Under the global warming condition, it is a great concern that a large scale linear heavy rainfall system causes severe flood disaster in a wide area. In such a case, it would be important to consider simultaneous floodings from multiple rivers. In this study, numerical inundation simulations were implemented under the consideration of simultaneous levee breaches in Kakehashi River and Tedori River in Ishikawa Prefecture, Japan. Based on the simulation results, water-related disaster risk was evaluated. At the same time, based on simulated inundation depth and flood water velocity at each simulation time, potential window time for evacuation was estimated. In the case of simultaneous levee breaches at the two rivers, in the right bank of the Kakehashi River, the maximum inundation depth became larger than in the case of levee breach at a single river. The window time for evacuation became shorter in the same area. In an area affected by the two rivers, arrival times of inundation flow from the two rivers are usually different. Depending on time lags between floods in two rivers, evacuation window time has to be estimated based on the time when the later flood level reaches the evacuation warning water level.
In recent years, there has been a tendency toward increased rainfall intensity, and sediment inflow disasters caused by mountain streams are increasing in number. As there is a significantly large number of mountain streams along railway lines, time and effort is spent on local surveys for the purpose of extracting dangerous streams. Additionally, as there is a mixture of diverse factors related to mountain streams, such as terrain, geological features, risk level assessments are differ among technicians. Above all, the risk level assessment of upstream areas located in positions vastly separated from the railway tracks and dispersed over a wide area require a huge amount of time and effort, and there may be a large disparity among engineers. In this paper, therefore, we describe a simple method of evaluating the risk level of mountain stream upstream areas using uniform criteria, without requiring local surveys. In concrete terms, our activity was the development of a scoring sheet that can assess the risk level mainly using the quantitative data of digital evaluation model. It was shown that the evaluation by the scoring table was almost the same as the evaluation by the local surveys.
The confluence improvement project has progressed, but the management accuracy of the quantitative control facility that is the base in the sewer management is low, and there are still issues in environmental load reduction and heavy rain measure effective in the pipe line system through utilization of stock and will be become problems in terms of maintenance management and project operation in the future. In this study, based on the hydraulic engineering theory and hydraulic experiment verification enabling diversion control with high accuracy, and the previous studies aimed to put them into practical use on extension of the knowledge of sewer standard books and practical cases, there is presented a method for planning a rational sewer pipe line system relating to the environment and safety in an urban area, such as a pollution load in a public water area and a heavy rain measure in a residential area still having issues even after the confluence improvement project. Promoting the efficiency of the sewer project requires reliable sewage flow rate management and the pipe line system through effective utilization of the stock, and the pipe line system utilizing the sewage flow rate control technique of this study contributes to the effective achievement of the project purpose with quantitative evaluation and cost reduction.
In this paper, an attempt is made to formulate the upstream water level of the flow over weirs with rectangular longitudinal cross-section in order to give basic information for flood manage planning of the river with weir(s). Experimental data by Govinda Rao and Muranlidhar, which gave the discharge coefficient relating the flow pattern over the crest, were selected as base data. Equations for the upstream water level as the functions of the critical depth, hc, were obtained with application limits almost correspondent to those of the formula by Govinda Rao and Muranlidhar. The obtained formulas gave proper evaluation of the upstream water level in spite of the need for a little correction.
One third of Joso City area was under water due to the flood caused by the Kanto-Tohoku torrential rain of September 2015, during which numerous delays and isolation of evacuation were experienced. Considering the above, we started a project of TimeLine by Everybody, aiming at reducing the number of people who fail to evacuate to zero, under which the concept of “My-TimeLine” was developed. To disseminate “My-TimeLine”, we developed the “Nige-Kid” as the teaching tools that help elementary and junior high school students to create their own “My-TimeLine” in less than one hour. In the process of developing the “Nige-Kid”, we conducted disaster resilience education to Joso-City elementary school children of producing their “My-TimeLine” using the prototype “Nige-Kid”. The results of education indicated that the knowledge of flood risk and preparedness were properly enhanced through the consideration process of the “My-TimeLine” using the “Nige-Kid”.