards from the shoreline downcoast of the harbor. The cause was diversion by the north jetty of the harbor of littoral sand movement into the Hueneme canyon, A sand bypass system was established in 1960 – 61 by construction, one mile upcoast, of Channel Islands Harbor fronted by an offshore breakwater 2,300 feet in length and located on the 30-foot-depth contour. This breakwater serves a dual function of sheltering the harbor entrance and acting as a littoral sand trap. Three cycles of biennial littoral sand bypassing havebeen successfully completed resulting in supply of 11,000,000 cubic yards of sand to the eroding shoreline at an average annual cost of $0.40 per cubic yard, including annual maintenance and amortization of structures. Comparison of design of the structure to the impounding characteristics experienced during three bypass cycles indicates that the dimensions and capacity of a sand trap formed by an offshore breakwater can be based upon the diffraction patterns of prevailing wave trains at the two ends of the structure and is independent of the depth and dimensions of the entrapment area. Rate of impoundment is equal to the rate of littoral drift at Port Hueneme.

The flow area of inlets on sandy coasts is a unique function of the tidal prism when equilibrium has been achieved. The size of material, the presence or absence of jetties, and the magnitude of general littoral drift does not appear to affect this equilibrium flow area within the accuracy of the data available.

A brief description is given of work being carried out in the Mersey Estuary, England. This work is part of a sedimentation study of the area, and has necessitated many days' field observations at stations distributed along and across the Estuary. Attention is drawn to the factors influencing the sediment movement and the variables, such as velocity, suspended solids, salinity and temperature that must be measured in order to define the sedimentation complex adequately.

An experimental investigation, utilizing an apparatus consisting of a counterrotating annular channel and ring, of the depositional characteristics of fine, cohesive sediment revealed that after an initial period of rapid deposition, the sediment concentration approaches asymptotically an equilibrium value. The ratio of this equilibrium concentration to the initial concentration is nearly independent of initial concentration and for a given sediment and environment depends only on the flow conditions. For the three water depths investigated, the ratio of equilibrium to initial concentration was found to he a single function of an average shear stress around the channel-section perimeter. A comparison of the size distributions of the parent material with the material retained in suspension when equilibrium was achieved indicated that the greatest losses occur in the clay-size fractions, suggesting that the deposition is controlled predominantly by flocculation, and that the strength and size of the floes exert a stronger influence on the deposition than does the particle weight. A silty-clay sediment with a mean particle diameter of 0.0009 mm was used in all experiments.

A mathematical model is developed to calculate the amount of bottom sediment moved by wave action. The simplified case of a horizontal bottom and spherical material of uniform size is presented here; however, with some further groundwork it is thought that the model may be extended to actual field conditions without too much difficulty.

Practical and effective methods for the measurement of and the determination of the type and the mode of wave action in a semi-enclosed basin are investigated. Pressure gages and flow meters are considered as instruments available for such measurement. The combination and arrangement of these instruments as well as the use of power spectral and cross spectral analyses as the basic means of data reduction are discussed. A special attention is given to the problem of estimating the contributions from the progressive and from the standing modes of oscillation separately. Significance of such estimation on engineering planning is briefly discussed. Examples are given.

As well known the coast of Japan is often attacked by tsunami. As a kind of disaster preventive facilities, breakwaters have been built or are now under construction in several ports in order to protect the harbour area by diminishing the energy of rushing water and by reducing the water level elevation inside the basin. The biggest work of this sort is found at the port of Ofunato, Iwate Prefecture.

The effect of breakwaters against such long-period wave as tsunami was investigated by the authors, using electronic computers. The principle is to solve the equations of motion and of continuity. Not only for the stationary state but also for the transient state. One of the most important items to be studied is the response of basin water to the incoming tsunami, of which the period is variable in a wide range from several minutes to more than one hour.

The result of calculation has clarified the behaviour of tsunami affected by breakwaters located in a bay open to the outer sea. The computing method, together with an approximate method divised from fundamental investigations made in advance, has also been applied to several other ports, supplying a plenty of data for harbour planning and design.

Hydraulic properties of a row of closely spaced circular piles as a breakwater have been studied both theoretically and experimentally. A theory is presented for the transmission of waves past the breakwater and also for the thrust and bending moment to be exerted by the waves upon each pile in the breakwater. Laboratory experiment has been made on a model structure. A pretty close agreement is shown in the comparison between the theory and the experiment with respect to the transmission coefficient and the bending moment distribution.

Special emphasis is laid on the remarkable rate of decrease of the thrust and bending moment to be exerted on each pile in the breakwater with the increase of the space of the piles. In taking this economical aspect of this structure into consideration, the closely spaced pxle breakwater has been concluded as a promising type of breakwater of comparatively light structure.

The Dolos, a new type of armour unit which closely resembles a normal ship's anchor, was developed and tried out under field conditions on the main breakwater of East London harbour. Since these full-scale Dolosse proved very successful, tests were made in a wave channel to compare the stability of Dolosse with other known types of armour blocks. The test results showed that the Dolos is outstandingly stable, and since manufacture and random placing of Dolosse offers no particular difficulties it is concluded that in many cases the use of Dolosse in armour layers may lead to more economical solutions for rubble mound breakwater and shore protection works.

The author's conception on the mechanism of continuous slope protection under wave action (elements of flexible screen theory) are given in the paper in brief. Slope structures with continuous revetments are widely used in the Soviet Union, not only in canals but even in large reservoirs where waves reach nearly sea wave height.

In the paper some results of study of active external pressure of wind waves acting on structures of sloping type are presented in brief. The pressure developed by waves and acting on the inclined wall is divided into impact pressure and pressure remaining after shock. For determination of maximum water pressure remaining after shock a prof. N.N.Djunkovsky scheme is used (R.-I). Pressure distribution curve of water remaining after shock along the slope is determined by means of consideration of jet pressure acting on inclined wall. Design ourve is compared with the data of laboratory wave flume tests. Measurement pressure data received at test zone in reservoir is statistically treated.

There have been several instances in the past four or five years of damage to the riprap protection of some earth dams and embankments in major reservoirs in the middle western portion of the United States. In particular, in small sections of the embankment of the Snake Creek sub-impoundment in the Garrison Reservoir in North Dakota, some riprap was removed by a severe storm in 1964. It was recognized at the time of construction that the riprap protection to be placed on this embankment was considerably lighter than desirable, and was knowingly placed as an experiment to see if lighter graded material might still provide sufficient protection in a reservoir where the water surface elevation changed periodically. High waves can develop over the 32-mile fetch in this area of frequent high wind velocity. Loss of some riprap in this area has led to an investigation of various schemes of upgrading the riprap. As a part of this investigation, tests have been made at the Coastal Engineering Research Center in Washington, D.C. of various types of riprap exposed to wave action. Tests have been made at both small and large scale.

This paper is a continuation of a paper under the same title, presented at the Vlllth Conference in Mexico City, 1962, where a mathematical model was proposed, intended to give a rough idea of the order of magnitude of velocities and accelerations in the downrushmg wave on a rubble mound breakwater front. Here observations of 85 individual waves of various dimensions are presented and compared with the formulae derived from the model. Considerable scatter is evident, but it is concluded that the model does correspond roughly to the actual displacements of the water surface during downrush, and therefore may be expected to give useful indications also of velocities and accelerations. The importance of the slope of the surface is emphasized, and, within the scope of the tests, this slope seems to stand in linear relation to the wave steepness.

To study the effect of the specific weights of armour block material and fluid on the stability of rubble mound breakwaters a total of 110 model tests were made, with varying specific weights of armour and fluid, sizes of blocks and slopes of the breakwater face. The tests indicate that in cases where the specific weights deviate much from usual values, the current design formula (Eq. (1)) should be modified by entering a variable quantity, φ, instead of the figure "1" in the denominator. Within the scope of these tests, values varying from φ = 0,37 to φ = 1,05 were indicated. Theoretical considerations seem to show that also higher values of φ may be expected, in particular on account of the effect of the sloping water surface on the buoyancy of the armour blocks. As neither tests nor analysis have given conclusive evidence as to under what conditions higher respectively lower values of φ should be applied, at present only model tests can give the answer in any particular case.

The energy in waves which impinge on a porous structure, such as a rubblemound breakwater, is divided into reflected energy, transmitted energy, and the energy dissipated by turbulence within the structure. To obtain information on the reliability of using models to predict the transmission of wave energy through a rubble medium, a series of three models were constructed and tested in the 1 ft. by 3 ft. by 106 ft. wave channel at the University of California. The models consisted of rectangular, vertical-faced, wire baskets (constructed of expanded metal lath) which were filled with crushed stone. The three models were 0.5, 1.0, and 2.0 ft. in length, respectively. All models were 1 ft. wide and 3 ft. high. Each structure was installed in turn in the wave channel and subjected to wave action with the wave height being measured both seaward (H₁ ) and leeward (H₂) by resistance-type wave gages. Using the Froude law for scaling and considering the largest basket to be the prototype which the smaller baskets are to model, the following conditions were used in the tests of the three structures:

In this paper, the relation between a reflection coefficient of waves and a void ratio of permeable face of a structure is firstly revealed, because of the fact that there is a close relationship between the reflection coefficient and the phenomena of scouring. Before the scouring depth is investigated, the relation of the scouring depth to subsidence is made clear. Then, it is found that the scouring depth which has great influence upon subsidence of blocks, becomes larger with the increment of the coefficient of reflection. Furthermore, a composite cross section which has an imaginary uniform slope of 20 degrees, is proposed as the stable cross section against the subsidence of blocks.

It has long been the opinion of many engineers that the primary cause of failure in certain coastal structures is due to an inadequate filter system. Normally, filters for granular soils are made up of layers of graded sand, gravel and stone materials in various combinations and thickness dimensions. Very often these materials are expensive and in some cases, due to geographic location, are unavailable. Even if the required materials are easily accessible, proper placement is tedious and demands strict supervision.

This paper discusses the use of "plastic filters" as a replacement for graded filter systems and filter blankets in coastal structures. While this discussion and illustrations are limited to coastal structures, plastic filters can and have been used in river, lake, canal, dam and other hydraulic structures.

A mobile breakwater concept based upon a perforated front wall and solid back wall is presented. The principles of energy dissipation by the system is discussed as well as the potential role of such a device within the framework of practical application. Model test results, comparing the perforated breakwater's response to waves with that of a caisson-type breakwater, are discussed. It is shown that the perforated breakwater experiences less force on the structure when it is fixed to the bottom and less force on the mooring lines when afloat than the caisson-type. However, the perforated breakwater is not more effective in reducing waves, for the conditions tested. Visual observations show that scouring is prevalent when the caisson-type is fixed to the bottom; there is no evidence of scouring with the perforated breakwater. Recommendations are made for future work.

Two experimental hydraulic-pneumatic floating fenders (camels) were in-service tested in protected and exposed harbors. Due to their high energy-absorption characteristics, the fenders were effective in reducing damage to piers, pier-fender systems, and berthing or moored ships. Their performance relative to a number of individual ship-impacts is discussed, conclusions drawn, and recommendations made.

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.

This report describes the history of beach erosion and the countermeasures against it extending over the last few centuries on the coast of "YAIZU" Pishing Port. It also includes a study on the causes of erosion by analysing geographical, topographical and oceanogrphical conditions of the coastal area.

The record of the construction work of training dikes at an outlet of a diversion channel is presented here. The discharge in this channel is very small throughout the irrigation season and this fact makes difficult to maintain open outlet against the drift sand. Therefore the training dikes must be extended to fairly large depth. The special difficulty of execution is the limitation of construction time in summer that is a sole season of quiet sea.

The city and harbor of Hilo, located on the northeast coast of the island of Hawaii, have been severely damaged by numerous tsunamis. It was decided that the best approach to arriving at a feasible solution to the problem would be by conducting hydraulic model studies. The purpose of this paper is to discuss the problems which were encountered prior to and during the model testing. Discussions will include such factors as the selection of the distorted model scale, the type of wave generator used in reproducing the tsunami bore, the test conditions employed during model operation, and the requirements in tsunami behavior which had to be met before the verification of the model was deemed acceptable. This paper will also cover results of the study regarding the causes of tsunami bore formation in Hilo and the various possible schemes of protection.

The tests described and the resultant information presented herein, unless otherwise noted, were obtained from research conducted under the Hilo Harbor Model Study of the United States Army Corps of Engineers by the Honolulu Engineer District. The permission granted by the Chief of Engineers to publish this information is appreciated.

This study deals with the motions of a neutrally buoyant rectangular parallelpiped moored by a linear spring system m standing waves. The results show that a linear theory which considers the response of the body as a smgle-degree-of-freedom oscillator adequately describes the surge motion for standing waves ranging from shallow-water waves to deep-water waves and for ratios of body length to wave length of from 0.1 to 15.

It was found that the response curves for surge motion become more selective with respect to frequency in the vicinity of resonance as the distance of the body from a reflecting surface increases. Therefore, coupling this with viscous effects, which are more important near resonance, it is possible to reduce the effect of resonance considerably for a moored body with a particular natural frequency by choosing the proper mooring location in its standing wave environment. This has possible application in the planning of berthing facilities in marinas.

This paper presents some aspects of the hydraulic model experiments in coastal engineering made at the Ujigawa Hydraulic Laboratory, Disaster Prevention Research Institute, Kyoto University, including the experiments performed by using an estuary model basin and a high speed wind wave channel. In particular, the problems to which attentions should be paid from view point of similitude between model and prototype will be discussed in addition to the presentation of experimental results.

A description is given of the land-reclamation works along the northern coast of the Netherlands. The works are placed in their historical background, and possibilities for their future are discussed. This opens an opportunity to regard them against a general frame of land-reclamation works and future plans in the Netherlands.

An examination of the hydraulic characteristics of the Hooghly river with particular reference to the pattern of salinity intrusion and the effects of fresh water flows has been made in this contribution. It is seen that the conditions prevailing are such that during the brief period of fresh water flows the problem of salinity intrusion is absent. The beneficial effect of fresh water flows in improving the navigable depths along the river is also shown. The cessation of fresh water flows causes the deterioration of navigable depths due to the landward movement of sediment; it also results in the upstream encroachment of salinity affecting the supply of drinking water to the City of Calcutta. It has also been shown that even during the period in the freshet when the salinity profiles exist the estuary remains well-mixed. The need for augmentation of fresh water flows for improving the conditions has also been brought out. A few remarks on the comparative features of Hooghly and other tidal rivers have also been added to spotlight on the vastly different characteristics of the Hooghly.

This paper presents some observational results on salt wedges obtained by the ultrasonic method at the mouth of the Ishikari River, with a description of some studies on the two-layer flow developed by the authors.

In this paper, the authors describe the salinity problems and their solutions which were encountered in the Obitsui River Water Scheme. The salinity problems in this water scheme are caused by differnt origins; The one is seepage of the sea water through the earth embankment, and the other is the diffusion of the saline water from the reservoir bed.

Laboratory experiments and field observations were performed to confirm the detailed design of the reservoir.

It was found that the salinity concentration of the reservoir water could be controlled less than 500ppm m weight, when the earth embankment of 1,000m width was released.

The another way of salinity control studied by the authors was the recharging channel. At the present stage of studies, the recharging channel is considered to be favourable.

Finally, the wind effect on the mterfacial mixing of the salt and fresh water in a reservoir was studied. An approximate theory to calculate the mixing rate of the salt water was derived from the field observations.

The observed salinity distribution in the Columbia River Estuary is used to predict the flushing times for various river discharge rates, varying tidal ranges, and varying salinity intrusions. Both the modified tidal prism method and the fraction of fresh water method are used, and the results are compared. The latter method predicts shorter flushing times, while both methods vary in a similar manner with changing river discharge and changing salinity intrusion. Both methods predict a relatively short flushing time for the estuary.

The observed salinity distributions under varying conditions are also used to predict the distribution of conservative and non-conservative pollutants. In this case the fraction of fresh water method and the diffusion equation are used. In general, the fraction of fresh water method predicts higher concentrations. When the lower estuary is divided into two channels, the two methods give quite different results. The diffusion equation method predicts a peak concentration upstream from the outfall rather than at the outfall, when the outfall location is arbitrarily placed at certain locations.

This report concerns study on a method of taking the cold water from bottom layer with relation to the design of the intake structure of cooling water for the power station sited on a bay.

The quantity of cooling water used for condenser system increases year by year along with the construction of thermal power stations of large capacity. If the bottom sea water of low temperature is taken into the condenser cooling system, remarkable saving of fuel expenses can be expected due to the improvement of heat efficiency of turbine. Especially, in case that the location of intake structure of cooling water is chosen at the interior of the reclaimed land or the bay, it is absolutely necessary to take the colder water from the lower layer of the sea, in order to prevent taking hot water over the sea basin where the water temperature of the surface layer is raised by the evacuation of heat of released industrial water.

Various hydraulic problems concerning thermal density flow phenomena were examined aiming to obtain the design method of the most effective intake works of cooling water, and the authors proposed a curtain-wall type intake structure. Some results of analysis are described in this paper.

Two hydraulic problems anticipated from the construction of a dike across Tokyo Bay, i.e. water circulation and 'harbor paradox' are discussed from results of numerical experiments

Especially, a new technique has been devised for the investigation of response characteristics of the bay to obtain all the information by only one run

This paper presents the analysis on the resisting torques and forces acting on the spuds mooring the pump dredger for the surface waves. Torque or force was expressed by the product of the system factor, the statical wave factor and the magnification factor.