Question

short note on dam in about 400 words..

Answer 1

Dams are structural barriers built to obstruct or control the flow of water in rivers and streams. They are designed to serve two broad functions. The first is the storage of water to compensate for fluctuations in river discharge (flow) or in demand for water and energy. The second is the increase of hydraulic head , or the difference in height between water levels in the lake created upstream of the dam and the downstream river. By creating additional storage and head, dams can serve one or more purposes: Generating electricity; Supplying water for agricultural, industrial, and household needs; Controlling the impact of floodwaters; and Enhancing river navigation. They can be operated in a manner that simultaneously augments downstream water quality, enhances fish and wildlife habitat, and provides for a variety of recreational activities, such as fishing, boating, and swimming. Classes of Dams Four major classes of dams are based on the type of construction and materials used: embankment, gravity, arch, and buttress. Embankment. Embankment dams typically are constructed of compacted earth, rock, or both, making them less expensive than others that are constructed of concrete. Consequently, more than 80 percent of all large dams are of this type. Embankment dams have a triangular-shaped profile and typically are used to retain water across broad rivers. Gravity. Gravity dams consist of thick, vertical walls of concrete built across relatively narrow river valleys with firm bedrock. Their weight alone is great enough to resist overturning or sliding tendencies due to horizontal loads imposed by the upstream water. Arch. Arch dams, also constructed of concrete, are designed to transfer these loads to adjacent rock formations. As a result, arch dams are limited to narrow canyons with strong rock walls that can resist the arch thrust at the foundation and sides of the dam. Buttress. Buttress dams are essentially hollow gravity dams constructed of steel-reinforced concrete or timber.