Improvement of flow condition in channelized river due to stacked boulders

Abstract

Recently, a channelized river was constructed in natural rivers from the point of flood control, and the river fell into drainage channel. During flood stages, it might be impossible for aquatic animals to stay at channelized river. Also, degradation and disappearance of gravel bed might be formed easily, because flood flow was concentrated into the same route for normal stage. The improvement of flow condition in channelized river must be required as soon as possible. As a short-terms of construction for the improvement, the installation of stacked boulders might be helpful for both habitat and refuge of aquatic animals. The installation of stacked boulders with about 1 m size was conducted at channelized portion with 20 m wide and 1/200 slope in Kando River, Shimane Prefecture, and a surface jet flow with three dimensional could be formed in both normal and flood stages. After the installation, several kinds of aquatic animals could be observed around stacked boulders, and movable gravels with 3 mm to 100 mm diameters were deposited below stacked boulders. The stability of stacked boulders during flood stages was investigated experimentally by using 1/15 scale model. Further, the possibility of refuge space in stacked boulders was investigated in proto scale by using 25 eels.