Study on disaster by water in urban rivers and urban spaces

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The main results through this study are as follows.1. A simulation model is developed to express the rapid change of river water depth and the consequent inundation in urban river basin by heavy rainfall. The model constitutes a runoff model based on the kinematic wave model and a 2-D horizontal inundation model with unstructured meshes. Small rivers and ditches are incorporated into the unstructured meshes. The model is applied to Isahaya city area, Nagasaki city area and Uji city area in Japan. Through the simulation analysis, the degree of flood hazard possibility in the urban river basins is clarified.2. An inundation simulation model based on a storage pond model is developed which can treat inundation of both ground and underground spaces in urban area. The continuity equation, momentum equation and drop formula are used as the basic equations in the model. The model is applied to Fukuoka city and Kyoto city in Japan. The results show that the large inundation into underground malls and subways may occur in the case the river in both cities overflows.3. Underground inundation is one of the important problems solved urgently. One of the effective measures to reduce the damage of underground inundation is quick evacuation from there. Evacuation from underground spaces is studied by use of the real scale hydraulic models of staircases and doors. From the experimental results, it is found that the water depth of 0.3m at the entrance on the ground is the critical depth for evacuation from underground space through staircases, and the depth of 0.4m in front of the door is the limit to open the door.