Input and output mass flux correlations in an experimental braided stream. Implications on the dynamics of bed load transport

Abstract : Through the development of a model experiment it is shown that there exists a correlation between input and output sediment fluxes in a micro scale braided stream that remains valid regardless of the stability of the braided river. This correlation has some important consequences on the mechanics of bed load transport by braided rivers. It enables the definition of both a dimensionless stream power and a dimensionless transport efficiency. These dimensionless variables in turn permit the definition of a braided river stability criterion with regard to bed load transport. The existence of such a correlation also suggests that the average critical shear stress or slope of motion may depend on the flux of mass input to the system. Using these findings together with a one-dimensional Exner equation for the conservation of mass, a kinematic wave equation for the average evolution of the riverbed is eventually derived and its significance analyzed.