Showing papers on "Breakwater published in 1998"

Wave Propagation Past a Pile-Restrained Floating Breakwater

Abstract: The present paper describes a numerical and experimental study of wave propagation past a pile-restrained floating breakwater. The numerical model is based on two-dimensional wave diffraction theory for wave interaction with a long horizontal cylinder and is applied to the common case of a rectangular-section breakwater subjected to normally incident waves. Comparisons with experimental measurements show excellent agreement and the effect of a gap between the piles and the breakwater is discussed. Relevant results for the wave transmission and heave motion of the breakwater in deep water are presented as functions of the relative wave frequency for various beam to draft ratios. *ISOPE Member. Received March 23, 1998: revised manuscript received by the editors September 15, 1998. The original version was submitted directly to the Journal.

Design and Construction of Rubble Mound Breakwaters

Abstract: The principal function of a rubble mound breakwater is to protect a coastal area from excessive wave action. The dissipation of wave energy through absorbtion rather than reflection distinguishes rubble mound breakwaters from other types of fixed breakwater. A principal design objective is to determine the size and layout of the components of the cross-section. Designing and constructing a stable structure with acceptable energy absorbing characteristics continues to rely heavily on past experience and physical modelling. This paper outlines key design and construction issues, with particular regard to armour stability.

The Fortaleza (NE Brazil) Waterfront: Port Versus Coastal Management

Abstract: The coastal conflicts originated by the succesive implementations of a harbour along the Fortaleza coast (NE Brazil) during the last century are illustrated in this paper. Because all the designed layouts and the different locations selected for the harbour were done without considering the local coastal dynamics, the use itself was affected (port shoaling) and the system was rapidly degraded (coastal erosion). Since the economical benefits generated with the port was a priority for planners, solutions were mainly designed to optimize port exploitation without paying attention to the coastal response. The interest in mitigating the resource degradation appeared with the occurrence of extensive coastal damages and the nearly full disappearance of the beach in some stretches. Moreover, the appearance of a new coastal use, i.e. tourism, with a potential economic importance higher than the previous one, i.e. port, has originated a growing awareness in coastal zone management in the Fortaleza's "coastal" way of thinking.

The Influence of Fish-Tail Groynes (or Breakwaters) on the Characteristics of the Adjacent Beach at Llandudno, North Wales

Abstract: Three Fish-tail groynes or breakwaters of rock rubble construction were installed during 1991 on the West Shore at Llandudno, North Wales as part of a coastal protection programme. This study considered the effect of the northern (Gogarth) breakwater on the adjacent beach. It was found that while the breakwater appears to be effective in protecting the sea wall forming the coastline behind, it has not been successful in increasing beach levels, as proposed, and has also resulted in the accumulation of a large amount of fine material in its lee which reduces its appeal to recreational users. From this study it is believed that beach levels at the site are controlled by the tidal flows across the beach, particularly by the scouring effect within the adjacent North Channel, which prevents the normal beach profile being attained. The build up of fine material is due to the quiescent conditions behind the breakwater, however, it appears that the conditions created are far calmer than anticipated at the design stage.

Coastal Morphodynamics in Subsiding Areas

Abstract: he coastline evolution for 3 sites along the Northern Adriatic was simulated by numerical modeling of the sediment transport mechanisms. The effects of relative sea level changes and external sediment sources such as fluvial sediment input and nourishments are included in the analysis. Prior to the coastline evolution studies, a baseline study was performed where the different process parameters of the coastal sediment balance have been identified and quantified. The calibrated coastline evolution model was used to study the coastline development for different land subsidence scenarios which were supplied by other CENAS partners. The present work has shown that land subsidence is a main factor in the coastal sediment balance. Its importance is of the same order of magnitude as the littoral transport and the sediment input from rivers. The simulations of the coastline evolution have shown that the coastal erosion, which is observed at almost all investigated sites, can be reduced considerably, or even disappear completely if no subsidence occurred. The problems associated with subsidence are mainly of local character. The general pattern of coastal erosion in the region must be subscribed to the reduced sediment supply from the rivers. The establishment of schemes of detached offshore breakwaters has reduced the coastline retreat locally. However, in the lee side of these structures, the problems have become worse due to the lack of sediment supply from the littoral currents. This type of coastal protection will not lead to a sustainable coastal protection.

Numerical analysis of the breakwater construction of Sergipe Harbour, Brazil

Abstract: The numerical simulation of the breakwater construction at Sergipe Harbour, Brazil, is described and the results compared with instrumentation data. The numerical simulation was carried out in plan...

Hydraulic Model Study on Reduction of Runup of Tsunami by Coastal Structures

Abstract: The object of this investigation is to estimate viability of coastal protection facilities, fishing port construction and so on against tsunami runup. As the first step, we carried out a hydraulic experiment on a detached breakwaters and with no structure. Detached breakwaters were of permeable, impermeable and continuous impermeable varieties. Offshore distance, slope of runup zone and characteristics of tsunami were varied. As a result of the experiment, it was clarified tsunami runup was mainly influenced by the diffraction and that surface elevation around shoreline was influenced by the detached breakwaters and the slope of runup zone. As a whole, the effects of opening width and overflow were great

Floating breakwaters : predicting their performance

Abstract: Current environmental and financial restrictions on harbour developments dictate that alternatives to traditional fixed rubble mound and caisson breakwaters are required. The most common solution is the Floating Breakwater, a concept which utilizes reflection, dissipation, and/or transformation to reduce incident wave energy. The design and construction of these for exposed coastal regions present major engineering challenges. -- The primary objective of this thesis was to develop a comprehensive design rationale to enable the designer predict local wave climate (exceedance probabilities, design spectra), optimize a breakwater design (structural parameters, mooring systems) and estimate costs. To facilitate this a number of aspects were reviewed including methods utilized in predicting the wind-wave climate in fetch limited regions, design criteria for inner harbour wave climates, and performance prediction techniques. Based on this review the author developed a simplified deterministic approach to performance prediction based on dimensional and regression analysis of model test data. This information was combined into a computer simulation to predict the local wave climate, optimize the floating breakwater size, design the mooring system, and determine the cost effective solution.

Local Morphological Evolution of the Coast in the Upper Adriatic Sea. Design and Management Strategies to Control Coastal Erosion

Abstract: The subject of the present paper is the control strategy of the dynamic processes affecting the coastline on the basis of the results obtained from simulations conducted under the CENAS Project, regarding the morphological evolution of the coastline. The first part of the paper describes the local evolution around offshore breakwaters from a qualitative point of view. The accumulation rates related to waves, tides and longshore currents behind offshore structures are considered. Between the three selected local sites the protection scheme of offshore breakwaters has been used in the past mainly at Ravenna and along the northern side of Rimini. The physical processes related to these structures are described by DHI. The second section of the paper briefly reports the results of the simulations conducted at the three local sites, highlighting the evolutionary factors which play a major role in determining coastal stability and the results of the macro and local scale flood risk analysis. The last two parts list the various territory management strategies which may be adopted through medium-to-long-term planning or short-term actions for the purpose of limiting the subsidence caused by anthropic factors and of enhancing as far as possible river sediment transport, and deal with the planning criteria for safeguarding the shoreline and for harbor and coastal works in general.

REMR Management Systems BREAKWATER Computer Program User Manual (Version 1.0)

Abstract: : This report documents the initial version of a computer program for maintenance management of coastal structures. This version of the program represents the first stage in developing an integrated maintenance management system for coastal navigation and protection structures. The computer software, currently called BREAKWATER, is a DOS based program intended to handle the most basic maintenance management functions and calculate the required condition index values. This initial version of BREAKWATER concentrates on breakwaters and jetties of rubble construction with either rock or concrete armor units. Future efforts will include system features for breakwaters and jetties of nonrubble construction, plus seawalls, bulkheads, and revetments, and other desired management functions. Future versions of the program will be developed for the Microsoft Windows operating system, and will otherwise be consistent with the most current operating and network systems in use at that time.

Prediction of Shoreline Change Behind Detached Breakwater

Abstract: A simple numerical model predicting the change of shoreline to be induced by the construction of detached breakwater is developed in this paper. The developed numerical model is first verified by comparison with the analytical solution of constant angle model. In comparison, it is found that the constant angle model has some problems. The difference of sediment volume between erosion and deposition becomes large as the diffracted wave angle is increasing, and the maximum erosion is always occurred at the same point regardless of the variations of wave angle. These problems can be overcome by considering the wave angle inside shadowed zone to be varied linearly due to the geometry of detached breakwater. From many numerical experiments, it is concluded that the shoreline change is very dependent on the geometry of detached breakwater. i.e., the nearer detached breakwater is constructed to the coastline, the more shoreline is changed. In particular, the equilibrium shoreline and the influence distance with respect to the geometry of detached breakwater under the given condition are calculated by the developed numerical model, which may be usefull for the practical purpose.

Semi-submerged multistage breakwater supported by hollow pontoon

Abstract: PROBLEM TO BE SOLVED: To weaken the wave pressure between breakwaters and impart a mutual interfering action by supporting the breakwaters provided in multistage by a hollow pontoon, and providing balance weight rooms on both ends of the pontoon. SOLUTION: On a hollow pontoon 5, a first breakwater 1, a second breakwater 2 and a third composite breakwater 3 each of which is made of steel plate are fused and fixed to positions dividing an inflow wave into three pieces. Further, a reinforcing material 6 is provided on each wall back surface, and the third composite breakwater 3 is formed by welding front and rear steel plates by a joint material 7, and pressurized in drum shape. The hollow pontoon 5 has balance weight rooms 9 on both ends, and sand, gravel or the like is filled therein to keep the balance of the breakwater body. The distance of each room 9 is determined by the distributed load of each wall. Further, the apex of A-A elevation is taken as the apex of the rear plate of the breakwater 3 to set the starting point of the A-A elevation by the total width, the advanced wave is divided into three to disperse the wave pressure, and a mutual interacting effect is imparted to prevent the wave. Thus, the advanced wave can be guided to a straight flow and a colliding counterflow to weaken the wave pressure.

Three-dimensional breakwater stability tests at Vale de Cavaleiros, Cape Verde /

Abstract: : A breakwater rehabilitation has been proposed for Vale de Cavaleiros, Republic of Cape Verde Rehabilitation would include extending the breakwater length, placing all salvageable tetrapods in the northernmost portions of the breakwater, and placing Core-Loc armor units on the remainder of the structure A breakwater stability model investigation was initiated by the US Army Engineer Waterways Experiment Station's Coastal Engineering Research Center The goal of the study was to evaluate the stability of the Core-Loc armor layer for the proposed breakwater rehabilitation This report describes the rehabilitation design and facilities used, as well as the three-dimensional stability test results

Breakwater type large floating body

Abstract: PROBLEM TO BE SOLVED: To dispense with a fixed type breakwater and to effectively use an upper deck so as to easily bring a ship alongside a pier by arranging a breakwater structure which is suspended downward from an overhang part and penetrates the water surface so as to be extended into the water, in the overhang part protruded above the wave side on the upper deck. SOLUTION: In a large floating body 1 provided with a wide upper deck 1a, an overhang part 1A protruded above the incident wave 4 side is provided with a breakwater structure which is suspended downward from the overhang part 1A and penetrates the water surface 18 so as to be extended into the water. As a breakwater structure, multiple box type floating bodies, which are suspended downward from the upper deck overhang part 1A, and grid type coupling members 3 connecting the box type floating bodies 2 mutually are arranged, so that the box type floating bodies 2 are arranged in a zigzag shape. In this way, an expensive fixed type breakwater or floating breakwater for forming a calm sea area is dispensable. In addition, a ship can be brought alongside a pier with ease because no breakwater structure, which approaches the outer circumference of the upper deck and moves relatively, is arranged.

Hydraulic Experiment for the Characteristics of Wave Forces Acting on the Mixed Type Breakwater Caisson

Abstract: The wave forces acting on coastal structures must be predicted to do optimal design because they play an important role to the stability of the coastal structures. In the Present study, hydraulic model experiments were conducted to not only calculate the wave forces acting on the non-perforated wall caisson breakwater from the wave pressure data but measure the wave forces directly through a three component load cell and the both wave forces were compared to each other The direct measurement of wave forces is strongly recommended because the safety factor could make a big difference even in the simplest shape of caisson according_ to the way of wave force acquirement.