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.
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