Breakwater System Research Articles

FLOATING BREAKWATERS AS PUBLIC PLATFORMS – IMPACT ON POSTURAL STABILITY

Floating Breakwaters are used extensively to provide cost effective protection from wind and vessel waves. Floating breakwaters are commonly multitasked, being used as a point of mooring for vessels or simply an access way to other pontoons in a small boat harbour, as well as their main function as wave dissipators. A floating breakwater does not completely stop the incident wave; rather it partially transmits, partially reflects and partially dissipates the wave energy. Cox et al (2007) completed wave flume testing of a number of floating breakwaters and reported on performance in irregular waves with particular emphasis on wave transmission and reflection, energy dissipation and restraining forces. Motion measurements were limited by the instrumentation. This paper discusses the results from a further series of laboratory experiments on the dynamic motions of an active floating breakwater system. The performance is related to wave attenuation, wave reflection and energy dissipation as well as safety considerations for standing persons based on high resolution measurements of accelerations in all six degrees of freedom.

LIVING BREAKWATERS: DESIGNING FOR RESILIENCY

In the aftermath of Hurricane Sandy, the Rebuild by Design competition was born to encourage cross-disciplinary collaboration and resilience planning in coastal and flood protection design. The Living Breakwaters project is a layered resilience approach to promote risk reduction, enhance ecosystems, and foster social resilience. Following the competition, the project was awarded $60 million by HUD (US Department of Housing and Urban Development) in June 2013. It is currently in final design and permitting with construction anticipated to begin the summer of 2019. The Living Breakwaters Project is a unique design of an offshore breakwater system to promote coastal resilience in Tottenville, Staten Island, New York. It combines physical risk reduction through wave attenuation and erosion prevention functions with ecological enhancement and habitat creation as an integrated part of the design. This paper explores the modeling and design of these unique coastal engineering and ecological structures.

Analytical Model of Wave Loads and Motion Responses for a Floating Breakwater System with Attached Dual Porous Side Walls

A set of two-dimensional analytical solutions considering the effects of diffraction and radiation are presented in this study to investigate the hydrodynamic interaction between an incident linear wave and a proposed floating breakwater system consisting of a rectangular-shaped body and two attached vertical side porous walls in an infinite fluid domain with finite water depth. The Matched Eigenfunction Expansion Method (MEEM) for multiple fluid domains is applied to derive theoretically the velocity potentials and associated unknown coefficients for wave diffraction and body motion induced radiation in each subdomain. Also, the exciting forces, as well as the added mass and damping coefficients for the floating breakwater system under the surge, heave, and pitching motions, are formulated. The displacements of breakwater motions are determined by solving the equation of motion. As a verification of the analytical model, the present solutions of the limiting cases in terms of exciting forces, moments, added masses, and damping coefficients are found to be well matched with other published numerical results. Additionally, the hydrodynamic performances and the dynamic responses in terms of Response Amplitude Operators (RAOs) of the proposed floating breakwater system are evaluated versus various dimensionless variables, such as wavelength and porous-effect parameter. The results show that the attached porous walls with selected porous properties are observed to have the advantages of reducing wave impacts on the floating breakwater system and at the same time its dynamic responses are also noticeably improved.

Dynamic response and liquefaction analysis of seabed-rubble mound breakwater system under waves

Dynamic response and liquefaction potential of granular seabed around a rubble mound breakwater is investigated under waves. Dynamic response of the system is assumed to be governed by coupled Biot equations of poroelasticity. Mathematical formulations in terms of governing equations of partially-dynamic and quasi-static cases are considered. Dynamic response of seabed soil is analyzed using classical finite elements and a number of parametric studies are performed to draw a complete picture of the response of the system. Vertical displacement, shear stress and pore water pressure distributions are considered as the most representative variables defining the variations of response of the whole system and which are thus evaluated along some key cross sections around the breakwater. The results indicate that inertial terms associated with solid skeleton have almost no effect on the dynamic response and liquefaction potential. It was found that large amount of wave-induced shear stresses are taken by a relatively rigid core layer contributing to the breakwater stability where also the pore pressures dissipate significantly towards the seabed interface. Standing wave-induced instability of the system is also investigated in terms of instantaneous liquefaction based on the effective mean stress criterion. There is liquefaction observed at the seaward surface of the rubble whose depth increases significantly with decreasing saturation. While the core overall provides more stability, the adverse effect of this is more liquefaction in the outer layer.

Parametric Guidelines of Tombolo Formations behind Detached Breakwater Systems in Spanish Mediterranean Coast

ABSTRACT Garcia, I.; Negro, V.; Lopez, J.S.; Esteban, M.D., and Del Campo, J.M, 2018. Parametric guidelines of tombolo formations beind detached breakwater systems in Spanish Mediterranean Coast. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1066–1070. Coconut Creek (Florida), ISSN 0749-0208. Detached breakwater systems used to enlarge and protect extensive stretches of coastline can be designed with various methodologies. The latter may differ greatly from one another; some mainly have the geometric parameters and characteristic of the formation to be obtained and do not take the site's sedimentary variables into consideration. Designing and constructing these structures face a great problem in the lack of knowledge as to the coastline's morphology in its final condition when the situation of equilibrium is reached. Different alterations carried out afterwa...

Performance characterization of a novel marsh shoreline protection technology: The Wave Suppression and Sediment Collection (WSSC) system

Minimizing coastal wetland loss is a high priority in coastal areas worldwide. Typical shoreline protection consists of hard structures placed near areas affected by wave action. These commonly used protection methods are costly, and may have negative impacts on the surrounding areas. The Wave Suppression and Sediment Collection (WSSC) system, made of multiple Wave Robber® units, is an alternative shoreline protection structure. The primary goal of this study is to determine the performance characteristics of the technology in terms of energy coefficients. Experiments were performed on three scaled units within a laboratory wave tank. Performance characterization showed that the units have wave energy reflections of 0.47–0.83, transmission ranging from 0.10 to 0.42, and wave energy dissipation between 0.49 and 0.88, depending upon unit geometry and wave conditions. Performance data were also compared to other studies on shoreline protection structures. WSSC units reflect more wave energy and transmit less energy compared to other breakwater systems. These units could be utilized in coastal marshes with a large fetch, to reduce wave-induced erosion.

Enhanced Rock Oyster Mounds As Breakwater System

The existing rock mound technology specifically those erected for rock oyster (saccustrea cucullata) posed several problems such as growth efficiency, water circulation, sediment accumulation and durability against waves. This paper investigated in a laboratory scale using a physical model of a coastal zone. About 141 test runs were made to measure and observe resilience, wave breaking ability, sediment transport and water circulation of five different rock mound shape and set-ups/arrangement. Data showed that the droplet and the diamond shape arranged in staggered formation was the optimum design. The droplet shape provided the more cost-effective design as a rock oyster mound and as a breakwater set-up. Validation of the design in an actual environment is recommended.

Countermeasures for breakwater foundation subjected to foreshocks and main shock of earthquake loading

ABSTRACTCoastal protective structures, such as composite breakwaters, are generally vulnerable to earthquake. It was observed that breakwaters damage mainly due to failure of their foundations. However, the seismically induced failure process of breakwater foundation has not been well understood. This study describes failure mechanism of breakwater foundation as well as a newly developed reinforcing model for breakwater foundation that can render resiliency to breakwater against earthquake-related disasters. Steel sheet piles and gabions were used as reinforcing materials for foundation. The experimental program consisted of a series of shaking table tests for conventional and reinforced foundation of breakwater. Numerical analyses were conducted using finite difference method, and it was observed that the numerical models were capable to elucidate the seismic behavior of soil–reinforcement–breakwater system. This paper presents an overview of the results of experimental and numerical studies of the seismic response of breakwater foundation. Overall, the results of these studies show the effectiveness of the reinforced foundation in mitigating the earthquake-induced damage to the breakwater. Moreover, numerical simulation was used for parametric study to determine the effect of different embedment depths of sheet piles on the performance of breakwater foundation subjected to seismic loading.

Assessment of coastal changes along Baltim resort (Egypt) using remote sensing and DSAS method

Baltim resort has exposed to severe erosion due to critical natural factors, especially after the establishment of Aswan High Dam. The number of detached breakwater along Baltim resort is 14 detached breakwaters; nine of them were constructed in the period (1993-2002). The other 5 segments were constructed in the period after 2003 with the same dimensions; in addition, 9 short groins were constructed on the west of Kitchener drain). The present study was conducted to evaluate the recent shoreline sedimentation patterns and to determine whether the implemented detached breakwater systems along Baltim resort have affected that patterns or not. Quality assessment through quantitative method has been used to validate the used data, since the used images in this research are from 4 different satellite sensors; where the special and spectral resolutions are not equal. In this study, the behavior of Baltim resort's coastline was analyzed after the construction of the detached breakwaters #9 to #14, to determine whether the general erosion/ accretion pattern along the resort has been reshaped or not. Shoreline change detection was calculated using the Digital Shoreline Analysis System (DSAS). The rate of shoreline change was estimated from three statistical models of DSAS: Linear Regression Rate (LRR), End Point Rate (EPR) and Least Median of Square (LMS). Accretion in the form of tombolo between breakwaters #9 to 14 is found out to be very high with a maximum value reached ~ +32.4 m/yr, which recorded in front of breakwater #11, followed to the east by down-drift erosion that reached its maximum rate value to be ~ -34 m/y in front of the 9 groins west of Kitchener drain. At the east of Kitchener drain severe erosion happened to a distance of 5.7 km and after that distance, the shoreline is almost stable and this pattern matches with the calculated alongshore rate of shoreline changes of the present study.

Morphodynamic changes as an impact of human intervention at the Ras El-Bar-Damietta Harbor coast, NW Damietta Promontory, Nile Delta, Egypt

Due to the absence of a national strategic plan for coastal management, the Nile Delta coast is no longer described as a fully dissipative, divergent, low-gradient beach face composed of fine to very fine sand. Instead, new patterns have emerged depending on rock type, geomorphology of the coast, direction of the shoreline in relation to waves and current, and the implemented defense measures. This study attempts to record the morphodynamic changes which occurred due to human intervention. Landsat satellite images acquired for the periods of time of 1973, 1984, 1989, 2003, and 2015 are used together with geomorphologic observations in order to monitor the changes along the coastal strip between Ras El-Bar and Damietta Harbor. This study reveals two beach segments; one of which lies to the east, it is protected with detached breakwater system, and shows average shoreline accretions of +4.73 myr−1, +5.0 myr−1, and +0.89myr−1 during the periods of 1984–1998, 1998–2003, and 2003–2015 respectively. This segment still has the geomorphologic imprints of the dissipative beach, wave divergence, low-gradient beach face, fine grained sand and spilling breakers. The second is to the west, between the detached breakwaters and the eastern jetty of the Damietta Harbor. It is an erosional segment with shoreline retreat of −7.43 myr−1, −10.90 myr−1, and −3.11myr−1 for the same periods. This segment shows intermediate “d” beach or intermediate-reflective, wave convergence, rip currents, with the characteristic steep sloped and cuspate beach face, cliffy, reworked sediments of coarse grained sands, mud clasts, discoidal gravels, shelly beach, and plunging breakings. The presence of convergent waves along this segment confirms the concept of an emergence of a new wave pattern of reversed eddy which enhances the steepness of the beach face, accelerates erosion, and increases the possibility of drowning of swimmers at Ras El-Bar resort. Under such circumstances the plunge step approaches the shore and its shell content forced by wave to accumulate forming the shelly beach. To secure the coastal strip against erosion and sea level changes the detached breakwaters should be extended to reach the eastern jetty of the Damietta Harbor. The protection of this segment is a matter of interest for investment projects related to industries and trading along the Damietta Harbor as well as the touristic investments at Ras El-Bar, as one of the important tourist destinations in Egypt. Millions of pounds spent by beach visitors and investment annually provide significant input to local and regional economy. Hazards associated with the morphodynamic effects on recreational beaches can influence the suitably of any given stretch of coast as a recreational resource, and thus impact tourist money spent in addition to the safety and well-being of beach visitors.

3D experimental study on a cylindrical floating breakwater system

The objective of the present study is to investigate the performance of a cylindrical floating breakwater system based on 3D experimental tests. The experiments were carried out in the wave basin (36m*60m*1.5m)of the Ocean University of China. The cylindrical floating breakwater system consists of 10cylindrical floating breakwater units and 10mesh cages with balls in them, connected by 18 connectors and moored by a taut mooring system. The wave transmission coefficients, reflection coefficients, dissipation coefficients and motion responses of the floating breakwater are measured in both oblique and beam sea conditions. It is found that with the increase of the wavelength, both of the wave transmission coefficients and motion response amplitude of the FB system suffers an increase before it reaches its peak value, followed by a decrease trend. It can be concluded from the experiments that the proposed FB system has a satisfactory performance and it can be used to a wide range of sea conditions.

Effects of reinforcement on the performance of breakwater foundation subjected to earthquake loadings

This paper deals with reinforcing technique for foundation of breakwater which provides resiliency to breakwater against earthquakes. Gabions and sheet piles were used in foundation of breakwater as reinforcing measures against earthquake loadings. Shaking table tests were performed to evaluate the effectiveness of the technique under different earthquake loadings, and comparisons were made between conventional and the reinforced foundation. Numerical analyses were also performed to elucidate the mechanism of the reinforcement–soil–breakwater system during earthquakes. The results of this study reveal the advantages of the technique in reducing settlement and horizontal displacement of the breakwater during different earthquake loadings.

Engineering of an island-style breakwater system for the Fort Pierce marina

The push to create shore and harbour protection that is environmentally more compatible often puts the reality of the needs for resilience and strength at odds with the needs of nature. Softer protection schemes, such as floating wave attenuators and non-bottom-founded protection methods, are typically inadequate to resist the ravages of a storm, whereas the construction of solid ring breakwaters changes the texture of the shoreline and affects the biota. Out-of-the-box thinking was required to find an approach that could both emulate the natural environment and yet still be resilient enough to protect against hurricane events, promote ecology and offer safe and manageable navigation. The solution was found in building a protection system of artificial islands configured to create wave sheltering, oriented to reduce long-term sedimentation effects by controlling tidal flow patterns and executed to be a living island archipelago with both benthic and terrestrial habitat.

WAVE TRANSMISSON STUDY THROUGH TWO ROW PILED BREAKWATERS

Pile type breakwaters, being a permeable and porous structure, come forward as an alternative design approach if appropriate. Aim of this study is to understand the transmission phenomenon of waves passing through two row piled breakwater system. There are some experiments in the literature examining transmission through one row pile system, yet less in two row systems. Thus, at this point of view, this experiment becomes more important. The model studies were implemented to comprehend how the transmission coefficient will change under the effects of; -Different incident wave angles -Different spacing distances between piles -Different wave steepness values

The effect of breakwaters on the structure of marine soft-bottom assemblages: A case study from a North-Western Mediterranean basin

This two-year study is the first attempt to analyse the ecological effects of breakwater systems on soft-bottom assemblages along the North Tyrrhenian coast. Differently from previous studies focusing on infauna of on-shore and off-shore sides, we compared the assemblages inhabiting the surrounding soft-bottoms not directly protected by the breakwaters, defining our sampling stations at varying distances from the breakwaters and at constant distance from the coast.Data collected revealed that abundance, species richness and M-AMBI ecological quality differed between northern and southern sides, and were related to distance from structures. Multivariate analyses of relationships between assemblages and abiotic characteristics support this hypothesis. The extension of these effects, that resulted to be weak and limited to a restricted area, could be a consequence of coastal current on local hydrodynamics. This study provides novel and critical information for the management of the coastal defence infrastructure spreading along the western coast of Italy.

A Kind of Floating Breakwater Sheltering Deep Water Aquaculture

This paper briefly introduces the design, construction and wave attenuation effect test of a kind of floating breakwater sheltering deep water aquaculture. This novel floating breakwater structure is composed of 28 standard modules and corresponding anchoring systems, and each standard module comprises a catamaran raft and a wave-attenuating and oscillation-inhibiting device, with a length of 30 m, a width of 7 m, a depth of 2 m and a draft of 1.1 m. Each catamaran raft employs a box-shaped multi-ribbed beam-and-slab structure, and was constructed using high-performance concrete and ferrocement materials and internally filled with polystyrene foam plastics. Each wave-attenuating and oscillation-inhibiting device uses a detachable split box-shaped structure and was pre-fabricated using high-performance concrete, with a length of 2 m, a width of 1.638 m and a height of 2 m. Each standard module is anchored using 6 anchor chains, each of which has an on-floor length of about 25 m. After construction, this floating breakwater system was tested for wave attenuation effect, and the data analysis results show that the floating breakwater system has a wave attenuation effect of up to 50 %.

Nonlinear and dispersive free surface waves propagating over fluids with weak vertical and horizontal density variation

AbstractWe consider the change in fluid density in a depth-integrated long-wave model. By allowing horizontal and vertical variation of fluid density, a depth-integrated model for long gravity waves over a variable-density fluid has been developed, where density change effects are included as correction terms. In particular, a two-layer fluid system is chosen to represent vertical density variations, where interfacial wave effects on the free surface are accounted for through direct inclusion of the velocity component of the interfacial wave. For the numerical implementation of the model, a finite-volume scheme coupled with an approximate Riemann solver is adopted for leading-order terms while cell-centred finite-volume methods are utilized for others. Numerical tests in which the density field is configured to vary either horizontally or vertically have been performed to verify the model. For horizontal variation of fluid density, a pneumatic breakwater system is simulated and fair agreement is observed between computed and measured data, indicating that the current induced by the upward bubble flux is responsible for wave attenuation to some degree. To investigate the effects of internal motion on the free surface, a two-layer fluid system with monochromatic internal wave motion is tested numerically. Simulated results agree well with the measured and analytical data. Lastly, nonlinear interactions between external- and internal-mode surface waves are studied numerically and analytically, and the model is shown to have nonlinear accuracy limitations similar to existing Boussinesq-type models.

Long-term assessment of an innovative mangrove rehabilitation project: case study on Carey Island, Malaysia.

Wave energy and storm surges threaten coastal ecology and nearshore infrastructures. Although coastal structures are conventionally constructed to dampen the wave energy, they introduce tremendous damage to the ecology of the coast. To minimize environmental impact, ecofriendly coastal protection schemes should be introduced. In this paper, we discuss an example of an innovative mangrove rehabilitation attempt to restore the endangered mangroves on Carey Island, Malaysia. A submerged detached breakwater system was constructed to dampen the energy of wave and trap the sediments behind the structure. Further, a large number of mangrove seedlings were planted using different techniques. Further, we assess the possibility of success for a future mangrove rehabilitation project at the site in the context of sedimentology, bathymetry, and hydrogeochemistry. The assessment showed an increase in the amount of silt and clay, and the seabed was noticeably elevated. The nutrient concentration, the pH value, and the salinity index demonstrate that the site is conducive in establishing mangrove seedlings. As a result, we conclude that the site is now ready for attempts to rehabilitate the lost mangrove forest.

Effect of under connected plates on the hydrodynamic efficiency of the floating breakwater

In this paper, the hydrodynamic efficiency of a floating breakwater system is experimentally studied by use of physical models. Regular waves with wide ranges of wave heights and periods are tested. The efficiency of the breakwater is presented as a function of the wave transmission, reflection, and energy dissipation coefficients. Different parameters affecting the breakwater efficiency are investigated, e.g. the number of the under connected vertical plates, the length of the mooring wire, and the wave length. It is found that, the transmission coefficient kt decreases with the increase of the relative breakwater width B/L, the number of plates n and the relative wire length l/h, while the reflection coefficient kr takes the opposite trend. Therefore, it is possible to achieve kt values smaller than 0.25 and kr values larger than 0.80 when B/L is larger than 0.25 for the case of l/h=1.5 and n=4. In addition, empirical equations used for estimating the transmission and reflection coefficients are developed by using the dimensionless analysis, regression analysis and measured data and verified by different theoretical and experimental results.

Hydrodynamic efficiency of suspended horizontal rows of half pipes used as a new type breakwater

The hydrodynamic efficiency (effect of structure on incident wave attenuation) of a new type breakwater was studied using physical models under regular waves. The breakwater was consisted of one or more horizontal rows of half pipes suspended on supporting piles. The hydrodynamic efficiency of the breakwater was validated through calculation of the wave transmission, reflection and energy dissipation coefficients for different wave and structural parameters. Results indicated that the transmission coefficient decreases with increasing the relative wavelengths (h/L and B/L), wave steepness (Hi/L) and relative breakwater width (B/d), and it increases with decreasing the relative draft (D/h). The reflection and dissipation coefficients take the opposite trend. The proposed breakwater system is more efficient than the smooth plate type by about 5 to 25%. The use of a second row improves the breakwater efficiency by about 20 to 50% and the use of the third row improves the efficiency by about 5 to 15% more than the two rows system. Empirical equations were developed for estimating the transmission and reflection coefficients. The results of these equations were compared with other experimental and theoretical results giving a reasonable agreement. The proposed breakwater type was efficient when compared with other breakwater systems.