Many floods caused by heavy rainfalls and typhoons hit Japan in recent years, and some floods attacked fully urbanized areas. Tokyo, Nagoya and Fukuoka were inundated by urban floods, and some parts of flood water intruded into underground spaces. During the floods, underground shopping arcades and subway stations were inundated. The inundation in underground space is one of the problems to resolve urgently. One of effective measures to reduce the damage of flood disaster is quick evacuation from the underground spaces. In this paper, evacuation from underground spaces has been tested by using real scale models of staircases and doors. From the results, it is found that water depth of 0.3m on the ground is a critical depth for evacuation from underground space through staircases and 0.4m deep in front of the door is the limit to open the door.

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Experience shows that debris flows containing large woody debris (driftwood) can be more damaging than debris flows without driftwood. In this study, the deposition process of debris flows carrying driftwood was investigated using numerical simulations and flume experiments. Debris-flow trapping due to driftwood jamming in a slit-check dam was also investigated. A numerical model was developed with an interacting combination of Eulerian expression of the debris flow and Lagrangian expression of the driftwood, in which the fluctuating coordinates and rotation of the driftwood were treated stochastically. The calculated shapes and thicknesses of a debris-flow fan and the positions and orientations of the deposited driftwood on a debris-flow fan were consistent with experimental flume results. The jamming of driftwood in a slit-check dam was evaluated based on geometry and probability. The simulated results of outflow discharge and the proportion of driftwood passed through the slit-check dam also agreed with the experimental results.

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Severe bank erosion is one of the most challenging problems in the management of large rivers in Bangladesh. This paper describes the detailed flow patterns around typical bank-protection works on the Brahmaputra/Jamuna River as well as their morphological implications. Based on field surveys at several locations along this large alluvial river that are highly susceptible to erosion, attempts are made to clarify the flow fields and mechanisms of bank erosion. The performance of existing measures such as revetments and spur dykes are evaluated, and possible solutions for further enhancements are proposed. It is found that existing conventional works are generally huge in both size and cost, potentially exerting great disturbances on the river's dynamism and ecosystem. That said, the Bandal -a historied and indigenous structure -is cost-effective and environmentally friendly. This study suggests the recurrent use of Bandallike structures for channel stabilisation and flood management of the braided Brahmaputra/Jamuna River.

Formation and failure of landslide dam are one of the significant natural hazards in the mountainous area all over the world. In the event of catastrophic failure of landslide dam, we have to predict resulting outflow hydrograph. It will serve as an upstream boundary condition for subsequent flood routing to predict flood hazard in the downstream. Most of the existing models are applicable to overtopping failure of landslide dam. In this study an attempt has been made to incorporate integration of three separate models to predict the outflow hydrograph resulted from failure of landslide dam by overtopping and sudden sliding through flume experiments and numerical simulations. The main advantage of an integrated model is that it can detect failure mode due to either overtopping or sliding based on initial and boundary conditions. The proposed model is tested for three different experimental cases of landslide dam failure due to overtopping and sliding and reasonably reproduced the resulting hydrograph.

Underground is an important space that supports function of cities, such as subways, shopping malls and basement parking. However in consequence a new type of disaster, the "urban flood" menaces these spaces. In the last decade, urban floods struck Tokyo, Nagoya and Fukuoka. When underground inundation occurs, people must evacuate to the ground as soon as possible. But, when such an inundation situation happens, aged persons may not be able to evacuate quickly to ground level. In this paper, the method of safety assessment for aged persons is discussed on the experimental results and flood simulation data in an underground space. As a criterion of the safety evacuation, the specific force per unit width is used in this study. From the result of experiments, it is difficult to implement safety evacuation when the specific force per unit width is over 0.100 m(2) for the aged male.