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Dams are also classified according to hydraulic design. Spill way is a overflow
dam when the crest of the dam is kept at lower elevation than the High Flood
Level. In case of non-overflow dam the top of the dam is kept at higher elevation
than the maximum High Flood Level.
Classification according to use
Storage diversion and detention dams
Storage dam, as the name signifies, store water in the upstream side of the
river by making a suitable obstruction structure. Such storage dam may be
constructed by a wide variety of materials like stone, concrete, earth, rockfill
etc.
The dam so constructed across the river raises the water level on the upstream
side causing a huge pool of water behind the dam, known as
reservoir, which is filled up during the rainy season to the desired level as per
the requirement of the project, i.e. irrigation water supply, power, multipurpose
etc. The submerged area of the reservoir depends on the local topography and
the height of the dam. On the contrary, a barrage or a weir which is classified
under diversion dam does not submerge any area by pool of water, but the
water level in the upstream side is slightly raised to divert water through canals.
If the major part or the entire ponding of water is achieved by a raised crest and
a small or nil part is diverted, it is known as weir. If, however, the water is raised
by means of installing gates, which can be used for controlled release of water,
the structure is known as barrage. Farakka Barrage is an example of diversion
of water by raising the water level of the Ganga through Farakka Feeder Canal.
Detention dams are widely used, particularly in the dry areas, to hold the water
during rainy seasons. Such detention dams also recharges groundwater which
can be used by constructing wells around the detention dams. They are
common in water shed development projects.
Various Types of Dams
Modern day engineers classify the dams into eight different types :
1) Earth Dams
2) Rockfill Dams
