Unstability of meandering streams and river bed erosion by meandering streams

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An formation process of meandering streams on river beds with non-uniform sediment was investigated experimentally and a simulation method for this process was developed using a 2-dimensional bed variation model. The results of this research are mainly as follows :(1) A formation process of meandering streamsAt the sirst step of the formation process observed in an experiment, the largest gravel stops at the crest of the untidunes. The gravel makes it easy for the transported sediment to be deposited just upstream of the gravel. A sand bar is formed through such a process and consequently a meandering stream is formed. The longitudinal and lateral sorting of bed material makes the stream more stable, but it turn unstable if the fine sediment flows out of the bar.(2) Development of simulation modelA method for simulating the formation process is developed using a 2-dimensional bed variation model. The comparison between the experimental and calculated results on the bed variation have shown the validity of the method.(3) ApplicationThe simulation model was applied to the formation process of the meandering streams observed in an experiment. The number and wave length of meandering streams are simulated by this method, but not the changeability of meandering streams. The simulated stream was fixed because the flow structure and sediment transport mechanism near the side walls are not precisely introduced in the model.