山間河道における流木の挙動に関する実験的考察

Abstract

Driftwood amplifies flood damage and makes restorations difficult, by heaping up in front of river structures and by remaining on farmlands and urban areas. Two kinds of fundamental experiments were carried on to elucidate transport process of driftwood in mountainous rivers. One of them was conducted to simulate supplying process of driftwood from riverside and to clarify its effects on stream channel changes. Driftwood models with a simple form had little influence on channel widening and bedforms when they were being conveyed downstream. Their effects on channel change became intense when a flow of large discharge concentrated them to heap up around a bed level retainer of iron angle installed at the downstream end. In another experiment, two types of driftwood models, which were devised to be more similar to actural one, were injected into a small depth flow over a rough bed covered with bed protection block models. The models traveled downstream sliding and rolling on the rough bed and stopped when they were sustained simultaneously by both a sidewall and bed roughness elements.