BED MORPHOLOGY IN STEEP OPEN CHANNELS STATE-OF-THE-ART AND FIRST RESULTS OF A FLUME STUDY

The present paper outlines first results of a research project currently performed at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of the Swiss Federal Institute of Technology (ETH) in Zurich. The purpose of the research project is to investigate the bed morphology and the stability in steep open channels hazard assessment. A better knowledge of bed morphology and stability is also required for the design of stable and nature-orientated man-made structures. First results concerning bed morphology show that within the typical step-pool geometry the predominant structures are steps that are orientated transverse to the direction of flow. The formation of ring-structures, clusters and oblique or curved steps depend on flume width, slope and discharge. The rising frequency of transversely orientated steps with increasing slope can be attributed to the adaptation towards a more stable structure. The occurrence of macroscale structures similar to alternate bars can be observed for larger channel widths, however, it is shown that they represent an independent bedform type.