急流河川泉川の多自然川づくりの報告

抄録

The Izumi River is a rapid, narrow and meandering stream. It locates at the foot of the Yatsugatake Mountains at Hokuto City, in Yamanashi Prefecture. The river improvement is an urgent work to control the floods caused by the heavy rain. Considering of ecology and natural landscaping, introducing of nature friendly river works was also indispensable. The river improvement has to be maintained the existing alignment and slope to save vegetation, trees, benthos and fishes along the river. Installation of steps and pools along the river was one of key in the improvement work for the restoration of its own environmental properties. The location, size, interval and width of existing natural steps was surveyed and the data was utilized for the basic design, being focused on the restoration of existing drops. Conducting the additional fields survey after the completion of the improvement, we recognized that the new artificially installed drops created quite similar flow to the previous one. We also observed the restoration of vegetation, benthos. It is expected that the restoration leads to prompt returning of original fishes lived there before the improvement.