Offshore Breakwater Research Articles

Feasibility studies on deepening Pondicherry Port to accommodate larger vessels explored

A Union territory in India, Pondicherry was a major trading port with the Chinese during the Chola era, having been active since 100 B.C. About 150 km south of Chennai, it was an open roadstead anchorage port. Until the late 1980s, the old port operated as a lighter-age port during French rule, beginning in the 17th century. From 1986 until 1989, the New Port was developed. An offshore (south) breakwater connected to a north breakwater by a bridge makes up the New Port. The channel, which is 2000 meters long and 40 meters broad, was built between 1986 and 1989. It also has a 150-meter container berth. An undersea tunnel has been built between the north and south breakwaters to facilitate maintenance dredging and allow cargo and fishing vessels to pass through without interruption. The port was in use until 2004, when it was shut down for a lack of maintenance dredging. Since 2004, there has been no freight business; only small fishing boats are currently in use. The viability of enhancing Pondicherry Port's current infrastructure to accommodate feeder-class vessels is investigated in this paper.

COMPARISON OF NUMERICAL AND EMPIRICAL ESTIMATES OF WAVE CONDITIONS IN THE LEE OF A DETACHED BREAKWATER

This paper presents a comparison of numerical and empirical methods routinely applied by practitioners to examine wave penetration in the lee of a breakwater, using a case study of a breakwater which is planned for Entrance Point, Broome in the northwest of Australia. Wave conditions representative of ambient and extreme conditions were determined from measured data captured directly offshore of the site, and an extreme cyclone metocean study (Baird, 2020). For ambient and extreme tropical cyclone conditions, waves are typically short crested at a peak period of between 4 seconds to 8 seconds. To examine the effectiveness of the offshore breakwater, empirical methods (Goda, 2000), a phase-averaged model (SWAN) and two phase-resolving model systems– the 2D Boussinesq wave model (MIKE21BW) and 3D non-hydrostatic model (MIKE3-Wave FM) - were applied.

Assessment of Wave Attenuation Performance of the Tanjung Piai Breakwater Using Spectral Wave Analysis

Tanjung Piai is a Malaysian heritage site situated at the southernmost tip of the Asian continent. Tanjung Piai provides a conducive coastal habitat for many mangrove species. Coastal erosion resulting in shoreline retreat was detected dating back to the 1930s. The erosion rate had accelerated until the early 21stcentury due to various factors including to coastal developments in the vicinity of Tanjung Piai. This led to significant land mass losses threatening the coastal eco-system. Previously, various measures were adopted to permanently harden the shoreline. Nevertheless, these approaches prevented sea water from reaching the mangroves, which in turn resulted in significant mangrove depletion along the shoreline. A series of offshore breakwaters were subsequently planned and constructed to reduce the wave energy prior to reaching the mangrove shoreline. The breakwaters are anticipated to be able to mitigate the erosion problems and extend the width of the existing mangroves belts along the wave-exposed coastline. The wave climate of Tanjung Piai has changed drastically in the past decades, potentially due to rapid coastal development in the vicinity. This study aims at re-evaluating the wave attenuation performance of the Tanjung Piai breakwaters subjected to the latest wave climate (i.e., offshore waves, squalls, and wind-generated waves) and bathymetry by means of two-dimensional numerical modelling –MIKE21 SW. The latest survey of the site and the most recent breakwater design details have been incorporated in this modelling study. Two scenarios have been conducted to determine the wave climates i.e., pre-and post-construction of the breakwaters. The alterations of the wave heights for both scenarios are taken as a basis to ascertain the actual wave attenuation performance of the breakwaters. The numerical results show that the breakwaters are able to reduce offshore wave heights up to 66%. The breakwaters can attenuate offshore waves more effectively than squalls and wind-generated waves.

Experimental Study on the Stability and Wave Force of a Breakwater Transition under Multiangle Oblique Waves

Based on the failure and instability of different structural transitions of offshore breakwater, this paper provides a basis for understanding the instability mechanism and also provides suggestions for engineering repair. Based on the breakwater project in the regulation of the bay of Shandong Province, physical model tests with a scale of 1:36 were carried out. This study revealed the wave characteristics, the force performance, and the instability mechanism in the transition. In the test, the relationships between 5°, 15°, 35°, and 75° oblique waves, the wave force, and the stable weight of the Accropode were simulated, revealing that the generation of a shock wave current is related to the wave direction angle, which results in the local wave height increasing by 2.05 times. The result that the design weight of the armour block is unstable and stable after optimization is obtained. The wave force of the caisson of the transition was concentrated in the anti-arc section of the superstructure, and the maximum horizontal force, buoyancy force, and impact pressure were 935.6 kN, 419.1 kN, and 65.9 kPa, respectively. The instability mechanism was determined as the poor connection between the accropode and the caisson, and the wave energy concentration. Compared with the calculation results of the standard formula, the correction coefficients of the overtopping volume, the wave crest elevation, the wave force, and the Accropode weight at the transition of breakwater were 1.95, 1.97, 1.60, and 4.0, respectively. The test results have solved the practical problems of the project and can also provide a reference for similar projects.

Investigation on innovative pile head breakwater for coastal protection

Coastal erosion is a global concern that has been augmenting due to the natural evolution of beaches, human activities and sea-level rise. One of the eco-friendly shore protection methods is to dissipate the wave energy by constructing offshore breakwaters. Conical pile head breakwater (CPHB) is one of the eco-friendly innovative offshore structures consisting of closely spaced piles with an enlarged cross-sectional area (conical pile head) in the vicinity of the free surface. In the present study, perforations are incorporated over the conical pile head to achieve higher efficiency by promoting energy dissipation. The influence of the perforations on the performance characteristics, namely wave transmission (Kt), wave reflection (Kr) and energy dissipation (Kd) of the perforated CPHB is comprehensively investigated through physical model studies. The effect of perforations and their distribution around the pile head (Pa), percentage of perforation (P) and size of perforations (S/D) on the wave attenuation characteristics are evaluated to arrive at an optimum configuration. The study is carried out under monochromatic waves of varying wave height (0.06–0.16 m) and wave period (1.4–2 s) at different depths of water (0.35, 0.40 and 0.45 m). A minimum Kt of 0.58 associated with Kr of 0.26 and Kd of 0.78 is obtained with an optimum configuration of Pa = 50%, P = 19.2% and S/D = 0.25. The Kt of the proposed CPHB is about 19 to 35% lesser than that of the perforated hollow pile breakwater under matching test conditions. Overall, providing the perforations is found to be effective in enhancing the wave attenuation capability by up to 12.4%. Further, empirical equations are formulated and validated with the experimental data. The empirical equations estimate the Kt and Kr values accurately with a high coefficient of determination ( R2 ≥ 0.90).

Planning of coastal protection structures in the area of Arung Dalam Beach, Central Bangka

Arung Dalam Beach underwent significant process of coastal erosion. This study aimed to determine the Hydro-Oceanographic conditions in Arung Dalam Beach using MIKE 21 FM and planning of coastal protection structures. The currents pattern during high tide was dominant from the northwest to the east with a rate of 0.042-0.09 m/second. The current pattern was dominant at low tide from the east to the northwest with a rate of 0.056-0.112 m/second. The wave pattern in the west season is prevalent from the north to the southwest with a height of 0.35-0.75 m; the wave pattern in the east season is prevalent from the northwest to the southwest with a height of 0.08-0.56 m. Sediment transport was perpendicular to the coast, which caused coastal erosion, with average coastal erosion occurring at -0.52 m/year. Coastal protection structures to overcome coastal erosion were offshore breakwater structures using crushed stone material. The length of the breakwater is 250 m; peak elevation 3.7 m; breakwater height 4.2 m; grain weight of protected layer 0.3 tons; the width of the crest of the breakwater is 2 m; 1.2 meters thick layer of protection; the number of grains per unit area of 1 m2, totalling 5 grains.

Experimental modeling of bed morphological changes and toe erosion of emerged breakwaters due to wave-structure interactions in a deltaic coast

Large-scale coastal erosion in the Mekong Delta has been dramatically increasing in severity in recent decades. There are several effective hard engineering solutions that have been implemented in this delta to efficiently prevent coastal erosion and stimulate sedimentation while supporting the local ecosystem conservation. These measures include Pile-Rock Breakwaters (PRBW), Hollow Triangle Breakwaters (HTB) and Semicircular Breakwaters (SBW). However, research on the sediment transport, morphological changes and toe erosion for these offshore breakwaters is very limited and is currently in the initial stages of understanding the specific conditions of sediment characteristics and foundations. The objective of this study was to reproduce the morphological changes and toe erosion of three breakwaters due to wave-structure interactions. This was investigated using 2D physical models with 3000 irregular waves during 8 experimental hours (equal to 15,000*Tp). To extract the bed morphological changes and toe erosion both specialized laser measurements (SW50M laser ruler) and analysis of high-speed video recording by images digitalization were applied. The experimental results show that the shape and structural design of offshore breakwaters can have a significant influence on the bed morphology on both the seaside and the leeside. We found that generally the toe of the construction on the seaside was eroded due to the occurrence of reflected waves, and that the flow is narrowed while passing through the construction, increasing the flow velocity and causing toe erosion. Additionally, the accretion of sediment at the leeside of the breakwaters was found to be mainly driven by the transport of sediment through the construction. Comparing the breakwater designs the experimental results showed that the HTB has the maximum accretion rate behind the structure, as well as the fastest accretion rate behind the breakwater. The SBW has high wave energy dissipation efficiency, although the toe erosion rate is faster than the other classes of breakwaters. The PRBW shows the fastest toe erosion rate in front of the structure and causes accretion at the leeside of the construction but at a lower rate than the HTB. The findings from this study will help practical designers to reinforce the foot of construction during real breakwater designing and inform stability calculations. We recommendation is to apply these three classes of breakwaters, especially the HTB and SBW, for stimulating sedimentation for mangrove restoration in the mangrove mud-coast delta.

Formulas for Uniaxial Capacities of Tetrapod Bucket Foundations Considering Group Effects in Undrained Clay

Suction bucket foundation is a novel and cheaper foundation used in marine structures, such as offshore wind turbines, breakwater and oil platforms. Compared with a single bucket foundation, tetrapod bucket foundations can bear larger loads because of the group effects. However, the vertical, horizontal and moment capacity factors of tetrapod bucket foundations have not been presented in existing specifications. A series of three-dimensional finite-element analyses were conducted to investigate the group effects on uniaxial capacities and failure mechanisms of tetrapod bucket foundations in undrained clay considering various foundation separation distance ratios, embedment depth ratios, soil-strength heterogeneity indices and load direction angles. Generalized formulas for undrained uniaxial capacities of tetrapod bucket foundations were proposed in order to establish a bridge connecting the capacities of tetrapod bucket foundations and those of the single bucket foundation, which can provide a reference for industrial designs of capacities of tetrapod bucket foundations. The results show that the vertical group effect factor of tetrapod bucket foundations is basically not affected by the foundation separation distance ratio, embedment depth ratio, soil-strength heterogeneity index and load direction angle, which can adopted 0.9 based on a conservative estimation. The normalized horizontal and moment group effect factors of tetrapod bucket foundations are both affected by the separation distance ratio, embedment depth ratio and soil-strength heterogeneity index, but the moment group effect factor is also obviously affected by the load direction angle. The value of the horizontal and moment capacity factors of tetrapod bucket foundations are about 2.3 and 13.8 times that of a single bucket foundation, respectively, when the separation distance ratio is 3.5, embedment depth ratio is 1.0 and soil-strength heterogeneity index is 10, which have both been significantly enhanced. A value of 3.5 is suggested for the separation distance ratio to attain good capacities and a relatively high global stiffness for the tetrapod bucket foundations.

Analysis of Long-Term Shoreline Observations in the Vicinity of Coastal Structures: A Case Study of South Bali Beaches

Recently, many rigid structures have been installed to cope with and efficiently manage coastal erosion. However, the changes in the coastline or isocenter and the movements of coastal sediment are poorly understood. This study examined the equilibrium shoreline and isocenter lines by applying a Model of Estimating Equilibrium Parabolic-type Shoreline (MeEPASoL) as an equilibrium shoreline prediction model. In addition, the inverse method was used to estimate littoral drift sediment transport from long-term beach profile observations. The movement of coastal sediments was analyzed using long-term beach profile observation data for three Indonesian beaches, namely, Kuta Beach for 13 years, Karang Beach in Sanur for 15 years, and Samuh Beach in Nusa Dua for 18 years. The littoral drift at every site was dynamically controlled by seasonal changes in the monsoon, the erosion and deposition patterns coupled with the presence of coastal structures, and limited sediment movement. Shoreline deformation in Kuta is generally backward deformed, with a littoral drift from south to north. In Sanur, the littoral drift vector carries sediment from the right and left sides and forms a salient behind the offshore breakwater. The littoral drift at Nusa Dua is dominantly from south to north, but the force of sediment transport decreases near the breakwater towards the north. Furthermore, the methods applied herein could aid the development of strategic coastal management plans to control erosion in subcells of coastal areas.

Coastal erosion assessment using remote sensing and computational numerical model. Case of study: Libertador Bolivar, Ecuador

The sea-level rise has intensified the erosion of coastal zones, whereby the coastal management requires tools to evaluate and predict the dynamics of shoreline. In this paper we evaluate the impact of erosion in a coastal zone of the active margin of Ecuador, where the subduction causes vertical movements of coast. The area chosen to develop this study Playa Bruja and Libertador Bolivar beaches in which activities such as tourism, fisheries, agriculture and gastronomy are the main sources of income. This study analyzes the shoreline retreatment from 1986 to 2019, by using aerial images (remote sensing), along to selected beaches to validate a computational numerical model as MIKE Zero. This calibrated model permitted us to evaluate possible scenarios and hazards until 2025 (with or without coastal protection such as offshore breakwaters), to promote integrated coastal management for decision-makers, especially considering the possible collapse of one of the main coastal highways (E15) of Ecuador country. The result from remote sensing suggests a mean rate of erosion of 0.64 m/yr, which well-correlate with the outputs from the numerical model (between 0.4 and 0.7 m/yr). The net transport, influenced by waves, was calculated in 470m3/day (1.71 E+5 m3/yr), predominant to the north. These results allowed us to categorize three levels of erosion threat such as high (45%), medium (46%), and low (9%) and this classification allows to observe which areas are more exposed or have a higher threat and then propose alternatives to protect. Future scenarios under natural conditions show a continuous retreat of the coast that put in risk the community and hypothetic scenario under an arrangement of 5 breakwaters generates accretion next to Playa Bruja Beach but a deficient supply at the north side at Libertador Bolivar.

Study on Brain Plasticity of Music Training Based on Network Technology

Spectral wave models have experienced constant development and vast improvements over the past decades. They are constantly being extended and refined in order to cover the complex wave transformation processes that take place in the coastal zone. Nevertheless, wave transmission due to overtopping has not been treated similarly yet. In this paper, a methodology to include wave generation due to overtopping in spectral wave models is presented. Incorporation of overtopping aims at better simulating the wave disturbance in the lee side of a system of offshore breakwaters and the induced hydrodynamic processes. So far, the waves generated due to wave overtopping were being neglected. The methodology consists of executing sequential simulations at small time step intervals and whenever wave overtopping occurs in a breakwater, waves are generated and transmitted in the lee side of the structure. This is achieved by modifying the boundary condition at the lee of a coastal structure to account for wave generation due to overtopping. Additionally, the transmitted spectrum source function was modified, to capture the observed transfer of energy in the higher frequencies of the spectrum due to the aforementioned overtopping process. The above methodology was implemented in the open source wave model TOMAWAC and verification with experimental measurements was carried out yielding satisfactory results. Inclusion of wave transmission due to overtopping in spectral wave models is considered to be a valuable asset, especially for the simulation of inshore hydrodynamic processes.

Coastal Structures as Beach Erosion Control and Sea Level Rise Adaptation in Malaysia: A Review

The shoreline of Malaysia is exposed to threats of coastal erosion and a rise of sea level. The National Coastal Erosion Study, 2015 reported that 15% of an 8840 km shoreline is currently eroding, where one-third of those falls under the critical and significant categories that require structural protection. The Study of Sea Level Rise in Malaysia, 2017 presented a sea-level increase of 0.67–0.74 mm on average yearly. This study reviewed selected coastal protection structures along the shoreline of Malaysia as an erosion control and sea-level rise adaptation based on coastal management strategies. Hard structures such as rock revetment and breakwater are commonly used as erosion protection systems in the “hold the line” strategy. Increased platform level of seawalls and earth bunds, considered as an “adaptation” approach, are effective in erosion protection and are adaptive to sea-level rise. Mangrove replanting is suitable as a “limited intervention” approach in minimizing the long-term impact of both threats. However, offshore breakwater, groyne, and geotextile tubes are solely for protection purposes and are not as effective for sea-level rise adaptation. As the sea level is continuously increasing, their function as coastal protection will also become less effective. In summary, this comprehensive review on coastal protection in Malaysia will benefit the related agencies on the future assessment.

Hydrodynamic Performance of an Asymmetry OWC Device Mounted on a Box-Type Breakwater

To share the construction and maintenance cost, an asymmetric oscillating water column (OWC) device integrated with a pile-fixed box-typed offshore breakwater is considered experimentally and numerically. A fully nonlinear numerical wave tank is established and validated with the open source solver OpenFOAM. The effects of the width and draft of rear box, and the incident wave height on the wave energy conversion efficiency, reflection and transmission coefficients, and energy dissipation coefficient are examined. In addition, the superiority of the present coupling system, compared to the traditional box-type breakwater, is discussed. With well comparisons, the results show that the existence of the rear breakwater is beneficial for the formation of partial standing waves and further wave energy conversion. In the range of wave heights tested, the higher the incident wave height, the larger the energy absorption efficiency except for the short-wave regimes. Moreover, the OWC-breakwater coupling system can obtain a similar wave blocking ability to the traditional one, and simultaneously extract wave energy and decrease wave reflection.

Using Fine-Grained Sediment and Wave Attenuation as a New Measure for Evaluating the Efficacy of Offshore Breakwaters in Stabilizing an Eroded Muddy Coast: Insights from Ca Mau, the Mekong Delta of Vietnam

Offshore breakwaters can be effective in reducing the energy of incident waves through dissipation, refraction or reflection. Breakwaters are increasingly constructed to stabilize eroded muddy coasts, particularly in developing countries. Accumulation of fine-grained sediment and wave attenuation are two attributes of a stable muddy coast. Effective interventions in stabilizing eroded muddy coasts include two important elements: accumulation of fine-grained sediment and wave reduction. The efficacy of offshore breakwaters in stabilizing eroded muddy coasts is, however, not yet adequately understood. A crucial question needing attention is whether accumulation of fine-grained sediment and wave attenuation should be used in evaluating the efficacy of these offshore breakwaters in stabilizing eroded muddy coasts. To address this issue, a pile-rock offshore breakwater in Huong Mai, Tieu Dua of Ca Mau, Vietnam was selected as an appropriate example in this regard. Accumulation of fine-grained sediment and wave attenuation were tested as means to investigate the efficacy of the Huong Mai structure in stabilizing the eroded muddy coast. The study was undertaken using field-based measurements and semi-structured interviews in three stages between October 2016 and December 2020. We found that this structure has had limited efficacy in stabilizing the eroded muddy coast. The structure was effective in dissipating the energy of incident waves, but we found no evidence of fine-grained sediment accumulation due to an inappropriate structural design. There was also no monitoring system in place, leading to difficulties in evaluating its efficacy in terms of wave attenuation and accumulation of fine-grained sediment. The gaps between the shoreline and the structure have not been adequately explained, resulting in substantial challenges in replicating the structure elsewhere. The Huong Mai structure should be strengthened using supplementary measures and granulometric tests in order to improve the efficacy in stabilizing eroded muddy coasts. The methods in this study provide new insights in this regard.

Hydro-morphological simulation for Blue beach, Gaza Strip, Palestine

Man-made improvements to the coastal areas can have a drastic short- and long-term impact on the sediment balance. This paper investigates the morphological changes at the Blue beach, Gaza Strip, Palestine. The Blue Beach resort is extremely deteriorated due to shoreline recession, where the width of the beach at some locations is less than 0.5 m. On the other side, the new recreational groin is unstable because it is not adequately designed to serve as a breakwater from a technical point of view. Firstly, this paper uses the integrated Digital Shoreline Analysis System (DSAS) with the Geographic Information System to detect changes in the coastline along the Blue Beach coast in Gaza during the 2011–2019 period. Shoreline change rates in the form of erosion and accretion patterns are automatically quantified by the End Point Rate. In addition, a proposed plan consists of two main stages to mitigate the current problems raised by severe erosion through numerical investigation; restoration of the existing beach by sand nourishment in addition to reducing the exposure of the coast to erosion and boost the protection of the recreational groin by implementing submerged offshore breakwaters. Hydro-morphological modeling is applied to study the processes of the coastal zone, hence, evaluating the diverse alternatives mentioned above. Delft3D software package is used to numerically simulate the different scenarios at different times: 1, 5, and 8 years, respectively. In addition, the existing structures are rehabilitated in accordance with current conditions. DSAS results show that during the period (2011–2019) there was a major recession to the shoreline with a peak erosion rate of -4.16 m/year. From the numerical modeling, it is concluded that the two submerged breakwaters managed to restore the beach by minimizing the amplitude of the wave and thus trapping the sediments behind it. In fact, the sediments grew offshore beyond the submerged breakwaters for the long term.

Simulation of Bay-Shaped Shorelines after the Construction of Large-Scale Structures by Using a Parabolic Bay Shape Equation

Among the various causes of coastal erosion, the installation of offshore breakwaters is considered the main cause that influences the most serious changes in shorelines. However, without a proper means for predicting such terrain changes, countries and regions continue to suffer from the aftermath of development projects on coastal land. It has been confirmed that the parabolic bay shape equation (PBSE) can accurately predict shoreline changes under the wave climate diffracted as a result of such development projects. This study developed a shoreline change model that has enhanced the previous shoreline change models by applying PBSE to shoreline changes into bay-shaped features. As an analytical comparison with the second term of the GENESIS model, which is an existing and well-known shoreline change model, a similar beach erosion width was obtained for a small beach slope. However, as the beach slope became larger, the result became smaller than that of the GENESIS model. The validity of the model was verified by applying it to satellite images that demonstrated the occurrence of shoreline changes caused by breakwaters for seaports on the eastern coast of Korea; Wonpyeong beach, Yeongrang beach, and Wolcheon beach. As a result, each studied site converged on the static equilibrium planform within several years. Simultaneously, the model enabled the coastal management of the arrangement of seaports to evaluate how the construction of structures causes serious shoreline changes by creating changes to wavefields.

REDUCED COMPLEXITY MODELING OF SHORELINE RESPONSE BEHIND OFFSHORE BREAKWATERS

Prediction of the shoreline response behind offshore breakwaters is essential for coastal protection projects. Due to the complexity of the processes behind the breakwaters (e.g., wave diffraction, currents, longshore transport), detailed modelling needs high computational efforts. Therefore, simplifying the process effect in a simpler coastline model could be efficient. In this study, the coastline evolution model ShorelineS is used. A new routine was implemented in the model to adjust the wave heights and angles behind the offshore breakwaters. Two approaches from the literature and a newly introduced one were tested in this study. The model free grid system was used to simply track the breaker line; such an advantage also helped to form tombolo, which is not common for these types of models. The tests showed promising results for single and multi breakwaters systems; however, the newly introduced approach still needs further testing and refinement for better performance and less computational cost.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/mdCpmSQFO1Y

New analytical solutions of oblique wave scattering by submerged horizontal perforated plates using quadratic pressure drop condition

This study develops new analytical solutions for oblique wave scattering by horizontal perforated plates submerged below the water free surface using a quadratic pressure drop boundary condition. Both kinds of submerged plates are considered: a) A horizontal perforated plate as an offshore breakwater; b) A horizontal perforated plate attached to a vertical wall as a wave absorber. The velocity potential decomposition method combined with an efficient iterative algorithm is adopted to obtain the analytical solutions, and the hydrodynamic parameters of engineering interest for the reflection, transmission and energy-loss coefficients as well as the vertical wave force are considered. A new simple formula for predicting the discharge coefficient in the quadratic pressure drop condition, which is critical to make the analytical solutions to be practically applicable, is developed by fitting the analytical results and an amount of experimental data in literature. The present analytical solutions are in good agreement with previous analytical solution for special case and the numerical results of an independently developed multi-domain boundary element method solution. The reflection and transmission coefficients calculated by the present analytical solutions are also in good agreement with experimental data when adopting a well-predicted discharge coefficient. The present analytical solutions are valuable for fast assessing the hydrodynamic performance of horizontal perforated plates in the initial stage of engineering design. The present analytical model can also be readily extended to the multi-layer horizontal perforated plates and similar structures.

Numerical and experimental modeling of water wave interaction with rubble mound offshore porous breakwaters

In the present study, regular water wave interaction with rubble mound offshore breakwaters (RMOB) is investigated. The porosity of the RMOB is uniform, and the breakwaters are placed on the uniform seabed. Three different types of breakwaters such as (i) RMOB with still water level at the crest, (ii) emerged RMOB, and (iii) submerged RMOB are considered for the present analysis. The associated boundary value problem is handled for the solution using the boundary element method. Further, model tests are conducted, and the experimental results are compared with the numerical solutions. Quantitative analysis is carried out to show the effect of wave height and the height of RMOB’s on the wave reflection, wave transmission, and wave energy dissipation. An emerged RMOB can effectively reduce the wave transmission compared to the submerged RMOB and RMOB with crest level at SWL (still water level). The results indicate that the minimum transmission coefficient (<0.2) can be achieved in the short wave regime. This study also suggests that 90% incident wave energy can be dissipated by emerged RMOB with 46% porosity.

Numerical study of nearshore hydrodynamics and morphology changes behind offshore breakwaters under actions of waves using a sediment transport model coupled with the SWASH model

ABSTRACT This paper presents the results of numerical study on the wave-induced currents and morphology changes due to the complicated interaction between waves and a sandy beach with shore-parallel breakwaters set on. The study was based on the SWASH wave model coupled with a sediment transport model developed in this research. The simulated results of the coupling model were compared with the published laboratory experimental data. The good agreements were obtained for both wave-induced currents and formation of salient and tombolo behind breakwaters. The models were also applied for studying the evolution of wave-induced currents associated with topography changes of a sandy beach. The wave-induced currents and sediment transport processes have a strong relationship and their interaction could reach a quasi-equilibrium state in which the changes of current pattern and bathymetry become very slow. Numerical results of shoreline response mode were also compared with a published empirical formula and confirmed good agreements.