VERIFICATION OF FLOOD CONTROL EFFECTS IN A WIDE SECTION AT THE BOTTOM OF A VALLEY IN A MOUNTAINOUS AREA

Abstract

 A linear rain band occurred due to Typhoon No. 7 on August 15, 2023, in Tottori Prefecture, and damage due to riverbank erosion occurred in the Saji River in the Sendai River basin. On the other hand, a village was not inundated from damage despite concerns about inundation due to overflow. It is possible that the wide valley bottom at the upstream curved part exhibited a water and sand storage effect, which may have prevented inundating damage in the village downstream. In this paper, we considered the wide valley bottom of a rapid river in a mountainous area as a local widening part of the river channel, examined the impact of water storage and sand deposition in the local widening part of downstream, and conducted a two-dimensional riverbed variation analysis to confirm the water storage and sand storage effect of the local widening part. The results showed that the local widening part in the mountainous area has the effect of depositing sediment of a wide range of grain sizes, including large boulders, reducing the amount of sediment discharged downstream and suppressing the rise in water level.