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Are higher seismic safety standards required
for dams forming dam cascades along rivers? |
M. Wieland
Poyry Switzerland Ltd., Zurich, Switzerland
ABSTRACT: Along major rivers, several large dams have been built or are being built, forming dam or runof-river power plant cascades. The cascades could consist of concrete or embankment dams or run-of-river power plants depending on the longitudinal profile of the river. As the failure of any storage dam in a cascade may cause overtopping and/or failure of the downstream dams, the probability of catastrophic release of water from a dam cascade is larger than that of the failure of a single dam. The paper is concerned with the probabilistic and deterministic seismic safety aspects of dam cascades. At present, in the design of large dams extreme floods and the worst earthquake ground motion at a dam site have to be taken into account. Due to the difficulties in determining the probability of failure of a dam subjected to earthquake action, it is proposed to determine the safety criteria of dams forming dam cascades by focusing on the consequences of a cascade failure rather than on the probability of failure of individual dams. As all dams are prototypes, and since only one large embankment dam has failed during a strong earthquake, statistical analyses of seismic failure of dams are meaningless
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