Dams

Topics: Dam, Dams, Embankment dam Pages: 12 (3502 words) Published: June 2, 2013
DAMS

[pic] INTRODUCTION

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 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. It can also be used to collect water or for storage of water which can be evenly distributed between locations.

PURPOSE OF DAMS

Intended purposes include providing water for irrigation to a town or city water supply, improving navigation, creating a reservoir of water to supply industrial uses, generating hydroelectric power, creating recreation areas or habitat for fish and wildlife, retaining wet season flow to minimize downstream flood risk and containing effluent from industrial sites such as mines or factories. Some dams can also serve as pedestrian or vehicular bridges across the river as well. When used in conjunction with intermittent power sources such as wind or solar, the reservoir can serve as pumped water storage to facilitate base load dampening in the power grid. Few dams serve all of these purposes but some multi-purpose dams serve more than one.

[pic] STRUCTURE OF DAMS

HEEL: Contact with the ground on the upstream side.

TOE: Contact on the downstream side.

ABUTMENT: Sides of the valley on which the structure of the dam rest.

GALLERIES: small rooms like structure left within the dam for checking operations.

DIVERSION TUNNEL: Tunnels are constructed for diverting water before the construction of dam. This helps in keeping the river bed dry.

SPILLWAYS: It is the arrangement near the top to release the excess water of the reservoir to downstream side.

SLUICE WAY: An opening in the dam near the ground level, which is used to clear the silt accumulation in the reservoir side.

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[pic] TYPES OF DAMS
I. MASONRY AND CONCRETE DAMS
i. ARCH DAMS:
In the arch dam, stability is obtained by a combination of arch and gravity action. If the upstream face is vertical the entire weight of the dam must be carried to the foundation by gravity, while the distribution of the normal hydrostatic pressure between vertical cantilever and arch action will depend upon the stiffness of the dam in a vertical and horizontal direction. When the upstream face is sloped the distribution is more complicated. The normal component of the weight of the arch ring may be taken by the arch action, while the normal hydrostatic pressure will be distributed as described above. For this type of dam, firm reliable supports at the abutments (either buttress or canyon side wall) are more important. The most desirable place for an arch dam is a narrow canyon with steep side walls composed of sound rock. The safety of an arch dam is dependent on the strength of the side wall abutments, hence not only should the arch be well seated on the side walls but also the character of the rock should be carefully inspected.

ii. GRAVITY DAMS:
In a gravity dam, stability is secured by making it of such a size and shape that it will resist overturning, sliding and crushing at the toe. The dam will not overturn provided that the moment around the turning point, caused by the water pressure is smaller than the moment caused by the weight of the dam. This is the case if the resultant force of water pressure and weight falls within the base of the dam. However, in order to prevent tensile stress at the upstream face and excessive compressive stress at the downstream face, the dam cross section is usually designed so that the resultant falls within the middle at all elevations of the cross section (the core). For this type of dam, impervious foundations with high bearing strength are essential. When situated on a suitable site,...
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