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A saddle dam is an auxiliary dam constructed to confine the reservoir created by a primary dam either to permit a higher water elevation and storage or to limit the extent of a reservoir for increased efficiency. An auxiliary dam is constructed in a low spot or "saddle" through which the reservoir would otherwise escape.
Similar distinctions are used in Egypt, where it is noted: "In this system a "dam" is a structure that forms a reservoir for the storage of water during the annual flood period of the Nile in order to supplement the natural flow of the river during the low-water period; a "barrage" merely raises the river or canal level, when necessary, to the ...
The fraction of storage volume in the reservoir above the spillway crest can only be used for the temporary storage of floodwater; it cannot be used as water supply storage because it sits higher than the dam can retain it. In an intermediate type, normal level regulation of the reservoir is controlled by the mechanical gates.
A reservoir (/ ˈ r ɛ z ər v w ɑːr /; from French réservoir [ʁezɛʁvwaʁ]) is an enlarged lake behind a dam, usually built to store fresh water, often doubling for hydroelectric power generation.
Usually, a dam is designed specifically to impound water behind a wall, whilst a weir is designed to alter the river flow characteristics. A common distinction between dams and weirs is that water flows over the top (crest) of a weir or underneath it for at least some of its length.
Tarbela Dam is a large dam on the Indus River in Pakistan, about 50 km (31 mi) northwest of Islamabad. Its height of 485 ft (148 m) above the river bed and 95 sq mi (250 km 2) reservoir make it the largest earth-filled dam in the world. The principal element of the project is an embankment 9,000 feet (2,700 m) long with a maximum height of 465 ...
Since there is only an extremely low flow within the reservoir so no water level gradient, the head can be clearly seen: where the farthest watercourse discharges into the reservoir. Upstream of the actual reservoir is likely to be a pre-dam, which typically have a constant water level so the head is reinforced.
The general design for a flood detention dam has a cross sectional shape of a trapezoid, where the longer of the parallel sides is the base of the dam, and the angled sides face upstream and downstream. The flood detention dam has an opening at the top to release the flood water at a controlled rate that the channels below can accommodate.