Study on effective measures for management of bars and low water channel in forested gravel-bed rivers

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Recently, riparian trees in the course of gravel-bed rivers have been very much increasing due to bed degradation in low water channel and increasing of relative height over vegetated gravel bars. Such a situation reduces the capacity of flood discharge. Furthermore, it brings about the degeneration of dynamic river system. This study aims to propose effective measures for reproducing gravel bars and for reducing of extreme relative elevation in cross section by leading flash floods over forested bars. The bed excavation over the vegetated gravel bar in Watarase River was conducted for the restriction of riparian trees and the recovery of gravel bars with geomorphic changes caused by flood disturbance. After experiences of several times of floods, significant bed variation was caused in the excavated area by active sediment transport. As results of the field survey and the numerical hydraulic calculation, it is confirmed that induced flood disturbance due to bed excavation is one of the effective measures for the management of gravel-bed rivers.