Prepared by Muneer AhmedDepartment of Water Resources
Engineering
Dam is a structure built across a STREAM,RIVER, or estuary to
store water. ARESERVOIR is created upstream of the damto supply
water for human consumption,IRRIGATION, or industrial use.
Dam is the central structure in a multipurpose schemeaiming at
the conservation of water resources.Auxiliary works for a dam
include spillways, gates, orvalves to control the discharge of
surplus water, anintake structure and means for permitting boats
orfishes to cross the dam.
A spillway is a section of a dam designedto pass water from the
upstream side ofa dam to the downstream side.Types of spillway
include:primary spillway,auxiliary spillway,emergency spillway,fuse
plug spillway etc.
Significant considerations when building a daminclude:
permeability of the surrounding rock or soilearthquake
faultslandslides and slope stabilitywater tablepeak flood
flowreservoir siltingenvironmental impacts on river fisheries,
forestsimpacts on human habitationscompensation for land being
flooded as well aspopulation resettlementremoval of toxic materials
and buildings from theproposed reservoir area
Dam erosion
Dam failure
I. By sizeII. By useIII. By structure
Large dams
Major dams
Major dams of the columbia river ecoregion
Major dams on sindhu river , Pakistan
By use dams can be classified as: 1.check dam 2.detention dam
3.diversionary dam 4.dry dam 5.saddle dam 6.storage dam 7.overflow
dam 8.wing dam 9.cofferdam
A check damreduces flowvelocity and controlsoil erosion.
Detention dams are constructed to minimize theimpact of
flooding and to restrict the flow rate of aparticular channel.
A diversionary dam diverts all or a portion ofthe flow of a
river from its natural course.
A dry dam is designed to control flooding. It normally
holdsback no water and allows the channel to flow freely,
exceptduring periods of intense flow .
Saddle dam under construction A saddle dam is an auxiliary dam
constructed to confine the reservoir created by a primary dam.
Storage dams are built to provide a reliable source of waterfor
short or long periods of time.
Storage dams
An overflow dam is designed to be over topped.
A weir is a type of small overflow dam that are oftenused
within a river channel .
A wing dam extends partway into a river and forces water intoa
fast-moving center channel which reduces the rate ofsediment
accumulation.
A cofferdam is a (usually temporary) barrier constructedto
exclude water from an area that is normally submerged.
By structure dams can beclassified as:1. embankment dam2.
timber dam3. arch dam4. gravity dam5. steel dam6. beaver dam
Embankment dams are made from compacted earth,they rely on
their weight to hold back the force of water.
The San Luis Dam,California is an embankment dam
A Timber crib dam, MichiganTimber dams were widely used early
due to ease and speed ofconstruction. Rarely built in modern times
by humans becauseof relatively short lifespan and limited
height.
Timber dams
In the arch dam, stability is obtained by acombination of arch
and gravity action.
Single arch dam Multiple arch dam
In a gravity dam, stability is secured by making it of such
asize and shape that it will resist overturning, sliding
andcrushing at the toe.
The Gilboa dam,NY is a solid gravity dam
A steel dam is a type of dam which uses steel plating (at
anangle) and load bearing beams as the structure.
Beaver dams are created as a protection against predators,such
as coyotes, wolves and bears, and to provide easy accessto food
during winter.
Garbage accumulated because of a dam
-> Kaptai Dam-> Rubber dams
Location- on the Karnafuli river at Kaptai in
Rangamatidistrict, 65 km upstream of Chittagong.Length-
670.56mHeight- 45.7m highWidth- 45.7m (at foundation level) 7.6m(at
crest level)The catchment area of the reservoir- 11,000 sq kmSince
it is an earthen dam a 16-gated spillway (each 12.2mby 11.3m) with
discharge capacity of 625,000 cusec has beenconstructed on the left
side of the main dam.
Kaptai dam
Kaptai dam
Compared to concrete barrage and regulators rubber dams are
cheaper and more flexibleand can be fully deflated during the flood
season . Rubber dams can be as long as 100mand used for irrigation
, small-scale hydropower generation and rural water supply.
Rubber dams in BANGLADESH
Feature Bakkhali Dam Eidgaon DamLength (m) 84 52Height (m) 3.5
3Maximum water retention depth (m) 4 3Maximum overflow discharge
(cumec) 256 80Maximum flood flow (cumec) 1073 600Length of concrete
floor (m) 40 33.5Protective works (m):Upstream 9 6Downstream 13
8Volume of inflated dam (cu m) 1200 800Weight of dam bag (ton) 14
7Filling pump capacity (cu m/hr) 150 100Filling/emptying time (hr)
8.1 8.1Total cost (million Tk) 36 18
,
About hoover damOfficial name- Hoover DamImpounds- Colorado
RiverLocale- Nevada-Arizona United StatesLength- 1244 ft (379
m)Height- 726.4 ft (221 m)Construction began- 1931Opening date-
1936Construction cost- $49 million