Free Meander of Major Rivers in Tohoku District

The writer studied the free meander in the flood plains of the Iwaki, the Yoneshiro, the Omono, the Mogami, the Kitakami, the Natori, and the Abukuma rivers by the analysis using aerial-photographs and topographical maps, and by hydrological data and field investigation. The following points are his conclusions.1. The meander rates of 1 > ρ≥ 0.80 (ρ: meander rate = (L-W)/L, L: meander wave length, W: meander wave width) are seen in the most downstream and the most upstream reaches of the flood plains. The meander rates of ρ<0.80 are found the reaches of midstreams. Free meander develops well in this part. These facts correspond with the results of experiments in model channel reported by Friedekin etc.2. The development of meanders in these main rivers under consideration are greatly affected by their tributaries. The facts also correspond to the results obtained by the experiments.3. In each of the flood plains, the present river in which meander develops runs through the area with numerous meander scars and meander scrolls clearly and widely preserved.4. Observing the meander scars and meander scrolls in the flood plains, it can be pointed out that these river channels have been shifted by means of cut-off-meander in the river reaches with the meander rates of ρ<0.80, as well as the fact that shifting is a lateral vibration between nodal points, and nodal point coincides with the confluence of each river or valley mouth. But in river reach with the meander rate of 1>ρ≥0.80 these river channels have shifted with a pendulum motion like a river on an alluvial fan.