· · · Repository Hydraulic Engineering Reports

Conference on various aspects of coastal engineering; additional to the International Conference of Coastal Engineering. In table of contents are links to the full papers.

A method is presented for the evaluation of an orthogonal coordinate system of particular use in the study of the diffraction of long gravity waves near islands of irregular shape. The problem involves a conformal mapping of the island onto a coordinate plane in which the island contour is a unit circle. The mapping relation is evaluated by an iterative procedure which is reminiscent of a method introduced by Theodorsen, but has the advantage that it is applicable to an island contour in which the island contour relation r(9) , in polar coordinates, is multivalued for a given range of 9. This generality is achieved by employing a parametric representation of the island contour in which the arc length on the island contour enters as the parameter. Application is made for two specific cases, Wake Island and Kauai.

The city and harbor of Hilo, located on the northeast coast of the island of Hawaii, have been severely damaged by numerous tsunamis. Physical features which play an important role in the formation of tsunami bores at Hilo are the submarine ridge formations in deep water outside the bay mouth and the nearly vertical cliffs along the Hamalcua coast which reflect the tsunami wave into the harbor. The purpose of this paper is to discuss the Hilo Harbor Tsunami Model and this reflected wave and its effects. 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 hy the Chief of Engineers to publish this information is appreciated.

This paper presents a brief discussion of structural damage by tsunamis based primarily on damage produced by recent tsunamis along the northern California coast. Of these recent tsunamis, by far the most damaging was the one of March 1964; which caused approximately $11,000,000 damage at Crescent City, about $300,000 damage at other coastal locations, and about $200,000 damage in San Francisco Bay. At Crescent City, where the maximum runup reached about 21 feet above mean lower low water, damage was largely to wood frame structures of relatively light construction and to floating vessels. At other locations, damage was primarily to commercial fishing and pleasure vessels and associated shoreside structures. Acknowledgement i s gratefully made to the Corps of Engineers for access and permission to use data on file in the San Francisco District, U.S. Army Corps of Engineers and the many other agencies and Individuals that gave their observations, records or photography for the writer.

Explosion waves were simulated by plunging a parabolic surface of revolution in and out of an indoor t est basin 3 feet deep by 92 feet square. These impulsively-generated Water waves are found to be dispersive as evident from the following properties : The period and the celerity of the individual waves increase with travel time, and the amplitude of each wave group decreases. It is shown that the eventual shoaling in approaching the coast limits the dispersion process, and that the waves eventually amplify like other gravity waves. The run-up on the beach is a function of the wave steepness (H/L) at the beginning of the slope and the steepness of the slope itself. The run-up of any one wave is also affected by the preceding and following waves in the group. Experimental results on dispersive wave attenuation in water of constant depth are in fairly close agreement with theory. The results on amplification due to shoaling indicate that a modification of Green's Law is necessary for describing these waves.

The successful design of a marina with respect to seiche conditions presupposes two categories of knowledge. Of these the more difficult to obtain is an adequate description of the local long period wave environment. Somewhat easier, but equally important, is a detailed knowledge of the responses various basin configurations present as a result of irradiation under some standardized wave environment. One such environment would be that provided by sinusoidal waves issuing from a distant line source maintained at unit amplitude, constant frequency; and fixed direction. Independently varying both the source orientation and frequency and measuring resulting responses at fixed locations is a procedure common to many wave scattering experiments. It is generally supposed that these scattered wave fields later may be superimposed. This will be the case if linear equations adequately describe the wave motion, as will be assumed here. However, in a medium with spatially inhomogeneous propagation properties, there is no unambiguous distinction between the incident and scattered waves; only in the case of uniform propagation are the real and imaginary parts of ei(k.x-wt) identical, apart from a translation in the direction of k. Interfering reflections and other scattering effects due to variable depth cannot be eliminated or treated separately from peripheral reflections. The complexity inherent in most practical situations requires that some sort of model be used.

The equation of continuity and the equation of motion for two-dimensional shallow-water waves are transformed into a set of difference equations which can be solved numerically to obtain the fundamental period and the periods of the higher modes of oscillation of a closed basin of arbitrary shape. From these periods and the difference equations the corresponding amplitude variations are obtained. By modifying the boundary conditions used, with certain restrictions, the modes of oscillation of a fully open harbor can be determined. The data necessary for the solution of both cases are the distribution of the cross section areas and the surface widths along the talweg of the basin (the line of maximum depth). The exact solutions which describe the lowest mode of oscillation of basins of simple geometry, e. g., circular and eliptical, are compared to the results of this approach. In addition the fundamental and the higher modes of oscillation of three actual harbors are discussed. The agreement obtained by this method compared to others is considered to be reasonably good. Some considerations of the case of three-dimensional forced oscillations are presented.

A computational formula is developed for determining, from the sea surface spectral density, the spectral density function of the force per unit length at a point on a vertical pile. A surprisingly accurate and simple approximation for the formula is presented and used to explain the near proportionality between the spectral densities of force and sea surface measured in the ocean near Davenport, California. The computational formula and its approximation are extended to provide procedures for the determination of the spectral density of either total force or total overturning moment on a structure consisting of an array of vertical cylinders. The approximation leads to a particularly simple relation in which the spectral density for the total structure is the spectral density for a single pile times a function which characterizes the geometry of the array. As an illustration of the procedure, the total force spectral density is computed for a four-pile instrument platform in 49 feet of water.

An 80- mile reach of the central California coast, extending from the mouth of the Russian River in the north to Half Moon Bay in the south, was studied for the characteristics of sediment movement in the nearshore zone. From the results of a large number of beach and offshore sediment samples and other information, several techniques were utilized in appraising the nature of sediment movement along the reach of the coastline under study. These techniques included: (a) the physical nature of the coastline from a consideration of the prevailing wave energy, (b) the distribution of light and heavy minerals and their sources, (c) the use of certain naturally radioactive minerals and their use as a tracer, and (d) the sedimentation experience at harbors where both natural and stabilized entrances exist.

Basic principles bearing on the nature of beaches and processes that act to modify them are considered in the light of present coastal development demands. A working hypothesis is developed that applies the principle of the conservation of mass to the mechanics of granular- fluid media. This hypothesis appears to have general application to sand transport processes in the littoral zone. Additional research must be done to provide basic information in some critical areas before application can be made with assurance.

During the past few decades, industrial demands for buried shell have been rapidly increasing. Highway construction, the petrochemical industries, and cement manufacturers are among the major users of shell. Semi-fossil oyster shell is found in tidal embayments in deposits of varying thickness and is dredged from depths varying from two or three feet up to forty feet by suction type hydraulic dredges which often discharge wash waters immediately into the surrounding embayment.

By-passing by natural action is mentioned with special reference to Florida Inlets and to some other inlets in the United States and abroad. Natural by-passing at harbors on open shores is dealt with briefly. Present status of by-passing plant operations in Florida is reviewed. Inasmuch as it is evident that by-passing plants - partly because of the tidal flow which discharges material in the ocean and in the bay and partly as a result of the rise of sea level - will not be able to solve more than a certain part of a beach erosion problem--replenishment by sand from other sources is indispensable. The most logical source is offshore deposits. Material may be brought to shore by "backpassing" using an offshore scraper (useful for maintenance) or by a special hydraulic dredge (for major improvements). If the borrow area is located close to shore, the question arises of whether the borrow pit will fill up again by material from further offshore material from the sides or from material dragged out by waves from the beach. The report describes briefly tests on Jupiter Island using an offshore scraper. The success of this operation is checked by fluorescent tracers placed on the beach and on all sides of the borrow pit.

This is a progress report on the Homer Spit Beach Erosion Study. Information is presented regarding the rapid acceleration of the erosion processes due to the subsidence of the Homer Spit during the 27 March 1964 earthquake. The effect on existing groins both before and after the quake are discussed. Immediately after the quake, emergency measures were required to prevent wave and high water damage to existing structures on the Spit. The results concerning the effectiveness of these measures are presented for evaluation, along with the basic data gathered for the erosion study and some of the problems encountered.

The study area encompasses 18 miles of Oregon coastline known as Clatsop Beach, which lies between the Columbia River south jetty and Tillamook Head, south of Seaside, Oregon. The physical changes (including man-made changes such as jetty construction which was initiated in 1885) that have occurred in the area since 1792 are described and presented graphically. Theories based on an analysis of the very complex joint function of sand supply and incident wind, oceanographic, and estuarine forces are proposed as to the cause of erosion and accretion over the long-time span.

Columbia River estuary is being conducted by the U.S . Geological Survey. The necessity for information on water discharge, suspended and bed sediments, and radioactivity prompted the development of new measurement techniques and equipment suitable for estuarine conditions. Flow velocities and directions throughout the entire depth at a single vertical are measured from an unanchored boat in about a minute with the new discharge measuring technique and it appears that approximately 20 verticals in cross sections up to 4 miles wide can be measured in 1.5 hours. Measured discharges in an upstream reach of the Columbia River agree fairly welll with those measured by conventional methods. In situ measurements of radioactivity sorbed on the bed sediments are obtained with a radiation detector that is mounted in an undenrwater sled. Samples of water and suspended sediment are obtained for radionuclide and sedimentation analyses with a high-volume sampler. The samples are separated with a high-flow membrane filter system for analysis. Core samples of the bed sediments, which range from silty clay to medium sand, are collected in depths up to about 70 feet and flow velocities up to about 5 feet per second with a newly devised portable vibratory sampler.

The maintenance of pole, stake, and pile structures in streams and waves has been important to man from antiquity. Because of the common occurrence of the flow of a fluid past a cylinder, and the simplicity of the boundaries, one might expect that long ago all related problems could have been solved . However, if one experiments with forcing a pole rapidly through still water, he ,rill find that the pole oscillates laterally and that he can reduce these oscillations, and thus move the pole more easily, by grasping it firmly. These observations suggest a lack of simplicity of the system and an explanation for the present dependence on empirical information in the solution of related engineering problems. The art of building surfaces above water level has been augmented by engineering and scientific investigations so numerous that even citation of all the most important is prohibitive. Current practice produces successful offshore structures, but more design information will be needed to build them competitively in ever deeper water. Marris (1964), Morkovin (1964), and others have summarized much of the pertinent data on the flow details around rigidly supported cylinders and described means of representing phenomena. This paper reviews progress toward solution of problems basic to the design of structures in moving fluids, and toward explanation of differences between force patterns imposed on actual structures under field conditions and on the idealized "infinitely long rigid circular cylinder in a steady stream".

The engineer required to calculate theoretical wave characteristics such as wave profiles and wave forces and moments on piling, is confronted with a problem which includes (1) selecting one of a number of available theories and (2) calculating the required information which, for some of the theories, is a relatively complicated procedure. This paper presents criteria for assessing the validity of various wave theories; these criteria are then applied to test the validity of several theories for two wave conditions and, it is found that for these conditions, the Stream function numerical wave theory is the most valid of those tested. The Stream function theory is developed into graphs of dimensionless crest displacement, and total maximum wave forces and moments on a vertical piling.

The classical problem of describing the characteristics of deep water waves of finite amplitude is considered. The method of analysis initially follows that of Nekrasov, but differs in that a non-linear algebraic equation is derived. This equation is solved to the third, fifth and fifteenth order by means of a digital computer and the data is presented in tabular form. Expressions for the wave speed and wave shape, predicted by the analysis, are compared with the results obtained by Stokes. The highest wave in water is also discussed.

It is common engineering practice in a hydraulic model study involving both gravity waves and a solid structure to measure the hydrodynamic forces on the model of the structure and then calculate the resulting internal structural stresses. Because of the large variety of available elastic material, and the latest development in solid state physics, it is now feasible to measure directly these structural stresses in a scale model study. It is shown how the similitude of elastic force s in structure s subjected to wave action can b e made compatible with the Froude similitude valid for hydraulic motion. Several examples are presented to illustrate the method . These include the study of the elastic response of an ice floe, the motion of an underwater membrane-type oil storage tank, the behavior of the Mohole riser, and the motion of a Texas Tower type of structure under wave action. Results obtained in the NESCO wave tank are also presented.

This is a presentation of recent computer results from a previously published theory of the deformation of solitary waves on a sloping beach. No attempt will be made here to review or derive the pertinent equations, and only those geometrical aspects of the theory will be introduced which are necessary for interpretation of the results. The method used here in solving Laplace's equation for the velocity potential W of the steady-state solitary wave and for its free surface determined jointly by a kinematic condition on the surface particles and by Bernoulli's equation with the pressure set equal to zero is illustrated in Fig. 1. The velocity potential is first defined inside a fixed region, the infinite strip, which will contain the solitary wave as a subdomain. Neumann conditions, are assigned to both the upper and lower boundaries of this strip of width b. Singularities producing the velocity field can be located anywhere between the free surface of the fluid and the upper edge of the strip; but, for convenience, the singularities of the trial potential function were constrained to the upper boundary.