河川堤防決壊口の拡大過程に関する実験的研究

Abstract

Flood damage due to a bank breach increases with a river water inflow through it, whichis enlarged by a hydraulic action of the inflow, while the influx rate is controlled by thegeometry of the breach as well as the stage and discharge of the river. For the purpose ofprediction on flooding inside the bank and mitigation of the damage, this process needs to beinvestigated to estimate the influx rate and to find out a efficient closure technique.We carried out fundamental experiments, and describe the enlarging process of modeledbank breaches as the results in detail, such as changes in geometrical characteristics, influxrates, water stages at the both sides of the bank models and their seepage states. These resultswere discussed on hydraulic properties at the breach, that is, flow resistanse, sediment transport, stage-discharge relationship between the water stage outside and the influx rate. It is found outthat the process has four enlarging phases. The first one is finished when carving of initialfailures, which are V-shaped grooves at the top of banks, reaches the outside slopes. During thesecond, scouring downward and widening of the breaches progress rapidly and increase in influxrate is very large. Gradual widening only continues at the third one and inflow increases alittle. Finally, geometry and influx rate become rather constant in the fourth phase.