Destruction of dams in connection with spillway discharges
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Despite the intuitively determined high danger which dams pose, long-time operating practice of a large number (about 33,000) of dams with a height of more than 15 m constructed by almost all countries of the world attests to their high reliability. The average annual number of victims in the entire world in connection with destruction or damage of these structures is 133 persons. The number of victims in mining coal equivalent in energy to its amount generated at a hydroelectric station is about 20 times higher, and in the case of energy consumption in motor transport, for example, 1000 times higher.
During the long period of operating concrete dams by all countries of the world, an insignificant number of cases of their failure in connection with operation of spillways has been recorded. Spillway damages and scouring of the channel in the lower pool develop over the course of a rather long time and, as a rule, it is possible to conduct repair works eliminating the danger of destruction of the entire dam.
The greatest (about 44%) number of failures of structures with high earth dams is related to the operation of spillways. As a rule, in this case the development of even insignificant damage of the dam cannot be prevented and within a short time interval partial or even almost complete destruction of the dam occurs.This should be taken into account when examining the problem of increasing the reliability of hydro developments with earth dams to the level characteristic on average for concrete dams or higher.
The main cause of failure of earth dams in connection with operation of spillways is their insufficient capacity. A number of countries, including the USA, have decided it is necessary to periodically check the sufficiency of the capacity of spillways of operating objects and are carrying out this work. When planning hydro developments it is necessary to examine the problem of the possibility of brief overtopping of the dam as a result of the formation of a breakthrough wave or collapse of an unstable mass into the reservoir if such an event is probable.High requirements should be imposed on the reliability of the main gates of spillways. In a number of cases a backup system is used, which provides operation of these gates.
KeywordsLower Pool Hydroelectric Station Average Annual Number Hydro Development Design Discharge
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