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The main difference between rural and urban area inundation is the existence of an impermeable layer and the complexity of the road and building configuration. Therefore, although surface overland flow can be appropriately simulated by the two‐dimensional diffusive model in a rural area, there also is a need for a more accurate and elaborate simulation model. Dual drainage concept has been popular to simulate urban drainage system. Although the concept has immense advantages, through which overland flow and pipe flow can be simulated simultaneously, many researchers set manholes as discharge exchange spots between ground surface and sewerage system, which causes lack of reality. Therefore, in this study, we developed a new urban inundation model that can reflect real field situation. Also, two kinds of simulations are carried out with homogeneous meshes and non‐homogeneous ones using manholes and storm drains as discharge exchange spots, respectively, and those results are compared to estimate the effect of road networks and building groups according to different discharge exchange spots. Two‐dimensional run‐off flow model and one‐dimensional slot‐model are used to simulate ground surface run‐off flow and sewer pipe flow. To connect both models, we used a newly suggested bi‐directional model and its coefficients. The simulated results showed that more reasonable results are obtained in the nonhomogeneous case; the results further reveal the importance of using storm drains as exchange spots in the model.

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.

The need to consider disaster risk reduction at the time of recovery is well-recognized. Viable disaster risk reduction measures should resolve the root causes of predisaster vulnerabilities. Accordingly, we investigated the recovery from the impact of Cyclone Aila in Koyra Upazila, Bangladesh, which was severely damaged by this 2009 cyclone. Our research focused on understanding pre-Aila vulnerabilities to cyclone impact and examined the degree of inclusion of vulnerability reduction measures within the recovery process. A composite methodology that included an institutional survey, key informant interviews, collection of the judgment of experts, focus group discussions, and a score-based quantification technique was adopted. Through a process of understanding pre-Aila vulnerabilities, recognition of the root causes of these inherent weaknesses, and identification of appropriate measures for pre-Aila vulnerability reduction, a set of 23 indicators were selected to represent the most desirable vulnerability reduction measures to implement during recovery. A score-based technique was applied to measure the degree of inclusion of vulnerability reduction within the recovery with respect to the indicators. The scoring result shows that the degree of inclusion of vulnerability reduction within the recovery was poor. The result specifies that among the 23 indicators of potential vulnerability reduction measures, 10 are completely missing and the rest are only partially included. The overall findings imply that the Koyra community continues to live with a vulnerability similar to that of the pre-Aila period.

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University (Katsura compus, Nishikyo-ku, Kyoto 615-8540, Japan) 2 Member of JSCE, Dr. of Eng., Prof., DPRI, Kyoto University (Yoko-oji, Fushimi, Kyoto 612-8235, Japan) 3 Member of JSCE, Dr. of Eng., Assoc. Prof., DPRI, Kyoto University (Yoko-oji, Fushimi, Kyoto 612-8235, Japan) 4 Member of JSCE, Dr. of Eng., Assis. Prof., DPRI, Kyoto University Fushimi, Japan) Recently, there have been a lot of numerical models for prediction of urban inundation damage due to heavy rainfall by using the combined drainage system. Although it is important to estimate inlet and overflow discharge through the storm drain, calculation method and formula are not clarified. Hence, in this study, the numerical model of storm water interaction between the ground surface and drainage system we have previously used is improved and validated based on physical experiments. From the comparison, they showed agreement in all the cases of steady state condition. In the unsteady state cases, it was found that simulation results agreed well with experimental results of the ground inundation start time and the maximum inundation depth as well as the water level increase process. However, piezometric head reproduced small differences when the downstream water level was decreased. It was judged that was caused by inadequate consideration of exit and entrance head loss between the tank and pipe.