BED FORMS IN STEEP CHANNELS WITH HETEROGENEOUS BED MATERIALS INDUCED BY BOTTOM ELEVATION INSTABILITY AND SORTING INSTABILITY

Linear stability analyses for steep channel flows with movable bed of heterogeneous materials following a Talbot grain size distribution were performed in order to investigate peculiar characteristics of the bed forms.It was found that two kind of instability exist in the system such that one would be a bottom elevation instability and the other would be a sorting wave instability. Test experiments exhibited the formation of alternating gravel bars on the bed when the maximum growth rate of the bottom perturbation was greater than that of the sorting wave perturbation, and exhibited the formation of longitudinally and laterally alternating coarse sediment fractions when the condition was reverse.