DAMS IN INDIA

A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees (also known as dikes) are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are often used in conjunction with dams to provide clean electricity for millions of consumers.

Classification of dams
According to their functions, dams serve three main purposes: storage, diversion, or detention.

Storage dams :
Theyare constructed to impound water in periods of surplus supply for use in periods of deficiency. Many small dams impound the spring runoff for later use in dry summers. Storage dams may also provide a water supply, or improved habitat for fish and wildlife. They may store water for hydroelectric power generation, irrigation or for a flood control project.

The specific purpose of a storage dam influences its design and determines the amount of reservoir needed. Where multiple purposes are involved e.g. both power and irrigation, reservoir allocation is usually made for each separate use. The volume of storage establishes the height and width of the dam.

Diversion dams :
They provide sufficient pressure for pushing water into ditches, canals, or other conveyance systems. Such shorter dams are used for irrigation, and for diversion from a stream to a distant storage reservoir.

Detention dams :
They minimize the effect of sudden floods and trap sediment.

Overflow dams :

They carry water discharge over their crests, and are made of materials that will not be eroded by such discharges. Non-overflow dams are designed not to be overtopped, and may include earth and rock in their structure. Often the two types are combined to form a composite structure.

To prevent a dam from being overtopped, spillway structures carry off excess water. In earthfill dams, essential spillways are built as separate structures, often a shaft or tunnel adjacent to the dam. With concrete gravity dams, the downstream side of the structure acts as the spillway.