Showing papers on "Breakwater published in 1980"

Wave attenuation and wave set-up on a coastal reef

Abstract: In attempting to specify criteria for the design of structures on coastal reefs, it was found that no adequate method existed to derive those criteria from the deep water wave conditions. In order to fill the gap, a program of measurements and analysis was initiated at the University of Hawaii. The program consisted of prototype and laboratory measurements. Great emphasis was placed on reliable field data, which were collected on Ala Moana Reef, in Honolulu. Laboratory investigations on the behavior of waves on shallow reefs are subject to scale effects; verification from field observations is required to obtain reliable results. As a result of this study, a mathematical model was developed for the calculation of wave attenuation and wave set-up on a shallow reef, using the incident waves in the ocean as boundary conditions. This paper discusses the general behavior of waves approaching a shallow reef and presents some essential characteristics of the mathematical model. The study is limited to waves approaching the shoreline at right angles. The results of this study can be extended to breakwaters with wide, submerged berms.

Two-Dimensional Tests of Wave Transmission and Reflection Characteristics of Laboratory Breakwaters.

Abstract: : Monochromatic and irregular wave transmission and reflection measurements were made for various subaerial and submerged breakwater cross sections. These two-dimensional laboratory tests included smooth impermeable breakwaters, rubble-mound breakwaters, and breakwaters armored with dolos unit. Wave transmission by overtopping was found to be related to breakwater freeboard wave runup, and breakwater crest width; a method of estimating transmission by overtopping coefficients is presented. The Madsen and White (1976) numerical procedure was found to be an important tool for predicting the amount of transmission through permeable breakwaters. Suggested procedures for estimating transmission coefficients have been incorporated into the computer programs OVER and MADSEN (included as appendixes) and these programs may be used to predict wave transmission coefficients for nonbreaking, breaking, monochromatic, and irregular wave conditions. (Author)

Zeta bays, pocket beaches and headland control

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

A study of submerged breakwaters

Abstract: The results of an experimental investigation on the damping action of impermeable, submerged breakwaters of various shapes are presented and discussed. The effectiveness of the breakwater in damping the incident wave energy is measured in terms of coefficient of transmission. The results are plotted in relevant non-dimensional parameters and comparisons are made with wellknown semi-empirical theories and other available experimental results wherever applicable. The results show that the damping action of the waves increases with the height of the barrier, and rectangular-shaped barriers are found to be the best among the various shapes tested.

Longshore transport evaluations at a detached breakwater

Abstract: A field experiment was conducted by the Coastal Engineering Research Center (CERC) to develop correlations between wave characteristics and longshore sediment transport. The waves were measured by two near-bottom mounted pressure transducers and the average longshore sediment transport rates were determined from sequential volumetric surveys behind an offshore breakwater which was regarded as a total trap. The data analyzed herein encompass a period of nine months during which a total accumulation of 675,000 m3 occurred as documented by eight surveys. Spectral analyses of the wave data were conducted and yielded one direction per frequency. The correlations include immersed weight sediment transport rate, I, versus (1) longshore component of wave energy flux at breaking, P&Sf and (2) the onshore flux of the longshore component of wave-induced momentum, S „. The most widely used correlation constant, K, in the relationship I = KPjig is 0,77. The best-fit values found from the data were K = 0.65 and 0.92 for linear and log best-fits, respectively, as based on the p£s values directed toward the trap. The corresponding values of KA (dimensional) relating I and Sxv are 4.98 m/s and 6.37 m/s, respectively. One feature of this type of trap is the potential for overtrapping if the waves are directed nearly normal to shore.

Have impact pressures on composite breakwaters

Abstract: Wave impact pressures and forces on composite breakwaters have been measured in the laboratory. A solid wall breakwater and a perforated breakwater were instrumented with small pressure transducers in a study designed to estimate the relative effectiveness of perforated breakwaters in reducing impact loads caused by breaking waves. Experimental results of maximum pressures and forces measured on the breakwater walls are presented as cumulative probability distributions. It is concluded that the perforated breakwater experiences significantly lower breaking wave loads although local impact pressures may be as high as those measured on the solid wall breakwater. Further studies are required on the perforated breakwater and alternative designs to determine the most suitable caisson type for the reduction of wave impact forces.

A detached breakwater system for beach protection

Abstract: Three segmented, detached breakwaters were constructed In the fall of 1977 at Lakeview Park, Ohio, on Lake Erie, to protect a beachfill to be used for recreation and shore protection. This paper documents the design procedures which established the configuration of the breakwaters and the beachfill, and determined the need for a terminal groin. The beachfill has been monitored by aerial photography and bathymetric profiling. During the second year, a storm of near design intensity generated severe waves concurrently with high Lake levels and eroded the updrift beach; however, the initial beach configuration was partially restored by natural processes during the following summer season. The project has functioned well, with very little loss of sand from the system and without adverse impacts on the downdrift coast.

Water waves diffracted by two breakwaters

Abstract: The theory of the diffraction of water-waves has previously been limited to twosimple cases; the diffraction around a semi-finite breakwater and the diffractionthrough an opening in a rigid plane. Another useful practical configuration consideredhere is two breakwaters at an angle, with a gap at the corner in one ofthe breakwaters. The parameters are the angle, the breadth of the gap and theangle of incidence of the wave train. The waves are assumed to be of small amplitude.Numerical results agree well with the classical solution for the case wherethe two breakwaters lie in the same plane. Experiments with two sets of parametershave been made in a tank and have also shown good agreement with the theory.

Stability of rubble mound breakwater

Abstract: The stability of a rubble mound breakwater section, with 3 in 2 armour slope, was tested under random waves attack. Tests analysis shows that the equivalent wave height characterizing the spectrum to be used in a stability formula elaborated with regular waves (for instance the Hudson's formula) is the upper twentieth height of the distribution for a storm duration of 6 hours. An analytical expression of the damage evolution as function of time modulates this choice according to the storm duration. The same rubble mound breakwater was also tested under the action of regular breaking waves. The damage was expressed in terms of the four following parameters : H0 : wave height T : wave period Dp : water depth at the toe of the structure Djj : breaker depth without the breakwater For a given wave height, the most important damage occur when : °b In this case the design wave height must be increased by about 30 % when using a stability formula elaborated for non breaking waves.

The design concept of dual breakwaters and its application to townsville, australia

Abstract: In Central and North Queensland the coastline is protected by the Great Barrier Reef over a length of some 1900km from Gladstone in the south to the tip of Cape York (Fig. 1). The fetch distance from the reef to the coastline is very variable from about 15km to 140km. Hence the coastal areas north of Gladstone have moderate to low wave climates except during abnormal weather events such as cyclones or long time interval bands of strong winds. In these events larger storm waves of significant wave heights of 10m may be superimposed, in the case of cyclones, on storm surges several metres in height. The design of breakwaters and shoreline structures for protection against all except cyclonic and strong wind band effects requires, in the main, readily available sizes of armour rock and relatively low crest elevations. To offer similar protection against cyclonic weather events often requires the use of artificial armour units of concrete and a substantial increase in crest heights. The resulting increase in costs makes many of the small projects uneconomic. In this paper the concept of using an offshore breakwater which is designed to fail under extreme wave conditions to protect an inner breakwater or revetment is examined and the results applied to Townsville Harbour where cost savings of the order of 40 percent were achieved over a conventional design.

Estimation of wave transmission coefficients for overtopping of impermeable breakwaters

Abstract: : Methods are presented for estimating coefficients of wave transmission by overtopping for smooth and rough impermeable breakwaters. These techniques can be used for monochromatic or irregular wave conditions and for submerged breakwaters. Example problems are worked to illustrate calculations. (Author)

Lightweight floating stage breakwater - is lattice structure on floats, with one sloping section partly submerged

Abstract: A lattice structure is mounted on one or more buoyant units turned towards approaching waves. It is used in a breakwater for floating stages in harbour installations. This is made up from lattice bars set at a lateral interval part, and vertically close together in the vertical plane projection. Their ends are interconnected by two horizontal rails. It is divided into two sections at an angle. The lower section slopes down, and is partly below the water surface. This is simple and light, but adequate on its own in lakes or relatively calm coastal waters.

Floating breakwater performance comparison

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

Response of Coastal harbours

Abstract: A numerical method able to evaluate the response of harbours of constant depth to periodic plane waves in the presence headlands of breakwaters near the harbour mouth is described and tested on a particular case. The method, based on Green's function theory, is rather general, and can also treat the response of an off-shore harbour, as well as the diffraction field due to only breakwaters or headlands, when the interaction with the coastline must be taken into account.

Oceanside Harbor and Beach, California, Design of Structures for Harbor Improvement and Beach Erosion Control; Hydraulic Model Investigation.

Abstract: : A 1:100 scale (undistorted) hydraulic model, reproducing Oceanside Harbor, approximately 5.7 miles of shoreline, and sufficient offshore area to permit generation of the required test waves was used to investigate the arrangement and design of proposed structures for (a) improving navigation and mooring and prevention of shoaling of Oceanside Harbor and (b) prevention of beach erosion. The proposed structures for the harbor consisted of (a) offshore breakwaters, (b) jetty extensions, (c) groin, and (d) interior breakwaters. The proposed structures for mitigation of beach erosion consisted of various groin and offshore breakwater configurations. A 190-ft-long wave generator, crushed coal tracer material, and an automated data acquisition and control system (ADACS) were used during model operation. (Author)

Extended approach to wave scattering through a harbor entrance

Abstract: The problem of the passage of waves through a gap in an infinite breakwater is analytically solved. This study provides a simple solution for the general case, where the two arms form between them an angle, a configuration that is met almost on any harbor. The main parameters of the problem are shown. The calculation method described is based on the solution of the problem of diffraction of plane waves obliquely incident on a semi-infinite rigid breakwater.

Can we develop new breakwater armour formulae

Abstract: The purpose of this paper is to draw attention to the limitations of present empirical methods for the design of rubble mound breakwaters, particularly those using concrete armour units. Although it is unlikely that analytical techniques could become an adequate substitute for model testing, they should contribute significantly to a major advance in our understanding of breakwater behaviour. This is now long overdue and the art of breakwater design should be capable of substantial development.

Coastal Engineering 1980

Abstract: One hundred eighty-six papers presented at the seventeenth coastal engineering conference are included in these three volumes. There are four parts: 1) Theoretical and observed wave characteristics, 2) coastal sediment problems, 3) coastal structures and related problems, and 4) coastal, estuarine and environmental problems. Part one explores recent advances in wave theories, orbital velocities in irregular waves, and laboratory generation of long waves. Subjects in the second part include sediment flux through reef-lagoon systems, sediment dispersal, natural beaches, and dune dynamics. Part three examines coastal pipelines, seawalls, marinas and breakwaters, and part four explores estuarine modeling, tidal channels, mooring forces induced by passing ships, and port planning. The conference was sponsored by the ASCE Coastal Engineering Research Council, the ASCE Waterway, Port, Coastal and Ocean Division, and the Australian Institution of Engineers.

Estimation of flow through offshore breakwater gaps generated by wave overtopping

Abstract: : This report presents a method for estimating the net flow through the gaps of offshore segmented breakwaters caused by wave overtopping of the breakwaters. The method was developed so that either monochromatic or irregular waves can be specified. Example problems illustrate the effects of wave height and period, breakwater freeboard, spacing between breakwaters, and shore attachment on the flow rate. Computations may be done manually or by using the computer program, BWFLOW2, available from the Corps of Engineers Computer Library, U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi. (Author)

Artificial resort beach protected by offshore breakwaters and groins

Abstract: In Japan, area of natural beaches has decreased in the vicinity of cities, towns and villages, in consequence of constructing ports and harbours, reclamating shore and beach, and building strom-surge prevention structures like sea dikes and sea walls. On the other hand, the demand of people for recreation area is increasing year by year with the improvement of living and economic conditions. Therefore, since several years ago, local governments have extensively been constructing artificial beaches and restoring eroded beaches on many places by the aid of the central government. Such artificial beaches, however, need large amount of natural sand, in spite of the deterioration of sand supply and the soaring of sand price. Moreover, local governments are able to get subsidiary payments of the central government for the construction of artificial sand beach, but not for replenishing sand lost by wave action after the completion of the construction works. Therefore, most artificial beaches in Japan are usually protected by groins and offshore breakwaters in order to retain artificially filled sand. But in summer when sea is in calm condition, pollutant produced by sea-bathing people or discharged from the land is likely to stagnate in the vicinity of the shoreline on account of such structures. From the above-mentioned, coastal engineering problems on construction and restoration of sand beach in Japan are: (1) suitable arrangement of offshore breakwaters and groins from standpoint of artificial beach protection (2) keeping the sea water of the beach clean (3) estimation of profile change of the artificial beach due to wave action after its construction. This paper presents the results of investigations conducted with the aim of solving the above coastal engineering problems related to artificial beach constructions at Suma and Ito beaches. The investigations are mainly conducted using model experiment.

Odd caisson for breakwater

Abstract: PURPOSE:To construct economically and easily a breakwater prominent in the wave pressure stability even under hard conditions by junctioning multi-staged cured slop ing walls to the body of an odd caisson. CONSTITUTION:Multi-staged, curved sloping walls 1, 2, 3 which constitutes a wave pressure receiving surface are junctioned to the body 4 of an odd caisson. These sloping walls 1 to 3 form an upper hollow portion A and a lower hollow portion B. The water entering these hollow portions A, B due to the wave effect is stored therein with a portion thereof sprayed upwardly. The inside of the caisson body 4 is full of water or sand and the offshore side of the hollow portions A, B is formed in a slit wall so that a high wave eliminating effect can obtained. Thus a breakwater prominent in the wave pressure stability even under large depth or high wave condition can be constructed economically and easily.

Design of an overtopping breakwater

Abstract: The Maritime Services Board of New South Wales, Australia, is constructing a major new port facility on the northern foreshores of Botany Bay. A principal part of this project has been the construction of a large armoured revetment from the northern shores. The entrance to Botany Bay faces southeast and it is from this direction that a large proportion of offshore wave energy arrives. Some of the wave energy which is directed onto the Bumborah Point revetment is reflected towards Yarra Bay on the northern shores of Botany Bay. Yarra Bay is largely undeveloped, but a sailing club has stood for many years on the beach at the southern end. As a consequence of this reflected wave energy being directed towards Yarra Bay, its wave climate has been changed considerably so that during the storms of May-June, 1974, Foster (6), damage was suffered by the club-house. Additionally the more severe wave climate and consequent steeper beach have made it much more difficult to launch sailing boats. The Maritime Services Board is charged with the responsibility to carry out remedial works where damage is caused by the port development. Figure 1 shows the revetment and sailing club site. To assist in coastal engineering design aspects of the port development, a large fixed bed wave model of Botany Bay has been built to an undistorted scale of 1:120. This model, some aspects of which have been described by Lawson (4), has pneumatic wave generators which enable offshore wave directions between east-north-east and south to be generated with prototype periods in the range of 5 to 16 seconds. A pneumatic tide generator enables a sinusoidal tide to be generated.

Breakwater for maritime combustible liquid storing tank yard

Abstract: PURPOSE:To reduce the external force acting on a hollow breakwater material constructing a breakwater at the part of a maritime storing tank yard. CONSTITUTION:A breakwater 3 partially consists of a plurality of supporting caissons 7 arranged at predetermined interval on the sea bottom and a hollow breakwater material 8 sunk into the sea and installed over the caissons 7. The material 8 is internally divided into a number of subdivision chambers 10 by vertical partition walls 9.

The effects of construction techniques & bulk terminal operational requirements on the design criteria for island breakwaters

Abstract: The title of the paper contains two important key words - CONSTRUCTION and ISLAND. The techniques for safe and economical construction of an island breakwater located some distance from the shore in exposed waters are radically different from the techniques required for conventional breakwaters with one end attached to the land. The differences in construction technique are so profound as to change the preferred basic design selection from rubble mound to caissons. The paper discusses:- 1. The circumstances in which island breakwaters will become increasingly necessary for unloading of bulk ships. 2. Reasons why prefabricated caisson breakwaters are preferable for construction in an offshore situation. 3. The economy to be gained by using the caissons as the structural support for ship unloading machinery. 4. A consequent necessity to develop a caisson breakwater configuration with adequate design criteria to ensure total safety of the equipment supported on it. 5. A research program aimed at deriving these criteria.

Constructing method for sunk breakwater by utilization of used tanker

Abstract: PURPOSE:To reduce the cost and work term of the construction of a breakwater as compared with conventional reinforced concrete breakwater by constructing a breakwater by sinking a used tanker to the seabed. CONSTITUTION:A used tanker 1 compreses a tank portion divided into a center tank 3 and wing tanks 4 and 4' by vertical partition walls 2 and 2'. The upper deck block 5 in the parallel ship body portion is cut up at a vertical plane A-A' on the side of the tank 3 close to the wall 2 and the bilge outer plate block 6 is cut up at a vertical plane B-B' on the side of the tank 3 close to the wall 2' so as to form blocks 7 and 7' each having an L-shaped cross section. The blocks 7 and 7' are sunk to the seabed with the tanks 4 and 4' up, to form a breakwater. The upper end faces of the blocks 7 and 7' are provided with passages 8, and stones 9 are piled up on the seabed to prevent the breakwater from swinging.