STUDY ON THE INSTABILITY OF BED FORM IN THE CHANNEL BIFURCATION ON MOVABLE BED UNDER SUBCRITICAL FLOW

Stability condition for a bifurcated channel system is not well known on the bed displacement and discharge ratio in branched alluvial rivers. Subcritical flow tests using a simple straight bifurcated channel with different slopes of movable channel bed were conducted to find hydraulic parameters relating to the unstable changes and instability conditions. Also, linear stability analysis on bed change was performed to the upstream area of a channel bifurcation with using the shallow water flow equations and continuous equation of sediment by applying the Galerkin method. The results show that instability of bed displacement and discharge is strongly influenced by nondimensional wave number k of bed undulations in the upstream area of channel bifurcation and parameter βwhich reflects the lateral inclination of a cross section caused by the difference of bed slopes of two bifurcated channels. In the range of 0.1