Showing papers on "Breakwater published in 1990"

Wave diffraction through offshore breakwaters

Abstract: The interaction of water waves with a long linear array of offshore breakwaters is examined to determine the reflection and transmission coefficients for these structures, providing data on the sheltering afforded by these structures. Two variational methods and an eigenfunction expansion method are used to determine the reflection coefficients for waves with wavelengths longer than the distance from gap to gap in the breakwater array. The eigenfunction method is also used for breakwaters, where the spacing between the gaps is longer than the water wavelength. For this case, analogous to scattering of light by a grating, numerous monochromatic directional wave trains can be generated in the region behind (and in front of) these breakwaters, which can lead to the generation of rip currents, beach cusps, and other periodic phenomena on beaches behind the structures.

Accretion behind single offshore breakwater

Abstract: This study notes that the main variables in evaluating apex postion of a salient behind a single breakwater parallel to the shore with waves normal to both are its length and distance offshore. Because the shape of the salient is related to wave diffraction patterns, the apex distance from the breakwater on its centerline, its radial distance, and angle from the tip of the breakwater are all useful measurements when related to the two main variables mentioned. It is also noted that values of breakwater length to distance offshore have been established for the limting conditions of tombolo and zero salient formation. Between these two extremities, the extent of salient accumulation in equilibrium state can be determined quantitatively for designing a single offshore breakwater.

Design and Performance of Reef Breakwaters

Abstract: mmmmmmmmmmmmmmmmmmmmmmmmmm AHRENS, J.P. and COX, J.., 1990. Design and performance of reef breakwaters. Journal of Coastal Research, SI#7, 61-75. Fort Lauderdale (Florida). ISSN 0749-0208. Reef breakwaters are potentially one of the most effective types of shore protection. In spite of this potential, there is very little quantitative information on the design and performance char acteristics of reefs. This paper discusses some of the practical considerations in choosing armor stone size as well as size and quantities of bedding material. The expected performance of reefs is presented in terms of wave transmission and reflection properties, energy dissipation char acteristics, and shoreline response caused by the reef. Numerous references are cited which can provide additional information. In some situations, it is cost effective to use a reef in tandem with either another conventional breakwater or revetment. This strategy uses a low crested reef to reduce the incident wave heights on a conventional structure. Some examples of the tandem reef approach are cited. ADDITIONAL INDEX WORDS: Reef breakwaters, low-crested rubble mounds, breakwater sta bility, wave transmission, shoreline protection.

Redondo Beach King Harbor, California, Design for Wave Protection. Coastal Model Investigation

Abstract: : A 1:75-scale, three dimensional hydraulic model was used to investigate the design of proposed breakwater modifications at Redondo Beach King Harbor, with respect to wave conditions in the harbor. The model reproduced approx. 8,800 ft of the shoreline and included the existing harbor and offshore bathymetry in the Pacific Ocean to a depth of -60 ft. Improvement plans consisted of raising the crest elevation of portions on the north breakwater both with and without installing a transition layer of small stone, and extending the length and crest elevation of the south breakwater. An 80-ft-long unidirectional, spectral wave generator, and an automated data acquisition and control system were used in model operation. Conclusions from test results include: 1) Existing conditions are characterized by very rough and turbulent wave conditions with wave heights up to 8 ft along the moles for 50-year conditions. 2) Of the 14 improvement plans tests, Plan 14 was considered optimal considering wave protection and construction costs. 3) Comprehensive wave-height tests conducted for Plan 14 indicated that the established wave-height criteria in the harbor would be met or only slightly exceeded for waves up to a 100-year recurrence from 240 and 260 deg.

Redondo Beach King Harbor, California, Development of Design Data for Harbor Improvements

Abstract: : A 1:75-scale three-dimensional hydraulic model was used to investigate the design of proposed modifications in various areas of Redondo Beach King Harbor. The model reproduced approximately 8,800 ft of the California shoreline and included the existing harbor and offshore bathymetry in the Pacific Ocean to a depth of -60 ft. Improvements consisted of raising portions of the north and south breakwaters, flattening the slope of the existing north breakwater in the vicinity of an adjacent mole, and installing a spur on the inside of the north breakwater. An 80-ft-long unidirectional, spectral wave generator and an automated data acquisition and control system were used in model operation. Conclusions include: For test waves from 260 deg, test results for existing conditions indicated severe overtopping of the breakwater adjacent of Mole A and subsequent flooding of the mole. The proposed improvement plan (Plan 1) with additional stone placed on a 100-ft-long section at the outer end of the Galveston seawall (Plan 1A) will minimize overtopping of the breakwater and flooding of the mole. For test waves from 240 deg, the proposed improvements (Plan 2) required modification to minimize overtopping of the breakwater and subsequent flooding of Mole A. Additional stone placed on a 150-ft-long section of the outer end of the Galveston seawall (Plan 2A) was required. The Plan 2 spur, it appeared, could be reduced in elevation (Plan 2A) and minimize wave energy reaching Mole A due to spilling waves propagating northerly over the breakwater.

Model Study of Shoreline Erosion and Beach Protection Schemes at Surfside-Sunset Beach, Long Beach, California

Abstract: : A 1:75 scale (undistorted) hydraulic model was used to investigate the design of proposed modifications at Surfside-Sunset Beach, California, with regard to the reduction of beach erosion at the site. The model reproduced approximately 4,600 ft of the California shoreline and included the Anaheim Bay East Jetty and offshore bathymetry in San Pedro Bay to a depth of 26 ft. Proposed improvements consisted of offshore breakwaters and a breakwater attached to the existing jetty extending in a beach-parallel direction. Waves were generated by an 80-ft-long unidirectional, spectral wave generator, and a crushed coal tracer material was used to qualitatively determine the movement of beach-fill material. It was concluded from test results that sediment transport at Surfside-Sunset Beach to the northwest for test from south and south- southwest, and movement to the southeast for test waves southwest and west- southwest.

Movement of Sand around Revetment under Water Pressure Variation

Abstract: Many hydraulic structures are damaged by under flood flow and storm waves year after year. Many cases of dike and breakwater failure are caused by the suck out of sand from behind the revetment. This type of failure will be in close relation to the dynamic behavior of sand bed around the revetment. In this paper, from this point of view, we investigated the basic characteristics of such sand movement by small model tests and tried to explain the hydro- and soil-mechanical mechanism of this phenomenon theoretically.

Wave Response of Proposed Improvements to the Shallow-Draft Harbor at Kawaihae, Hawaii

Abstract: : This is a study using mathematical models to determine the wave response of two proposed plans of improvement to the shallow draft harbor at Kawaihae, Hawaii. The existing harbor consists of an 850-ft-long, 120-ft-wide entrance channel, a 1.2-acre turning basin, and an 850-ft-long breakwater. Plan 1 includes a 640-ft-long, 80-ft-wide main access channel, a 375-ft-long extension to the existing 850-ft-long west breakwater with a 200-ft-long stub on the harbor side, a 425-ft-long access breakwater with a 400-ft-long wave absorber, a 1,025-ft-long east breakwater, and a 650-ft-long offshore breakwater. Plan 2 includes the same improvements as Plan 1 with the exception of the removal of 200 ft of the west breakwater tip. These plans were developed to provide protection to the existing harbor. Study results indicated that Plan 1 met the requirements to protect the harbor adequately from the incident wave climate. It was determined that this plan will keep the wave height in the harbor berthing areas at 1 ft or lower and in the harbor channels and turning basin at 2 ft or lower approximately 90% of the time per year.

Finite difference scheme for wave transmission in a rubble mound breakwater

Abstract: The new harbour of Zeebrugge is protected by two large breakwaters with a backfill. The stability of the open filter construction which separates the core and the backfill has been evaluated using the HADEER computer program. This program is suitable for modelling water wave penetration in a coarse rubble mound breakwater and takes into account phreatic storage, porous turbulent flow and virtual mass effects. Results show a substantially internal set-up and cyclic water table motion at the filter

Field verification experiment of wave power extracting caisson breakwater : design and construction of caisson, generating equipment and planning of field experiment

Abstract: The Ministry of Transport of Japan has been conducting a research project to develop a wave energy converter called a wave power extracting caisson. This paper describes the latest developments in the wave power extracting caisson and the designing of the caisson breakwater and energy converter for the field verification at Sakata Port, as well as the outline of the experiment plan

Artificial bank for preventing coastal erosion

Abstract: PURPOSE:To prevent coastal erosion for reducing the deformation of seashore by providing buffering banks having a large wave transmissibility at the ends of a body bank, so that the deflection of waves can be restrained to reduce the flow of sea water. CONSTITUTION:An offshore bank 1, which is installed long- and narrow-wise along the direction toward the coast at a place away from the beach line 2 before deformation by an appropriate distance, is made up of a body bank 3 consisting of a breakwater or a wave-breaking bank, and buffering banks 4, 5 which are continuously provided on both sides of the body bank 3, and each of which is consisted of a wave-breaking bank having a larger wave transmissibility than the body bank 3. Then, since the deflection of waves at the ends of the offshore bank 1 is reduced, the sea water flow 6 to be turned in behind the offshore bank 1 can be further reduced than that in the case where the buffering banks 4, 5 are not provided. Thus, the magnitude of tombolo being produced on the beach at the back of the offshore bank 1 can be reduced, and the degree of deformation of the beach line 9 after deformation to that of the beach line before deformation can also be reduced.

Submerging type caisson composite breakwater

Abstract: PURPOSE:To prevent a caisson itself from falling or moving and to make the restoration of a composite breakwater easy by constructing a top mound-type breakwater between a projection provided to the front of the upper part of a submerging type caisson installed on the sea-bottom and a wall erected behind. CONSTITUTION:A projection 7 combined with a caisson body or a lid body as a unit is provided to the front of the upper part of a submerging type caisson 1 installed on a rubble-mound 3 on the sea-bottom, and a reverse T or L shaped wall 2 is placed behind the upper part thereof. (The wall may be installed together with the body and the like as a unit.) After that, a top mound-type breakwater 8 is constructed of a rubble mound 3 and wave dissipation blocks 4 or either of them between the projection 7 and a wall 2 to subject it to strong wave force as indicated in the direction of the arrow (W). In case an anomalous wave height higher than a designed wave height storms, the damage is minimized except that the mound-type breakwater 8 is only destroyed thereby, and the restoration of the submerging type caisson composite breakwater is easy.

Arviksand fishing port breakwater extension

Abstract: After severe storm damage to existing breakwaters at the port of Arviksand in Northern Norway, a breakwater extension was planned. Wave data were collected and a risk analysis carried out as part of the design process.

Numerical solutions to wave interaction with rubblemound breakwaters

Abstract: The interaction of a wave with a rubblemound breakwater results in a complex flow field which is both nonlinear and turbulent, particularly within a region close to the surface of the structure. Numerical models describing internal flow in a rubblemound breakwater are becoming increasingly important, particularly as the influence of scale effects on internal flow in physical hydraulic models are becoming understood as important. A number of numerical models to predict the internal breakwater flow kinematics have been produced in the past two decades. This paper provides a review of the state-of-the-art of numerical modelling of wave interaction with rubblemound breakwaters. Details of the theoretical development and the resulting numerical solution techniques are presented. Methods for incorporating secondary effects such as two-phase (air–water) flow, inertia, and unbalanced boundary conditions are discussed. Limitations of the models resulting from the validity of the assumptions made in order to effect...

Field verification experiment of wave power extracting caisson breakwater

Abstract: The Ministry of Transport of Japan has been conducting a research project to develop a wave energy converter called a wave power extracting caisson. This paper describes the latest developments in the wave power extracting caisson and the designing of the caisson breakwater and energy converter for the field verification at Sakata Port as well as the outline of the experiment plan. It is still difficult to design a system offering both economy and stability against destructive wave conditions. Development of the wave power extracting caisson, therefore, attempts to incorporate economical utilisation of wave energy into a breakwater with small reflection and wave overtopping.