The Widening Process of Straight Stream Channels in Alluvial Rivers

Abstract

The widening process of straight stream channels is the most fundamental and simple fluvial process in alluvial rivers, though it is hardly observed in natural rivers. Prediction of this process based on the hydraulic consideration is a first step for the elucidation of more complicated fluvial processes in alluvium which relate to extreme river disasters. In this paper, as for the straight channel widening, the movement path of the sand eroded from a side bank and the lateral sediment transport are clarified by tracer tests and changes with time of cross sectional shape in detailed experiments, and by using these results the process of cross sectional variation is simulated under longitudinally uniform condition and problems in the analysis are pointed out. In addition, the widening process under longitudinally varying conditions are dealt with by a extended one-dimensional analysis with the consideration of the initial and the boundary condtions. The applicability of this analysis proves to be high till the beginning of channel meandering mainly caused by well-developed alternating bars, though the analysis has two major points to be improved. One of these points is to find out the equation of the side bank erosion expressing the actual process including the conditions of bank collapse and effects of bed and water level variations, and the other is to give the upstream boundary conditions suitably for the case when an initial ability of sediment transport of the stream channel differs largely from the rate of sand supplying.