 |
| Titel |
On mechanisms triggering the levees failure along the Foenna stream on 1st January 2006 and which caused the flooding in the urban area of Sinalunga, Tuscany Region (Italy). A case study |
| VerfasserIn |
Stefania Camici, Tommaso Moramarco, Luca Brocca, Florisa Melone, Vincenzo Lapenna, Angela Perrone, Antonio Loperte |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042286
|
|
|
|
|
|
| Zusammenfassung |
| On 1st January 2006, during an ordinary flood event, a levee failure along the Foenna stream
caused the flooding in the urban area of Sinalunga, a small town located in Tuscany region
(Italy). The event was monitored by a public agency with the responsibility for the control
and maintenance of the natural channel networks. Long time before of flooding,
people living in the surrounding area of the stream blamed the presence of wild
animals and of numerous burrows along the levees. Although the numerous actions of
maintenance along the levees mainly for removing the burrows, a levee seepage occurred
during that flood. The presence of an outflow located on the downstream face, almost
2 m below the levee top, caused the spurt of brown water denoting the presence
of sediment erosion. On the upstream face of levee, a little hole of about 30 cm
at the same height of the outflow was discovered. Although the agency workers
tried to close the hole by using appropriate blankets, in short time the top of the
levee subsided and the overtopping flow caused a trapezoidal breach typical for an
earth-fill embankment. The formation of breach was so fast that in a little more
of one hour the urban area near to the Foenna stream was flooded causing high
economic damages. Mechanisms triggered the levees failure are the object of this
work.
The analysis of the event has been first addressed to assess the state of-fact of levees
conditions along the Foenna stream, thus to understand how much the activity of wild
animals, in particular that of porcupine, may have affected the hydraulic safety of the
embankment. At the purpose, after the event, topographical surveys of cross sections have
been done along with tomographic surveys by geoelectric technique for investigating the
possible presence, besides of burrows, also of tunnels dug into the levees by animals. Then,
the analysis of hydrometeorological conditions of the event has allowed to better understand
the evolution of the flood and if its magnitude was able to affect the hydraulic holding of
levees. Finally, the seepage vulnerability of these levees has been also assessed to address
their hydraulic safety applying two models based on a steady and unsteady infiltration,
respectively.
Based on the obtained results, the following findings can be drawn. 1) The levees failure
near the Sinalunga urban area is certainly due to the presence of the porcupine burrow at
middle height of upstream face of levee that has addressed the flow into the embankment and
then triggered the seepage phenomenon. 2) The works of the maintenance finalized to the
closure of the burrows carried out before of the flood event were necessary but not sufficient
to prevent the failure of levees. 3) To prevent the failure due to burrows presence, the levees
maintenance should have been addressed through both the closure of burrows and
the capture of wild animals; if this action had been done for the Foenna stream
then the probability of failure would have been truly low. This last aspect has been
also inferred through geoelectrical tomography surveys that showed the possible
presence of at least two tunnels along both faces of levees, so emphasizing as the
various closure of burrows made in the past by maintenance agency were totally
useless. 4) The seepage vulnerability analysis has shown that levees might be to risk
of failure for floods whose durations are consistent with the ones might occur in
the Foenna basin. However, for this particular event the levees failure can be only
ascribed to wild animals activity, seeing that the seepage was caused by a burrow hole. |
|
|
|
|
|
|