1. No category

Physical modelling of sediment transport in
mountain torrents upstream of open check dams
Authors:
Sebastian
SCHWINDT
Dr. Mário J.
FRANCA
Prof. Dr. Anton J.
SCHLEISS
Check dam in the region of Trent (Italy)
Paper Code: EGU2015-6166
14/04/2015 Programme Session GM7.1
Physical modelling of sediment transport in mountain torrents upstream of open check dams
OVERVIEW
►RESEARCH
►CASE
BACKGROUND
STUDIES
►MODEL
DESIGN
►MEASURING
SYSTEM
►EVALUATION
TARGET
OVERVIEW
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Research background
► Sediment
and habitat dynamics (Wasserbau & Ökologie)
» funding: Swiss Federal Office for the Environment (FOEN)
Promotion of sediment continuity
» conditioned sediment retention in upstream reaches
» avoid sediment scarcity in draining channels
BACKGROUND
picture: Rhône, Switzerland
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Situation in the terrain (1)
typical
location for
check dam
BACKGROUND
picture from Hübl (2009)
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Situation in the terrain (2)
► At
channel slope change: varying sediment transport capacity
Change of
channel slope
BACKGROUND
picture from Hübl (2007)
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Hydraulic aspects
► Floods
► Large
and sediments are crucial for river ecology
floods threaten infrastructures
► Challenge:
Design flood protection which
» provides sufficient safety for dwellers
» allows dynamic river development
Bank full discharge
(Krimml, Austria)
optimization of open check dams in terms of sediment
transport continuity is required
or
what impact on sediment transport have flow obstacles
in steep gravel bed rivers?
BACKGROUND
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Research approach
► Physical
model most suitable
► Model
design based on case studies of torrents and open
check dams in the Alps
► No
specific scale, but assures practical relevance
» length ratios
» similarity of sediment transport
APPROACH
pictures: Jenbach, Germany
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
MODEL DESIGN
flow obstacle
(open check
dam)
removable channel
(tests with local widening)
MODEL DESIGN
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Design aspects – Channel
► Roughness
» channel bed composed of grains > D84 of mobile sediment
► Geometry
»J=2/4/6%
MODEL DESIGN
Variable
longitudinal slope
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Design aspects – Sediment feeding
► Used
sediment mixture based on dimensionless curve for
Alpine rivers established by Hersberger (2003)
Percent by weight [%]
100
75
50
25
Alps
Alps60(own study)
Hersberger
(2003) 2003)
Alps (Hersberger,
0
0.00
Used
Usedmixture
mixture
1.00
2.00
3.00
Dimensionless grain diameter Di/Dm [-]
MODEL DESIGN
4.00
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Design aspects – Sediment feeding
► Supply
system: Release container + conveyor belts
MODEL DESIGN
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Sediment output
► Measurement
system: filter basket + scale
suspended with a mobile crane
wireless data
transfer [1/s]
MEASURING SYSTEM
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Water level recording
probes
Probe distance to surface [m]
► Ultrasonic
MEASURING SYSTEM
13
Physical modelling of sediment transport in mountain torrents upstream of open check dams
Surface flow velocity
► Particle
image velocimetry
» industrial CMOS camera (SMX-160C)
» wide lens opening (1.4-1.8)
t
t + Δt
t
MEASURING SYSTEM
t + Δt
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Surface flow velocity
► Particle
image velocimetry
» image abstraction
Cropped region of interest
Original image
Flow direction: left to right
Apply binary filter
MEASURING SYSTEM
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Surface flow velocity
► Particle
image velocimetry
» identification of particle movement
t
Flow direction: left to right
t + Δt
MEASURING SYSTEM
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Surface flow velocity
► Particle
image velocimetry
» time average of image series
Channel width [m]
Stream wise velocity u [m/s]
Channel length [m]
MEASURING SYSTEM
17
Physical modelling of sediment transport in mountain torrents upstream of open check dams
Surface flow velocity
► Particle
image velocimetry
» time average of image series
Channel width [m]
Stream wise velocity u [m/s]
Channel length [m]
MEASURING SYSTEM
18
Physical modelling of sediment transport in mountain torrents upstream of open check dams
Surface flow velocity
► Particle
image velocimetry
» time average of image series
Channel width [m]
Horizontal velocity v [m/s]
Channel length [m]
MEASURING SYSTEM
19
Physical modelling of sediment transport in mountain torrents upstream of open check dams
Surface flow velocity
► Particle
image velocimetry
» time average of image series
Channel width [m]
Horizontal velocity v [m/s]
Channel length [m]
MEASURING SYSTEM
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Sediment depositions
► Zenithal
photography
» same principal as for flow velocity
» different time resolution (4 frames per minute)
front velocity
front velocity
MEASURING SYSTEM
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Evaluation target
► Derivation
of flow energy balance + energy losses …
► Derivation
of transport capacity …
… along the whole channel …
… across obstacles (i.e. open check dam) …
EVALUATION TARGET
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Acknowledgements…
… to the Swiss Federal Office for
the Environment (project funding)
Partners:
Swiss federal institute of
aquatic science and technology
Swiss federal institute
for forest, snow and
landscape research
Laboratory of hydraulics, hydrology and
glaciology ETH Zurich
THANKS TO …
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Physical modelling of sediment transport in mountain torrents upstream of open check dams
Thank you for your attention.
Questions?
[email protected]
http://lch.epfl.ch
Krimmler Wasserfälle (Austria)