Safety Of Dams And Reservoirs

There are Several types of reservoirs as defined by their locations. The common type is a reservoir behind a dam in a valley. Increasing use is being made of tidal-storage reservoir for power generation along coast lines and excavated reservoirs for water storage for municipal or other use. In the latter type the excavated material commonly is employed to construct an embankment on one or all sides of the reservoir.

Reservoirs and their associated dams serve many purposes including electric power generation, storage and diversion of irrigation water, storage of industrial and municipal water supplies, recreation, and flood control. Less frequent uses of reservoirs include storage and control of stream water for navigation, and storage of sewage and waste products from mining or manufacturing operations. In some stances fuel powered and thermonuclear power plants require large volumes of cooling water, and reservoirs are constructed for this purpose. Whether a dam backs up water for a long or a short distance is not important from the structural point of view. Pressure depends not upon how far water is backed upstream but upon its depth at the dam. But the length of the reservoir and its capacity may change the risk associated in the case of failure.

There are no accurate records of the number of dams that have failed throughout the history of their construction. However, ruins of dams built through a long span of history in both ancient and more recent times indicates that the number must be high, probably in the thousands, if dams of all heights are included in the count. The magnitude of floods generated by dam failure or by collapse of the walls of a reservoir are not related to the height of a dam. More pertinent is the volume of water stored in the reservoir behind the dam, and the configuration of the valley below it, wether the dam is low or high.

The cost in human life, goods, and property damage of a flood generated by breaching of a dam or collapse of reservoir wall depends to a large extent on the magnitude of flood and what lies in the pathway of the flood. With an expanding population in many part of the world and an increasing occupation of floodplains by dwellings, commercials and industrial facilities , and highways, dam built long ago and dam built in recent times present a growing potential for massive destruction of life and property. the cause of floods associated with failure of dams and reservoir are numerous. In embankment dams a common cause of breaching is overtopping of existing spillways or waterlevel control facilities, although some failures have been attributed to slope failure, foundation subsidence, or earthquake damage. Failure of concrete dams usually is attribute to imperfect design or construction, to use of inferior materials in the dam, or to failure of foundation and/or abutment rocks. Construction of a dam and reservoir imposes new loads on foundation materials. Initial adjustment in the dam and foundation occurs as the dam is being built and as the load on the foundation is increased to a final load equal to the weight of the dam. Filling of the reservoir impose additional loads not only on the floor and wall of the reservoir but also on the upstream face of the dam. As the reservoir level is decreased and increased these loads fluctuate , and a cycle dynamic system of changing loads is superimposed on the static load of the dam on its foundation. Seepage of water through or beneath the dam may produce slow deterioration that may promote eventual failure. The responsibility for the safety of dams and reservoirs no longer belongs only to the designer and builder but must be shared by those who have knowledge and understanding, however imperfect they may be, of the expected behavior of natural materials under the condition superimposed by the loads of dams and reservoirs. Modern technology and social responsibility require that safe construction and maintenance of dams and reservoir shall be the shared responsibility of engineers, geologists, and rock mechanical expert.

Recognition of the need for worldwide surveillance of dams and reservoirs with emphasis on their safety has resulted in the formation of the International Commission on Large Dams (lCOLD) a unit of the World Power Conference within individual countries increasing efforts are being made to regulate and maintain continued safety of dams and reservoirs through the close cooperation of engineering organizations and government agencies. In spite of these good works, dams continue to fail, and intensification of efforts to assure the safety of existing dams and reservoirs and those that will be in the future is an increasingly urgent necessity.

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