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| Titel |
Check dams effects on sediment transport in steep slope flume |
| VerfasserIn |
Guillaume Piton, Alain Recking |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250090753
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| Publikation (Nr.) |
 EGU/EGU2014-5007.pdf |
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| Zusammenfassung |
| Depending on many influences (geology, relief, hydrology, land use, etc.) some mountainous
watershed are prone to cause casualties and facilities damages. Large amounts of sediments
episodically released by torrents are often the biggest problem in torrent related hazard
mitigation. Series of transversal structures as check dams and ground sills are often used in
the panel of risk mitigation technics.
A large literature exits on check dams and it mainly concerns engineering design, e.g. toe
scouring, stability stress diagram, changes in upper and lower reaches equilibrium slopes.
Check dams in steep slope rivers constitute fixed points in the bed profile and prevent general
bed incision. However their influence on sediment transport once they are filled is not yet
clear. Two flume test campaigns, synthetize in Table 1, were performed to investigate this
question:
Table 1 : experiment plan
Run (duration) Ref1 (50h)CD1a (30h)CD1b (30h)Ref2 (92h)CD2 (18h)
Solid feeding discharge (g.s^-1) 44 44 44 60 60
Number of check dams none 1 3 none 2
A nearly 5-m-long, 10-cm-wide and 12%-steep flume was used. The water discharge was
set to 0,55 l/s in all runs. A mixture of poorly sorted natural sediments with diameters
between 0.8 and 40 mm was used. An open solid-discharge-feeding circuit kept the inlet
sediment flux constant during all experiments.
As both feeding rates did not present variation, changes in outlet solid discharge were
assumed to be due to bed variations in the bed storage. We observed strong fluctuations of
solid flux and slope in each reaches of all runs between: (i) steep aggradating armoured bed
and (ii) less steep and finer bed releasing bedload sheets during erosion events and inducing
bedload pulses.
All experiments showed consistent results: transported volume associated with erosion
event decreased with the length between two subsequent check dams. Solid transversal
structures shorten the upstream erosion-propagation and avoid downstream change in the bed
level. As long as they are not buried by too strong aggradation they allow a “bed level
independence” between reaches.
On the long term, as the total inlet flux is kept constant, a decrease in transported
volumes induces an increase in the erosion event frequency: sediment releases are more
frequent but littler. As proposed by Poncet (1995), check dams participate efficiently in
hazard mitigation because “they release in retail what torrents would too abruptly delivered
wholesale”.
Reference : Poncet, A. "Restauration et conservation des terrains en montagne." Office national des
forêts, Paris (1995). |
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