This study aimis to investigate the influence of difference of radar rain gauge on the runoff and flood analysis. The target of this study is huge rainfall event due to 2017 Northern Kyushu flood. As radar rain data, we used the rader/rainguage – analyzed precipitation data by JMA and C-X composit data by MLIT. We conducted runoff analysis by using RRI model. Flood analysis was conducted using iRIC Nays 2 DH with the upstream boundary condition obtained by the runoff analysis. The results indicated that the difference of the radar rain gauge gives significantly those of outflow discharge, flood volume and maximum inundation depth.

 This paper examines the effect of inundation mapping utilizing local flood information obtained in Joso city and the surrounding area, which were damaged by the Kanto-Tohoku torrential rainfall in September 2015. The mapping method assimilates a number of preliminary conducted inundation simulation results and flood-related information from the locals. The authors compare four different scenarios of local information acquisitions and two scenarios without the data assimilation. The result indicates that a more effective assimilation method for getting better mapping of inundation is to measure higher inundation depths, which take place along small tributary rivers, comparing with another method to measure relatively lower inundation depths at designated evacuation shelters. In addition, the accuracy of inundation depth distributions can be improved by assimilation even with fragmented and uncertain information, compared to a case without the assimilation and simply selecting a preliminary conducted inundation estimate.

 The influences of the land gradient and spatial resolution on the applicability of a shallow water equation was investigated with the Fully-nonlinear and strongly-Dispersive Internal wave equations. Likewise, the comparisons between a shallow water equation and its inertial formulation were carried out. The results indicated that the shallow equation model and its inertial formulation were valid with mild land gradients. The result also implied that the performance of the shallow water model became better with finer resolutions such as 5m. Finally the inundation simulation with the fine resolution using K-supercomputer was demonstrated

 Recent global warming and resultant floods have lead to increase in the frequency of flood inundations and the importance of forecasting such events. The current flood forecasting primarily forcuses on streamflow level. Flood forecasting methodology has evolved over the years from lumped runoff models to spatially distributed grid cell-based models. In recent years, the practical application of grid cell-based models that simulate for both the rainfall-runoff and the flood inundation have evolved, and these models are expected to see application in flood forecasting including inundation predictions. In this study, the Rainfall-Runoff-Inundation (RRI) model is selected as an example, whose structure has limitation in distinguishing the right and the left banks of a river channel. This study proposes a new method capable of simulating the detailed interaction with the right and the left banks by separating the two sides of a river channel. The study also applies the proposed algorithm to the actual levee breach case on the Kinu River and confirmed its performance.

 In the present study, the hydraulic model experiment was executed to obtain the information of flow field of the river, the river bed variation and the flood, etc. needed for the design, the operation and maintenance of the plan river channel and neighboring residential area damaged on July 12, 2012 by the Shirakawa flood for the river improvement and to evaluate the flood control safety. As a result of the experiment, the plan river channel was proven it had the ability to flow in 2,300 m³/s. Moreover, it has been understood to decrease the flood flow velocity at the design flood discharge greatly. In addition, the risk evaluation by the flood flow velocity was greatly improved, and the improvement of the personal suffering in the plan river channel was clarified.

 Intentional inundation by preparing partial levee openings is now considered for practice of resilient flood risk management of some valley bottom plains where immediate construction of high embankment is not easy because of the budget restriction, but theoretical background of the strategy is not well developed yet. In this study, eleven examples of levee openings were sampled using aerial photographs in 1970s, and their locations and functions were discussed qualitatively. Hydraulic function of levee openings placed in a reach of Sayou River in Hyogo Prefecture was investigated in detail numerically using a shallow water model. Results showed that the flood retention by the system was rather small, and their main hydraulic function was to drain the inundation area soon after the flood peak. The results also suggested that paddy field along the river was used as a temporary sub-channel to increase at the time of emergency.

 To enhance the soft-countermeasure on increasing heavy rain and disaster, research on increasing the accuracy of two-dimensional (2D) flood inundation model is necessary. The objective of this study is to grasp the effect of anisotropy of porosity in calculation grid on a flood inundation pattern by comparing a hydraulic model experiment with numerical simulations by a 2D flood inundation model wich includes an isotropic porosity in each grid. In experiments, anisotropy was represented by changing the aspect ratio of large roughness elements mounted on a plain. Large velocity differences was observed for the propagation speed of floods in the experiments on the floodplain model with the shape of the roughness elements. Numerical simulation results demonstrated that the difference could be represented by changing the drag coefficient, however, the tip of the inundation current, and the reflection or shielding effect by the elements could not. The needs are clearly shown to develop the anisotropy effect in the numerical model.