Author(s): R. Weichert; G. R. Bezzola; H. E. Minor
Linked Author(s):
Keywords: Bed roughness; Flow resistance; Geomorphology; Stability; Step-pool-systems
Abstract: Steep headwater streams are often characterised by alternating steps and pools. The specific pattern can be seen as image of the complex interaction between topography, hydrology, geology and vegetation of a river catchment area. As bed roughness is large relatively to flow depth, the flow field and thus flow resistance and stability are largely influenced by bed morphology. Flume experiments with two widely-graded sediment mixtures are being performed to simulate the formation and destruction processes of step-pool systems. Laser profiling is used to provide digital elevation model data that allows for the detailed recording and analysis of the bed topography. The geometry of step-pool system as observed in the flume experiments is attributed to a formation process controlled by slope and discharge (streampower) on the one hand and the location and size of the large boulders on the other hand. In preliminary experiments different failure mechanisms could be identified. As the stability of step-pool systems is primarily determined by the stability of the large boulders the destruction processes are initiated by loss of their support by inner erosion, scour at the step toe or by direct erosion of the large boulders. However, the collapse of a single step does not trigger the collapse of a step-pool system, because single destabilized boulders could even enhance the stability of the following step. As a result the definition of stability in conjunction with the significant destabilizing processes needs further investigation to assess hazards of mountain torrent quantitatively.
Year: 2003