Design Of Seawalls Research Articles

Stakeholders support marine eco‐engineering, but what are the perceived benefits and who should pay?

Abstract Despite the ecological and socio‐economic benefits of nature‐based solutions (NbS), the application of ecological principles to the design of seawalls (termed ‘seawall eco‐engineering’) to mitigate their impacts remains low. We investigated stakeholder perspectives of, support for and willingness to pay (WTP) for seawall eco‐engineering in one of the most diverse and urbanised harbours in the world, Sydney Harbour, in Australia. Using a series of workshops and surveys targeting the general public, Local Government, built environment and natural environment professionals, we identified and ranked perceived risks and benefits of eco‐engineering seawalls, the most common infrastructure in the Harbour. Additionally, WTP for seawall eco‐engineering was investigated using an existing, large‐scale eco‐engineering project. Overall, workshop participants rated benefits of seawall eco‐engineering to be almost double the risks. The key perceived benefits were increased habitat/biodiversity, improved water quality and enhanced environmental stewardship/awareness. Key perceived risks were potential damage to infrastructure and use of greenwashing to facilitate new development. Across all stakeholder groups, participants were very supportive of statements regarding the benefits of eco‐engineered seawalls and the need for eco‐engineering principles to be included in the design of new seawalls. Despite strong support for seawall eco‐engineering, WTP was estimated at one third of the actual cost and was, in part, attributable to a lack of a shared evidence base from successful projects, and unclear guidance and policy around implementation. Synthesis and applications: Our results showed that establishing rigorous monitoring and evaluation programs that facilitate cost–benefit analyses are critical to enhancing WTP for and uptake of eco‐engineering projects. Furthermore, more cost‐effective technologies and shared funding models may overcome existing financial impediments. We also found integrative legislation may be key to increased implementation of such NbS, given that existing policies were viewed as unsupportive. Read the free Plain Language Summary for this article on the Journal blog.

Marsh restoration in front of seawalls is an economically justified nature-based solution for coastal protection

A marsh-fronted seawall is a hybrid nature-based coastal protection solution because it attenuates wave energy, reduces erosion, and provides ecosystem services. However, we still have a limited understanding of how to quantify the marsh wave attenuation benefits for economic analysis. Here, we incorporate a prediction of wave attenuation that accounts for species-specific morphology and structural stiffness into a 1-D wave model and validate it with field measurements. Our results show that the wave attenuation varies by a factor of two across different vegetation species. Further, we performed a benefit-cost analysis, in which the economic benefits represent the environmental services value and avoided seawall heightening cost that would otherwise be required to deliver the same overtopping rate without vegetation. We applied the model to a real-world, marsh-fronted seawall design at Juniper Cove, Massachusetts. Although the benefit of marsh-fronted seawalls is sensitive to discount rate, they have benefit-cost ratios greater than one, indicating that it is an economically justified nature-based solution. Further, we found that wave attenuation and benefit-cost ratio are more sensitive to water depth than wave height. Our study demonstrates the importance of considering the coastal protection of marshes and economic benefits in one framework.

Seepage Analysis and the Reservoir Water Pollution Potential under Vertical Dam Structure Planning

A prospective resolution to the intricate predicaments of flooding, sanitation, and the availability of unprocessed water for the populace of Jakarta residents is the implementation of the coastal reservoir paradigm. This paradigm entails harnessing the latent capacity of the Cisadane River flow and its subsequent storage within a retention pond, and then subjecting it to reprocessing to serve as a viable source of raw water. The selection of a vertical seawall design was based on the objective of creating an effective barrier between the reservoir and the sea, while also considering several environmental factors. This design was selected with the aim of minimizing the need for extensive soil excavation and rock placement. However, it is important to note that the risks of construction failure associated with seepage under hydraulic structure and dam stability pose significant challenges. Besides preventing saltwater intrusion and maintaining the integrity of the reservoir as a freshwater source, dam must be designed to mitigate potential seepage failure and intrusion issues. To address these concerns, this study employed numerical simulation using the SEEP/W and CTRAN/W software. The simulation was carried out to analyze seepage discharge under a vertical dam and predict potential seawater intrusion into the reservoir. The dam was examined over a ten-year period, with varying embankment widths of 10m, 20m, and 30m. The analysis considered changes in water level (ΔH) and the addition of a cut-off wall at depths of 5m, 10m, and 15m. The obtained results showed that seepage discharge rates amounted to 3,14x10-4 m3 s-1, 2,67x10-4 m3 s-1, and 2,50x10-4 m3 s-1 for embankment widths of 10m, 20m, and 30m, respectively, under a 1m level difference condition. Following this, the safety factor for piping on vertical embankment was determined as 1.10, 1.34, and 1.39 for widths of 10m, 20m, and 30m, respectively. This factor was found to increase to 4.03 when the embankment distance was widened, and a 15m deep cut-off wall was installed. It is important to note that the seawater intrusion model predicted a seawater concentration of 65,12 g m-3 at the bottom for an embankment width of 10m, while no intrusion was observed at widths of 20m and 30m with ΔH=1m. This study aims to assess potential risks of piping due to seepage and seawater contamination at the Cisadane Estuary.

Wave distribution and proposed seawall design around Tanjung Emas Port, Semarang

On May 23rd, 2022, an extreme coastal event occurred around the northern coast of Java. This event had caused the collapsed of several seawall segments around Tanjung Emas Port, Semarang. Combined with wave overtopping, it led to severe flooding and economic damages to the port operation. Responding to the event, this research aimed to characterize the hydrodynamic condition around the port and proposed a seawall design. The research was done through field observation, wave climate characterization, and numerical simulation. The field observation confirmed the extent of the damage and wave condition around the harbour. The wave climate study, based on a global wave reanalysis data, confirmed that the offshore wave height could reach 3 m during high wave season, with wave period of 4 – 6 seconds coming from the northwest. The tidal range is up to 1 m with highest astronomical tide (HAT) is at +0.65 MSL. The extreme value analysis gave a 3.7 meter of offshore design wave height for 100-year return period or up to 1.7 meters wave height nearshore. The proposed seawall crest elevation is at least at +3.40 meters above the mean sea level to avoid overtopping, which is 1.1 m higher than the existing seawall.

Numerical Analysis of Wind Effect on Wave Overtopping on a Vertical Seawall

Onshore wind significantly affects wave run-up and overtopping, thereby representing a major variable to account for in the design process. The aim of this study is to analyze the ability of numerical models to properly reproduce the wind effect on the overtopping at vertical seawall and to use them to understand how the wind influences the overtopping process as well. We use the RANS model, FLOW-3D, and the NLSW model, SWASH; both model the action of wind through the shear stress that it exerts on the sea surface. Although a simplified modelling of wind has been adopted, the CFD model has led to physically consistent results. On the other hand, SWASH seems to be unsuitable for reproducing the enhancement of the overtopping rate due to wind. CFD numerical results show that the wind affects only the lower overtopping regime (i.e., q < 1 l/s/m); as the mean overtopping discharge decreases, the influence of wind increases. Specifically, wind plays a key role in pure “white overtopping”, where the advection of spray is the predominant mechanism of the overtopping process. The effects of wind thus seem to be important in the design of seawalls, but are difficult to quantify through hydraulic models because of the unknown scaling laws. Therefore, we have found that a full-scale numerical approach is suitable to study the influence of wind on wave overtopping and to evaluate the wind factor to take into account in the design process.

Tensile properties of cement-stabilised clays and their contribution to seawall design

Deep cement mixing is a typical ground improvement technique, and has recently been introduced in some large-scale reclamation projects in Hong Kong. There is a lack of internationally recognised testing standard for determining the tensile strength of cement-stabilised soil. In this study, tensile properties of cement-stabilised clays have been investigated using direct tension test and Brazilian test. The interpretation of tensile strength in Brazilian test is not straightforward due to the formation of multiple cracks during loading. As such, focus is placed on the validation of the fundamental assumption on crack initiation mechanism. A consolidated database of tensile strengths of cement-stabilised soils is compiled. A constitutive model in the finite-element program Plaxis, namely concrete model, has been studied. This model, originally aiming to simulate the behaviour of concrete and shotcrete, duly considers the cracking and the strain-softening characteristics, and is able to reasonably simulate the fundamental tensile behaviour of cement-stabilised soil. Numerical simulations have been carried out using the concrete model to assess the stability of seawall founded on cement-stabilised clay. Tensile properties are found to have an important bearing in maintaining the stability of the seawall when column-pattern stabilisation is adopted.

Increased wave load on the Gudong seawall caused by seabed scour

Seawalls play an important role in protecting coastal regions by resisting storm surge and waves. However, a seawall can cause seabed erosion at its foot by facilitating hydrodynamic scouring, but the effects of seabed scour on wave loads have not been sufficiently considered. This paper presents a case study of increased wave load on the Gudong seawall in the Huanghe delta, China, which has experienced serious erosion since its construction. Four commonly-used empirical formulas, which were also verified through our physical simulation experiments, were used to calculate the wave loads on the crown wall of the seawall based on observed wave conditions. The maximum allowable wave load on the seawall was also determined based on historical extreme sea conditions that caused severe damage to the seawall. Our calculations showed that, the wave load has increased at least two times since the seawall's construction due to seabed scour, and the present crown wall cannot resist large waves with a 5-year return period, much less than the 50-year return period it was designed to resist. This suggested that the reasonable design of seawalls needs to adequately consider seabed scour as well as the associated increase in of wave loads.

Risk And Mitigation Analysis of Tidal Flooding Disaster in Medan Belawan Sub-Distric, Medan City

Medan Belawan is one of sub-district in Medan City North Sumatera which is the coastal area. The area is particularly vulnerable to coastal hazard that of all people living near coastal line. The most influential of disaster is tidal flood. Tidal flood almost occurs every year with the total inundation area is 26,25 Km2, for example from 2010 until 2017 recorded that the tidal flood inundated around 0,5 m to 2 m in average. There were 98 113 people and 3000-4000 houses, schools, public health facility (puskesmas), highway, fishponds, and international harbor affected. The disaster is not only threatening the community life but also disturbance their sustainable livelihood especially people with low socio-economic condition. This paper provides risk index analysis of the flood and propose the disaster risk reduction measures to reduce the impact of risk. Regarding the analysis, Medan Belawan Sub-district was categorized into high-risk area to the tidal flood, so that its need disaster risk reduction measures. Disaster risk reduction aims to protect affected communities, reduce damage and losses when the disaster happens and make sure sustainable livelihood. Mitigation is one of disaster risk reduction effort that can be divided into structural and non-structural. In structural measure, one of solution is building the impervious seawall which is designed based on increasing of sea level rise due to some factors such as tidal, wave, wind, climate change, land subsidence, and flood which is caused by rainfall with the high intensity. Overall basic design of seawall can build in Medan Belawan Coastal Area is around 4,95 m for its height and will be in residential area that is directly bounded by the sea. In the other hand non-structural approach can be implemented if people permanently live in that area. They can do some adaptation activities to reduce negative impacts and if possible, for taking any advantages of its positive impacts. People can modify their settlements, public facilities and livelihood. Some area in Medan Belawan sub-district also have mangrove forest, there is around 747 hectares. Combination both of approaches aim to reduce the disaster risk.

Catatan tentang Perencanaan Tembok Laut untuk Mitigasi Bencana Tsunami

Many coastal structures or structures in coastal areas were destroyed by a tsunami attack. Such destructions were due primarily to the fact that such structures were not designed to withstand a tsunami. Those which were designed to withstand tsunami force may also have been destroyed due to some damaging factors which were not included in the design. The damage of the coastal structures is one of the important factors that have caused casualties. Especially, when the destroyed structures were originally aimed to mitigate the area against tsunami, they may cause higher fatalities. Examples of such structures are sea walls in many parts of Japan which were destroyed by the 2011 tsunami. This paper discusses the important factors relevant to the damage of seawall as tsunami mitigation structure such as impact force due to tsunami front, hydrostatic force, and hydrodynamic force, debris force and scour due tsunami. The study was carried out based on literature about the damages of seawall as tsunami protection structures and laboratory experiment reports. The destructions to the structures were divided into three classifications namely instantaneous direct destruction due to impact and drag forces, slowly direct destruction due to drag force, and slowly indirect destruction due to scour. Finally, important aspects to be considered in the design of seawall as tsunamis protection were proposed.

Modular floating structures (MFS) for offshore dwelling a hydrodynamic analysis in the frequency domain

The concept of Modular Floating Structures (MFS) offers a unique avenue to explore new and sustainable ways for addressing issues of coastal urbanization and sea level rise in the proximity of coastal cities. This concept is easily implemented in calm waters without the interference of waves. Yet, its implementation in open water, poses greater challenges, particularly in terms of habitability and comfort. The current study examines the feasibility of the concept in two locations: in mild sea zone near Singapore and in open water conditions at the Eastern Mediterranean Sea. Both conditions are examined in operational and extreme storms. It is shown that the MFS configuration can attenuate incident waves of short periods. This reduces the motion amplitudes of the inner modules with respect to the exterior modules facing the waves. It is also presented that during extreme storms, the chosen configuration is less effective, and the motion amplitudes of all modules within the MFS fabric are almost identical. To further increase the acceptable sea states, the study proposes a unique floating seawall design, which provides a substantial wave reduction in long wave periods. The study presents the efficiency of the new configuration in operational weather and a 100-years storm.

Analysis on the current situation and key problems of artificial island development in China

The artificial island is an important way to develop and utilize the resources of sea areas, islands, and mudflats. The land formed by it has increased artificial shoreline. It is the way of reclamation with advanced concepts in the world and has been paid more and more attention. Based on the investigation and analysis of the current situation of artificial island development in China, the key problems of artificial island development were analyzed. The exploitation of artificial islands can be divided into 4 categories: industrial production land, transportation place, tourism and entertainment place, and urban construction land of comprehensive utilization. The key issues in the development of artificial islands include the fundamental data, site selection, plane shape, foundation treatment, seawall design, ecological environmental impact, full consideration of extreme events and abundant funds. Site selection is the core of the key problems of artificial island development, which is mainly restricted by functional requirements and also influenced by natural conditions.

Mitigation of Tsunami Environmental Implications on Nuclear Facilities through Improvement of Seawall Design

Mitigation of Tsunami Environmental Implications on Nuclear Facilities through Improvement of Seawall Design

The impact of sea-level rise on the coast of Tianjin-Hebei, China

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.

REDUCTION OF THE WAVE OVERTOPPING DISCHARGE AT DIKES IN PRESENCE OF CROWN WALLS WITH BULL NOSES

The effects of climate change with increased sea level and intensity of the extreme storms leads to an increase of the loads and of the expected overtopping at existing seawalls. The inclusion of bull-noses in the design of seawalls seems to significantly reduce the wave overtopping discharge q and may be an effective solution to face climate change while limiting the increase of the seawalls height and the costs. The experimental work by Van Doorslaer et al. (2015), VD hereinafter, is the only systematic study available so far about the effects of bull-noses on the reduction of q. They developed a number of formulae, adopted then by EurOtop (2016), in case the seawall is placed on a dike slope or at the end of a promenade. The work we are proposing here starts from these findings, to analyze a different case: dikes with a finite crest width and an inshore crown wall with and without a bull-nose. The aim is to verify whether the formulae developed by VD can still be used or require some modifications to complete the existing design formulae.

A METHOD FOR EVALUATING THE MAXIMUM TSUNAMI LOADINGS ON SEAWALLS

A seawall in a nuclear power station is one of the important structures to protect from tsunami. Estimation of tsunami loadings on structures is an important part of the proper design of seawalls. In this study, hydraulic flume tests was conducted to investigate the characteristics of tsunami loadings. Correlations between the loading on a seawall and the Froude number as characteristics of the tsunami flow were investigated. Finally, we proposed a new evaluation method to evaluate the design wave pressure on a seawall. A new evaluation method can predict the design wave pressure on a seawall with taking the characteristics of the tsunami flow into consideration.

Reliability-based assessment and design of stone-filled crib seawalls for shoreline protection

ABSTRACTIn this study, an efficient reliability-based design tool for stone-filled crib seawalls is developed. The first-order reliability method is integrated into spreadsheet to facilitate the reliability analysis for practical application. Using this spreadsheet tool, the effects of several major uncertain factors on the seawall design, including design water level, material property, and wave forces, are explicitly explored. In addition, the impact of progressive scour on the seawall stability is demonstrated through a time-dependent reliability analysis. This developed reliability-based design tool for seawalls is validated through comparing with the Monte Carlo simulation. This seawall design tool is easy to use and can be readily adapted in various aspects in the seawall design for shoreline protection.

Stability of seawalls using modified pseudo-dynamic method under earthquake conditions

By using the modified pseudo-dynamic method for submerged soils this paper explores the seismic stability of seawall for the active condition of earth pressure. Different forces such as seismic active earth pressure, seismic inertia forces of the wall, non-breaking wave pressure, hydrostatic and hydrodynamic pressures are considered in the stability analysis. Limit equilibrium has been used, and expressions for the factor of safety against sliding and overturning mode of failure have been proposed. The proposed methodology overcomes the limitations of existing pseudo-dynamic method for submerged soils. A detailed parametric study has been conducted by varying different parameters and results are presented in the form of design charts for computation of factor of safety against sliding and overturning mode of failures. It was noticed that the influences of soil friction angle, seismic acceleration coefficient, wall inclination and excess pore pressure are significant when compared to the other parameters. The value of factor of safety against the sliding mode of failure is increasing by about 62% when the value of soil frictional angle is increased from 30° to 40°. It was also found that the factor of safety against overturning mode of failure is decreasing by about 22% as the value of excess pore pressure ratio increases from 0 to 0.75. The proposed method with closed-form solutions can be used for the seismic design of seawalls.

Effects of sea level rise and typhoon intensity on storm surge and waves in Pearl River Estuary

Climate changes, including sea level rise (SLR) and typhoon intensification (TI), have had widespread impacts on natural systems. Through the use of coupled ADCIRC+SWAN models, this study investigates the effects of potential SLR as well as TI on storm surges and waves in Pearl River Estuary, China. Meanwhile, examination of how SLR and TI impact seawalls has been conducted. Results demonstrated that TI has a greater impact on storm surge, whereas SLR has a greater impact on wave heights in the estuary. There is no substantial difference of peak surge height (referring to the mean sea level of the corresponding SLR scenarios) in response to the increase of sea level in the study area. However, by combining the sea level rises of 0.5–1.0m, the surface elevations of peak storm surge increased under SLR conditions. Besides, enhanced typhoon intensity was found to cause the increase of peak surge height as well as wave height in some shallow areas. Furthermore, the combination of those two factors also increased peak surge height and greatly increased wave height. By running the coupled ADCIRC and SWAN models, the simulated results can be employed in flood mitigation and design of seawalls in Pearl River Estuary.

Developing new formulae for prediction of mean overtopping discharge at vertical walls

In this paper, a comprehensive nonlinear regression analysis has been conducted on widely known dimensionless parameters associated with the overtopping phenomena as one of the highest priority design criteria in seawall design, using CLASH (Crest Level Assessment of coastal Structures by full-scale monitoring, neural network prediction, and Hazard analysis on permissible wave overtopping) database, as the most viable source in this regard. Accordingly, new formulae have been put forward for calculation of mean overtopping discharge at vertical walls on horizontal as well as sloping foreshore. It has statistically shown that presented formulae have a comparatively better correlation with related CLASH data when compared with the existing ones. Therefore, implementing new formulae will hopefully result in a more reliable design of vertical walls with respect to overtopping discharge performance.

Canons of Coastal Engineering in the United Kingdom: Seawalls/Groynes, a Century of Change?

ABSTRACT Williams, A.T.; Giardino, A., and Pranzini, E., 2016. Canons of coastal engineering in the United Kingdom: Seawalls/groynes, a century of change? A Royal Commission on Coast Erosion and Afforestation, 1911, investigated the state of coastal erosion and the resulting protection measures carried out in the U.K. This paper looks at progress undertaken with respect to seawall and groyne protection in the more than 100 years since publication of the report. Seawall design has been greatly modified, although curved and stepped designs were built in the Victorian era, as well as the more common vertical ones. Groynes have also been modified from invariably using wood and rock to other materials, e.g., metal, concrete precast elements, geotextiles, as well as shape, e.g., Y, gamma, or T shaped groynes rather than orthogonal to the beach. Numerical/physical modelling has now made both structures much more robust and rigorous, although arguments are still ongoing regarding how they are used. A strong envir...