NEAR NATURAL DESIGN FOR MASONRY DROP WORKS IN MOUNTAIN RIVERS

Abstract

  In many cases, the existence of consolidation dam has been obstructing the passing of fishes, and it has been losing the environment of shoals and pools. To improve this problem, the authors constructed the group of low distributed drop works to the Iwatake River, Fukuoka Prefecture, for trial purposes, which united big and small boulders as the model of natural difference steps in the mountain river. Their basic form was the masonry arch, and was applied the stability theory of body in the flow. In the execution, Japanese traditional masonry technique was used. After the completion, we investigated the situation of river channel before and after floods and observed their structural changes after the floods. As a result, even if the stones or gravels between the keystones were moved, the steps are replenished and reproduced with stones from upstream because the keystones were stabilized. From the trial construction by the design method of riverbed structure learnt from nature, it was able to be confirmed that distributed drop works maintained shoals, pools, and bed height in mountain rivers.