PREDICTION OF ALLUVIAL CHANNEL PATTERN OF PERENNIAL RIVERS

Purely braided, meandering and straight channels can be considered as end-members of a continuum of alluvial channel patterns. Several resea rchers have succeeded in separating channel patterns in fields defined by flow related parameters. However, the discriminators of the princi pal channel patterns derived from these diagrams all require some a pr iori knowledge of the channel geometry. In this paper a method is pres ented which enables prediction of the equilibrium conditions for the o ccurrence of braided and high sinuosity meandering rivers in unconfine d alluvial floodplains. The method is based on two, almost channel pat tern independent, boundary conditions: median grain size of the river bed material, and a potential specific stream power parameter related to bankfull discharge or mean annual flood and valley gradient. This c an be regarded as a potential maximum of the available flow energy cor responding to the minimum sinuosity condition, P = 1. Based on an anal ysis of 228 datasets of measurement sites along rivers from many parts of the world an independent discriminating function was found that se parates the occurrence of braided rivers and meandering rivers with P > 1.5. The function applies to equilibrium conditions of rivers that n either incise nor show rapid aggradation, with a bankfull or mean annu al flood discharge above 10 m(3)/s and a median bed material grain siz e between 0.1 and 100 mm.