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| Titel |
Sediment depositions upstream of open check dams: new elements from small scale models |
| VerfasserIn |
Guillaume Piton, Jules Le Guern, Costanza Carbonari, Alain Recking |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105039
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| Publikation (Nr.) |
 EGU/EGU2015-4483.pdf |
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| Zusammenfassung |
| Torrent hazard mitigation remains a big issue in mountainous regions. In steep slope
streams and especially in their fan part, torrential floods mainly result from abrupt
and massive sediment deposits. To curtail such phenomenon, soil conservation
measures as well as torrent control works have been undertaken for decades. Since the
1950s, open check dams complete other structural and non-structural measures in
watershed scale mitigation plans1. They are often built to trap sediments near the fan
apexes.
The development of earthmoving machinery after the WWII facilitated the dredging
operations of open check dams. Hundreds of these structures have thus been built for 60
years. Their design evolved with the improving comprehension of torrential hydraulics and
sediment transport; however this kind of structure has a general tendency to trap most of the
sediments supplied by the headwaters. Secondary effects as channel incision downstream of
the traps often followed an open check dam creation. This sediment starvation trend tends to
propagate to the main valley rivers and to disrupt past geomorphic equilibriums. Taking
it into account and to diminish useless dredging operation, a better selectivity of
sediment trapping must be sought in open check dams, i.e. optimal open check dams
would trap sediments during dangerous floods and flush them during normal small
floods.
An accurate description of the hydraulic and deposition processes that occur in sediment traps
is needed to optimize existing structures and to design best-adjusted new structures. A
literature review2 showed that if design criteria exist for the structure itself, little information
is available on the dynamic of the sediment depositions upstream of open check dams, i.e.
what are the geomorphic patterns that occur during the deposition?, what are the relevant
friction laws and sediment transport formula that better describe massive depositions in
sediment traps?, what are the range of Froude and Shields numbers that the flows tend to
adopt?
New small scale model experiments have been undertaken focusing on depositions processes
and their related hydraulics. Accurate photogrammetric measurements allowed us to better
describe the deposition processes3. Large Scale Particle Image Velocimetry (LS-PIV) was
performed to determine surface velocity fields in highly active channels with low grain
submersion4. We will present preliminary results of our experiments showing the new
elements we observed in massive deposit dynamics.
REFERENCES
1.Armanini, A., Dellagiacoma, F. & Ferrari, L. From the check dam to the development of functional
check dams. Fluvial Hydraulics of Mountain Regions 37, 331–344 (1991).
2.Piton, G. & Recking, A. Design of sediment traps with open check dams: a review, part I:
hydraulic and deposition processes. (Accepted by the) Journal of Hydraulic Engineering 1–23
(2015).
3.Le Guern, J. Ms Thesis: Modélisation physique des plages de depot : analyse de la dynamique de
remplissage.(2014) .
4.Carbonari, C. Ms Thesis: Small scale experiments of deposition processes occuring in sediment traps,
LS-PIV measurments and geomorphological descriptions. (in preparation). |
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