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| Titel |
Memory effect triggered by exceptional event: the Rio Cordon study case |
| VerfasserIn |
Riccardo Rainato, Luca Mao, Lorenzo Picco, Adriana García-Rama, Mario Aristide Lenzi |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250128693
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| Publikation (Nr.) |
 EGU/EGU2016-8703.pdf |
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| Zusammenfassung |
| In the mountain environment, the steep channels play a key-role in the drainage networks.
Notably, the sediment transport processes that here occur, can affect aspects as the
geomorphic changes, channel evolution, reservoir management, infrastructure design and
hazard assessment. Due to the complex and changeable hydraulic and morphological features
that characterize the mountain environment, the steep channels can exhibit fluvial and/or
debris-flow transport with magnitude of sediment delivery that, in the same basin,
may strongly vary from event to event. In the light of these challenging conditions,
appears clear as an accurate monitoring and investigation of sediment dynamics is
of critical importance in the steep mountain channels. Such monitoring has even
more significance if it is maintained over long-period, enabling to investigate even
the role of high magnitude/low frequency events. Using a dataset 29 years-wide,
this work aims to investigate the temporal trend of sediment dynamic in the Rio
Cordon (Eastern Italian Alps). The Rio Cordon is a steep mountain channel (mean
slope = 13%) characterized by step-pool and riffle-pool morphology. The basin (5
km2)exhibits a prevalent nivo-pluvial runoff regime. Since 1986, the catchment is
equipped with a monitoring station, that continuously records water discharge,
bedload and suspended load (at 1 hr intervals, and 5 min intervals during floods). In
September 1994 an exceptional event (RI > 100 years) occurred in the study site,
mobilizing about 4000 tons of material. Currently, the structure is managed by ARPA
Veneto – Regional Department for Land Safety. In terms of magnitude, the 31 floods
recorded by the monitoring station show a wide range of hydraulic forcing (i.e.
peak discharge and effective runoff) and amount transported. Specifically, Qpeak
ranges within one order of magnitude (1.02 - 10.42 m3 s−1), while the amount
of bedload and suspended load varies by more than 3 orders (i.e. 0.9 t < BL <
1541.7 t). The amounts transported by the floods are investigated as a function of
Qpeak, using a power-law regression. Bedload (r2= 0.739) and suspended load (r2=
0.565) appear positively correlated with Qpeak, also showing that floods of a certain
magnitude transported more sediments after the exceptional 1994 flood. A comparable
behavior can be observed by the Qpeak/D50 relationship (r2= 0.688). The ratio between
sediment load and effective runoff of the events allowed the temporal trend of transport
efficiency to be inferred. The results highlight that nearly a decade with high transport
efficiency appears to have occurred subsequently to the September 1994 event. This
result confirms that exceptional floods, rarely assessed by short-term monitoring
programs, can strongly affect the long-term sediment fluxes. In the case of Rio
Cordon, the exceptional event triggered a “memory effect” in the basin, altering
the sediment dynamics for roughly 10 years. This research was supported by the
Italian Research Project of Relevant Interest PRIN2010-2011, prot. 20104ALME4,
ITSE; and by the University of Padova Research Project CPDA149091- WoodAlp. |
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