2014 年 2 巻 1 号 p. 94-101
Numerous cases of hazardous flooding attributed to irrigation tank overflows under concentrated downpours have recently been reported. Using a hydrograph to predict overflows is an important countermeasure against hazardous flooding in downstream areas. However, many studies have considered only the peak flow discharge without a hydrograph timescale when predicting runoff characteristics due to irrigation tank overflows. This paper uses numerical simulation to emphasize the importance of runoff characteristics and proposes a new hydrographic index to evaluate flooding risks in downstream areas. The proposed index includes both the peak flow discharge and the hydrograph timescale. The applicability of this two-dimensional numerical simulation model is examined by comparing examples of actual damage with the results of in situ experimentation carried out in a narrow channel located at a mountainous site.