Showing papers on "Breakwater published in 2007"

Irregular breaking wave transmission over submerged porous breakwater

Abstract: A numerical model based on time-averaged continuity, momentum, and energy equations is developed to predict the mean and standard deviation of the free surface elevation and horizontal fluid velocities above and inside a porous submerged breakwater. The energy dissipation rate due to irregular breaking waves is estimated using an existing formula that is modified for intense wave breaking on the steep seaward slope of the breakwater. This computationally efficient numerical model is an extension of the existing time-averaged model which is widely used to predict irregular breaking wave transformation on impermeable beaches. The developed model is shown to predict the cross-shore variations of the mean and standard deviation of the free surface elevation measured in a laboratory experiment where a submerged porous breakwater was placed on a gentle impermeable slope. The agreement for the measured horizontal velocity is marginal partly because this one-dimensional model does not predict the vertical velocity variation. This semiempirical model calibrated using the present experiment will need to be compared with additional experiments.

Performance Characteristics of Horizontal Interlaced Multilayer Moored Floating Pipe Breakwater

Abstract: The paper presents the results of model scale experiments for the study of wave attenuation by horizontal interlaced, multilayer, moored floating pipe breakwater. A review of some significant floating breakwater models proposed by earlier investigators is included. For a floating breakwater the transmission coefficient ( Kt ) is influenced by relative width of the breakwater (W∕L) . Nondimensional graphs indicating the variation of Kt with respect to W∕L (with Hi ∕L as a parameter for different Hi ∕d values) and Kt versus Hi ∕L (for a range of d∕L values from 0.09 to 0.24) have been plotted. Further variation of Kt with relative depth d∕L for different W∕L values is also studied. From the experimental study and results obtained, it is found that the transmission coefficient decreases with an increase in relative breakwater width W∕L and wave steepness Hi ∕L for all Hi ∕d values. In the present study it was observed that performance was better for breakwater configurations of W∕L⩾0.7 when compared with con...

Small-Scale Field Experiment on a Submerged Breakwater for Absorbing Wave Energy

Abstract: This technical note shows some results of a small-scale field experiment on Boccotti’s submerged caisson breakwater, which absorbs wave energy and is able to defend a coast with a very small environmental impact. The experiment on the 1:10 scale model of a caisson of this breakwater was carried out on a 2.6-m -deep seabed. All the records of the experiment confirm that it is possible to obtain a strong natural resonance between the random process of wave pressure at the outer opening of the caisson and the random process of oscillations inside the caisson. Finally, a test of the computational algorithm is given by means of the output of the field experiment, and a procedure for tuning the plant is also given.

Data Report: Laboratory Testing of Longshore Sand Transport by Waves and Currents; Morphology Change Behind Headland Structures

Abstract: : Data from five series of movable bed laboratory experiments are presented in this report. These experiments were conducted in the Large-scale Sediment Transport Facility at the U.S. Army Engineer Research and Development Center, Vicksburg, MS. The data collected from these experiments is being used to improve longshore sand transport relationships under the combined influence of waves and currents and the enhancement of predictive numerical models of beach morphology evolution, in particular, with respect to modeling of tombolo development at detached breakwaters and T-groins. These data were instrumental in the development and validation of GENESIS-T, an enhanced version of GENESIS that allows for continued simulation of shoreline evolution after tombolo formation at detached breakwaters.

A comparison of overtopping performance of different rubble mound breakwater armour

Abstract: This paper describes a major programme of tests to establish better the influence of armour roughness and permeability on overtopping. Specifically, the tests determined the relative difference in overtopping behaviour for various types of armour units. Roughness factors γf for the database and for use in the neural network prediction of overtopping were determined for rock (two layers), cubes (single-layer and two-layers), Tetrapod, Antifer, Haro, Accropode, Core-Loc and Xbloc.

Shoreline response to detached breakwaters and tidal current : comparison of mumerical and physical models

Abstract: Shoreline response behind a detached breakwater and at a T-head groin observed in a large-scale physical model was validated with an updated GENESIS model A new total load longshore sediment transport rate formula, introduced in this paper, was developed and incorporated in GENESIS to address engineering predictive requirements at coastal inlets The relationship represents the contribution from obliquely incident breaking waves, their gradient alongshore, and external non-wave induced currents, such as the longshore components of a tidal current or wind-induced current The principle of superposition of current components in the transport relationship is validated against transport rate measurements from physical model tests at the Large-Scale Sediment Transport Facility of the US Army Engineer Research and Development Center (Less)

Improvement in Calculation of Resistance Force on Caisson Sliding Due to Tilting

Abstract: The aim of the present paper is to investigate the long-term deformations of the rubble mound of a breakwater during its working life. Understanding these deformations is essential for the sliding ...

Dynamic Numerical Simulation of Medium-term Coastal Evolution of the West Coast of Portugal

Abstract: SILVA, R., COELHO, C., VELOSO-GOMES, F. AND TAVEIRA-PINTO, F., 2007. Dynamic numerical simulation of medium term coastal evolution of the West Coast of Portugal. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 263 – 267. Gold Coast, Australia, ISSN 0749.0208 Coastal erosion is a common problem within Europe. The main causes of this phenomenon are the generalised sea-level rise, the coastal interventions (defence and harbour structures), which cause serious perturbations in the littoral drift system, the littoral occupation and the river sediment supply reduction caused by dams, dredging and fluvial regularisation. Numerical models are helpful tools in future planning and management of coastal policies, by allowing the projection and analysis of different scenarios of medium term coastal evolution. A numerical coastline evolution model (LTC – Long Term Configuration) is being developed to support coastal zone planning and management in relation to erosion problems. The model simulates the dynamic variability of sandy beaches, where the alongshore sediment transport is controlled by waves, currents, wind, water level, sediments’ sources and sinks and sediments’ properties. The model also simulates different coastal interventions (groins and breakwaters, longitudinal revetments, artificial nourishments, river sediments supply). It may be applied to extensive coastal areas up to one hundred years time scale. In this paper, LTC will be used in the evaluation of the relative importance of each of the identified causes of coastal erosion at the Northwest Portuguese coast at a medium term horizon. Special attention will be given to the discussion of common coastal defence interventions influence in the littoral drift system and impact in what concerns erosion.

A brief overview of plan-shape disequilibrium in embayed beaches: Tangier bay (Morocco)

Abstract: Embayed beaches commonly exhibit long-term equilibrium plan shape configurations that reflect either swash-alignment or drift-alignment (Davies, 1980) relative to the wave field, involving, respectively, virtually no longshore drift, and a balanced longshore drift over space and time. Within the context of an overall sediment budget in equilibrium, imbalances in longshore drift in embayed beaches are essentially generated by medium-term (order of several years) wave modifications in the incident wave field due to: (1) cyclic changes in deepwater wave approach directions caused by climatic oscillations; (2) human constructions, notably port breakwater structures. The latter type of engineered modification is perfectly exemplified by Tangier Bay. The beach in the eastern part of this bay has been steadily eroding over the past 50 years as a result of important port development in the western end of the bay that has perturbed waves from the Atlantic, generating, in particular, destabilization of a hitherto equilibrium drift-aligned system. The long-term resolution of problems generated by such perturbations requires a clear integrated management approach.

Beach Morphology Behind Single Impermeable Submerged Breakwater Under Obliquely Incident Waves

Abstract: Small-scale physical model tests were conducted to investigate the morphodynamics of a sandy beach of uniform grain size in the lee of single impermeable submerged breakwater under oblique incident...

Analytical Research on Wave Diffraction on Arc-Shaped Bottom-Mounted Perforated Breakwaters

Abstract: An analytical method is developed to study wave diffraction on arc-shaped and bottom-mounted perforated breakwaters. The breakwater is assumed to be rigid, thin, vertical, immovable and located in water of constant depth. The fluid domain is divided into two regions by imaginary interface. The velocity potential in each region is expanded by eigenfunctions. By satisfying the continuity of pressure and normal velocity across the imaginary fluid interface, a set of linear algebraic equations can be obtained to determine the unknown coefficients of eigenfunctions. Numerical results, in the form of contour maps of the relative wave amplitude around the breakwater, are presented for a range of wave and breakwater parameters. Results show that the wave diffraction on the arc-shaped and bottom-mounted perforated breakwater is related to the incident wavelength and the porosity of the breakwater. The porosity of the perforated breakwater may have great effect on the diffracted field.

An experimental study of wave forces on vertical breakwater

Abstract: In this study, a series of hydraulic model tests with regular/irregular waves was carried out in a wave flume to investigate the wave forces acting on a composite-type breakwater. Waves in front of the breakwater, wave pressures on the vertical wall and at the bottom of caisson were measured simultaneously. The maximum horizontal force and uplift force were calculated and compared with Goda's wave force theories. The results had shown that Goda's theories offer higher safety factor. However, the measured uplift force was smaller than Goda's and nonzero at the land-side end of the bottom which might be caused by the path of water flow in the porous media beneath the caisson. It also shows that the results from different irregular wave train with the same spectrum are different, and thus the effectiveness of conventional irregular wave tests with several repeats of the same wave train should be reconfirmed.

The effects of porosity of submerged breakwater structures on non-breaking wave transformations

Abstract: Development of an innovative porous submerged breakwater structure which could be used for the purpose of coastal restoration is underway in the Coastal & Offshore Engineering Institute’s research laboratory. Prior to developing the structure, laboratory investigations on models (typifying porous submerged breakwater structures) that could provide experimental information of the influence of porosity on non-breaking wave transformations have been undertaken. A series of tests to study the effect of porosity of submerged breakwater model structures on the process of non-breaking wave transformations have been carried out. A hollow framework-shaped test model was used. Three models each with three different porosities ranging from 0.40 to 0.80 were constructed. From laboratory tests, results obtained have been analysed to check the performance of the models to attenuate waves. Test results have indicated that the transmission coefficient, KT increased with increasing model porosity. The wave reflection coefficient, KR of the model tested ranged from 0.01 to 0.31. Energy loss of the primary waves was found to be highest when the parameter kd was equal to 1.9 and lowest when the porosity of the model was found to be large.

Erosion problems in Alexandroupolis coastline, North-Eastern Greece

Abstract: This paper deals with the coastal erosion processes and the related problems around the city of Alexandroupolis, NE Aegean Sea, N. Greece. The area is very fast developing, as the city is an important port and a summer resort center in SE Balkans, and will become soon a transportation and energy center, as well. The coastline under study exhibits an east–west orientation and has a length of more than 50 km. The spatial distribution and the characteristics of the changes in the shoreline were studied by comparing old and new air photographs and topographic maps, as well as through repeated series of field observations and local measurements regarding the erosion process. From these studies it was concluded that the greater stretch of the western part of the coast, under consideration, is of moderate to high relief, with a considerable participation of coastal cliffs. It consists of conglomerates of varying granulometry and consistency and is under moderate to severe erosion process. The erosion phenomena in the western part of the coast may be attributed, primarily, to strong S, SW winds, blowing in the area and to trapping of sediments by Alexandroupolis’ port breakwaters; the port stops or/and diverts the sediments to the open sea; and to the east to west longshore sea current, prevailing in the area. The eastern stretch of the coast is a plain area, formed by sandy–silty sediments; being a part of the river Evros’ Delta, it is under deposition and accretes seawards. The majority of the coasts under consideration are classified as coasts of high wave energy potential. Hard structures, as shore protection measures, have been constructed in some places, but they were proved, in rather short time-period, ineffective and suffered extensive failures. Thus, it is argued that for a long-term cost-effective tackling of the various erosion problems on any stretch, priority must be given to soft engineering measures; although, certain hard measures, carefully selected and locally implemented, can contribute to forming a rational combination of protection/mitigation measures. Besides, the development pressures in the coastal zone have to be confronted, in a sustainable way, through new integrated coast management regulations.

Scattering of Surface and Internal Waves by Rectangular Dikes

Abstract: The scattering of surface and internal waves by a single dike or a pair of identical dikes in a two-layer fluid is analyzed in two dimensions within the context of linearized theory of water waves. The dikes are approximated as cylinders of rectangular geometry and are placed in a two-layer fluid of finite depth. In the study, both the cases of surface-piercing and bottom-standing dikes are considered. The solution of the associated boundary value problem is derived by a matched eigenfunction expansion method. Because of the flow discontinuity at the interface, the eigenfunctions involved have an integrable singularity at the interface and the orthonormal relation used in the present analysis is a generalization of the classical one corresponding to a single-layer fluid. The reflection coefficients and force amplitudes are computed and analyzed in various cases. The computed results in a two-layer fluid are compared with those existing in the literature for a single-layer fluid. The results obtained by the matched eigenfunction expansion method are compared with that of wide-spacing approximation method, and it is observed that the results from both the methods are in good agreement when the dikes are widely spaced. The general behavior of reflection coefficients for interface-piercing and non-interface-piercing obstacles is found to be different in both cases of surface-piercing and bottom-standing dikes. Moreover, for surface-piercing dikes, the results show the possibility of very large resonant motions between the dikes but with a very narrow bandwidth for the frequency of interest. DOI: 10.1115/1.2786473 Floating and submerged structures are generally used to reduce the transmitted wave height and protect various types of coastal structures from a high wave attack in the downstream of wave motion. In recent years, there is a significant interest in the use of partial breakwaters to attenuate the wave energy. Most of these breakwaters are extended from the bottom up to the water surface, while partial breakwaters only occupy a segment of the whole water depth. In coastal engineering, partial barriers as breakwaters are more economical and sometimes more appropriate for engineering applications. These kinds of breakwaters also provide a less expensive means to protect beaches exposed to waves of small or moderate amplitudes and to reduce the wave amplitude at resonance. A bottom-standing partial breakwater not only resists the wave propagation but also allows the navigation of vessels over it. The bottom-standing breakwaters are being used for fish farming in coastal fishery. These breakwaters create a calm region in the downstream of the wave motion and act as a sheltered region for a large group of marine habitats during severe wave conditions. Moreover, with the environmental concerns, the bottom-standing breakwater resists the sediment transport and provides a strong protection against coastal erosion. On the other

Impact of Coastal Erosion and Sedimentation along the Northern Coast of Sinai Peninsula

Abstract: Coastal engineering activities during the past five decades have resulted in considerable shoreline change along the northern coast of Sinai Peninsula. In the west of El Arish Power Plant, sediment accretion has reached the tip of the breakwater of the cooling water intake basin necessitating extensive dredging inside the basin. In the east of El Arish Harbor, the shoreline is continuously retreating. Previous activities to mitigate the erosion have not succeeded. For example, the groin field in the east of the El Arish Harbor has transferred the problem to the neighboring beaches farther downcoast. In this study predominant coastal processes affecting the erosion of the Sinai northern coastline were investigated. Wave-induced longshore currents were found to be responsible for transporting the littoral drift along the coastline. Longshore sediment transport, from Port Said to Ashqelon, was quantified and the general patterns of erosion-accretion were determined by looking upon the gradients between transport rates along the coast. Particular emphasis was placed on shoreline change due to perturbations introduced by infrastructure sited at the coastline near El Arish. The shoreline change at El Arish Power Plant and Harbor were modeled using the coastal evolution model GENESIS. Having understood the coastal processes driving the shoreline change at these two locations, appropriate remedial measures were proposed to mitigate the problem. In this regard, a combination of hard and soft coastal engineering methods are presented to alleviate the dredging problem at the power plant while sand-bypassing/beach-nourishment is suggested as an effective sustainable solution to the erosion problem in the east of El Arish Harbor.

Wave Transformation between Submerged Breakwater and Seawall

Abstract: This paper investigated numerically the wave transformation and the wave set-up between a submerged permeable breakwater and a seawall. The modified time-dependent mild-slope equations which involve parameters of the porous medium are adopted to compute the wave height transformation and the mean water level evolution. The numerical solutions are first verified with the experimental data. The computed results show that the modulations of the wave height and the wave set-up are clearly observed between the submerged breakwater and the seawall. The wave node can be found between the submerged breakwater and the seawall. The higher wave set-up can be found if the node or pseudo-node of wave height appeared near the submerged breakwater. The influence of the porous material characteristics of the submerged permeable breakwater on the wave transformation and set-up are also discussed in the paper.

Effect of Short-Crestedness and Obliquity on Non-Breaking and Breaking Wave Forces Applied to Vertical Caisson Breakwaters

Abstract: This paper addresses wave forces applied to vertical caisson breakwaters. Design diagrams are proposed to evaluate the reduction of the wave force induced by breaking and non-breaking short-crested...

Stability analysis of rubble mound breakwater using ann

Abstract: The stability analysis of coastal structure is very important because it involves many design parameters to be considered for the safe and economical design of structure. In the present study neural network technique is adopted to predict the stability number and damage levels of rubble mound breakwater. Four network models were constructed based on the input parameters, which affect the stability of breakwater. A good correlation is obtained between network predicted stability number and estimated ones.