Coastal Structures and Solutions to Coastal Disasters 2015: Tsunamis

Numerical simulations are performed to develop tsunami inundation maps for the U.S. East Coast (USEC), as envelopes of surface elevations caused by the probable maximum tsunamis (PMTs) in the Atlantic Ocean basin. These PMTs are triggered by various sources, identified from historical records or hypothetical, including : (i) near-field submarine mass failures (SMF) on or near the continental shelf break; (ii) an extreme hypothetical M9 seismic event occurring in the Puerto Rico Trench; (iii) a repeat of the historical 1755 M9 (Lisbon) earthquake occurring in the Madeira Tore Rise; and (iv) large scale volcanic flank collapses (80 and 450 km³) of the Cumbre Vieja volcano (CVV) on La Palma, in the Canary Archipelago. Tsunamis caused by: (1) earthquakes, are obtained from the estimated coseismic seafloor deformation; (2) SMF sources, modeled as rigid slumps, are generated using the 3D non-hydrostatic model NHWAVE; and (iii) the CVV sources are modeled as subaerial flows of a heavy fluid, using a 3D Navier-Stokes model. For each source, tsunami propagation to the USEC is then modeled in a series of nested grids of increasingly fine resolution, by one-way coupling, using FUNWAVE-TVD, a nonlinear and dispersive (2D) Boussinesq model. High-resolution inundation maps have been developed based on these results, so far for about a third of the USEC. A comparison of coastal inundation from each tsunami source shows similar alongshore patterns of higher and lower inundation, whatever the initial source direction; this is due to wave focusing and defocusing effects induced by the shelf bathymetry. Once developed for the entire USEC, inundation maps will fully quantify coastal hazard from the selected PMTs and allow developing site-specific mitigation measures and evacuation plans. Besides maximum inundation, other “products” available at high-resolution are maximum momentum flux, currents, and vorticity, although these are not systematically developed as maps in this phase of work.

We present numerical simulations of the April 27, 1975 landslide event in Kitimat Arm, British Columbia. The event caused a tsunami with an estimated wave height of 8.2 m and 6.1 m at the northern and southern ends of Kitimat Arm, respectively. We use the non-hydrostatic model NHWAVE to perform a series of numerical experiments with different slide configurations and with two approaches to modeling the slide motion: a solid slide with motion controlled by a basal Coulomb friction, and a depth-integrated numerical slide based on Newtonian viscous flow. Both models are capable of reproducing observations of the event if an adequate representation of slide geometry is used. Comparable results are obtained using estimates of either Coulomb friction angle or slide viscosity that are within reasonable ranges of values found in previous literature. Preliminary results are presented for an alternate model based on a granular debris flow slide layer.

We investigate the surface gravity and hydro-acoustic wave fields, generated by the 2011 Tohoku-Oki tsunamigenic event using a numerical model based on a computationally efficient depth-integrated equations for a compressible water column coupled to a dissipative sedimentary layers. Spectral analysis of bottom pressure time series obtained in deep water revealed the role of underlying layer on the formation of hydro-acoustic waves and carrying frequency range, damping and trapping behaviors. The presented methodology can enhance the promptness and the accuracy of tsunami early warning systems (TEWS).

The new tsunami loads chapter in the upcoming edition of ASCE 7, Minimum Design Loads for Buildings and Other Structures, requires debris impact to be considered in design of structures in the tsunami inundation zone. If a building site is near a shipping container yard, the standard specifies a procedure to determine if impact by shipping containers must be considered in the structural design. We apply these new provisions to the vicinity of a container yard at Hilo Harbor, which is subject to tsunamis. The procedures to determine the susceptibility to container impact involve a number of separate steps, as specified in the design load standard. These procedures are demonstrated and applied to calculate the impact forces at a number of locations. Contour lines of impact force are then drawn for the impact zone for the container yard. The paper demonstrates the application of several new procedures that are proposed by ASCE 7. To the authors’ knowledge, this paper represents the first publication of a comprehensive application of these new provisions, and it represents a valuable resource for practicing engineers needing to apply the provisions.

Determining the location of floating or partially submerged objects during an extreme hydrodynamic event is an important task the investigation of impact loading resulting from debris impacts. This study investigates the application of a novel tracking system which is based on the radio frequency identification (RFID) technology and exploits the measured angles of arrival and time of arrival of radio waves used to locate an object in space. The system is deployed in a carefully controlled laboratory environment to analyze the performance and accuracy of the system. The standard error and standard deviation are used as metrics for the system’s performance. During testing, the system is subjected to linear and oscillatory motions. Good accuracy and repeatability is found for the tests conducted; however, a number of factors can compromise its accuracy and precision, such as a cluttered environment exhibiting solid obstacles, protruding walls or other disturbing items in the tracking area. In hydraulic and coastal engineering, this RFID technology has significant potential for use in laboratory investigations involving not only the tracking of debris but also in tracking the elements of the coastal structures’ armor layers and also for locating and recording of vessel motions.

This paper reports on an experimental test program investigating the motion and entrainment of flow-entrained debris. The motion of debris in large scale hydraulic events can cause severe damage to the impacted communities: the dynamic characteristics of the debris’ motion is crucial in identifying high-risk areas in affected communities. Determining the motion of flow-entrained debris has been historically difficult to quantify as many traditional techniques, such as post-mortem site assessment, cannot provide sufficient information about the kinematic and environmental conditions that affect the debris motion. This paper presents a novel non-invasive system for tracking the 6 degrees-of-freedom debris motion. The experiments examined the effect of various debris configurations on their entrainment as well as their overall motion. Using video footage, the debris entrainment mechanisms and surrounding flow features common to all experiments were examined and using this tracking system, the motion of the debris was accurately tracked and further used to validate other debris spreading observed in real field conditions.

The aim of this project is to review and assess debris management for the USGS science application for risk reduction (SAFRR) tsunami scenario affecting the coast of California. The tsunami scenario, generated from a hypothetical but realistic Mw 9.0 earthquake in the Eastern Aleutian Islands, was developed for emergency planning. Understanding the amount of debris that is generated by a tsunami in Southern California will help the port authorities, tenants and local community better plan its management and the recovery process. The first phase of the study, discussed herein, provides a comprehensive assessment of debris management at the Ports of Los Angeles (POLA) and Long Beach (POLB), CA. The study assessed and evaluated the generated debris by the tsunami scenario, by analyzing physical damage projections from SAFRR. An estimate for time and associated costs with clean up, sorting and removal/disposal of debris was determined. Our study finds that the ports of Long Beach and Los Angeles could generate over 177 thousand tons of debris combined, having a disposal cost of approximately $8 million. With the assistance of two temporary sorting facilities, the generated debris could be collected and disposed within 22 days.

Greece is vulnerable to tsunamis, due to the length of its coastline, its islands and its geographical proximity to the Hellenic Arc, an active subduction zone. Historically, about 10% of all world tsunamis have been reported to have occurred in the Mediterranean region, although this number is possibly an overestimation given that, other than Japan, the region has the most extensive historic written records worldwide. Here, we review existing tsunami disaster risk management capabilities in Greece. We analyze capabilities across the disaster management continuum, including disaster prevention, hazard mitigation and disaster preparedness. Specifically, we focus on regulatory requirements, stakeholders, hazard mitigation practices, emergency operations plans, public education and early-warning systems. Our research is based on a review of our earlier fieldwork on previous projects, as well as on interviews with civil protection officials in Greece, and findings from a large tsunami disaster exercise conducted in 2011, the first ever in the European Union.

The wave forces on the typical coastal twin bridge decks under Stokes 2^nd order waves have been investigated using the Escambia Bay Bridge as the prototype one. The shear stress transport (SST) k-ω model is adopted as the turbulence closure for the RANS equations. Different still water depths with various structure elevations for prescribed gaps between the twin bridge decks (seaward bridge deck and landward bridge deck) are considered to represent different scenarios in field. Both the horizontal and vertical forces under the prescribed conditions are analyzed in details. The results show that at most times the wave forces on the landward bridge deck are relatively smaller than those on the seaward bridge deck. However, the comparisons of the wave forces between the single bridge deck and the twin bridge decks show that much larger wave forces (based on those on the single bridge deck) will be induced on the seaward bridge deck due to the hydrodynamic interference effects caused by the landward bridge deck. As such, it is extremely important to recalibrate the prediction equations proposed by the AASHTO code since these equations are based on the data acquired through the laboratory study regarding the wave forces on one single bridge model.

The huge tsunami generated by the Great East Japan Earthquake attacked the Northern Pacific Coasts of Japan, most severely the Sanriku Coasts, in 2011, killing over 1500 people and inflicting severe coastal damage. The Sanriku Coasts have been frequently attacked by tsunamis historically. The people of the region had learnt from history and so were well prepared for tsunamis. Most of the people evacuated safely and consequently the number of the casualties was limited to 3% of the population in the inundated areas. Still, both the casualties and the economic loss were huge. Recovery from the disaster is still slow; the coastal communities were never resilient. The reason for the scale of the devastation is that the people were completely unprepared for a worst-case scenario. This paper discusses various countermeasures for resilient coastal communities, focusing on a worst-case scenario using a performance design scheme.

Tsunamis pose a considerable risk to life and property along the shorelines of the Hawaiian Islands. To help mitigate this risk, the federal emergency management agency (FEMA) has included tsunami runup mapping on coastal flood hazard maps in the County of Hawaii. In 2007, the U.S. Army Corps of Engineers (USACE) collected high-resolution airborne bathymetric and topographic LiDAR data along the Hawaiian Island coasts. Recently, FEMA funded a study to update the tsunami runup mapping for the City of Hilo, which was previously completed with topographic data collected in the late 1970s. Because the tsunami analysis is dependent on topographic characteristics, a re-delineation of the existing runup elevations onto the new terrain data would not be accurate. This paper includes a description of the updated tsunami runup analysis, a comparison between the old and new results, and details on some of the unique challenges that arose from incorporating high resolution data and results into existing coastal flood hazard maps.

The tsunami generated by the 2011 off the Pacific Coast of Tohoku earthquake caused massive damage to coastal dikes. In order to protect human lives and properties from tsunami, the tenacity of coastal dikes should be improved to secure sufficient time for evacuating residence. In this study, clay or lean cement mixed soil are used for embankment materials. The embankment materials of coastal dikes that can enhance its tenacity are investigated by means of both laboratory experiments and numerical simulations. It was cleared quantitatively from laboratory experiments that tenacity of coastal dikes was improved by using clay or cement mixed sand for embankment materials. In addition, the results from numerical simulations show that the coupled fluid-sediment interaction model considering clay cohesion has possibilities of evaluating the tenacity of coastal dikes composed of clay mixed sand.

To establish a numerical analysis method for quantifying the resilience of coastal dikes, tsunami overflow on a coastal dike and resulting local scouring at its landward toe were investigated using a three-dimensional coupled fluid-structure-sediment-seabed interaction model and its verification hydraulic experiments. From a comparison between numerical results and experimental data, the predictive capability of the model was demonstrated in terms of water surface fluctuation and the profile of a scour hole after the tsunami overflow. Furthermore, it was found that armor blocks below the crown and the berm on the landward slope of the dike received large landward and upward force because of an increase in pore-air pressure inside the dike and a decrease in water pressure induced by the separation of flow, suggesting that these blocks would be vulnerable against the tsunami overflow.

During the Great East Japan Earthquake of March 11, 2011, many protective structures were damaged by tsunami overflow. Some previous results of researches indicate the declining of the safety factor of bearing capacity due to scouring near the foundation of structures. However, the relation between scouring depth and overflow parameters has not yet been well understood. In this study, the scouring depth due to tsunami overflow is investigated by using numerical model based on SPH method and the numerical results are compared with those of the physical model tests. The analysis of numerical results concludes that the maximum depth of scouring is proportional to the height of overflow and is inversely proportional to the falling height of the overflow over the dike.

Tsunamis are able to move large amounts of sediment during their inundation process. However, previous studies conducted to assess tsunami hazard have not considered tsunami-induced sediment transport in their simulations, although it is possible that morphological adjustments during tsunami inundation increase the levels of hazard. In this paper, we present a model which is able to simulate sediment processes caused by tsunami action. The model is validated by comparing results to an experiment of sediment transport under breaking solitary waves. Finally, the model is applied to the simulation of sediment transport over a typical barrier island geometry, and we study the resulting changes in tsunami runup on the mainland behind the barrier, as compared to fixed bathymetry/topography conditions. We show that considering morphological changes during tsunami inundation modeling can increase the runup on the mainland behind the barrier. We conclude that assuming a fixed bathymetry when modeling tsunami coastal hazard may lead to underestimating runup and inundation values and cause errors in estimating the tsunami inundation line.

The influence of the initial beach profile on the tsunami-induced profile change was examined by numerical simulation. The simulations were conducted by using the estimated offshore water levels due to the 5-m-high tsunami in 2011 at the Hasaki Coast in Japan and five different initial profiles: the profile measured on March 11, 2011 (just before the tsunami), the profile on March 11 approximated by a quartic equation, the profiles on March 11 elevated and lowered, and the profile with a developed bar. The simulation results showed that a shallower initial profile increased the magnitude of the overall elevation change. However, the magnitude of the elevation change at the foreshore and backshore increased with a deeper initial profile for the shoreface. These results suggest that a tsunami may damage the foreshore and backshore of an erosive beach more heavily than those of an accretive beach.

The 2011 Tohoku earthquake tsunami occurred resulting a complex waveform which had never been observed before where slowly and small wave initiated by the first impulsive tsunami wave and increases gradually. Then the water surface elevation rose dramatically and quickly reached its maximum level and was followed by a wave train with high constant height with quite long periods. From this evidence, the paradigm of solitary wave-based tsunami wave representation was categorized as outdated for physical modeling. Therefore, to reproduce the 2011 Tohoku earthquake-like tsunami including a steep wave with very long period or current, a new mechanism of tsunami generation in physical modeling is needed. In this study, we conducted the performance test of a cutting-edge tsunami wave generator, which is equipped with three types of wave generation mechanisms: mechanical piston-type wave generation, head storage tank-driven wave generation, and pump-driven wave generation.

Tsunami overtopping a caisson breakwater is reproduced by a numerical model to evaluate the stability of armor units covering the harbor-side of the rubble mound. This model solves the overflow jet above the water surface and the harbor-side flow field separately to avoid entrainment of excessive bubbles. Using this model, the applicability of the Isbash formula for the stability of armor stones and concrete blocks against tsunami overflow is examined. The relationship between the Isbash number and the degree of movement of armor stones is clarified. In the case of concrete blocks, the Isbash number of the stability limitation varied with the thickness of the overflow jet. The Isbash formula by CERC tends to overestimate the effect of slope angle, when applied to concrete blocks. A stability prediction method for armor blocks based on fluid forces acting on each armor block is presented as well.

This paper deals with the stability of the breakwater with pile method by the hydraulic model tests. A kind of breakwaters cross-sections was used in the tests to clarify the failure mechanism of breakwater under tsunami overflow with the method using the combination of the wall (composed of steel pipe piles) and the filling as the reinforcing countermeasure of the caisson. The main experimental result shows that the method improves stability of breakwater under tsunami overflow.

A series of hydraulic model experiments were performed to clarify the effects of wave-dissipating works on force reduction of a tsunami with soliton fission. First, the process of tsunami deformation was examined to understand the characteristics of tsunami profiles with soliton fission. Then, the effects of wave-dissipating works on tsunami force reduction were investigated by comparing the tsunami forces acting on the caisson with and without wave-dissipating works. The effects were then introduced into an existing empirical formula of tsunami pressure as the reduction factor to estimate the tsunami force due to wave-dissipating works.

A flap-gate type movable seawall, which usually lies down on the ground, rises up automatically by buoyancy during inundation by tsunamis or storm surges, and then it forms a continuous seawall. This structure keeps lying in usual time to secure traffic and landscape. In emergence time, it protects a target area against inundation without power machineries and human operation. This structure is named as NEORISE which means No Energy and no Operation RIsing SEawall. The 2011 Tohoku Earthquake gave damages to power machineries and communication systems of tsunami barrier gates and these tsunamis caused many casualties who tried to operate and close these gates. Structures for tsunami protection are required so as to avoid machinery failure and risk of operators. The NEORISE satisfies both of these requirements. In this paper, hydraulic experiments for confirming efficiency of the NEORISE, inspection for the practical structure, and installation on a field are described.

In the context of a comprehensive research project investigating the hydrodynamic loading on structures with openings, this paper focuses on the wave generation techniques currently used and the test results associated with it, proposing a particular tsunami-like wave using a vertical water volume release mechanism. The latter allowed a certain volume of water to flow gravitationally from an upper reservoir into a lower basin through a set of pipes. The propagation of the resulting wave took place in a horizontal channel where wave height and velocities were measured. Both dry bed surges and wet bed bores were investigated, however the present paper mostly focuses on dry bed surges. The study indicated that the surges generated with this mechanism had similar behavior to those resulting from a dam-break technique and a good agreement between the experimental points and the theoretical solutions of Ritter (1892) and Whitham (1955) was found. Lastly some differences between wet bed bores and dry bed surges are presented and briefly discussed herein.

Pile-supported reinforced concrete buildings were uplifted and overturned due to the 2011 Great East Japan Earthquake and Tsunami. It is important to understand the mechanism that caused such damage to enable us to build resilient coastal communities against mega tsunami. In the present paper, we study numerically the difference in tsunami response among overturned buildings and surviving buildings in Onagawa town. The following conclusions have been obtained. (1) We cannot explain from the view point of only the hydrodynamic force whether these buildings overturned or not. (2) The pile resisting moment makes a significant contribution to overturning resistance for most of overturned buildings, but not for the surviving buildings. (3) The failure of the piles of overturned buildings could be caused by only the tsunami hydrodynamic force.

Proof-of-concept model tests on a novel self-deploying on-shore tsunami barrier were executed. The tsunami barrier consists of a membrane, floater, and cables that are stored underground. Due to buoyancy the barrier self-deploys when struck by a tsunami. The membrane and cables consist of the strong, flexible, and light-weight material Dyneema that can resist a 20 m high water column. A novel tsunami generating method was applied to generate a high-velocity initial bore, followed by a long duration high water level, using a normal piston type wave maker in a wave flume. Numerical calculations using a numerical volume-of-fluid code were used to tune the tsunami generation. The tests showed that the tsunami barrier indeed automatically deployed and completely blocked a 19 m high (reflected) tsunami for bore velocities up to 7.5 m/s. For higher bore velocities the barrier still deployed. For larger tsunamis (with a 33 m reflected water depth) the barrier remained erected, although overflow evidently occurred.

Lessons from the 2011 Tohoku Earthquake Tsunami disaster highlighted the importance of stable coastal dikes against overflowing tsunami. While a dike with sloping faces may enhance such stability, it may weaken dike’s function to reduce the overflow. This study carried out laboratory experiments to investigate how sloping faces of the dike affect the overflow characteristics. Through the experiment, we found: (i) sloping faces on both side of the dike clearly increase the overflow rate and the fluid force of the inundating flow and bring forward the arrival time of the first runup flow; (ii) sloping front face is the dominant factor to increase the overflow rate; (iii) a vertical wall type dike has the best ability in reduction of the overflow. These findings suggest that designs of optimum dikes need to account for such trade-off relationship between stability and damage-reduction effects of dikes.

When the reflected tsunami inundation depth at the front of RC building is estimated, it can be possible to roughly estimate the horizontal and vertical tsunami forces acting on the RC building. Two methods using the incident tsunami inundation depth and flow velocity are developed for estimating the inundation depth at the front of RC building with an arbitrary width, connection space, and aperture. The energy loss coefficient in a broad sense, newly defined in one of the developed methods, and the validity of the method are examined through a comparison between the inundation depth estimated and that obtained in the past laboratory experiments. The validity of another proposed method is also examined through a comparison between the inundation depth estimated and that newly experimentally obtained, and it is confirmed that both methods are valid for estimating the reflected inundation depth.