Breakwater System Research Articles

Reversed responses within a segmented detached breakwater, the Tuscany coast Italy—a case study

A multiple detached breakwater system was designed to protect an extended length of shoreline in front of the presidential villa located in the Gombo region, Tuscany, Italy. The purpose of this empirical field study was to examine the impact of the surface-piercing segmented breakwater on the subaqueous morphology and to follow the effect of the breakwaters on the beach. Shoreline mapping was performed on rectified, stereo-plotted air photos and was also based on topographic field surveying. Bathymetric mapping was based on interpolation of profile lines extending to 10 m water depth. Building the breakwaters in a downstream order caused the trapping of the longshore-driven sediments mainly at the southernmost breakwaters that faced the longshore sediment supply. The longshore down-current direction controlled the hierarchy of the beach response. Two relatively coherent behavioral domains were found to exist: (1) the “permanent tombolo stage” of segments 1–3 and (2) the “no sinuosity” response of the beach opposite the northern segment no. 5. The segment no.4, in-between, did not exhibit a coherent behaviour, indicating a drastic reversal in the sedimentary regime. The three southernmost tombolos facing the longshore current became the main sediment trap, causing a lee-side erosional effect to emerge within the protection scheme of the segmented detached breakwaters. The oblique incident waves enter through the gaps and maintain in the inshore the depleted longshore drift, causing the shoreline configuration in the lee of the northern breakwaters to develop into a prograding log-spiral bay.

Field and numerical comparisons of the RIBS floating breakwater

A new concept in floating breakwaters was successfully field-tested offshore Cape Canaveral, FL in May 1999. The Rapidly Installed Breakwater System (RIBS) has a hybrid design of rigid and membrane components, similar to a ‘Venetian blind’, to permit rapid and expedient deployment. The objective of the RIBS is to reduce Sea State 3 (SS3) wave conditions to Sea State 2 for safe vessel operations. This field study was probably one of the most heavily instrumented floating breakwaters ever deployed. Measured wave transmission coefficients and dynamic wave pressures are compared to two different numerical models. This is the first verification of the numerical model WAMIT with field data.

Wave motion over a breakwater system of a horizontal plate and a vertical porous wall

A two-dimensional analytical solution is presented to study the reflection and transmission of linear water waves propagating past a submerged horizontal plate and through a vertical porous wall. The velocity potential in each fluid domain is formulated using three sets of orthogonal eigenfunctions and the unknown coefficients are determined from the matching conditions. Wave elevations and hydrodynamic forces acting on the porous wall are computed. Reflection and transmission coefficients are presented to examine the performance of the breakwater system. The present analytical solutions are found in fairly good agreement with the available laboratory data. The results indicate that the plate length, the porous-effect, the gap between plate and porous wall, and the submerged depth of the plate all show a significant influence on the reflected and transmitted wave fields. It is also interesting to note that the submerged plate plays an important role in reducing the transmitted wave height, especially for long incident waves.

EFFECT OF BREAKWATER FOR EXCANGE OF SEAWATER AT KONOURA FISHING PORT IN AKETA PREFECTURE

The breakwater with hole for exchange of seawater is being constructed at Konoura fishing port in Akita prefecture. The system of this breakwater is intending to take outside seawater through the hole by differential water pressure which made by breaking wave compulsory at underwater bound It was designed to apply low wave height during summer season in order to get required seawater quantity effective way. As the breakwater has completed partially, the field investigation was conducted to consider effect of the breakwater system. This paper is stating the design method, field investigation and the result of the system for breakwater with hole.

A Spatial–Temporal Analysis of the Development of a Log-spiral Shaped Embayment

With the use of semi-annual data collected from May 1985 to May 1995, this study assesses the evolution of a log-spiral shaped embayment at the Northeast Beach, located at Canada's southernmost promontory. The emplacement of stone breakwaters initiated scour of the shoreline, and the embayment which developed thereafter adjusted to reflect changes in lake levels, and naturally occurring variance in wave and sediment dynamics. Each of the 21 recorded measurements of the embayment configuration is assessed for characteristics of log-spiral morphology. The results demonstrate that logarithmic-spiral curves fit the 21 recorded embayment configurations very closely. The significant parameters and statistics associated with each log-spiral curve show that no heteroschedacity of variance is present among the residuals and only one significant autocorrelation is observed. The appropriateness of the log-spiral fits is verified by the coefficients of determination which, with the exception of the November 1988 dataset, are all over the required value of 0·98. Both the spiral angle and the radius show decreasing trends through time, and the graphical plots illustrate only minor fluctuations after May 1991. These results suggest that the embayment may have shifted from some form of quasi-equilibrium condition to approach a state of dynamic equilibrium. The persistence of the logarithmic-spiral configuration through time supports the findings of other investigators who claim that the log-spiral planform represents the equilibrium embayment shape that might be expected on the flank of a breakwater system. © 1997 John Wiley & Sons, Ltd.

DESIGN OF DETACHED SUBMERGED BREAKWATER TO IMPROVE HABITAT ENVIRONMENT OF BIVALVES

The author proposes a design method of a detached submerged breakwater system to improve the habitat environment of Spisula sachalinensis (Japanese surf clam), which is one of the most expensive bivalves in Japan. According to the recent investigations, a general description of the ecological condition of the bivalve is given, in which a hydrodynamic explanation on the phenomena of the winter casting-up of Spisula sachalinensis due to waves is also given. Then a general design method of a detached submerged breakwater system, which is suited to the propagation of thekind of bivalves, is shown. Wave force on cover stones through sea weeds, such as Eisenia bicyclis and Ecklonia cava, is made clear as well on the basis of wave flume experiments.

Oblique wave diffraction by segmented offshore breakwaters

This paper presents a theoretical model to examine oblique wave diffraction by a detached breakwater system consisting of an infinite row of regularly-spaced thin, impermeable structures located in water of uniform depth. The fluid is assumed incompressible and inviscid and to undergo irrotational motion. Wave heights are assumed to be sufficiently small such that linear wave theory is applicable. The eigenfunction expansion solution of Dalrymple and Martin (1990) for normal wave incidence on this breakwater geometry is modified herein to study oblique wave effects. Numerical results, in the form of contour maps of the relative wave height behind the structure, or complex reflection coefficients, are presented for a range of wave and breakwater parameters. The accuracy of the present model is verified by a comparison with existing results for the limiting cases of an isolated detached breakwater, and a breakwater with a single gap. Also, for the multi-gap breakwater, the present solution is further verified for both normal and oblique wave incidence with results in the open literature.

A Study on the Hydroelastic Response of Very Large Floating Structure with Floating Breakwater in Waves

In recent years, the use of very large floating structures in the seafront areas for various infrastructure facilities such as a floating airport is becoming more popular and important. For such a huge floating structure like an airport, the elastic deformations due to the dynamic effects of waves cannot be neglected in comparison with the motion as rigid body, because it has a very small vertical dimension compared to its longitudinal and lateral dimensions.A linearized analysis of the motions of a very large floating structure with floating breakwater is presented in this paper. The hydroelastic interactions of the elastic deformations and the hydrodynamic forces are discussed. Present predictions are compared with the avail results based on the other method and experimental data. The influences of some parameters (bending rigidity and water depth) to the motion responses have been investigated by the present method.For the floating airport, it is imperative that investigations on the effectiveness of floating breakwater and rigidity of the floating airport to decide and understand its sea worthiness. In the present mathematical model, the hydrodynamic interactions between the floating airport and the floating breakwater are considered. The effectiveness of the floating breakwater (including the multiple floating breakwater) as the protection of the floating airport is investigated. According to sea condition and design criteria, many parameters related to floating breakwater system can be discussed by the proposed method.

Oblique-Wave Diffraction by Noncollinear Segmented Offshore Breakwaters

A theoretical solution is presented for oblique-wave diffraction by a segmented offshore breakwater system consisting of an infinite array of equally spaced vertical barriers oriented at an arbitrary angle to the line joining their centers. The solution is obtained by a Green's function approach. The geometrical periodicity of the breakwater system reduces the problem to that of a singular integral equation for the potential difference across a single breakwater element. Zero-order reflection and transmission coefficients are defined in terms of the amplitudes of the asymptotic (propagating) diffracted waves traveling in the opposite direction to or the same direction as the incident waves, respectively. Numerical values of these coefficients are presented for a range of angles of wave incidence and breakwater orientation, for various breakwater geometric configurations. For certain parameter combinations, significant wave reflection can be achieved using this type of breakwater system.

Equilibrium Shoreline Response to Breakwaters

An empirical analysis of the shoreline response to both single and multiple detached breakwaters is presented. In the analysis, equilibrium conditions are assumed. The analysis is based, in part, on previously published experimental data, which are also the basis of a previous study of equilibrium shoreline response to breakwaters. The current analysis differs from the previous analysis in several ways: (1) The effects of wave steepness and beach slope are included; (2) waves are allowed to approach from any direction in deep water; and (3) the effects of segmented breakwaters can be analyzed. Neither analysis includes the effects of grain size. The current analysis can be used to predict the formation of tombolos and salients, and to predict the maximum shoreline retreat or shoreline advance. To demonstrate the utility of the analysis, the shoreline response to the 11‐unit breakwater system at Bay Ridge, Md., is predicted. The predicted and actual shorelines are shown to be in good agreement.

Numerical Simulation of Shoreline Change at Lorain, Ohio

Design of detached breakwaters for shore protection is difficult because the response of the shoreline to these structures is governed by at least 14 geometric‐, wave‐, and sediment‐related variables. Numerical models of shoreline change have the potential of incorporating these variables to predict the time evolution of the beach plan shape; however, wave transmission at breakwaters has been a major process absent from such models. In this paper, a pragmatic method of calculating the breaking‐wave height and angle under combined transmission, diffraction, refraction, and shoaling is tested to predict shoreline change measured at Lorain, Ohio, the site of a three‐segment transmissive breakwater system. The model successfully simulated observed shoreline change at the site that occurred over three time periods ranging from one to five years. Model sensitivity to changes in key parameters and simulations of alternative shore‐protection designs to the Lorain project are also described.

WAVE INTERCEPTION BY SEA-BALLOON BREAKWATER

When a submerged, flexible bag is filled with air about 60~T0 % of its full volume ( it is called " sea-balloon " ), it has a stable shape with vertical axis of symmetry, on which several vertical wrinkles appear with folds of membrane. If two or more such sea-balloons are arranged to the direction of wave travel and connected pneumatically, balloons are deformed periodically and the air flows reciprocally in connecting pipe, following to the fluid pressure fluctuation due to incident waves. Such a system of sea-balloon intercepts incident waves effectively ( it is called " sea-balloon breakwater "). The wave interception by the breakwater is analyzed numerically by three-dimensional boundary integral method, assuming that the fluid motions both in- and out-side of the balloon are potential and that the tension in balloon membrane is proportional to the apparent elongation of membrane with virtual elastic constant. After analysis and experiments, it is made clear that in relatively long waves the incident wave is canceled by the radiation wave which is generated by volumetric change of sea-balloons, being affected by airflow resistance in connecting pipe. In short waves, sea-balloons seem to behave like as rigid piles and the incident wave is absorbed by airflow resistance in pipe and by the turbulence of fluid motion around balloons. Moreover, the effect of gaps between sea-balloons along wave crest on wave interception for relatively long waves is expressed by a simple empirical formula, by which the transmission coefficients at various types of sea-balloon breakwater is easily estimated by twodimensional computation. For the improvement of wave interception effect and from the point of practical use, the effects of other sea-balloon breakwater system are investigated by two-dimensional computation and experiments.

Sediment transport and morphology at the surf zone of Presque Isle, Lake Erie, Pennsylvania

A four-year investigation of surf zone sedimentation at Presque Isle, Pennsylvania, was undertaken in preparation for the design of a segmented breakwater system. Sediment transport calculations were based on hind-cast annual wave power statistics and “calibrated” by known accretion rates at the downdrift spit terminus. 30,000 m 3 of sediment reaches the peninsula annually from updrift beaches. The transport volume increases downdrift due to shoreface erosion and retreat of the peninsular neck. At the most exposed point on Presque Isle (the lighthouse) the annual transport is 209,000 m 3. East of the lighthouse is a zone of net shoreface accretion as the longshore transport rate progressively decreases. The downdrift variation in sediment supply, combined with increasing refraction and attenuation of the dominant westerly storm waves produce a systematic change in prevailing surf zone morphology. Storms produce a major longshore bar and trough along the exposed peninsular neck. The wave energy during non-storm periods is too low to significantly alter the bar which consequently becomes a permanent feature. The broad shoreface and reduced wave energy level east of the lighthouse produce a morphology characterized by large crescentic outer bars, transverse bars, and megacusps along the beach. At the sheltered and rapidly prograding eastern spit terminus the prevalent beach morphology is that of a ridge and runnel system in front of a megacuspate shore. The morphodynamic surf zone model developed for oceanic beaches in Australia is used as a basis for interpretation of shoreface morphologic variability at Presque Isle. In spite of interference by major shoreline stabilization structures, and differences between oceanic and lake wave spectra, the nearshore bar field at Presque Isle does closely correspond to the Australian model.

Laboratory study on the shoreline changes behind a coastal structure

This study investigates the effects the presence of an airport to be constructed offshore of the Sennan Coast will have on the coastal process, using hydraulic model tests. The consideration of the study area suggested the use of a scaled model, since natural sand was used as bed material in the tests. The wave height to be dealt with in the tests was determined in preliminary tests to satisfy the similitude relation. The ratio of the longshore transport rate in the model to that in nature, obtained by the energy flux method, gave a time-scale. To simulate the wave condition in the model tests to that in nature, two different wave directions were used and the duration of each wave direction was determined based on the time-scale. The positions and the rates of erosion and deposition expected to occur in the future in the presence of the airport were estimated by using the time-scale. Finally, to protect the shore from erosion a combined system of groins and offshore breakwaters was found from the results.

Performance Analysis of Tethered Float Breakwater

Describes laboratory experiments at one-half scale using simulated random seas and field tests at full scale of an installation of a dynamic floating breakwater system in a limited fetch situation. An analytical model is described which successfully predicted the performance of a tethered float breakwater configuration, given the incident wave spectrum. The methodology for selecting the arbitrary resistance coefficients in the predictive model is considered. Predicted and measured performance data for a total of 60 laboratory and field experiments are displayed, covering a very broad range of wave climates.

COASTAL STRUCTURES' EFFECTS ON SHORELINES

Coastal structures have caused significant impacts to adjacent shorelines, especially when these shorelines are composed of sand. Many times, these shoreline impacts have not been expected due to improper planning prior to the design and construction of these structures. Consequently, excessive erosion and/or deposition of sediment as a result of these structures has necessitated costly, and in some cases, continuous maintenance operations. This paper reviews the expected shoreline effects for an offshore pier-trestle and breakwater system for an LNG marine terminal. Coastal structures originally proposed for the LNG marine terminal consisted of a 4,600-foot-long pile supported "T" head pier/trestle system and a 1,000- foot-long detached rubble-mound breakwater. This investigation involved field and historical aerial photographic examination of 30 structures in the Southern California Bight and a literature review of similar structures in other environments. Also, a review of theoretical and physical model studies applicable to structures within the coastal marine environment was conducted. The results of this investigation of existing structures, in conjunction with theory and model studies, indicate that within the study region, pile-supported piers have no appreciable impact of £he adjacent shoreline. This investigation also indicates that detached breakwaters produce only minimal impact when the offshore distance of the structure is greater than six times the breakwater length. Of course, consideration was also given to the structure's position relative to the littoral zone, to the depth of water at the shoreward face of the structure, and to the wave climate approaching the structure. This study included a review of such factors as the local topography, nearshore bathymetry, beach processes, shoreline configuration, beach materials, range of water levels, and local wave climate. The controlling parameters identified in this study are discussed, and the final recommendations presented. This paper illustrates the importance of proper advance shoreline planning before the final design and construction of shoreline facilities.

FIELD AND MODEL STUDIES FOR VISAKHAPATNAM HARBOR

Model studies and analysis of oceanographic and littoral drift data were undertaken to advise Howe India (Private) Ltd. on littoral drift, siltation and shore erosion problems to be encountered during and after the construction of Visakhapatnam Outer Harbor Project. Distorted fixed-bed and movable-bed models with a horizontal scale of 1:300 and a vertical scale of 1:80 were calibrated to reproduce the integrated net effect of an average southwest and northeast monsoon season. Experiments were conducted to assess and predict seasonal changes resulting from the construction of the system of breakwaters under normal and extreme conditions. Recommendations were made concerning breakwater and sand trap location, shore protection, dredging and disposal of dredged material.

DESIGN OF A DETACHED BREAKWATER SYSTEM

Beach erosion is one of the serious problem in Japan. As a countermeasure against beach erosion, many preventive works, such as sea walls and groins, have been constructed during the past 20 or more years. However, as the result of field investigations, it has become clear that sea walls and groins are not always effective on beach erosion prevention, and inversely, in some cases, they accelerate the beach erosion. Based on the above cognition, the author has proposed and tried to apply the detached breakwater system as a measure against beach erosion for the last 8 years. This is for the purpose of developing the sand deposition behind the breakwater. Therefore several experimental works of the detached breakwater system were carried out under the guidance of the present author, and most of these tests were successful. The design method of this system was composed by the author on the basis of the result of field investigations, which have been conducted for more than 8 years. The numerous construction works of detached breakwaters have been carried out in accordance with the design method proposed in this paper, and the effectiveness of detached breakwaters has been proved on the several coasts in Japan where severe beach erosion occurs.

The fish grazing of rocky shore algae in the Gulf of Guinea

There is a conspicuous absence of large algae on five breakwater systems surveyed along the northern shore of the Gulf of Guinea. Such algae are a distinctive feature of most natural, rocky areas in the region and their absence on these artificial structures may be accounted for by heavy sedimentation and pollution inside the harbours, and as a result of fish grazing on the outside. Herbivorous pomacentrids ( Abudefduf, Pomacentrus), parrot fish ( Pseudoscarus) and surgeon fish ( Acanthurus) are common along parts of the breakwaters sheltered from direct wave action. Preliminary experiments and observations show the importance of fish grazing and indicate diurnal differences in its intensity. The ‘broken-up’ nature of the breakwaters with moderate wave action is the probable reason for the occurrence of large fish populations and hence the presence largely of grazing-tolerant algae.

Methods Of Optimum Shaping Of Port Entrance

The shape of port entrance (a system of breakwaters) should meet two basic requirements: be safe to the vessels lying in the port. be safe to the vessels entering and leaving the port. The problem has been solved by the author by means of simulation methods of optimization. In the methods, the objective function is to minimize the costs of constructing and operating the port entrance. The simulation tests are carried out for maximum vessels expected to be operated in a given port in various hydrometeorological conditions prevailing there. The paper presents the methods illustrated with real solutions for the entrances to the ports of Kolobrzeg, Leba and Darlowo. These port entrances (their improvement) have been designed by means of the presented simulation method of optimization and are. at present, at different stages of reconstruction. 1 Parameter optimization of port entrance On the basis of the general model assumptions for optimization of waterway parameters using simulation methods [1], the objective function of parameter optimization of port entrance can be presented as follows: Z( a k + b t + c r + d-l )-* min (1)