Showing papers on "Breakwater published in 1976"

Water motion on a beach in the presence of a breakwater: 1. Waves

Abstract: For a long breakwater on a slowly varying bottom as asymptotic theory is given which accounts for the combined effects of refraction and Fresnel diffraction of water waves. Numerical examples are given for two cases: an offshore breakwater and an isolated jetty.

Adjustably submersible breakwater

Abstract: A plurality of elongated tanks positioned in parallel relationship with respect to each other are swingably interconnected at their aligned ends to provide a yieldingly undulating breakwater apparatus. The buoyancy of each of the tanks is individually adjustable so that the ratio of floating tanks to submerged tanks, and the various depths thereof, can be altered to suit the prevailing wave and current characteristics of a particular installation site.

Fundamental armor module in breakwater net linked system

Abstract: A breakwater composed of a network of interconnected elements of similar size and configuration, each of which has a body with a through axial recess and vertically projecting portions so that when the bodies are arranged in levels, the portions interlink in the recesses forming a network of bodies which are adapted to be assembled at a job site as a breakwater to resist wave action.

Application of a sediment transport model

Abstract: A mathematical model for sediment transport under waves has been developed from concepts that have been used successfully for unidirectional flow. This model has been combined interactively with numerical models of wave refraction, wave diffraction, longshore currents and circulation currents in order to predict local topographical changes in the vicinity of a cooling water intake basin for a nuclear power station. The sediment model is calibrated using field data of sediment concentration profiles. Verification and adjustments may be made by analysing deep water wave statistics corresponding to periodic beach and hydrographic surveys. The model can be used to investigate the effects of any wave climate and consequently different layouts of coastal structures can be examined very rapidly. For the particular problem considered it was necessary to optimise the configuration of the breakwaters forming a cooling water intake basin in order to minimise the sediment concentration at the intake, estimate maintenance dredging quantities and investigate extreme events.

Water motion on a beach in the presence of a breakwater: 2. Mean currents

Abstract: A semiempirical theory of breaking-induced mean currents on a beach is developed here to study the combined effects of refraction and diffraction. With the omission of convective inertia and lateral turbulent diffusion the resulting averaged equations are solved by finite differences. The case of an offshore breakwater is studied in detail, and the predicted current pattern is consistent with laboratory observations and the known tendency of tombolo formation near sandy beaches. Numerical results for an isolated breakwater extending from the shore are also presented, and observational evidences cited.

Protection by means of offshore breakwaters

Abstract: The coast of Tel-Aviv is characterised by a narrow sandy beach, and the seabed is the nearshore shallow waters is strewn with rocky ledges and outcrops. These rocks are of a marine conglomerate type and are covered with layers of fine to medium grained sand of various thickness. At depths greater than 5 m the seabed is predominantly sandy. During the summer season, when waves and swells seldom exceed 2 m in amplitude, the sandy strip of the beach maintains its minimum width of about 20 m. However, winter storms reduce the width of the beach in some places to zero, and there is a marked tendency to erosion and scour of the beach in front of the retaining walls of the alongshore promenade or in front of the coastal bluff. In order to prevent this erosion and at the same time to enlarge the sandy beach area, we have proposed to erect in front of the beach a series of offshore breakwaters, either detached or groyne-connected. (Fig. 1) The first of the series was erected off the Tel-Baruch beach just north of Tel-Aviv. There beach sand was practically non-existent, and in order to enable bathers to enter the water, a breach in the shallow rocky belt had to be blasted. The Tel-Baruch breadwater is of a rubble-mound type, 200 m long and connected with the shore by a 100 m long groyne. It is founded on a rocky seabed at -3.0 m below M.S.L. and consists of a quarry-run core (0.5 to 250 kg units), protected on its seaward slope by a rock armour (2-6 tons units) laid on a 1:3 grade, and on its landward slope by a secondary armour (1-2 tons units) laid on a 1:1.5 grade. Its crown is topped by R.C. 0.25 thick slabs to a level of +1.0 m above M.S.L. Shortly after its erection in 1965, a sandy tombolo has formed at both sides of the groyne, increasing in area until a permanent equilibrium has been achieved. Erosion of the beach on both sides of the breakwater was avoided, owing to a belt of beach rock which protects the foreshore to the south and to the north of the breakwater.

Changes op sea bed due to detached beeakwatees

Abstract: Since most of the coast lines of Japanese Islands are faced on the open sea and are always attacked by severe waves, beach erosion is one of serious problems in the coastal engineering field. Although Japan has all types of coastal land-forms except the glacial shoreline, remarkable recessions of coast line have been observed at sea cliffs and sandy beaches. The recession of sea cliffs has been found at several districts in Japan since old times. But, beach erosion has become increasingly severe since the early 1950's. The main causes of beach erosion are the reduction in sediment supply from rivers and the interception of the longshore paths of sediment. The former is caused by the river improvement works and by the construction of dams and debris barriers or Sabo works. The later is caused by the coastal structures, such as jetties, groins, breakwaters, and flood-control outlets. In addition a new type of beach erosion has been observed at the coast where coast protection works such as seawalls and bulkheads exist. The beach erosion defence works are being executed at more than 300 sites in Japan. Considerable number of the works were commenced in the 1960's.

Floating breakwater performance

Abstract: The Pacific Northwestern United States contains large areas of protected waters with abundant recreational boating opportunities. The area also supports many commercial fishermen who use small boats in their fishing operations . As a result, there is a large demand for sheltered moorage for all these vessels. Traditionally, this demand has been accommodated by constructing rubble-mound breakwaters for marina protection. At present, most of the sites where rubble-mound breakwater construction is economically feasible have been used. Conditions at many of the remaining areas"for marina development are unsuitable for traditional techniques of marina construction. In general, the cost is too great because the water is too deep, or the environmental degradation resulting from marina development is unacceptable. To satisfy the demand for moorage, while at the same time overcoming the other restrictions, floating breakwaters have been employed at many new marina facilities. In order to optimize the configuration of floating breakwaters and to overcome the problems which have been encountered with their use, the University of Washington has undertaken a continuing program of research. The aim of this research has been to monitor the performance of existing breakwaters and to develop a theoretical model to predict performance. Using the theoretical model supplemented with appropriate model-scale tests, a series of parametric variations will be tested to determine the effects of these variations on breakwater performance. At present, several comparisons of the theory with model tests and full-scale performance have been reported by Adee (1975a, 1975b, 1976). This report is a continuation of this effort incorporating data obtained at the Friday Harbor, Washington floating breakwater.

Slit-type Breakwater; Box-type Wave Absorber

Abstract: A box-type wave absorber, which is composed of a perforated vertical front-wall and a perforated, horizontal bottom-wall, has been proved by a number of experiments to show lower coefficients of reflection and more distinguished reduction of wave pressures than the perforated vertical- wall breakwater. A breakwater of composite-type, which is 1500 m long and to be built at a water depth of 10 to 11 m below the Datum Line in the Port of Osaka, is being designed to set this new type of wave absorber in the concrete caissons of the vertical-walls which is named "a slit-type breakwater". The typical cross-section of the breakwater and the advantages of the slit-type breakwater are presented herein.

Waianae Small-Boat Harbor, Oahu, Hawaii, Design for Wave Protection.

Abstract: : A 1:50-scale (undistorted) hydraulic model, reproducing approximately 1.4 miles of shoreline along the proposed Waianae Small-Boat Harbor site (beginning at Kaneilio Point and extending northwesterly), the surrounding reef, and sufficient offshore area to permit generation of the required test waves, was used to investigate the arrangement and design of proposed harbor configurations with respect to wave action. The basic harbor configuration consisted of (a) an outer breakwater, (b) a stub breakwater, (c) an entrance channel, turning basin, and main access channel, and (d) revetted fill areas in the harbor interior. Variations to the basic configuration involved changes in the alignments and lengths of the breakwater structure, the cross section of the breakwaters used, the size and shape of the turning basin, the location of fill areas, and the location of the launching ramp inside the harbor. A 60-ft-long wave generator and an automated data acquisition and control system (ADACS) were used in model operation.

Local scour amd current around a porous breakwater

Abstract: Scour at the foot of vertical homogeneous crib style walls which were used as models for detached breakwaters, and the rise of mean water level in the shoreside region of the breakwaters were experimentally investigated, and the experimental results were compared to some field data.

Floating breakwater field assessment program, Friday Harbor, Washington

Abstract: A theoretical model for predicting the dynamic behavior of a floating breakwater is presented along with a report on a field experiment designed to provide basic data for verifying the model. Additional data were taken from the literature and from auxiliary laboratory experiments. The dynamic behavior characteristics investigated were: (1) Total transmitted and reflected waves and their components; (2) wave forces on the breakwater; (3) motions of the breakwater; and (4) forces on the mooring lines. The prediction model was developed from two-dimensional, linearized solutions of the hydrodynamical equations formulated in terms of a boundary value problem for the velocity potential. Some nonlinear effects are considered. Results for the predicted transmission coefficients were in good agreement with laboratory and field data, and they showed how the influence of fixed-body transmission, and of sway, heave, and roll motions on the transmission coefficient changed with increasing values of the parameter, beam (width) to wavelength ratio. The shape of the curves predicting the mooring line forces as a function of the beam (width) to wavelength ratio (or of wave frequency) followed those for the measured responses, but predicted magnitudes did not agree closely with measured values. The floating breakwater at Friday Harbor, was instrumented. Statistical summaries of all data are presented with analyses of selected transmitted waves, transmission coefficients, and acceleration components.

Tethered Float Breakwater: A Temporary Wave Protection System for Open Ocean Construction

Abstract: Marine construction costs are strongly influenced by the local wave climate. Some of the effects of the use of a transportable breakwater on these costs are examined. The tethered float breakwater, a transportable ocean based system under development by a Federal/State consortium, is described and the current program status reviewed. Representative incident and transmitted wave climates are selected and the factors leading to hardware design choices to meet these requirements are presented. The resultant breakwater design is described and a range of operating costs is projected for a commercial wave abatement service. Typical offshore construction applications are illustrated. A program for commercial development of a tethered float breakwater for marine construction is suggested.

Cylindrical Caisson Breakwater: Strain Model Tests

Abstract: The distribution of shook pressures on a vertical face breakwater is so random from one shock to the next that the determination of the internal forces in a thin-balled reinforced-concrete structure is difficult even when a large number of pressure cells is used in a model test. Therefore a technique has been developed that allows the direct determination of the internal stresses by means of strain gauges. The new technique has been applied to a breakwater consisting of a series of cylindrical caissons. The results show that a strain gauge model is more advantageous than a pressure cell model because of its simpler data analysis and better determination of the quantities required for design.

Topographic Change Resulting from Construction of a Harbor on a Sandy Beach: Kashima Port

Abstract: This paper presents some general properties on topographic change on the shore and sea bed in the vicinity of ports and harbours constructed on the sandy beach, mainly with the case study of Kashima Port. Following three characteristics of the topographic change due to prolongation of breakwaters are discussed; that is, i ) The shoaling and the change of topography in the area surrounded by breakwaters and shoreline, ii ) Topographic change of artificial beach in the updrift beach of breakwater having the long oblique part, iii. ) Erosion and accretion of downdrift beach due to the prolongation of the oblique part of breakwater.

Coastal engineering. Volume III: Breakwater design

Abstract: General considerations, types of breakwaters, rubble mound breakwaters, wave run-up and overtopping, construction materials, armor computations, te core, filter and toe constructions, rubble mound breakwater construction, optimum design, example, monolithic breakwater, construction materials, wave foreces on vertical walls, monolithic breakwater foundations, influence of breakwater on waves, construction of monolitic breakwaters, optimum design, Rotterdam-Europoort entrance design.

Prototype Performance Characteristics of Two Floating Breakwaters

Abstract: The performance characteristics of floating breakwaters, ie, the transmission coefficients, anchor forces, and accelerations in heave, roll, and sway, are evaluated from field measurements on a concrete modular type installed at two different locations in Alaska, and a pontoon-type installed at a location in the State of Washington In all three instances, the installations served to protect small boat harbors from local, wind generated waves The measurements were planned with the combined purpose of evaluating the breakwater types under different wave exposures and to supply basic data for the verification and development of a theoretical predictive model for breakwater performance The instrumentation system was designed with multiple-channel, digital recording capability and packaged for use in remote locations, requiring only periodic maintenance checks and tape changes The system can be set to be activated by any selected wind speed and sample the various input sensors at prescribed intervals and durations of time

Laboratory study on pervious core breakwaters

Abstract: Effects of permeable core layer installed in trapezoidal and rectangular breakwaters have been studied experimentally and analytically. As the materials for armour and core use of the lattice composed of circular cylinders was made in addition to rocks. Perforated plates were also applied as a kind of very thin core. Expermental results show that the reflected wave heights from breakwater could be reduced considerably by locating the core layer shoreward within it while core thickness controls the transmitted wave heights in the protected water area. Harmonic analysis about the water surface in lattice armour reveals that the second harmonic waves take a pattern of standing wave distribution having a node at the seaward face of breakwater. Thin perforated plates work success-- fully for reducing the transmitted wave heights when they are installed at the rear face of breakwater. An analytical approach to predict the transmission and the reflection coefficients is applied for the present experimental data and shown to be useful.