CCES-APUNCH: Hydrological extremes and sediment transport
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Riedbach
(Mattertal, canton Valais) upstream of the water intake (Foto D. Rickenmann, WSL)
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Background
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 WSL part focuses on sediment transport mechanisms in steep
streams.
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. This will be achieved by a
multidisciplinary project context, where a combination of targeted laboratory experiments
with comprehensive and concurrent multiprocess field monitoring is expected to
provide the new insights into the interaction mechanisms of the process chain,
thus allowing 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 modeling 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 Torrents 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 (i) to perform measurements on
bedload transport and flow hydraulics in two steep streams, and (ii) to develop
a new theoretical approach to describe initiation of particle motion and
sediment transport in steep channels.
Approach
and methods
Field investigations will be made at the
WSL hydrologic experimental catchment at Erlenbach (Alptal, canton Schwyz)
using an existing bedload measuring site including geophone sensors, automatic
bedload basket samplers, and a sediment retention basin. Complementary field
measurements will be made at a new geophone measuring site in the Riedbach
(Mattertal, canton Valais) upstream of a water intake during glacier meltwater
flows. In addition to the automatic bedload transport measurements with the
geophone sensors, we will perform a particle tracer study using a passive radio
system (RFID) to obtain data on travel distances and dispersion of bed load
particles.
The analysis of the measurements will focus
on assessing the effect of several factors, which are likely responsible for
the large variability of sediment transport in steep and rough streams: (i)
form resistance losses due to important bed structures; (ii) limited
availability of mobile particles; (iii) initiation of particle motion in
step-pool morphologies with a wide grain size distribution; (iv) effect of
unsteady flow on initiation of motion and bed load transport. Although many
bedload transport equations have been proposed for gravel-bed streams, none of
them does adequately account for the factors mentioned above.
More information
Participants
- Dieter Rickenmann
- Johannes Schneider
- Jens Turowski
- Bruno Fritschi
- Alexandre Badoux
Contact
