Bed morphology and flow resistance in steep open channels with varying widths

Abstract

Steep open channels are often characterised by bed forms in different scales. In the meso-scale,the typical bed features are usually described as successions of steps and pools. Depending on the channel width,the step-pool morphology can be superposed by macro-scale bed forms as e.g. bar structures. In steep headwaterstreams bed roughness is large relatively to flow depth. Consequently, flow field and flow resistance are signifi-cantly influenced by the bed morphology. In order to study the flow resistance in steep open channels, flume exper-iments were carried out at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of the Swiss FederalInstitute of Technology (ETH) in Zurich, Switzerland. The results show that for experiments where bar structuresoccurred, a significant influence of the macro-scale bed features on flow resistance could be ascertained. A newapproach is proposed to compute flow resistance in steep-open channels with macro- and meso-scale bed features.