Keiichi Toda

Assessment of Safety on Evacuating Route During Underground Flooding

Heavy rainfalls over 50 mm/hr have been observed frequently in the last decade in Japan. If a sewage system in urban area could not drain such rains, flood water would be flooding and flowing into underground spaces such as subway or basement of building. As the area of underground space is limited, flood water fills up the area in a short time. It is very dangerous situation and people should evacuate from there as soon as possible in order to save their life. To draw up an evacuation plan, it is important to assess the safety of evacuating route. In this paper, the method of safety assessment on the evacuating route is discussed on the basis of experimental results and flood simulation data in an underground space. In order to assess the safety on an evacuating route, the value of the specific force per unit width, M=0.125m2, is used in this study, of which value has been obtained in the previous work. Using the relation between M values and evacuating speed, the assessment of safety on evacuating routes during underground flooding has been carried out well and the data for preparing an evacuation plan have been shown. The data are very useful for the people to evacuate from when and through which route.

Evaluation for emergency escape during stair climbing in a simulated flood evacuation

The objective of this study was to measure muscle activity during stair-climbing in order to estimate the water depth at which people can evacuate safely from urban underground. A life-size model of a staircase with a water pump that generated water flow from the top of stairs was constructed. In the study, electromyogram data were measured for six muscles on the right lower extremity, namely, the rectus femoris, vastus lateralis, long head of the biceps femoris, medial gastrocnemius, tibialis anterior, and gluteus maximus. From the results, the GA exhibited the highest muscle activity in the latter part of the stance phase, suggesting that the subjects tended to avoid stumbling against the stream of the water during ankle planter flexion. The results obtained from this study would be used for the construction of a guideline for evacuation from urban underground in flood disaster.

Numerical Analysis for Evacuation Possibility From Small Underground Space in Urban Flood

This study aims to precisely predict the inundation process occurring in small underground spaces including staircases by means of a numerical simulation. A three dimensional numerical simulation model with the volume of fluid (VOF) method is applied to a staircase and a small underground space under an urban flood condition. The simulated staircase is a full-sized hydraulic model, and the small underground space is a hydraulic model at a 1/15 scale. It is found that the numerical simulation model can be applied to the staircase during urban floods, and the computation result involving the small underground space is in good agreement with the experimental result. Furthermore, we examine the evacuation possibility from an underground space by comparing the computed water depths with the indexes. As a result, we can obtain a lot of information about the evacuation possibility from the studied underground space.

Underground Inundation Analysis by Integrated Urban Flood Model

Recent urban flood induces inundation into underground space and causes extensive damage. An inundation flow model is developed which can treat inundation in both surface and underground space. We combine a horizontally 2-D inundation flow model based on unstructured meshes with an underground inundation model by use of pond model. A runoff model based on the kinematic wave model is also incorporated. This model enables us to predict underground inundation by imposing rainfall condition in an urban river basin. This model is applied to Sannomiya area and Sannomiya underground mall in Kobe City, Japan. As a result, it is found that the underground mall there is likely to be dangerous by inundation due to heavy rainfall such as that observed in Tokyo in September 2005. It is also found that setting of step at each entrance is one of the effective measures to reduce the risk at underground inundation.

STUDY ON VULNERABILITY OF MEGA-UNDERGROUND SPACE TO EXTREME FLOOD

Japanese cities have many underground spaces such as subway and shopping malls. These cities locate in lowland of coastal zone near river mouths and are prone to extreme floods. The vulnerability of underground spaces to extreme floods are treated in this paper by using the results obtained by numerical method in densely urbanized area, Osaka, Japan. Pluvial, fluvial, storm-surge and tsunami flood cases were calculated. It is found that up to 60% of flooded water intrude into underground spaces if no counter measures were taken. Inundation depth and area in the underground shopping mall are different in the four types of extreme floods, and the flooded water enters into connected subway stations. This means that administrators of underground space have to make different counter measures for each type of extreme floods.

Three-dimensional numerical analysis to predict behavior of driftage carried by tsunami

This study aims to develop a three-dimensional (3D) numerical analysis code for the prediction of driftage behavior during a tsunami. The main features of this code are as follows: (1) it can simulate the six degree-of-freedom motion of driftage in a 3D flow field; (2) it can consider the interaction between fluid flow and driftage motion; and (3) it can compute the impact of the collision with a wall based on the Lagrangian equation of impulsive motion. In this code, we assume that the fluid pressure and viscosity cause driftage motion and that driftage motion affects fluid flow through deformation of the boundary between the fluid and itself. The code was applied to a hydraulic experiment carried out by subjecting a wooden body to an abrupt flow of water. The obtained numerical solution of driftage motion agreed well with the experimental result. It is concluded that our code can be used to successfully predict the behavior of driftage carried by a tsunami.

FIELD INVESTIGATION OF THE FLOOD DISASTER IN SOUTH-WEST AREA OF SRI LANKA OCURRED IN MAY 2003

In the southwest of Sri Lanka, a heavy flood occurred on 17-18 May in 2003, which caused severe river inundations and landslides in a wide area. About 300 persons were killed, and houses, farm products and infrastructures were heavily damaged. In order to investigate this flood and sediment disaster from the hydrological and hydraulic aspects, the committee on Hydroscience and Hydraulic Engineering, Japan Society of Civil Engineers (JSCE) delegated its members whose major are hydrology, hydraulic engineering and river engineering as a flood investigation team by JSCE. In this paper, results of the field investigation are shown for three river basins in Sri Lanka that were severely damaged by flood and landslide disaster induced by the heavy rainfall.

INUNDATION ANALYSIS FOR GROUND AND UNDERGROUND SPACES IN URBAN AREA

A storage pond model is developed which can treat inundation of both ground and underground spaces in urban area. The continuity equation, momentum equation without advection, and drop formula are used in the model. The model is applied to Fukuoka city with the underground spaces in JR Hakata station, and Fukuoka flood (1999) is simulated. The computation results show good agreement with the actual record. In the case of Kyoto city, overflow from the Kamo river is assumed. As a result, the underground malls downtown and adjacent subways are inundated. Also the underground spaces which are far from inundation area of ground are inundated by the water flowing through subways.

REFINEMENT OF INUNDATION FLOW MODEL APPLIED TO NEYA RIVER BASIN

Many inundation flow models have been developed in Japan. In this study, a comprehensive inundation flow model, that we developed last year, is refined by adding the process of overtopping flow from the river network into the drainage basin, replacing the sewerage model into the one based on the dynamic equations. The effects of buildings, bankings of railway and flood control facilities are also considered. This model is applied to Neya River basin, Osaka Pref., and the validity of this model is considered by comparing with the actual records of inundated area and water level of the river network.

Numerical study of evacuation system for overland flood flow due to storm surge

The aim of this study is to examine the refuge system under storm surge flooding in an urban bay area. First, through the overland flood flow computations under the various breach point conditions, a two-dimensional horizontal distribution of the maximum overland flood flow depth ( a flood hazard map due to storm surge ) is obtained. Next, a numerical model is developed which can simulate the behavior of evacuee in flooding caused by storm surge, and the characteristics of evacuation system is examined. By this study, the importance of evacuation order and the danger of refuge after inundation are presented. These results show that evacuee should take refuge before inundation.