自然堤防帯河川の高水敷掘削後の土砂再堆積～揖斐川と長良川の相違点とその要因～

抄録

Flood-channel excavation is being implemented as a flood countermeasure in lowland rivers. The purpose of this research is to examine the cause of the difference in the sediment deposition phenomenon occurring after flood-channel excavation among each river system. The re-sedimentation process at the excavation site was investigated in the Ibi River and the Nagara River. The difference between the two rivers became clear by investigating the grain size distribution of sediments accumulated in the past and last flood term. In the Ibi River, the accumulation of wash load was observed, whereas in the Nagara River, it did not occur after excavation work. In two study sites, the accumulation potential of suspended-load was estimated by a simple model while changing the water level and particle size. The model expected that deposition of wash load occurred at both sites. The model result was consistent with the observation in the Ibi River. However, there was no deposition of wash load at the site of the Nagara River. Our results and past observations indicate that the difference between the two rivers is attributed to wash load concentration of flowing water dominated by watershed characteristics.