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Submerged breakwaters are emerging as a viable solution to mitigate the adverse effects of increased wave action on coastal structures such as seawalls. This study undertook a comprehensive and rigorous numerical investigation to illustrate the hydrodynamic performance of a nonporous submerged breakwater positioned at varying distances seaward of the seawall under various wave conditions. An open-source computational fluid dynamics-based numerical model, REEF3D, which solves the Reynolds-Averaged Navier–Stokes equations using the finite difference method, was used for the numerical modeling of wave–structure interaction. The numerical model was meticulously validated, ensuring its accuracy and reliability, with experiments conducted in a wave flume using the seawall model. The validated model was then applied to simulate wave interaction between the seawall and submerged breakwater for different pool lengths subjected to regular waves. The study primarily focused on assessing wave elevation in proximity to the seawall, wave reflection characteristics, and hydrodynamic pressures exerted on the seawall when the seawall is defended by a submerged breakwater. The numerical model also analyzed the spatial and temporal distribution of free surface elevation and generation of higher harmonics along the numerical wave tank. This thorough approach ensures a deeper understanding of the complex wave–structure interaction processes within the pool zone. This study found that incorporating a submerged breakwater seaward of the seawall may not consistently result in wave attenuation. The results showed that reduction in free surface elevations and pressures follows a nonmonotonic trend with variations in the pool length. Further, the influence of pool length is not significant when interpreting the maximum pressure reduction for varying pool lengths. These findings have significant implications for the design and implementation of coastal structures. [ABSTRACT FROM AUTHOR]

Beach erosion and coastal protection are complex and interconnected phenomena that have a substantial impact on coastal environments worldwide. Among the various coastal protection measures, seawalls have been widely implemented to mitigate erosion and protect coastal assets. However, the interrelationship between beach erosion and seawalls remains a critical topic for investigation to ensure effective and sustainable coastal management strategies. Seawalls impact the shoreline, particularly through the "end effect", where the seawall functions similarly to a groin, causing erosion on the downdrift side relative to the direction of wave approach. This study provides a detailed analysis of the interplay between beach erosion and seawall structures in Loc An, Vietnam, employing both remote sensing and numerical approaches. Sentinel-2 images were employed together with an analytical solution to observe the shoreline change at the Loc An sand spit and to determine input values for the numerical model. Based on the shoreline dynamics, a numerical scheme was employed to study the shoreline evolution after the construction of a seawall. Our findings show that the shoreline evolution can be divided into three stages: (1) The first stage corresponds to the elongation of the sand spit without interference from coastal structures. (2) The second stage shows the effect of jetties on the shoreline, as signaled by the buildup of sand updrift of the jetties. (3) The third stage shows the effectiveness of the seawall, where the shoreline reaches its equilibrium condition. The study provides a quick and simple method for estimating shoreline diffusivity (ε) in situations where measured data is scarce. [ABSTRACT FROM AUTHOR]

The purpose of this research is to develop a new method for automatically optimizing the seawall cross-section with composite slopes and a berm, considering both overtopping discharge and construction cost. Minimizing these competing multi-objectives is highly challenging due to the intricate geometry of seawalls. In this study, the surrogate model optimization algorithm DYCORS (Dynamic COordinate search using Response Surface models) is employed to search for the optimal seawall geometry, coupled with the ANN (Artificial Neural Network) model for determining the overtopping discharge. A total of 20 trials have been run to evaluate the performance of our methodology. Even the worst-performing Trial 7 among these 20 trials shows a satisfactory performance, with a reduction of 17.67% in overtopping discharge and a 12.1% decrease in cost compared to the original solution. Furthermore, compared to other optimization schemes using GAs (Genetic Algorithms) with the same decision vectors, constraints, and multi-objective functions, the methodology has been proven to be more effective and robust. Additionally, when facing different combinations of wave conditions and water levels, there was a 27.8% reduction in objective function value compared to the original solution. The optimal results indicate that this method can still be effectively applied for optimizing the seawall cross-section as it is a general method. [ABSTRACT FROM AUTHOR]

Settlement prediction based on monitoring data holds significant importance for engineering maintenance of seawalls. In practical engineering, the volume of the collected monitoring data is often limited due to the restrictions of devices and engineering budgets. Previous studies have applied the fractional-order grey model to time series prediction under the situation of limited data volume. However, the performance of the fractional-order grey model is easily affected by the inappropriate settings of fractional order. Also, the model cannot make dynamic predictions due to the characteristic of fixed step size. To solve the above problems, in this paper, the genetic algorithm with enhanced search capabilities was employed to solve the premature convergence problem. Additionally, to solve the problem of the fractional-order grey model associated with fixed step size, the real-time tracing algorithm was introduced to conduct equal-dimensionally recursive calculation. The proposed model was validated using monitoring data of four monitoring points at Haiyan seawall in Zhejiang province, China. The prediction performance of the proposed model was then compared with those of the fractional-order GM(1,1), integer-order GM(1,1), and fractal theory model. Results indicate that the proposed model significantly improves the prediction performance compared to other models. [ABSTRACT FROM AUTHOR]

During hurricanes or typhoons, wave forces acting on low-lying coastal bridges can cause significant damage to their decks. However, current research has paid little attention to the impact of topography on wave forces. This paper aimed to propose an analytical model based on potential flow theory to analyze the impact of topography on wave forces on bridge decks. The model employs the eigenfunction-matching method to solve the boundary value problem of waves acting on bridge decks over a step bottom. The validity of the model was confirmed by comparing it with published hydrodynamic experiment results. We also examined the effect of the truncation order on wave forces and selected a proper truncation order. The wave forces on the bridge deck located ahead or behind the bottom step were calculated. This study examined the water depth, distance from the bottom step to the bridge deck, and coastal boundary on wave forces. The calculated results indicate that the coastal boundary would significantly influence wave forces on bridge decks, especially for long-period incident waves. The wave forces can be mitigated by an optimized configuration of the wave–structure–topography system. This paper contributes to understanding the impact of topography on wave forces acting on bridge decks during extreme wave conditions and provides insights into optimizing the design of coastal bridges. The proposed analytical model can supply preliminary guidance at the initial stage of bridge design without costly numerical simulations or physical model tests. [ABSTRACT FROM AUTHOR]

In the design of the ecological seawall project for storm surge prevention on the north coast of Lingshan Island in the Greater Bay Area, to solve the contradiction between urban flood tide prevention and the hydrophilicity of the coastal landscape ecological seawall, the design is transformed from the traditional single tidal wave prevention seawall to the diversified coastal landscape ecological seawall by the concept of innovative technology. This paper innovatively proposes the following two technologies: the multi-stage wave dissipation platform technology and the upstream drainage system technology of coastal landscape belts to solve the problem of wave dissipation and drainage. In practice, the paper proposes the concepts of "horizontal for vertical" and "external drainage of external water and internal drainage of internal water" to break the traditional "blocking" and "resisting" of seawalls to the waves. It adopts the horizontal multi-stage wave dissipation platform technology to eliminate the waves and sets up a multi-stage drainage system to realize the self-exhaustion of the waves. The flexible articulation of "pass" and "discharge" for the waves on the waterfront can effectively reduce the vertical dike top elevation to solve the problem of "dike surrounding the city" and realize the purpose of coastal landscape ecological seawall. The research results have been applied to the project and have been tested by several storm surges to prove that the expected results have been achieved. In terms of the resilient city, especially in the design of the ecological dike, Lingshan Island exchanges the width for the height, which can not only prevent floods but also meet the requirements of water, leisure, and landscape. It provides experience and reference for the Lingnan region of ecological construction, and even the same type of construction in China's coastal estuarine areas.

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Major differences in beach erosion between two neighboring artificial beaches Xiangluwan Beach (XL beach) and Meiliwan Beach (ML beach) in Zhuhai, China, were studied after Super Typhoon Hato. In this study, a fully nonlinear Boussinesq wave model (FUNWAVE)-Total Variation Diminishing (TVD) was used to distinguish the main impact factors, their relative contributions, and the hydrodynamic mechanisms underlying the different beach responses. Results show that compared to the ML beach, the main reason for the relatively weak erosion on Xiangluwan (XL) beach was the smaller beach berm height (accounting for approximately 75.9% of the erosion response). Regarding the beach with a higher berm, the stronger wave-induced undertow flow, along with the higher sediment concentration, led to a higher offshore sediment transport flux, resulting in more severe erosion relative to the beach with a smaller berm height. The second most important reason explaining the weak erosion on XL beach was the absence of seawalls (accounting for approximately 17.9% of the erosion response). Wave reflection induced by the seawall could cause higher suspended sediment concentration, resulting in a toe scouring near the seawall. The offshore submerged breakwater protected XL beach slightly (accounting for approximately 6.1% of the erosion response). Due to the higher water level induced by storm surge, most of the wave energy could penetrate through the submerged breakwater. The effect of the larger berm width of XL beach was negligible. Compared to the beach with a larger berm width, the erosion/deposition regions in the beach with a narrower berm width showed shoreward migration, without significant changes in the erosion/deposition extent. Despite of this, the larger berm width could reduce the wave energy reaching the shoreline. This study of the storm stability of artificial beaches may be applied to beach restoration design. [ABSTRACT FROM AUTHOR]

Copyright of Jurnal Teknologi dan Rekayasa Sumber Daya Air is the property of Brawijaya University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Existing seawalls along the eastern coast of China are increasingly becoming the focus of upgrade operations. Concerns arise regarding the settling and stability of seawalls built on soft clayey seabed during upgrade operations. Pore water pressure (PWP) and horizontal displacement accumulations induced by combined tide and wave loadings are observed in in-situ measurements of the clayey seabed underneath the seawall. The measurement results show clear correlations between the oscillations of excess PWP and variations in the tidal height. To reproduce the quasi-static interaction behaviors of the gravity-type seawall and clayey seabed under combined cyclic loadings from waves and currents, a finite element model has been built after incorporating a stiffness degradation law that is evaluated from laboratory triaxial tests on the seabed soil. Demonstrably, with a suitable stiffness degradation law for the seabed soil, the accumulative behaviors can be reasonably reproduced using finite-element modeling. [ABSTRACT FROM AUTHOR]

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Admittedly, deformation prediction plays a vital role in ensuring the safety of seawall during its operation period. However, there still is a lack of systematic study of the seawall deformation prediction model currently. Moreover, the absence of the major influencing factor selection is generally widespread in the existing model. To overcome this problem, the Chaotic Particle Swarm Optimization (CPSO) algorithm is introduced to optimize the wavelet neural network (WNN) model, and the CPSO-WNN model is utilized to determine the major influencing factors of seawall deformation. Afterward, on the basis of major influencing factor determination results, the CPSO algorithm is applied to optimize the parameters of Long Short-Term Memory (LSTM). Subsequently, the monitoring datasets are divided into training samples and test samples to construct the prediction model and validate the effectiveness, respectively. Ultimately, the CPSO-WNN-LSTM model is employed to fit and predict the long-term settlement monitoring data series of an actual seawall located in China. The prediction performances of LSTM and BPNN prediction models were introduced to be comparisons to verify the merits of the proposed model. The analysis results indicate that the proposed model takes advantage of practicality, high efficiency, stable capability, and high precision in seawall deformation prediction. [ABSTRACT FROM AUTHOR]

As China enters a new stage of high-quality ecological development, higher demands are placed on the ecological effects of coastal protection projects. Because the traditional hard seawall pays little attention to its impact on the coastal ecological environment, the construction of seawalls along the line cuts off the habitats inside and outside the pond, which makes the regional habitats fragmented, and hinders the migration of organisms. In order to restore and protect the coastal zone, build an ecological seawall, improve the seawall's ability to resist typhoon, storm surge, and other marine disasters, and protect the beach wetlands, water quality, and biodiversity along the seawall, this project started with the study of biological channels, and then systematically carried out the investigations, research, and analysis on the biological resources inside and outside the seawall and along the seawall. The results of research and field investigation showed that there were mainly natural plant communities such as Bolboschoenoplectus mariqueter and Phragmites australis on the beach of Jianshan section. The back slope of the pond was the soil slope with human afforestation as the main vegetation, and the foot of the slope was the protection pond river. Crab was the dominant species in beach and intertidal zone. Referring to the domestic and international biological channel cases, we proposed to set up 8 biological channels in the Jianshan section of the pond as a test section without affecting the structural safety of the seawall, and set up video monitoring equipment to evaluate the use of the channels and provided data support for future design or optimization of the channels. [ABSTRACT FROM AUTHOR]

This study utilized a two-dimensional numerical viscous wave tank to simulate the run-up and run-down processes of non-breaking solitary waves on a steep seawall. The research aimed to investigate the transformation between wave potential energy and kinetic energy, the evolution mechanisms of the wave and flow fields, and the correlation between the dynamic pressure gradient and the reverse flow near the sloping bed. The numerical model results were consistent with laboratory measurements of free surface elevations and flow velocity profiles, demonstrating the accuracy of the numerical model. This study focused on a solitary wave with a wave-height-to-water-depth ratio of 0.15, propagating on a representative seawall with a steep slope of 1:3 along the western coast of Taiwan. The simulation results indicate that the maximum run-up height occurs when the potential energy is at its highest. Undertow is caused by the adverse pressure gradient within the flow field, and the dynamic pressure on the sloping bed is directly proportional to the free surface elevation. Therefore, by observing the spatial changes in the free surface elevation, we can indirectly determine the occurrence time of undertow. [ABSTRACT FROM AUTHOR]

Copyright of Ecology & Civil Engineering is the property of Ecology & Civil Engineering Society and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Local scour and wave loading are two key factors that affect the safety of seawalls under tsunami attacks. In this study, the scouring process at the toe of and wave impact force on a vertical seawall under consecutive solitary wave attacks are simulated using a quasi-three-phase (air, water, and sediment) flow model, which models the air and water as a fluid mixture phase and sediment as a solid phase. The air and water interface is modeled by a VOF method and the sediment–fluid interaction is modeled using the Eulerian two-phase flow method. A comparison between the beach profiles with and without the seawall shows that, with a seawall, a deeper scour hole is generated at the toe of the seawall. Besides, the presence of the seawall causes the eroded sediment to be deposited further offshore. The numerical results are then analyzed in detail regarding the flow field and sediment transport process to reveal the mechanisms of the above eroding/depositing patterns. The wave impact force on the seawall is also analyzed to understand the effect of scouring on the wave loading. It is shown that the wave impact force, despite being stochastic for a specific wave, increases in general with the deepening of the scour hole because the latter increases the exposure of the seawall to wave slamming. • A numerical model capable of tracking air, water and sediment is used to simulate sediment transport in front of a seawall. • The seawall is found to cause sediment loss at its toe. • The wave impact force exerted on the seawall is found to be enhanced by the scour hole at the toe. [ABSTRACT FROM AUTHOR]

FETSWCM-SWAN and DualSPHysics models are used to study the storm flooding process of Dazuo Seawall in Quanzhou city, Fujian province, China. Firstly, a storm over-topping assessment method is proposed. Secondly, the water level and storm wave at the foot of Dazuo Seawall calculated by FETSWCM-SWAN during the process of Typhoon Usagi in 2013 and Typhoon Dujuan in 2015. Finally, the typical wave and storm run-up processes at Dazuo Seawall are modeled by DualSPHysics. The results show that the typical wave run-up of Dazuo Seawall is less than 2 m, but the storm wave run-up can reach 6.85 m under Usagi. The risk is high when high tide is encountered. The risk of storm flooding is classified into three grades. This risk assessment could provide decision-making support to government departments in warning against storm flooding threats. [ABSTRACT FROM AUTHOR]

The present study reports on a series of laboratory experiments aiming to understand and to optimize the deployment of seawall defences over low-lying coral reef flats. The study is performed in a purely cross-shore configuration, with varying wave forcing, water depth, and seawall shapes and positions along the reef flat. The observations reveal the individual and combined effects of the external parameters. A higher seawall efficiency is reached for low waves, shallow water depth, seaward position, and a stepped seawall shape. A dimensionless formulation is proposed to predict the short wave transmission coefficient dependency on the seawall freeboard, incoming wave height, berm width, and seawall shape. [ABSTRACT FROM AUTHOR]

Zhan, Y.; Aarninkhof, S.G.J.; Wang, Z., and Zhou, Y., 2022. Monitoring yearly change patterns of the surface tidal trail (STT) in tidal flats: A novel morphological indicator extracted from a near-infrared terrestrial laser scanner. Journal of Coastal Research, 38(5), 1011–1020. Coconut Creek (Florida), ISSN 0749-0208. Tidal flats play an important role in the geomorphological and biological dynamics of coasts. Research on the morphological evolution of tidal flats constitutes one of the key research issues pertaining to the sustainability of coastal ecosystems and related coastal defense issues. In this work, a novel indicator, the surface tidal trail (STT), was extracted from a near infrared terrestrial laser scanner and studied. The results show that the area intensity and size of STTs decline yearly. Meanwhile, the position shift of the peak value on the STT curves presents a similar pattern of hydrodynamic force in response to the seawall, which has been studied in previous works. Although no direct correlation between the STT intensity and the deposition rate was found, the corresponding hydrodynamic force data were not available in this work. The change process of STTs still provides a possible speculation that hydrodynamic force and the softness of tidal surfaces are two main factors that form and influence STTs. For future research, establishing the direct quantitative relationships among hydrodynamic force, topography, and STTs on different temporal and spatial scales would help to better understand this novel indicator. [ABSTRACT FROM AUTHOR]

A tidal bore is known for its abrupt change in water flow with a complex and violent leading front. The powerful tidal bore can quickly move up the sloped beach and overtop the seawall, leading to significant damages along the coast. In the past, many coastal seawalls were constructed to shield the coastal regions from the destructive power of tidal bores. The typhoon-induced shear force and pressure imbalance can significantly affect the tidal bore height and its propagation speed. Therefore, it is important to evaluate how strong winds impact the hydrodynamic transformation and overtopping of tidal bore at the seawalls. However, there are few research on this topic. To address the limitations of previous research, this study applies a high-resolution two-phase flow solver to numerically examine how strong winds impacts the overtopping characteristics of tidal bore at coastal seawalls. The effects of main factors, including wind speed, tidal bore height, water depth, and beach slope, are thoroughly examined. Research findings indicate that the presence of wind can cause notable changes in the hydrodynamic evolution and overtopping characteristics of both undular tidal bore and weak breaking tidal bores, whereas its impact on the overtopping characteristics of breaking tidal bore is relatively limited. Simultaneously, the presence of wind can significantly increase the intensities of the undular tidal bore and weak breaking tidal bore at the seawall. The high nonlinear behavior of the breaking tidal bore at the seawall is demonstrated by its impactful intensity when influenced by wind. It is hoped that the present study will enhance knowledge on the hydrodynamic overtopping characteristics of tidal bores in harsh weather conditions. • Hydrodynamic overtopping processes of different types of tidal bores at the seawall under the wind have been numerically investigated by applying a high-resolution two-phase flow solver. • Influences of major factors, such as wind speed, tidal bore height, initial water depth, and beach slope are investigated in detail. • Research results reveal that the wind can noticeably reshape the hydrodynamic evolution and overtopping characteristics of the undular tidal bore and weak breaking tidal bore, except the breaking tidal bore. [ABSTRACT FROM AUTHOR]

Estimation of nonbreaking wave forces on seawalls for design is generally carried out through either empirical or analytical formulations with some inherent assumptions. Computationally intensive solutions, such as those based on Smooth Particle Hydrodynamics (SPH) and mixed Eulerian-Lagrangian (MEL) schemes, may not always be feasible for this purpose. In this paper, a numerical approach that employs Bernoulli's equation at the free surface and continuity equation over the fluid domain is proposed to accurately obtain the dynamic wave pressure. Subsequently, the wave forces on a rigid seawall are determined following the Froude-Krylov theory, with diffraction effects approximately accounted for by a horizontal force coefficient. The method is both computationally efficient and applicable to a wide range of irrotational wave propagation conditions, including large amplitude waves. The nonbreaking wave forces evaluated for a large amplitude travelling wave profile taken from literature are found comparable, but with some differences, to those obtained using the existing design standards. Hence, results from the proposed method for varying water wave propagation conditions are utilized to derive correction factors that can be applied to the existing stipulations in design standards for a more accurate assessment of wave forces for seawall design, without undertaking rigorous numerical computations. • Computationally efficient numerical scheme for nonbreaking wave forces on seawalls. • Accurate estimation of wave flow parameters from an exact nonlinear formulation. • Wave forces determined from Froude-Krylov theory with correction for diffraction. • Valid for wide range of wave propagation conditions and large amplitude waves. • Correction factor given for accurate wave force estimation from existing standards. [ABSTRACT FROM AUTHOR]

Tidal bores are a natural phenomenon with high flow velocity and destructive potential. A spur dike is a widely used river regulation and embankment protection structure that minimizes erosion, promotes deposition, and protects riverbanks. However, the scouring mechanism around a spur dike under the action of a tidal bore is not fully understood, and accurately estimating the maximum scour depth has always been a challenge, limiting the construction and maintenance of spur dikes in estuarine and marine environments. This study analyzed the scouring characteristics around a spur dike induced by tidal bores via field observation and model experiments. The results show that the scours around a spur dike can be divided into dike head scour and upstream side scour. The scour depth is related to the geometric shape of the spur dike and its surrounding riverbed, hydrodynamic forces, and sediment characteristics. The least squares method obtained the fitting formulas for the depth of the scour at the dike head and upstream side. Overall, the present study indicates an agreement of the scouring characteristics around a spur dike between the field observations and laboratory experiment, and the fitting formulas can be effectively applied to engineering practices of a macro-tidal estuary. [ABSTRACT FROM AUTHOR]

Seawalls are important in protecting coastlines from currents, erosion, sea-level rise, and flooding. They are, however, associated with reduced biodiversity, due to their steep orientation, lack of microhabitats, and the materials used in their construction. Hence, there is considerable interest in modifying seawalls to enhance the settlement and diversity of marine organisms, as microbial biofilms play a critical role facilitating algal and invertebrate colonization. We assessed how different stone materials, ranging from aluminosilicates to limestone and concrete, affect biofilm formation. Metagenomic assessment of marine microbial communities indicated no significant impact of material on microbial diversity, irrespective of the diverse surface chemistry and topography. Based on KEGG pathway analysis, surface properties appeared to influence the community composition and function during the initial stages of biofilm development, but this effect disappeared by Day 31. We conclude that marine biofilms converged over time to a generic marine biofilm, rather than the underlying stone substrata type playing a significant role in driving community composition. [ABSTRACT FROM AUTHOR]

In the past few decades, huge surges and waves generated during tsunami events have caused devastating destruction to both onshore and offshore infrastructures, seriously threatening the safety and intactness of coastal communities around the world. As one of the most important coastal protection infrastructures, a seawall can effectively reduce the impact intensity of surges and waves, thus playing a vital role in protecting coastal regions. Most previous studies have systematically investigated the hydrodynamic characteristics of seawalls under the action of regular and irregular waves. Meanwhile, solitary wave models are often used as the wave model for tsunamis. However, vast hydrodynamic differences exist between solitary wave models and real-world tsunamis in terms of both wave profile and wave period. Hence, our understanding of the performance of seawalls in mitigating the damaging power of real-world tsunamis is still insufficient. Hence, it is of great significance to systematically study the performance of seawalls in mitigating the huge surges and waves generated during real-world tsunamis. In comparison to previous research, where the wave profiles of solitary waves were used as tsunami wave models, a parameterized tsunami-like wave based on the recorded wave profile of the 2011 Japan tsunami is applied in this study to evaluate the performance of different seawalls in mitigating tsunami surges and waves by using a nonhydrostatic numerical wave model (NHWAVE). The effects of the prominent factors, such as incident wave height, still water depth, beach slope, and the side slope of the seawall, on the hydrodynamics of the seawall are systematically discussed. It is believed that the research findings drawn from this study can further broaden our understanding of the performance of seawalls in mitigating tsunamis. [ABSTRACT FROM AUTHOR]

Seawalls are important in protecting coastlines from currents, erosion, sea-level rise, and flooding. They are, however, associated with reduced biodiversity, due to their steep orientation, lack of microhabitats, and the materials used in their construction. Hence, there is considerable interest in modifying seawalls to enhance the settlement and diversity of marine organisms, as microbial biofilms play a critical role facilitating algal and invertebrate colonization. We assessed how different stone materials, ranging from aluminosilicates to limestone and concrete, affect biofilm formation. Metagenomic assessment of marine microbial communities indicated no significant impact of material on microbial diversity, irrespective of the diverse surface chemistry and topography. Based on KEGG pathway analysis, surface properties appeared to influence the community composition and function during the initial stages of biofilm development, but this effect disappeared by Day 31. We conclude that marine biofilms converged over time to a generic marine biofilm, rather than the underlying stone substrata type playing a significant role in driving community composition.

Tsunami that happened along Sunda Strait on 22 December 2018 was generated by the collapse of the flank of Anak Krakatau volcano in Indonesia. The tsunami hit Lampung and Sunda beaches areas. The hydrodynamic force of the tsunami hit everything on its course severely including seawalls that are used to protect the beach from erosion due to wind waves. The stability of such structure is limited to the design wind wave force. Tsunami has a significantly different nature compare to wind waves. When tsunami arrives at the coastline it becomes surge where, the water particle movement is significantly faster than that of the wind waves. The force of such high speed of water particles at a seawall may destroy and drag away the material far from the original location. Field survey was conducted following the tsunami event along Sunda Strait in Banten area. Based on the survey, a hydraulic simulation of seawall destruction due to tsunami was carried out in the laboratory. It was found that there were two distinct mechanisms of seawall destruction. When the land support of the seawall is relatively weak, the seawall may be dragged landward. However, when the land support behind the seawall is relatively strong, for example more than 40% of the seawall’s total height that stabilize the seawall against the turning moment, the seawall may be dragged seaward by the tsunami return flow (run down). These mechanisms are relevant to tsunami mitigation. Consideration of seawall collapse due to return flow of tsunami should be taken into account since, normally tsunami is a wave train that attacks the beach in a series.

A tsunami is a destructive wave that can cause massive damage to coastal infrastructure. One of the disaster mitigation measures that can be chosen is the construction of coastal protection infrastructure, such as a seawall. Seawalls play a crucial role in protecting coastal areas as they can reduce wave energy and minimize the impact of tsunami-induced damage. However, during the 2011 Japan tsunami, the seawall built in Taro city failed as it proved to be less effective in handling the tsunami waves. The research conducted aims to model the propagation and overtopping of tsunami waves on the seawall, initially carried out through physical laboratory experiments, and later transformed into numerical test models using the Smoothed Particle Hydrodynamics (SPH) method and the Cornell Multigrid Coupled Tsunami (COMCOT) model. In this study, the parameters being compared include wave height, wave propagation, and overtopping on the seawall under two scenarios : the run-up of solitary waves on a shore without a seawall and the overtopping condition with a seawall using the Solitary Wave generation type, following the experiments conducted by Huang et al en 2022. Several parameters in the laboratory case study should be considered to expand our understanding of the systematically discussed tsunami propagation and overtopping processes and evaluate the capabilities of the SPH and COMCOT models.

The infrastructure reconstructions after the Great East Japan Earthquake (GEJE) and related attempts on biodiversity conservation were categorized and reviewed. Seawalls and wave-dissipating blocks reconstructed after the GEJE are examples of gray infrastructure. Reconstructed coastal protection forests and constructed green spaces are "green" infrastructure in the sense of using plants; however, they also seriously damage coastal ecosystems. Present states of coastal protection forests and green spaces would not sufficiently provide ecosystem services expected for a coastal environment. Attempts to conserve biodiversity and landscape, i.e., unreconstructing or downsizing seawalls, setting back seawalls, designating conservation areas, and laying coastal sand on seawalls or mounds of coastal protection forests, have been made and established. However, they were not applied with the concept of green infrastructure, were designed not to deliver ecosystem services, and were independently implemented and isolated without a strategically planned network. Therefore, the network of the sites of these attempts should be planned to deliver the expected ecosystem services. Laying coastal sands on facilities is probably useful for building a type of corridor that links isolated conservation areas. Studies on the present state of biodiversity and other environments and sociological studies are needed to improve ecological services from reconstructed coastal area. [ABSTRACT FROM AUTHOR]

Using artificial constructions is one of the most important ways to protect shores against wave actions and the consequent erosion. Due to costly nature of large scale marine projects, it is considered an efficient approach to study small scale model of the structure for simulation of sea conditions, measurement of hydraulic parameters and wave-structure interactions. In present research, construction of a small wave flume has been reported. Water up to 15 cm deep is filled in the flume and a DC motor directly rotates a flap in oscillations as a result of which regular waves of less than 10 cm height are produced. Wave lengths are around one meter, and wave periods are about one second. High quality fast images were analyzed in order to characterize the waves. Test runs were performed with different combinations of the wave parameters and the water depth, on five different revetments including: vertical seawall, simple slope, stepped slope, curved and recurved. Wave discharge with the aid of a small reserve tank at the far end of flume was measured. Results show that the recurved structure for most of the test cases reduce the wave overtopping to zero. The stepped slope has an efficient performance in dissipating the wave energy and reducing the wave run-up and overtopping. Simple slope recorded maximum discharge. Curved structure creates a water column of high speed vertical jet, and lastly the vertical seawall undergoes severe wave impact. Quantitative test results have been compared with well-known Owen’s formula for wave overtopping.

ABSTRACT: Bulletins of China’s National Sea Level show that the average rising rate of sea-levels in China is 3.3 mm/a over the past 40 years, with an obviously accelerated rising trend in the last decade. The rate of relative sea-level rise of the Yangtze River Delta reached >10 mm/a after considering the land subsidence, and Bohai Bay is even greater than 25 mm/a. The impact of the sea level rise to the coastal area will be greater in the coming years, so carrying out an assessment of this rising trend is urgent. This paper, taking the coastal area of Tianjin and Hebei as examples, comprehensively evaluates the impact of sea-level rise through multitemporal remote sensing shoreline interpretation, ground survey verification, elevation measurements for both seawall and coastal lowlands. The results show that the average elevation of the measured coastal areas of Tianjin and Hebei is about +4 m, and the total area of >100 km2 is already below the present mean sea level. More than 270 km, ca. 31% of the total length of the seawall, cannot withstand a 1-in-100-year storm surge. Numerical simulations of the storm flooding on the west coast of Bohai Bay, for 1-in-50-years, 1-in-100-years, 1-in-200-years and 1-in-500-years, show that if there were no coastal dykes, the maximum flooding area would exceed 3000 km2, 4000 km2, 5300 km2 and 7200 km2, respectively. The rising sea has a direct and potential impact on the coastal lowlands of Tianjin and Hebei. Based on the latest development in international sea-level rise prediction research, this paper proposes 0.5 m, 1.0 m and 1.5 m as low, middle and high sea level rise scenarios by 2100 for the study area, and combines the land subsidence and other factors to the elevation of the existing seawall. Comprehensive evaluation results indicate that even in the case of a low scenario, the existing seawall will not be able to withstand a 1-in-100-years storm surge in 2030, and the potential flooding areas predicted by the model will become a reality in the near future. Therefore, the seawall design in the coastal areas of Tianjin and Hebei must consider the combined effects of land subsidence, sea level rise and the extreme storm surges caused by it.©2019 China Geology Editorial Office.

The present study reports on a series of laboratory experiments aiming to understand and to optimize the deployment of seawall defences over low-lying coral reef flats. The study is performed in a purely cross-shore configuration, with varying wave forcing, water depth, and seawall shapes and positions along the reef flat. The observations reveal the individual and combined effects of the external parameters. A higher seawall efficiency is reached for low waves, shallow water depth, seaward position, and a stepped seawall shape. A dimensionless formulation is proposed to predict the short wave transmission coefficient dependency on the seawall freeboard, incoming wave height, berm width, and seawall shape.

FETSWCM-SWAN and DualSPHysics models are used to study the storm flooding process of Dazuo Seawall in Quanzhou city, Fujian province, China. Firstly, a storm over-topping assessment method is proposed. Secondly, the water level and storm wave at the foot of Dazuo Seawall calculated by FETSWCM-SWAN during the process of Typhoon Usagi in 2013 and Typhoon Dujuan in 2015. Finally, the typical wave and storm run-up processes at Dazuo Seawall are modeled by DualSPHysics. The results show that the typical wave run-up of Dazuo Seawall is less than 2 m, but the storm wave run-up can reach 6.85 m under Usagi. The risk is high when high tide is encountered. The risk of storm flooding is classified into three grades. This risk assessment could provide decision-making support to government departments in warning against storm flooding threats.

This paper reports on an experimental study on a new self-centring retaining wall system. Four post-tensioned segmental retaining walls (PSRWs) were experimentally tested. Each of the walls was constructed using seven T-shaped concrete segments with a dry stack. The walls were tested under incrementally increasing cyclic lateral load. The effect of the wall height, levels of post-tensioning (PT) force, and bonded versus unbonded condition of PT reinforcement on the structural behavior of the PSRWs was investigated. The results showed that such PSRWs are structurally adequate for water retaining structures. According to the results, increasing the wall height decreases initial strength but increases the deformation capacity of the wall. The larger deformation capacity and ductility of PSRW make it a suitable structural system for fluctuating loads or deformation, e.g., seawall. It was also found that increasing the PT force increases the wall's stiffness; however, reduces its ductility. The residual drift and the extent of damage of the unbonded PSRWs were significantly smaller than those of the bonded ones. Results suggest that this newly developed self-centring retaining wall can be a suitable structural system to retain lateral loads. Due to its unique deformation capacity and self-centring behavior, it can potentially be used for seawall application. [ABSTRACT FROM AUTHOR]

Tidal bores are a natural phenomenon with high flow velocity and destructive potential. A spur dike is a widely used river regulation and embankment protection structure that minimizes erosion, promotes deposition, and protects riverbanks. However, the scouring mechanism around a spur dike under the action of a tidal bore is not fully understood, and accurately estimating the maximum scour depth has always been a challenge, limiting the construction and maintenance of spur dikes in estuarine and marine environments. This study analyzed the scouring characteristics around a spur dike induced by tidal bores via field observation and model experiments. The results show that the scours around a spur dike can be divided into dike head scour and upstream side scour. The scour depth is related to the geometric shape of the spur dike and its surrounding riverbed, hydrodynamic forces, and sediment characteristics. The least squares method obtained the fitting formulas for the depth of the scour at the dike head and upstream side. Overall, the present study indicates an agreement of the scouring characteristics around a spur dike between the field observations and laboratory experiment, and the fitting formulas can be effectively applied to engineering practices of a macro-tidal estuary.