Search

Hydraulic experiments using a wave flume with a wind tunnel at a scale of 1/40 were carried out to investigate the effect of wind on wave overtopping of a vertical seawall. To ascertain the possible effects of wave breaking, incident waves with various wave steepness (0.0102 to 0.0371) and three kinds of wind forcing (0 m/s, 6.84 m/s, 10.04 m/s) were used. The authors found that winds significantly increased the overtopping rate in general, and that there is a clear relationship between the overtopping rate and the wave steepness. Velocity fields obtained from PIV analysis revealed that the onshore winds directly enhanced the transport of overtopping water mass. The influence of the wind on the wave hydrodynamic processes that indirectly have an effect on the overtopping rate (such as the formation of a partially standing wave, breaker location, and breaker type) is also discussed. The perspective of treating wave overtopping as a transport of water mass could provide a novel understanding of complex fluid behavior, which would help to formulate countermeasures against future disasters influenced by intensive wind forcing. [ABSTRACT FROM AUTHOR]

The actions of wind and atmospheric pressure associated with tropical cyclones (e.g. typhoons) are considered the primary factors behind the generation of storm surges, though the fields used in meteorological models can sometimes deviate from observations. To improve these, the direct modification method (DMM) has been previously proposed, though this only modifies the wind field of a typhoon, and further development is necessary for applying it to storm surge hindcasts. The present work describes the development of a semi-empirical gradient wind balance-based method (GWB-M) for modifying both the wind and pressure fields in meteorological models, based on the dynamic relationship between the wind and pressure in typhoons (i.e. gradient wind balance). The applicability of GWB-M was assessed through a storm surge hindcast based on Typhoon Faxai in 2019, which generated powerful waves and a storm surge at Tokyo Bay. GWB-M improved the time series of 10 m wind speed and sea level pressure, with their spatial distributions being more realistic than those in DMM and blending parametric typhoon models (BM), which cannot take into account the influence of the complex topography around Tokyo Bay. Further, the maximum sea level anomalies after the typhoon made landfall were also captured by GWB-M with a higher accuracy than DMM. [ABSTRACT FROM AUTHOR]

Haiyan in 2013 was one of the most powerful typhoons to have affected the Philippines, devastating in its path a wide portion of Leyte, and causing extensive damage to structures in Tacloban City. To understand the likely impacts that would be exerted by a storm surge on a structure deemed important, the authors used a coupled model that hindcasted the flooding that took place during Haiyan. This coupled model included the use of the Weather Research and Forecasting (WRF) Model (with Bogussing scheme) to simulate the atmospheric conditions during the passage of Haiyan, the Finite Volume Coastal Ocean Model (FVCOM) to simulate the storm surge and obtain the boundary conditions for the wind and flood (hydrostatic, hydrodynamic, and breaking wave), and the Structural Analysis and Designing Program (STAAD.Pro) to calculate the corresponding axial, shear, and bending moment envelopes based on the storm surge simulation. A 4-floor public school building in Tacloban was modeled and the effects that the storm surge would have on a corner column were analyzed. Based on the results, the axial, shear, and moment at the corner column significantly increased when considering flood loads, indicating the importance of including such loads in the design of essential structures. [ABSTRACT FROM AUTHOR]

A field survey of Fukuura Coast (in Tokyo Bay, Japan) revealed during the passage of Typhoon Faxai in 2019 waves with considerable momentum caused significant wave overtopping, resulting in structural damage to coastal defenses and localized flooding. The hindcasted wave height using a third-generation wave model was not high enough to explain the extent of the local damage at Fukuura Coast, likely due to such methods failing to take into account the strong gust-winds recorded during the passage of the typhoon. To solve such problems the authors developed a new numerical model that takes into account the dynamic interaction of air and water, based on the finite volume method (FVM) and the volume of fluid method (VOF). Although this model still slightly underestimates the measurements in the experiments previously conducted by different authors, it is better than existing methods when estimating the overtopping rates under strong winds. The model was then applied to a real-scale model of Fukuura Coast, where by taking into account strong gust-wind speed of 41 m/s the authors were able to explain the phenomena that took place. [ABSTRACT FROM AUTHOR]

Inland tsunami flows can be greatly affected by the presence of coastal buildings. The present study experimentally and numerically investigated the effects of nine different building layouts on 1) the tsunami inundation process and spatial velocity distribution, 2) the flow depth and velocity at a specific point, and 3) the extent of the area where shielding effects take place. High-speed video footage, PIV analysis, and the time history of flow depth, surface velocity and momentum flux demonstrated significant differences in the tsunami run-up behavior among the different building layouts considered. However, it was also shown that a decrease in the surface velocity of flow always appears in front of and immediately behind the building(s), regardless of their layouts. The OpenFOAM simulations performed revealed that significant shielding effects appear in the leeside of the building. These findings can be used when considering where to place evacuation buildings, as constructing them directly behind another study structure could reduce construction costs and increase their stability. The obtained results were also applied to partially validate the method for calculating the channeling effects of tsunami loads provided in ASCE 7–16. [ABSTRACT FROM AUTHOR]

The 2011 Tohoku Tsunami caused severe damage to many coastal defenses along the Japanese coastline, including areas where two adjacent upright sea dikes of different heights met. There are many places along the coastline where structures of different heights and shapes meet due to the various design codes. In this study, the authors aim to examine the tsunami flow around such dikes by conducting three-dimensional hydraulic experiments in a tsunami wave basin and numerical simulations using the fluid dynamics model OpenFOAM. Twelve experimental cases were tested by changing the waveforms, and also by keeping the height of one side of the dike model constant while adjusting the dimensions of the other side. The results show that the difference in height between the structures significantly influences the volume of overtopping over the relatively lower dike and the inundation depth and velocity behind the dikes. Furthermore, different characteristics of inundation patterns are observed between the inundation depth and velocity. Hence, this study illustrates the necessity to re-assess the effectiveness of such structures against tsunami events. [ABSTRACT FROM AUTHOR]

The September 28 2018 Palu tsunami surprised the scientific community, as neither the earthquake magnitude nor its strike-slip mechanism were deemed capable of producing the wave heights that were observed. However, recent research has shown that the earthquake generated several landslides inside Palu bay. The authors conducted a post-disaster field survey of the area affected to collect spatial data on tsunami inundation heights, nearshore and bay bathymetry, and carried out eyewitness interviews to collect testimonies of the event. In addition, numerical simulations of the tsunami generation and propagation mechanisms were carried out and validated with the inferred time series. Seven small submarine landslides were identified along the western shore of the bay, and one large one was reported on the eastern shore of Palu City. Most of these landslides occurred at river mouths and reclamation areas, where soft submarine sediments had accumulated. The numerical simulations support a scenario in which the tsunami waves that arrived at Palu city 4–10 min after the earthquake were caused by the co-seismic seafloor deformation, possibly coupled with secondary waves generated from several submarine landslides. These findings suggest that more comprehensive methodologies and tools need to be used when assessing probabilistic tsunami hazards in narrow bays. [ABSTRACT FROM AUTHOR]

In the present study, three different types of landslide-generated tsunamis (subaerial, partially submerged and submarine) were investigated through laboratory experiments that used 261 different experimental conditions. The results show that, for the near-field region, the subaerial landslide generated a higher leading wave, while the submarine landslide generated a higher second wave. However, frequency dispersion considerably influenced their propagation, with the leading wave decaying and the trailing waves being enhanced. The present study also revealed that the leading wave has higher values for wave celerity, period, and length than the second wave, regardless of landslide type. It was also shown that the celerity of the leading wave and second wave can be approximated by the solitary wave theory and third-order Stokes theory, respectively. Using the extensive experimental dataset obtained, predictive equations to estimate the maximum crest amplitudes generated by partially submerged and submarine landslides were also developed. A comparison with the experiments of previous researchers and field survey data from the 2018 Palu Tsunami indicated that these equations can estimate reasonably well the height of the generated tsunami. It was also shown that the relative mass and initial position of the landslide are influential nondimensional parameters to determine the tsunami amplitudes generated. [ABSTRACT FROM AUTHOR]

Five cases of ports in Japan and Indonesia that have subsided by a metre or more were analysed. The findings suggest that there are no unsurmountable technological, cost-benefit, financial and social limits to the progressive raising of these ports, at least for the magnitude of climate-induced sea-level rise expected during the 21st century. In Indonesia observed adaptation is a sequential process: only part of the port is raised at one time, allowing port operations to continue elsewhere and spreading costs in time. Jumps in unit costs are apparent as the elevation height increases. In addition, the possibility of sea-level rise triggering innovative changes in port design to lower costs (e.g., a move to floating ports) is being considered. For traditional ports to upgrade by up to 1 metre, unit costs are found to be somewhere between 50–360 USD/m3 rise (not including the cost of piling). Nevertheless, such adaptation costs would represent a significant burden and adaptation is often reactive rather than proactive, leading to significant damage costs, as in the case of Hurricane Katrina's impact on Gulf Coast Ports. [ABSTRACT FROM AUTHOR]

Tsunamis can cause large damage to breakwaters and other protection structures placed along the coastline. The strong flows generated by such waves can move the armor units of composite breakwaters, leading to large impact forces on the caissons behind them. In the present work laboratory experiments were carried out in a flume to determine the forces that can result from such impacts. Then, an empirical equation that would allow the estimation of these forces was proposed, with the aim of facilitating the construction of returning walls and parapets situated on top of caissons. [ABSTRACT FROM AUTHOR]

The object of the present study is to numerically evaluate the characteristics of future potential typhoons and storm surges around Tokyo Bay under a RCP8.5 scenario usinga simple one-way model system composed of ARW-WRF and FVCO. In order to evaluate the effect of the expected future increase in sea surface temperature (SST), air temperature (AT) and relative humidity (RH) four types of cases were considered in the 2041–2060 and 2081–2100 horizons. The results show how higher SST will likely lead to more intense typhoons and storm surges, though higher AT in troposphere and tropopause will somehow moderate this effect. In addition, a simple method to estimate the most influential wind direction that can generate surge elevations in Yokohama, Tokyo and Funabashi was examined by using the results of a numerical simulation. Finally, a simple methodology to calculate the required design height of sea walls and dykes in Tokyo Bay was developed, which shows how current design levels will be insufficient to maintain the present acceptable risk levels in the area. [ABSTRACT FROM AUTHOR]

On the 22nd of December 2018 the shorelines of Sunda Strait, Indonesia, were hit by tsunami waves generated by the flank collapse of the Anak Krakatau volcano. The authors conducted a field survey of the affected areas in both Sumatra and Java islands to collect information on tsunami inundation and run-up heights, damage patterns at each coastal community, and the evacuation behaviour and tsunami awareness of the affected people. The survey results showed that in Sumatra island inundation heights of more than 4 m were measured along the coastline that was situated to the north-north-east of Anak Krakatau, while less than 4 m were measured along the north-western direction. Inundation heights of over 10 m were measured at Cipenyu Beach (Pandeglang Regency) in Java island (south-south-eastern direction from Anak Krakatau). A questionnaire survey conducted by the authors revealed residents' perception of danger and evacuation patterns during the event. The results indicate the importance of having an operational tsunami warning system in Sunda Strait and the establishment of an appropriate evacuation plan so that residents can start evacuation immediately and reach a safe place without facing severe congestion along evacuation routes. [ABSTRACT FROM AUTHOR]

A new semi-empirical formula for calculating the breaking depth of plunging breakers is proposed in this study. The shallow water equation is used as the governing equation, and the wave front slope, which is one of the key parameters that governs the breaking criterion, is obtained from it analytically. The analytical formula was then modified based on both physical considerations and historical laboratory data. The accuracy of the resulting semi-empirical formula was examined using two sets of new laboratory data – including laboratory experiments performed by the authors – in order to verify its applicability. The results indicate that the proposed new formula is more accurate than existing formulas. [ABSTRACT FROM AUTHOR]

In response to criticism, greenfield smart and sustainable city developers have paid increasing attention to their social impact by prioritizing placemaking and citizen involvement in their planning and development. However, citizens’ participation remains limited, and little is known about their everyday experiences, perceptions, and communities. While cultural mapping is an established process to build communities and articulate their identity, it has rarely been used in greenfield developments. This paper presents the Kashiwanoha Monogatari Project to demonstrate that cultural mapping can strengthen community ties and encourage citizen participation in new smart urban development. The paper details the cultural mapping project and its outputs, including lessons learned about citizen perception of their smart city. The findings suggest that cultural mapping provides citizens and planners with tools to visualize their emerging place-based narratives and communities by providing an alternative approach to co-creation with citizens. [ABSTRACT FROM AUTHOR]

Effective adaptation to climate change impacts is rapidly becoming an important research topic. Hitherto, the perceptions and attitudes of stakeholders on climate adaptation actions are under researched, partly due to the emphasis on physical and engineering aspects during the adaptation planning process. Building on such considerations, the paper explores the perceptions of port decision makers on the effectiveness of climate adaptation actions. The findings suggest that while port decision makers are aware of potential climate change impacts and feel that more adaptation actions should be undertaken, they are skeptical about their effectiveness and value. This is complemented by a regional analysis on the results, suggesting that more tailor-made adaptation measures suited to local circumstances should be developed. The study illustrates the complexity of climate adaptation planning and of involving port decision makers under the current planning paradigm. [ABSTRACT FROM AUTHOR]

On 11 March 2011, an exceptionally large tsunami event was triggered by a massive earthquake offshore, the northeast coast of Japan, which affected coastal infrastructure such as seawalls, coastal dikes and breakwaters in the Tohoku region. Such infrastructure was built to protect against the Level 1 tsunamis that previously hit the region, but not for events as significant as the 2011 Tohoku tsunami, which was categorized as a Level 2 tsunami [Shibayama, T., Esteban, M., Nistor, I., Takagi, H., Thao, N. D., Matsumaru, R., Mikami, T., Aranguiz, R., Jayaratne, R. & Ohira, K. [2013] 'Classification of tsunami and evacuation areas,' Nat. Hazards 67(2), 365-386]. The failure mechanisms of concrete-armored dikes, breakwaters and seawalls due to Level 2 tsunamis are still not fully understood by researchers and engineers. This paper investigates the failure modes and mechanisms of damaged coastal structures in Miyagi and Fukushima Prefectures, following the authors' post-disaster field surveys carried out between 2011 and 2013. Six significant failure mechanisms were identified for the coastal dikes and seawalls affected by this tsunami: (1) Leeward toe scour failure, (2) Crown armor failure, (3) Leeward slope armor failure, (4) Seaward toe scour and slope armor failure, (5) Overturning failure, and (6) Parapet wall failure, in which leeward toe scour being recognized as the major failure mechanism in most surveyed locations. The authors also propose a simple practical mathematical model for predicting the scour depth at the leeward toe of the coastal dikes, by considering the effects of the tsunami hydrodynamics, the soil properties and the type of structure. The key advantage of this model is that it depends entirely on quantities that are measurable in the field. Furthermore this model was further refined by conducting a series of hydraulic model experiments aimed to understand the governing factors of the leeward toe scour failure. Finally, based on the results obtained, key recommendations are given for the design of resilient coastal defense structures that can survive a level 2 tsunami event. [ABSTRACT FROM AUTHOR]

Category 5 Typhoon Haiyan was one of the strongest typhoons to hit the Philippines in modern times, and introduced the term 'storm surge' to the vocabulary of many local residents, who had not heard about such phenomena prior to this event. The storm surge manifested itself on the 8th November 2013 as Haiyan made landfall, devastating large areas in the islands of Leyte and Samar. To attempt to gain an understanding of the level of awareness that local residents had about storm surges the authors conducted structured questionnaires () and focus group interviews with local residents, and discussed the results obtained with key informants (government officers and disaster risk managers). One of the key problems identified during the interviews was how people were not able to clearly understand the concept of a storm surge, with many respondents emphasizing how it would have been better for authorities to describe it as a 'tsunami'. A discussion is also made on the recent evolution in world-wide coastal disaster awareness, comparing it to recent developments in storm surge awareness in the Philippines and other countries in the area, such as Vietnam and Japan. The authors conclude that, in terms of its influence on world-wide disaster awareness, typhoon Haiyan constitutes an event of similar importance to major recent high-impact tsunami events such as the 2004 Indian Ocean and 2011 Tohoku events. As a result, the authors will outline a number of lessons learnt from Haiyan, such as the necessity for creating multi-layer safety strategies and improving how information about storm surges is transmitted to local residents. [ABSTRACT FROM AUTHOR]

Following typhoon Haiyan in November 2013, the government of the Philippines organized massive housing reconstruction programs that are currently facing complex implementation issues. The present study investigated the mechanisms of three types of housing reconstruction programs (i.e. owner-driven on-site reconstruction, community-driven off-site relocation and contractor-driven off-site relocation) and discussed sustainability challenges by assessing the gaps between community needs and program performance, measured through the level of beneficiary satisfaction. The study conducted semi-structured questionnaire surveys with beneficiary households and key informant interviews with government officials and nongovernment organization representatives in March 2015. Results showed that on-site reconstruction was delayed due to insufficient and poorly implemented assistance schemes relating to reconstruction (e.g. materials, skills training), while off-site relocation was delayed by prolonged land acquisition and subcontracting issues. Disruption of critical infrastructure, such as water utility services, and lack of livelihood opportunities significantly affected the satisfaction levels of respondents with the recovery progress. The study also found that the no-dwelling-zone policy was not strictly enforced as houses were still being rebuilt in high-risk areas near the coast. Finally permanently relocated residents continue to struggle, especially with regard to their source of livelihood, as relocation sites are inaccessible and located away from employment opportunities. [ABSTRACT FROM AUTHOR]

Typhoon Haiyan (Yolanda) struck the islands of Leyte and Samar, the central part of the Philippines, on 8 November 2013, bringing large-scale devastation to coastal areas due to the high winds and large storm surge and waves associated with it. In order to obtain the distribution of storm surge heights and damage covering the wide stretch of affected coastline, the authors carried out a series of field surveys in the aftermath of the typhoon (in December 2013, May 2014, and October 2014). In the present paper, the authors detailed the results of these field surveys and summarized the characteristics of the storm surge and main causes of the damage, especially focusing on the Leyte Gulf coast, which is surrounded by the eastern coast of Leyte and the southern coast of Samar. Finally, the wide range of types of storm surge disasters were also discussed by comparing Typhoon Haiyan with other recent major events. [ABSTRACT FROM AUTHOR]

The authors propose a new method to estimate the tilting failure of caisson breakwaters, using a Monte-Carlo simulation that can quantitatively and stochastically estimate failure probability. An index, referred to as "Expected Frequency Exceeding of a Critical Load (EFEC)" that expresses the potential tilting failure probability of caisson breakwaters is proposed and adopted in this model. Application of the model to 40 breakwaters in Japan reveals that the threshold value of EFEC that specifies whether a caisson breakwater is safe or unsafe could lie in the range from 0.02 to 0.04. The authors also found that unstable caisson geometry, showing a large value in the aspect ratio of the caisson, can provide additional indication of when tilting failure is likely to occur. It is expected that the present method can provide a practical way for engineers to judge the possibility of tilting failure in caisson breakwaters. [ABSTRACT FROM AUTHOR]

Susami West Breakwater, a composite caisson breakwater located in Japan, was damaged by high waves caused by typhoon Tokage on the 20th of October 2004. The failure mode was characterized by the sliding/tilting of the caissons and the removal of the concrete armoring units. The failure of these armor units is believed to increase the pressures exerted by the waves on the caisson, and thus exacerbate the expected deformations in the rubble mound foundation, a fact which has thus far been ignored in previous research. The present paper proposes a methodology to take into account the effect of these concrete armor units to estimate the deformations that took place in the rubble mound foundation. The methodology uses a modification of the method by Goda [1985] proposed by Esteban et al. [2009] that can approximate to the right order of magnitude the vertical deformations at the back of the caisson by using a Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

At 14:46 on March 11, 2011 (local time), a large earthquake of magnitude Mw 9.0 took place, generating a tsunami that caused severe damage to the east coast of Japan. To comprehensively record tsunami trace heights and impacts along the coastal region, the Tohoku Earthquake Tsunami Joint Survey Group was organized immediately after the event. As part of this group, the authors conducted a field survey in Miyagi and Fukushima Prefectures. The surveyed area can be divided into 2 parts from the point of view of its geographical features: the northern part (a rias coastal area) and the southern part (a coastal plain area). In this paper, the characteristics of the damage due to the tsunami in each area are analyzed by using both the results of the authors' own field survey and the Joint Survey Group. In the rias coastal area, inundation heights were more than 10 m, which resulted in the flooding of the low-lying grounds located at the inner part of the bays. The tsunami wave caused widespread destruction in this area, and coastal buildings (including reinforced concrete buildings) suffered severe damage. In the southern coastal plains, inundation heights were 5-10 m and the tsunami reached a few kilometers inland, though unfortunately there were not enough high locations or buildings for the residents to evacuate. In addition, an extensive line of coastal dikes and forests, which had been placed to protect the wide plains behind them, also suffered extensive damage. From these geographically dependent inundation and destruction patterns, a number of important lessons on how to modify and improve future risk management strategies can be obtained. [ABSTRACT FROM AUTHOR]

Climate change is expected to lead to increases in both sea level and typhoon intensity, which could threaten the stability of breakwaters in the future. In this study, calculations using the SWAN model showed that a 10% potential increase in the future wind speed of typhoons resulting from the warming of surface sea temperatures can lead to a 21% increase in the significant wave heights generated by these winds. To understand the effect that this would have on breakwater stability, the expected sliding distances for the breakwaters at Shibushi Ports in Japan were estimated using a probabilistic design method. The results show that in the future the expected sliding distances may become five times greater than at present, due to a combination of increases in sea level and wave height. [ABSTRACT FROM AUTHOR]

This article examines the emergence of offshore renewable energy (i.e., offshore wind, ocean, and tidal energy) in the Asia-Pacific region with a particular focus on developments in China, South Korea, Australia, and New Zealand. It outlines plans for the development of offshore wind, tidal, and wave energy projects as well as emerging legal and policy measures supporting the growth of offshore renewable energy in the region. The article highlights that, although some progress has been made on laws and other measures to facilitate offshore renewable energy in the Asia-Pacific region, clear regulatory frameworks are still emerging in these jurisdictions. [ABSTRACT FROM AUTHOR]

This paper presents a method to simulate the construction of a caisson breakwater in order to evaluate the risks involved in its construction. A computer model of the construction process that a contractor would follow to build a caisson breakwater was developed, with the wave climate for each month of the duration of works modeled using data obtained from the NOWPHAS Reports. Possible damage to the caisson was determined using a deformation-based reliability design method that included sliding, tilting, overturning of the caisson and erosion of the toe armour and foundation material. The model included possible delays due to adverse weather, reconstruction of damaged sections and construction accidents. By using the Monte Carlo simulation technique, the expected cost and time to finish the breakwater could be obtained, allowing to determine the risk associated with the breakwater construction. Thus, it is possible to determine when would be the most appropriate time to begin construction and the likelihood of encountering problems during the construction phase. A case study of the breakwater construction for Honshu island in Japan is shown, with the results comparing well with the experience of Japanese contractors. [ABSTRACT FROM AUTHOR]

The aim of the present paper is to investigate the long-term deformations of the rubble mound of a breakwater during its working life. Understanding these deformations is essential for the sliding and tilting to be able to be measured effectively. In order to do so, laboratory experiments were carried out, from which probability distribution functions of sliding and tilting were obtained for a series of three storms of similar intensity. The laboratory results were then reproduced using a computer model, which decomposed the movement of the caisson into its vertical and horizontal components. The horizontal movement uses the equation of Shimosako and Takahashi [1998] as modified by Kim and Takayama [2005], whereas for the vertical deformation the method of Esteban and Shibayama [2006] is employed. A new methodology for the calculation of the resistance force caused by the caisson tilting is proposed. The results obtained overestimate the deformation slightly during the first storm but can predict well the deformation during the subsequent storms. [ABSTRACT FROM AUTHOR]