Showing papers on "Breakwater published in 1981"

Floating breakwaters: State of the art, literature review

Abstract: A multitude of conceptual models of floating breakwaters have been proposed without extensive or complete evaluation of most of these concepts. The technical literature regarding floating breakwater applicability and design procedures is fragmentary and sometimes confusing. Clear, concise guidance does not always exist for those responsible for planning and developing wave protection measures which utilize floating breakwaters. This study reviewed and evaluated the existing technical literature (theoretical, field, and laboratory) on floating breakwater concepts. While floating breakwaters provide a lesser assurable degree of protection than a permanently fixed breakwater, they are in general less expensive and can be moved from one location to another. The cost of a floating system is only slightly dependent on ,.,rater depth and foundation conditions. Adequate wave reduction or energy attenuation can be attained by a floating breakwater only if the incident wave is of a relatively low height. A reasonable magnitude appears to be an incident wave height not exceeding 4 feet, with a corresponding wave period not exceeding 4 seconds. Floating breakwaters can attenuate waves with these incident characteristics to a magnitude tolerable in a small-craft mooring area (wave heights up to 1.5 feet). Open-ocean applications of a distinctly different concept can be formulated to withstand substantial increases in the incident wave characteristics. A group of prismatic structures contains the simplest forms of floating breakwaters. This group offers the best possibilities for multiple use as walkways, storage, boat moorings, and fishing piers. In addition to mass, the radius of gyration and the depth of submergence appear to significantly influence the attenuation characteristics. As the ratio of breakwater width-to wavelength increases to values greater than 0.5, the wave attenuation features of the structure not only improve markedly, but the net result of the forces on the mooring and anchoring system becomes substantially less. This occurs because the wave dynamics are exerting forces on a part of the structure in a direction opposite to those forces on other parts of the breakwater.

Wave dissipation caisson

Abstract: This is a wave dissipation caisson made of concrete wherein trapezoidal wing pieces having an appropriate number of holes are fixed in combination to the inside of a box-type frame formed only by angled sections of a framework. The caisson has a permeable structure wherein the waves advancing into the frame are shifted and divided by wing pieces so as for the energy of the waves to be dissipated and is placed on a seabed to be utilized as a revetment and a breakwater.

Beach Processes in the Vicinity of Offshore Breakwaters

Abstract: Present knowledge concerning the influence of offshore breakwaters upon beach processes is reviewed with particular reference to the mechanism and conditions for formation of a tombolo.

Prevention of Shoaling at Port Orford, Oregon

Abstract: A 1:100-scale undistorted hydraulic model of Port Orford, Oregon, and sufficient offshore area to permit generation of the required test waves were used to develop and test several plans of improvement proposed to eliminate harbor shoaling without adversely affecting wave heights at the existing pier. Improvement plans consisted of removal of portions of the existing breakwater, realignment or lengthening of the existing breakwater, and construction of new breakwater structures in the vicinity of Fort Point and Battle Rock. A 54-ft-long wave machine, electrical wave height measuring and recording apparatus, and coal and nylon tracer materials were used in the model. Tests were conducted with prebreakwater and existing breakwater conditions, and the results were compared to determine the causes and sources of harbor shoaling. Improvement plans were then tested and compared with existing prototype conditions. Of the plans tested, the optimum configuration appeared to be an 1100-ft-long angled breakwater extending from Fort Point.

Structure for breakwater

Abstract: PURPOSE:To obtain the structure for a breakwater, which can sufficiently withstand strong wave pressure even when its own weight is light, by a mechanism wherein connection between caissons and a mound is strengthened. CONSTITUTION:An L-shaped block 12 is installed onto a created riprap mound base portion 11. A rear mound 13 is prepared behind the L-shaped block 12. A caisson 14 with a rectangular projection 15 is towed to a port outside portion and carried on the mounds 11, 12, 13 the rectangular projection 15 is fitted to the L-shaped block 12, and a base of the caisson 14 is placed on the mound 13. After the caisson 14 is installed, a front mound 16 forming a front part of the caisson 14 is formed, and structure for a breakwater is constructed.

A Coastal Process Investigation, Coffs Harbour, NSW

Abstract: An investigation of the active coastal processes in the Coffs Harbour region of northern N.S.W. has been undertaken. The aim of the study was to provide a factual basis for coastal planning decisions in the region. The harbour construction has intersected the northerly longshore drift which is estimated at 75,000 cubic metres per annum. Boambee Beach to the south of the harbour and Jetty Beach within the harbour are accreting. Shoaling is occurring to the south and east of the breakwaters and the harbour is infilling at an increasing rate, presently estimated at 25,000 cubic metres per annum. The longshore supply to the northern beaches has been interrupted and the beaches reflect this sediment deficit. They are narrow with prominent erosion escarpments and the sediments are coarser than on the southern beaches.

Coastal Changes due to the Construction of Artificial Harbour Entrances and Practical Solutions, including Beach Replenishment

Abstract: When longshore sediment transport is interrupted by a construction along a coast, e.g harbour moles or a dredged approach channel, the equilibrium of the coastline may be disturbed. When the disruption is caused by breakwaters, the longshore transport that is held back will cause accretion updrift of the breakwaters and erosion downdrift of them. The updrift accretion may eventually result in the harbour entrance shoaling. The downdrift erosion might cause difficulties when valuable areas are situated close to the coastline or when the coastline forms a coastal protection for land behind it. When the disruption is (caused by a dredged channel, no accretion updrift of the channel will occur since the material is trapped in the channel. This means, however, that here too there is a lack of material downdrift and erosion will again occur there.

Wave Penetration and Rubble Mound Breakwater Stability Model Studies for Tidal Inlet Training Works

Abstract: This paper presents the results of model tests carried out at the Queensland Government Hydraulics Laboratory as part of the design of training works for the Nerang River Entrance in South East Queensland. Various techniques for absorbing wave energy which has penetrated through the entrance are examined and the results of breakwater stability tests using quarry stone, dolosse and cubes are discussed.