Abstract
Channel narrowing triggered by forced channel widening in three reaches of the Powder River in the US and the Sendai River in Japan was investigated. The reaches have been narrowed by newly formed flood-plains, main deposits of which originate in wash load material, much finer than the bed material of gravel. Wash load transport calculation was made to evaluate deposit rates on the beds with/without vegetation. Calculation results and the hydraulic conditions governing possibility of vegetation growth on the beds strongly suggest that the flood-plain accretion should be attributed primary to the vegetation growth. Hydraulic and geomorphic roles of vegetation and wash load were analyzed, and their practical application was proposed in terms of designing a stable width channel and controlling geomorphic change in a riparian bank.
