Narrow Results

A field survey to document the event that occurred in the coast of the Andaman and Nicobar Islands, India on December 26, 2004 was undertaken along the Tamil Nadu coast to estimate several items, including the wave run-up height, damage assessment and inundation areas in the different parts of the affected regions. The results of this field survey indicate that the tsunami inundation was heavier in the southern region along the Nagapattinam coast than the northern coast near Chennai; this was most likely due to differences in onshore topography. Consequently, the role of the onshore topography and its relationship with near-shore bathymetry needs to be evaluated in detail in order to prevent future catastrophes.

Japan Society of Civil Engineers (JSCE) and Philippine Institute of Civil Engineers (PICE) jointly collaborated to carry out the field survey on severe storm surge disasters caused by Typhoon Haiyan/Yolanda from 12 December to 16 December, 2013 in Leyte and Samar. Based on interviews with local residents, the joint survey team obtained measured inundation and run-up heights at almost 80 different locations along the coast and also at more than 70 locations inside the cities of Tacloban and Palo. Clear contrast of inundation characteristics was observed especially among east coast of Eastern Samar, inner and southern parts of San Pedro Bay. While inner part of San Pedro bay, as was expected, showed relatively high inundation heights, east coast of Leyte also had comparably high inundation heights even outside the San Pedro Bay. It should also be highlighted that surprisingly high inundation heights were observed along the east coast of Eastern Samar, which faces to the Pacific Ocean with deep Philippine Trench. This paper aims to report primary results obtained through the first joint field survey of JSCE and PICE.

From Tuesday, 16 December 2014, until Thursday, 18 December 2014, Hokkaido was battered by strong winds and high sea waves caused by a passing low pressure system intensified to typhoon levels. In the city of Nemuro, a rise in sea level influenced by the storm surge which exceeded quay height in port areas was observed from predawn Wednesday, 17 December 2014. Flooding was experienced in areas of central Nemuro, the Nemuro Port and estuaries of rivers. This technical note provides a comprehensive meteorological analysis and the results of a local flood survey carried out by the authors from 19 to 21 December 2014, and summarizes the characteristics of the 2014 Nemuro storm surge disaster.

A numerical model for the prediction of storm surges over complex landscapes is assembled using state-of-the-art techniques. The model is based on the full nonlinear depth-averaged long wave equations solved via an explicit finite volume scheme. The interfacial fluxes are computed from slope limited reconstructions of the state variables using Osher’s approximate Riemann solver. The geometric source terms are treated in a simple manner that is well balanced and consistent with the numerical flux. The numerical solution technique has been chosen to enable the accurate simulation of flows over complex topography. Importantly, the scheme conserves both mass and momentum even when the flow involves wetting–drying fronts. This approach makes the model extremely robust in cases that involve bathymetries which include large spatial gradients and even discontinuities. Another important feature of the model is the use of a simple underlying Cartesian mesh with quad-tree-based static and dynamic refinement. This permits the simulation of highly unsteady flows over complex landscapes (including localized features such as canals) by locally increasing (or relaxing) grid resolution in a dynamic fashion. If it is deemed desirable, the numerical and physical boundaries can be aligned. This alignment is achieved by a cut-cell-type approach in combination with quad-tree-based mesh refinement. In this paper, we describe the model and then present a number of tests that have been carefully chosen to verify various aspects of the solution algorithm.

Debris in high-volume, high velocity flows, such as tsunamis, storm surges, and dam breaks, cause widespread damage to coastal communities. Evaluating the motion of the debris within the flow is difficult due to the variety of variables that can affect the motion, therefore techniques must be developed to quickly and accurately track the motion of the debris within the flow. This paper presents an optical tracking technique to track the motion of debris over a horizontal bottom under laboratory conditions. The debris consisted of scaled-down shipping containers, made of polyethylene (PE), placed on a dry, raised, flat section of the basin floor. Container movement was measured using two overhead cameras and a novel object tracking and detection algorithm implemented in MATLAB. The algorithm was developed to be able to quickly and accurately track uniform containers throughout an experimental run. The algorithm combines image-processing techniques such as Color Thresholding and Blob Analysis with tracking methods such as the Kalman Filter and Hungarian (Munkres) Algorithm. The algorithm was evaluated by comparing the results to those from a manual tracking method. For experiments with one, three, and six containers, the algorithm showed good agreement with the results of the manual method. However, with nine containers, the increase in the amount of container–container collisions and the agglomeration of the containers resulted in poor results compared to the manual method. While the algorithm is only evaluated here to track the motion of the shipping containers, there is potential for its use in many other fields of hydraulic and coastal engineering.

In this study, we projected the future beach loss in Japan’s 77 coastal zones due to sea-level rise (SLR) based on representative concentration pathway (RCP) scenarios and 21 models of the Coupled Model Intercomparison Project Phase 5 (CMIP5). The beach-loss curve for SLR in Japan was constructed, and uncertainties associated with SLR projections and sediment sizes were evaluated. Beach-loss rates in the future (2081–2100) were projected to be 62% for the ensemble mean RCP2.6 scenario, 71% for RCP4.5, 73% for RCP6.0, and 83% for RCP8.5, and the rates projected by the CMIP5 models for RCP4.5 ranged widely from 61% to 87%. The effect of the spatial distribution of SLR in each CMIP5 model on beach-loss rate in Japan is insignificant, while the effects of differences in the SLR values among RCP scenario and CMIP5 models are significant. The maximum uncertainties associated with sediment sizes (0.2–0.6mm) against the same SLR were assessed to be 38%. Despite significant uncertainties in the projected beach loss, results in the near future (2046–2065) reveal that the beach-loss rates between 18% and 79% differed by 60% in the near future and between 28% and 96% differed by 70% in the future. For the worst case scenario in the near future, the projected beach width is less than 10m in more than half of the 77 coastal zones, which would cause serious damage to coastal structures such as seawalls and revetments in beach areas. Thus, the development of effective measures to combat beach loss is critical for Japan’s coastal management.

This paper reports the post-disaster survey results of storm surge and waves due to Super Typhoon Meranti (local name: Ferdie), along the coastline of the province of Batanes, Philippines. The survey was conducted by a joint survey team of the University of Tokyo and University of the Philippines from 9 to 12 October 2016, about one month after the disaster. Water levels in the inundated area or runup heights were measured at 37 locations along the coast of the islands of Batan and Sabtang by interviewing local residents and by examining wave runup evidences remaining along the coast. Obtained runup and inundation levels showed significant variations along the coast of islands and higher levels were found on the coast facing north. Especially at Ivana, a small coastal community located at the southwestern tip of the island of Batan, the coast was covered by a convex-shaped fringing reef and observed inundation heights were locally concentrated behind the peak of the convex-shaped reef.

The 2004 Indian Ocean tsunami caused enormous loss of lives and damage to property in Sri Lanka and in several other countries bordering the Indian Ocean. One way of mitigating potential loss of lives from a similar event in the future is through early warning and quick evacuation of vulnerable coastal communities to safer areas, and such evacuation planning is usually carried out based on inundation maps. Accordingly, the present paper outlines the numerical modelling carried out to develop tsunami inundation maps on a grid of 10 m resolution for three cities on the south coast of Sri Lanka. The results give the tsunami arrival time contours and the spatial distribution of the extent of inundation, the maximum flow velocities as well as the hydrodynamic force in these three cities due to an event similar to the 2004 tsunami.

In current tsunami prevention and mitigation, evacuation is the most important method of saving people’s lives. Tsunami evacuation is analyzed for a given travel time and a specific inundation area. Before evacuation analysis, the tsunami inundation and tsunami travel time are first calculated by numerical modeling. This paper analyzes the tsunami evacuation of Haimen Town, Jiaojiang District, Taizhou City, China, under the hypothesis of a magnitude 9.0 earthquake scenario in the Ryukyu Trench. The Cornell multi-grid coupled tsunami (COMCOT) model and Tsunami Travel Time (TTT) model are used to calculate the tsunami inundation and tsunami travel time, respectively. GIS techniques are used to solve the evacuation problem. Both horizontal and vertical evacuations are adopted based on the Chinese community characteristics, disaster prevention facilities, land use, and other practical conditions. A cost raster is used to analyze the arrival cost of each grid in the study area. The location allocation and cost allocation methods are used to solve shelter selection and coverage problems, respectively. The network analyst is applied to provide evacuation routes for each community. The evacuation analysis results can provide a scientific reference for the development of tsunami evacuation plans.

This paper quantifies the impacts of inundation risk and soil salinization on the family structure and income of coastal households in Bangladesh. The analysis is based on a household decision model that relates spatial deployment of working-age, migration-capable members to inundation and salinization threats. The empirical analysis uses appropriate estimation techniques, including adjustments for spatial autocorrelation. The findings are consistent with a model that treats urban migration of working-age family members as both an income source and the only feasible form of disaster insurance for coastal households. Greater inundation risk unambiguously decreases the rural household share of working-age members, while the direction of the salinity effect depends on households’ income elasticity of demand for disaster insurance. The econometric results suggest that this elasticity is significantly greater than one, yielding higher rural household shares of working-age members in areas with higher salinity (ceteris paribus). Both increased inundation risk and greater salinity increase the incidence of extreme poverty among coastal households. However, powerful poverty reduction results for market access indicate that road improvements would provide an important countervailing force. The benefits of increased market access for coastal households are present with or without inundation and salinization threats, making such investments an attractive no-regret option.

Numerical analysis of the inundation of the land behind the Roxas Boulevard Seawall is carried out to study the impacts of critical historical typhoons on coastal flooding. The numerical implementation based on ADCIRC with a coupled surge-inundation capability is discussed relative to existing conditions of the seawall. The simulative analyses are undertaken to study the implications of a “do nothing” scenario wherein the critical typhoons cause overtopping and inundate the land behind it. The results indicate the inland extent of potential inundation, reduced depth of the peak storm tide in front of the seawall, a rapid gradient of inundation depth behind the seawall, and the prominent role of Pasig River in inundation propagation inland, among other things.

Tsunami flow and sediment transport is simulated using Delft3D, a three-dimensional coupled hydrodynamic/sediment transport/morphological model. Tsunami flow characteristics and sediment erosion and deposition are recorded in 1 second intervals, and the temporal and spatial variations are examined to determine which phases of inundation dominate sediment transport and morphological change. For the simulations conducted here, most of the sediment deposited onshore originates in shallow water. While some sediment is eroded by the passing wave front, sediment is predominantly eroded during backwash and advected onshore by the subsequent wave. The extent, composition, and structure of the onshore sediment deposit is a function of the tsunami wave form, as well as the local conditions, including the nearshore morphology, local topographic variations, sediment source characteristics, and bed roughness.

The Eastern Scheldt tidal basin has changed drastically in the past five centuries under the influence of both human interventions as well as extreme events. In 1530 A.D. a storm-surge inundated large parts in the landward end of the basin, and in the following four centuries local inhabitants reclaimed about as much land as was inundated in that storm. To investigate the effects of these processes on basin morphology, several different simplified geometries of the basin are used in order to gain insight into the evolution of the tidal currents over the centuries. From this model it appears that the large-scale inundations cause the basin to scour to greater depth. This in turn causes the ebb-tidal delta to grow, and causes the disappearance of the tidal watershed between the Eastern Scheldt and the Grevelingen tidal basins. Land reclamations have not been able to turn these trends around.

A methodology to estimate storm-induced morphodynamic risks is presented. The storm-induced coastal response is separately assessed in terms of inundation, beach profile and transport potential. Inundation is calculated by means of the run-up Ru_2% at the peak of the storm. Erosion is characterized by the eroded volume from a beach profile and, overall sediment transport is parameterized in function of the integrated wave power during the storm impact. These three parameters are used to calculate the resulting risk by estimating their probabilities of occurrence using the event and response methods. In the first one, the probability of occurrence is assigned from the extreme wave distribution (events) which is used to calculate the corresponding morphodynamic processes. In the response approach, storm wave data are used to build a data set of storm-induced responses which are later fitted to an extreme distribution. These two methods have been applied to characterize storm wave-induced morphodynamic risks at Costa Brava (NE Spanish Mediterranean coast). Results show that for this case, the use of the event approach significantly under-predicts the morphodynamic response for any probability of occurrence and, in consequence, its use will under-predict storm risks.

This article discusses the processes that contribute to storm surges and coastal flooding and describes numerical techniques used for modelling such processes, particularly with regard to overland coastal flooding. A storm surge model, which features a nesting capability and inundation algorithm, is described. The flooding and draining is dependent on the modelled current in adjacent ‘wet’ grid cells which ensures realistic and smoothly varying results. Several examples of the application of this system are presented. Through these examples, it is demonstrated that the inundation model is robust in a variety of geographical locations and under a range of grid resolutions. Surge heights at the coast are also compared with simulations where overland inundation is switched off and it is found that elevations are greater by up to 17% when the coastal boundary is approximated by a fixed wall. The applications of this system to hazard management and impact studies are also discussed.

Two case histories dealing with post-disaster investigations are presented. The first one deals with evaluating possible damage to runways at the Galveston Airport on the coast of Texas after Hurricane Ike in 2008. The airport pavements were covered by 6 ft of sea water for more than a day. Continuous pavement deflection profiles measured with the Rolling Dynamic Deflectometer (RDD) were used to evaluate the pavements. The second case history involves investigating soil liquefaction and lateral spreading that occurred in residential areas during the 2010 Darfield, New Zealand Earthquake. Nonintrusive seismic testing with surface waves was used to evaluate shear wave velocity (V_s) profiles at sites of residential damage. The V_s profiles were used to perform a liquefaction triggering analysis and identify the critical soil layers involved.