Abstract
This paper describes structural and historical changes of floodplains, and reviews three key components of flood disturbance (inundation frequency, hydraulic forces, and deposition rate) in natural and regulated rivers to examine the use of flood-channel excavation as a floodplain recovery method in Japanese lowland rivers. Pristine floodplains once had broad backswamps, but land development and levee construction eradicated their natural configuration. Inter-levee floodplains changed from dynamic systems with active channels to static systems with dense riparian trees between 1975-2007 in the Kiso River. Flood-channel excavation increases inundation frequency to equal or greater levels than original floodplains. However, hydraulic forces and sedimentation also greatly increase with excavation and cause physical instability, making it difficult to autonomously maintain itself for a long period of time. Consequently, we suggest a cyclic flood-channel excavation as an approach to better managing inter-levee floodplains.
