2021 Volume 77 Issue 2 Pages I_409-I_414
Because of a concern of the frequency of intense rainstorm due to global warming, increase of the capacity of retarding basin is required against floods exceeding the present design level is considered, but the space for expansion of existing basins are limited. We examined the feasibility of a retarding basin against excessive flood utilizing an old floodplain in a small scale closed basin using a numerical flow simulation. The study site was a land side plain of a basin of about 300 ha located in the upper reach of Abukuma River, which received an inundation of excessive flood in 2019. Three places were considered for a possible site of an overflow dike, one in the upstream, or two in the mid-stream, and a sluice gate was placed at the downstream end of the basin. The numerical results showed; all three cases reduced about 6-8 percent of the flood discharge exceeding the high water level; and the influence of flooding on houses on the land was minimum by the overflow dike placed at the most downstream. In conclusion, an accumulation of retarding basins of this kind will be feasible as a facility for control of excessive floods, because there are many small closed basins in the upper reach of rivers in Japan.
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