Monitoring and Modeling the Transport of Coarse Single Particles in Mountain Riversby Peter Ergenzinger, Freie Universitaet, Berlin, Germany,
Carmen de Jong, Freie Universitaet, Berlin, Germany,
Abstract: The dynamics of single cobbles was studied in the alpine river Lainbach using the Magnetic Tracer Technique (MATT) and radiotransmitters (PETSY = PEbble Transmitter SYstem). Our measurements were based on the approach of H.A. Einstein (1937) determining total travel length of single particles during a flood and different step lengths and rest periods of radio tacked cobbles. Special studies were undertaken to continuously measure lift and shear forces at the beginning of erosion of a coarse sphere using the CObble Satellite SYstem (COSSY). The main results of the COSSY investigations support the theories of H.A. Einstein suggesting that shear forces are dominant for erosion only when the particle is situated on the river bed. When the particle is level with its neighbouring particles, the dominant force is lift and erosion occurs only in cases when lift is about twice as great as shear. Step lengths of the PETSY cobbles was studied both in the laboratory and in the field. In contrast to the proposals of H.A. Einstein, the best approach to describe step lengths distribution is by a Gamma function. The rest periods in between the movements are best described by an e-function. The model of single particle transport was developed on the basis of these results. What must be known in addition are the geomorphic properties of the related mountain rivers. In a step pool system the probabilities of accretion are e.g. far higher in the pool. The results of the model were tested against the results of the observed transport lengths of the MATT tracered material.
Subject Headings: Particles | Shear forces | Erosion | Rivers and streams | Hydrologic models | Mountains | Mathematical models | Sediment transport
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