Bed erosion in steep open channels

Abstract

A new model is proposed to predict the bed topography in steep open channels once the bed stability is exceeded. Existing relationships describe bed stability by defining an entrainment state, usually expressed by a threshold shear stress or a discharge. The approach proposed herein focuses the self-stabilization potential of the channel bed at discharges larger than the entrainment value for which there is no sediment supply from upstream. Flume experiments carried out at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of the Swiss Federal Institute of Technology (ETH) Zurich, indicated that the self-stabilization potential occurs in various geomorphologic scales. These scales are associated with typical features of the channel bed morphology. As the self-stabilization process is always combined with erosion, the novel approach interrelates the product of water discharge and channel gradient with the channel bed degradations associated with the different geomorphologic scales.