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| Titel |
Simulating dam-breach flood scenarios of the Tangjiashan landslide dam induced by the Wenchuan Earthquake |
| VerfasserIn |
X. Fan, C. X. Tang, C. J. Westen, D. Alkema |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 12, no. 10 ; Nr. 12, no. 10 (2012-10-02), S.3031-3044 |
| Datensatznummer |
250011141
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| Publikation (Nr.) |
 copernicus.org/nhess-12-3031-2012.pdf |
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| Zusammenfassung |
| Floods from failures of landslide dams can pose a hazard to people and
property downstream, which have to be rapidly assessed and mitigated in
order to reduce the potential risk. The Tangjiashan landslide dam induced by
the Mw = 7.9 2008 Wenchuan earthquake had impounded the largest lake in
the earthquake affected area with an estimated volume of 3 × 108 m3,
and the potential catastrophic dam breach posed a serious
threat to more than 2.5 million people in downstream towns and Mianyang
city, located 85 km downstream. Chinese authorities had to evacuate parts of
the city until the Tangjiashan landslide dam was artificially breached by a
spillway, and the lake was drained. We propose an integrated approach to
simulate the dam-breach floods for a number of possible scenarios, to
evaluate the severity of the threat to Mianyang city. Firstly, the
physically-based BREACH model was applied to predict the flood hydrographs
at the dam location, which were calibrated with observational data of the
flood resulting from the artificial breaching. The output hydrographs from
this model were inputted into the 1-D–2-D SOBEK hydrodynamic model to simulate
the spatial variations in flood parameters. The simulated flood hydrograph,
peak discharge and peak arrival time at the downstream towns fit the
observations. Thus this approach is capable of providing reliable
predictions for the decision makers to determine the mitigation plans. The
sensitivity analysis of the BREACH model input parameters reveals that the
average grain size, the unit weight and porosity of the dam materials are
the most sensitive parameters. The variability of the dam material
properties causes a large uncertainty in the estimation of the peak flood
discharge and peak arrival time, but has little influence on the flood
inundation area and flood depth downstream. The effect of cascading breaches
of smaller dams downstream of the Tangjiashan dam was insignificant, due to
their rather small volumes, which were only 2% of the volume of the
Tangjiashan lake. The construction of the spillway was proven to have played
a crucial role in reducing the dam-breach flood, because all the other
natural breach scenarios would have caused the flooding of the downstream
towns and parts of Mianyang city. However, in retrospect improvements on the
spillway design and the evacuation planning would have been possible. The
dam-break flood risk will be better controlled by reducing the spillway
channel gradient and the porosity of the coating of the channel bottom. The
experience and lessons we learned from the Tangjiashan case will contribute
to improving the hazard mitigation and risk management planning of similar
events in future. |
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