CCES-APUNCH: Hydrological extremes and sediment transport
Background
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Figure 1: Glacierforefield Riedbach, Ct. Valais (photo J. Schneider,
WSL)
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Figure 2: Bedload
transport measurements using portable bedload traps (photo J. Schneider, WSL)
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Figure 3: Calculated
against measured bedload transport rates for the Riedbach(circles) and the
Erlenbach (triangles). In grey: lab based equation of Wilcock and Crowe (2003).
In black: Within the APUNCH project adjusted equation based on field data of
about 45 rivers and mountain streams (preliminary analysis – publication in preparation).
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APUNCH is a
poly-project within the ETH Competence Centre for Environment and
Sustainability; the project includes experts from 9 different institutes at EPF
Lausanne, ETH Zürich, MeteoSwiss, and WSL.
The goal of APUNCH
is to gain a comprehensive and process chain based insight into the response of
Alpine watersheds hit by storm rainfall events. These insights will allow the
formulation of improved or new process models. Among others, some major
challenges of the project are: (i) the investigation of the space-time
structure of rainfall in mountainous regions; (ii) the laboratory and field
experiments on initiation and evolution of sediment transport in steep channels
and under rapidly varying flow conditions; (iii) the combination of physical
modelling, field testing and numerical simulations to analyse and predict the
conditions that lead to failure of dykes; (iv) the across-scales monitoring and
modelling effort, which is expected to lead, on the long-term, on a
process-based integrated watershed model system that can simulate the response
of a watershed to set of complex hydrological hazards.
Objectives
Within
APUNCH the Research Unit Mountain Hydrology and Massmovements focuses on the
assessment of flow conditions, on the initiation of sediment motion and on
sediment transport in steep channels with irregular bed morphology. The
objectives of this part are to perform measurements on bedload transport and flow
hydraulics in steep streams, and to develop a new theoretical approach to
describe initiation of particle motion and sediment transport in steep channels.
Current Issues
At the Riedbach,
Ct. Valais, field investigations of channel morphology, flow conditions and
bedload transport rates were conducted. Bedload transport was measured using so-called
bedload traps, which consist of a nylon net attached to a aluminium frame (Figure 2). The bedload
traps were mounted on the channel bed to collect bedload for about 1-60
minutes, depending on transport intensities. For further analysis, bedload
transport measurements from the Erlenbach moving bedload baskets are used additionally.
Measured transport rates were compared to calculated transport rates. As often
observed in steep streams commonly used transport equations, developed either
on lab data or on field data of lower gradient streams, overestimate transport
rates. Within the APUNCH project, a sediment transport equation was re-analyzed
(paper in preparation) based on field data of about 45 streams with channel
gradients ranging from 0.05 to 17%. With this equation it is possible to significantly
reduce the overestimation of sediment transport rates for the Riedbach (Figure 3).
More information
Participants
- Dieter
Rickenmann
- Johannes
Schneider
- Jens
Turowski
- Bruno
Fritschi
- Alexandre
Badoux
- Manuel
Nitsche
- Bastian Schmid
Contact
