流路形態の形成過程に関する研究

Abstract

The patterns of stream channel and their related problems are important in the fields of geo-morphology and river mechanics. These have attracted the attention of many researchers andengineers.In this paper, the problem is elucidated in connection with fluvial processes of stream channels.On the basis of the authors' results from previous investigations employing large scale experiments, a diagram depicting the formation of stream channel patterns is obtained. It is found that thewidening of channel and sand bar development, particularly alternating bar, play the leadingrole in it. The geometrical characteristics of bars in lateral erodible channels are compared withthose in fixed wall cases. Their critical values are then determined at the alternation between thechannel patterns.Accordingly, a classification of channel patterns is tentatively resulted from the diagramabove-mentioned, based on the visual states of river channels in fluvial processes. Four distinctivegroups are proposed, namely, straight channel 1, straight channel 2, meandering channel, andbraided channel. The governing hydraulic conditions to these patterns are clarified by using thecriterion for river bed configuration of meso-scale, and are compared with the equations obtained byother investigators for channel pattern criteria.The consideration of bar development in the case of lateral erodible channel renders a expres-sion from which the increase of bar height can be estimated. The process of stream channelpatterns, predicted from using this equation and an one-dimensional analysis of river channelvariation, shows a fairly good agreement with that observed in experiments.