Showing papers on "Breakwater published in 1989"

GENESIS: Generalized Model for Simulating Shoreline Change. Report 1. Technical Reference

Abstract: : This report documents a numerical modeling system named GENESIS which is designed to simulate long-term shoreline change at coastal engineering projects as produced by spatial and temporal changes in longshore sand transport. Typical longshore extents and time periods of modeled projects can be in the ranges of 1 to 100 km and 1 to 100 months, respectively, and almost arbitrary numbers and combinations of groins, detached breakwaters, seawalls, jetties, and beach fills can be represented. GENESIS contains what is believed to be a reasonable balance between present capabilities to efficiently and accurately calculate coastal sediment processes from engineering data and the limit in both the data and knowledge of sediment transport and beach change. The modeling is operated through a structured and user-friendly interface so that the operator need not become familiar with detailed aspects of the computer code. This report serves as a technical reference to Version 2 of GENESIS and is also designed to be an operator's manual by providing instructions for using the interface. The method for applying the model is described from the perspective of the needs of both engineers and planners who deal with evaluate shore- protection projects. A fully documented case study involving application of the modeling system and exercise of many of its features is provided. Sweden.

A Mathematical Model of Wave Transformation over a Submerged Breakwater

Abstract: A mathematical model of wave transformation over a submerged permeable breakwater is developed on the basis of the equations for waves on a permeable bed which are newly derived under the mild-slop...

Wave overtopping on coastal structures

Abstract: Monochromatic wave overtopping over the crest of an impermeable coastal structure located on a sloping beach is predicted numerically by expanding the numerical model developed previously for predicting wave run-up on such a structure located on the horizontal seabed The expanded numerical model predicts the temporal variations of the velocity and depth of the flow over the crest of the structure from which the average overtopping rate per unit width is computed The model accounts for the effect of wave shoaling on the sloping beach in front of the structure located in relatively shallow water The computed average overtopping rates are shown to be in agreement with available small-scale test data for which smooth impermeable structures were fronted by a 1:10 slope The numerical model also predicts the decrease of wave reflection due to the increase of wave overtopping However, more detailed measurements will be required to further calibrate and evaluate the numerical model which may be extended to examine the armor stability of overtopped breakwaters

Stability of Reef Breakwaters

Abstract: This paper discusses the stability of a class of rubble mounds referred to as reef breakwaters. Reef breakwaters do not have a multilayer cross section like conventional breakwaters but are a homogenous pile of stone. Individual stone weights are similar to those used in the armor or first underlayer of traditional breakwaters. Findings are based on a study which includes an extensive series of physical model tests conducted with irregular waves. An unusual method to quantify reef stability is presented. The method is unusual because it measures stability in terms of reduction in crest height due to wave attack. Reduction in crest height has less scatter than damage measured by number of stones displaced. Such an approach directly links stability to the primary performance characteristic of wave transmission. A stability model is developed which can accurately predict damage to the reef from very minor to very severe levels. The model also works for both submerged and subaerial mounds and for a wide range of wave conditions including those with heavy overtopping.

Longshore Transport at a Detached Breakwater, Phase II

Abstract: The second phase of a field experiment conducted by the Coastal Engineering Research Center (CERC) to develop correlations between wave characteristics and longshore sediment transport is reported herein. Wave heights, periods, directions, and longshore currents were measured by visual observation 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 covers a period of seventeen months from 20 April 1976 through 30 August 1977. During this period there were twelve surveys of the sediment volume trapped behind the offshore breakwater. The correlation constant, K, in the relationship I = K P lb ( Shore Protection Manual , 1984) is tested and compared with earlier longshore sediment transport results of others as well as the Phase I data at Channel Islands reported on by BRUNO et al . (1980).

Stem waves along breakwater

Abstract: Based on Boussinesq equations and parabolic approximation, the forward diffraction of cnoidal waves by a straight breakwater is studied numerically. The formation of stem waves along the breakwater and the relation between the stem waves and the incident wave characteristics are discussed. A numerical scheme for computing uniform cnoidal waves also is presented.

Measuring Longshore Transport with Traps

Abstract: The Nearshore Sediment Transport Study (NSTS) included two total trap experiments conducted to evaluate the longshore sediment transport relationship I ( = KP (s in which I ( is the total longshore immersed weight sediment transport rate, P (s is the longshore component of wave energy flux and K is a proportionality factor which could depend on a number of wave and sediment parameters. The locations of the two experiments were at Santa Barbara, California and Rudee Inlet, Virginia. The trap characteristics for each of these two sites are quite different. The Santa Barbara trap consists of the spit formed in the lee of the Santa Barbara breakwater. At Rudee Inlet, the trap is inside of a weir-type jetty with a crest elevation at about mean sea level.

Seismic Prospecting Method Applied to the Detection of Offshore Breakwater Units Settling in the Seabed

Abstract: In solving a problem of offshore breakwater subsidence, it is important to investigate the shape of an existing breakwater whose crown hits been repeatedly raised in the past. In this context, a se...

Wave reflections in harbours: Reflection performance of rock armoured slopes in random waves

Abstract: Wave reflections from sea walls or breakwaters often cause difficulties in the navigation and/or mooring of ships, and may also cause or exacerbate toe scour or local sea bed erosion. Such erosion is a common cause of the failure of many coastal structures. Rock armoured rubble structures often provide efficient energy dissipation reducing both wave run-up levels and wave reflections. This report presents the results of a short series of hydraulic model tests on rock-armoured rubble sea wall sections under random waves. Wave reflections were measured for 9 wave conditions on structures of simple slopes of 1:1.5, 1:2.0, and 1:2-5; and 3 berm widths with upper and lower slopes of 1:1.5. The results of these measurements are presented as values of the reflection coefficient, Cr. The results may be used to predict, and/to to compare, the performance of rock armoured sea walls and breakwaters. The coefficient derived can be used to give boundary conditions for mathematical models of wave action in harbours. The work reported here has been conducted by Hydraulics Research for the British Overseas Development Administration. For further information on this-work, please contact Mr N W H Allsop, manager of the Coastal Structures Section within the Maritime Engineering Department, Hydraulics Research.

On the stability of berm breakwaters roundheads and trunk erosion of oblique waves

Abstract: The stability of a berm type breakwater (sacrificial breakwater) was tested in a 3-dimensional model at rhe Hydraulics Laboratory, Department of civil Engineering, university of Aalborg. The object was to study the stability/erosion of the breakwater head and the trunk, the latter exposed to both head-on and oblique irregular waves. To avoid too many parameters a simple breakwater geometry and only one class of stones were used.

Reef breakwater response to wave attack

Abstract: A reef breakwater is a low-crested rubble-mound breakwater without the traditional multilayer cross section. This type of breakwater, in essence, is a homogeneous pile of stone with individual stone weights similar to those used in the armour and first underlayer of conventional breakwaters. Because of their high porosity, reef breakwaters are suprisingly stable to wave attack and, at the same time, can dissipate wa ve energy effectively.

Salients Leeward of Multiple Offshore Breakwaters

Abstract: Offshore breakwaters are normally placed parallel to the shoreline with narrow gaps between segments. Whilst it is not recommended as an economical solution to coastal stabilisation, the parameters involved should be considered that can be used to predict salient or tombolo dimensions adequately. The role of wave diffraction in shoreline changes leewards of these structures is emphasized in choosing suitable dimensionless parameters.

Double-inclination type breakwater

Abstract: PURPOSE:To reduce the amount of reflected waves by a method in which the first breakwater having a sloped face against the advancing direction of waves and the second breakwater having a greater inclined angle than the first breakwater are set at an interval in the advancing direction of waves CONSTITUTION:The first breakwater 1 having a sloped face 7 against the advancing direction of waves is supported and fixed by vertical piles 9 and a slant pile 11 driven into the seabed 6 in such a way as to match their upper ends with the level of sea surface The second breakwater 2 having a greater slope than the face 7 is supported and fixed by vertical piles 14 and a slant pile 16 behind the advancing direction of waves on the breakwater 1 by projecting its upper end by 1/2 or more of a planned height of waves to be broken from the sea surface Waves can thus be dissipated by agitation and interference and the amount of reflected waves can be reduced

Physical Models of Coastal Structures As Designed and Used by the US Army Corps of Engineers

Abstract: This paper presents an overview of physical models as applied to design of coastal structures at the Coastal Engineering Research Center (CERC), of the US Army Corps of Engineers. A review of similitude laws is followed by the philosophy of two- and three-dimensional stability modeling of rubble-mound coastal structures. A brief summary of the San Juan National Historic Site breakwater and revetment stability study, conducted at CERC for the Jacksonville District of the US Army Corps of Engineers, is presented as an example of a typical physical model stability study.

Breakwater capable of intaking and discharging seawater

Abstract: PURPOSE:To contrive preservation of pollution-free water, while keeping calmness inside a harbor, by a method wherein a seawater guide passage with an inlet opened at the upper part of a breakwater wall, facing to the outside part of a harbor, is constructed inside a breakwater body to connect with an outlet prepared at the lower part of the breakwater wall, facing to the inside part of the harbor, through an intrinsic-oscillation-period regulating tank installed inside the breakwater body CONSTITUTION:At the upper part of a breakwater body 11 facing to the outside part 3 of a harbor, a seawater guide passage 13 is constructed with an inlet opened to the outside part 3 of the harbor The seawater guide passage 13 is composed of a horizontally extended ceiling 17, a bottom plane 18 being elevated toward its innermost end and converging side-walls making the passage narrower as it approaches the innermost portion An intrinsic-oscillation-period regulating tank 14 is prepared at the lower part of the innermost portion of the seawater guide passage 13 and, at the same time, the bottom of the tank 14 is connected with an outlet 16 installed at the foot of the breakwater body 11, and opened to the outside part 4 of the harbor With this device, wave dissipation can be achieved, while making it possible for the breakwater to intake and discharge seawater to and from the harbor

Optimization of Breakwater Extensions: HMAS Stirling

Abstract: A description of a numerical short wave penetration model for HMAS Stirling is presented. The purpose of the study was to provide a basis for breakwater length optimisation.

Comparison of Various Defense Measures

Abstract: Various measures to stabilise sandy coasts are discussed, these being seawalls, groynes, offshore breakwaters, perched beaches and beach renourishment. A concept called 'headland control' which applies the knowledge of shape of the crenelate shaped bays sculptured between headlands is introduced.

Solving a harbor accretion problem: the case of Miller and, Îles-de-la-Madeleine, Quebec

Abstract: This paper summarizes a group of studies regarding Millerand harbor, located on the Iles-de-la-Madeleine coast, which blocks most of the local littoral drift. The understanding and quantification of this sedimentological problem was first carried out using numerical models. Various schemes were then tested in two mobile-bed physical models. Finally, the impact of these solutions on the wave climate in the harbor and in the entrance channel was compared using a diffraction–reflection numerical model. The results show that accretion in Millerand harbor will only be controlled by the construction of a breakwater. This breakwater must close the east side of the harbor and must reach at least 2 m depth at its toe. It is also strongly recommended that two groins be built on the east-side beach to control the erosion of the cliff. The results of the diffraction–reflection model finally give some latitude to the harbor planners, as several schemes present satisfactory wave agitation maps. Key words: erosion, accr...

Hydraulic performance of berm breakwaters

Abstract: Rubble mOlJnd breakwaters have been used for centuries for the protection of harbours. In many cases breakwaters were built in relatively deep water and exposed to waves too severe in relation to the size of rock used for construction. Furthermore, they were often built with a steep slope, and consequently, severe damage occurred. In some cases, breakwaters have been repaired by a continuous supply of stones until an almost stable equilibrium slope developed. In this way, the breakwaters at Cherbourg, Plymouth and Holyhead, Refs. /2/ & /3/ were developed. At certain places in nature the same may be observed for gravel beaches, where the available material by wave and tidal action is reshaped until an almost equilibrium situation occurs. In recent years, the concept of unconventional rubble mound breakwaters, i.e. berm breakwaters, has gained much attention among researchers and engineers as an economical method to build breakwaters at certain sites. At DHI, the principle of berm breakwaters was first used in 1978 for the Skopun Breakwater Extension, Faroe Islands .

Wave Grouping and Harbour Design. Safe Underkeel Allowances for Vessels in Restricted Depths

Abstract: Random wave physical models of harbours have been employed at Hydraulics Research (HR) since the early seventies. The change from using single period waves of uniform height to wave where heights vary within groups and energy is spread over a number of periods, led to a profound reassessment of the way harbours and moored vessels respond to waves: responses occurred at wave group periods as well as at wave periods; the conventional solution of providing shelter for berths by building breakwaters was found to be ineffective in sheltering from long period disturbances with wavelengths of kilometres which arose naturally due to wave grouping; downtime at berths due to excessive vessel movement was no longer just related to the wave height at the berth and it became essential to use models of moored ships to evaluate berth tenability.

Wave Damping Effects of a Submerged Vertical Thin Barrier

Abstract: Recently submerged breakwaters have emerged as an effective measure to prevent beach erosion due to waves. In a preceding study, the authors conducted the experiments on wave transformation over a ...

Construction work of breakwater for preventing soil deposition and water swirling

Abstract: PURPOSE:To prevent the deposition of sand and swirling of water in harbor as well as keep the function of the harbor by providing an escape hole in the upper part of a breakwater base. CONSTITUTION:A breakwater base is formed on the lowest breakwater ground- improved foundation 2, and a breakwater 1 is constructed on the breakwater base. An escape hole 3 is formed across the breakwater base and the breakwater 1. The deposition of soil in the harbor can thus be reduced, and damage to the harbor by natural disaster such as shock waves, etc., can also be prevented.

The Colonial Beach, Virginia, Detached Breakwater Project

Abstract: : The Colonial Beach, Virginia segmented detached breakwater and beach fill project consists of two sites, Central and Castlewood Park Beaches, constructed in October 1982 to protect a cohesive bluff (6 to 10 ft in height) eroding at a preproject rate estimated at 1.5 ft/year. The project sites were cooperatively monitored by the US Army Engineer District, Baltimore, and the US Army Engineer Waterways Experiment Station Coastal Engineering Research Center from October 1982 through June 1985. This report presents the data collected during the monitoring program and documents the bathymetric and shoreline response to the structures. Although the water level increase due to storm conditions was not fully considered in the original design of the beach fills, the project sites have successfully prevented erosion of the beach bluff. Results from the monitoring program were used to modify the Central Beach fill elevation, eliminating inundation of the beach during storms and increasing its recreational value.

Analysis of wave-induced uplift force acting on caisson and pore-water pressure around breakwater by using poro-elastic theory

Abstract: The wave-induced pore-water pressure acting on the bottom of a caisson and around the composite breakwater is analyzed by a poro-elastic theory, Biot's consolidation theory, using a finite element method. Effects of the stiffness and permeability of a rubble mound and the rocking of the caisson are examined. The spatial distribution of uplift force mainly depends on the permeability of the rubble mound. When the permeability is large, the distribution is almost linear at any phase of standing waves in front of the caisson. However, when the permeability is small, the distribution is not linear and the profile is different at each phase of standing waves; furthermore, it is affected by the magnitude of rocking of the caisson. The rocking of the caisson increases the upward pore-water pressure gradient which seems to increase the occurrence probability of a seabed liquefaction around the toe of rubble mound as one of the causes of scouring at the toe and sinking of foundation materials.