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How to harness the water potential of a river optimally?
Headworks :
Any hydraulic structure which supplies water to the off-taking canal
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HeadworksHeadwork
1. Storage headwork.
2. Diversion headwork.
Storage headwork : the construction of a dam on the river. to store water during the period of excess supplies
to releases it when demand overtakes available supplies
Diversion headwork :
serves to divert the required supply to canal from the river.
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Storage headworks Dams) Impervious barrier the river to store water in the upstream side
(reservoir) the storage of water
reduce the impact of a flood down stream
to use the water beneficially in future
Hydropower
Irrigation
Water for domestic consumption
Drought control
For navigational facilities
capacity of reservoir : height of the dam and the shape of the river
valley on the up stream
Spillways: to discharge excess flood water
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DAMS
Principal components of a storage dam :
storage a structure to obstruct river flow,
a spillway for discharging excess flood water
outlets for allowing the storage water to be with drawn for
some useful purpose or to flow downstream at a regulated
quantity
Dam engineering brings together a range of disciplines,
like structural, hydraulics and hydrology, geotechnical,
environmental etc
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DAMS : Choosing a suitable location of dam
Topography:
i. a gorge which is most narrow, which would require minimum
quantities of dam construction material.ii. the volume of the water that may be able to store in the reservoir
behind the dam
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Geotechnical suitability (foundations)i. foundation should be geo technically sound to sustain the
high stresses due to
i. the self weight of the structure,
ii. water pressure of the reservoir
iii. and earth quake vibration induced forces at the dam body and the
water in the reservoir
ii. No dams should be erected across a fault
iii. Formations in which alternate hard and soft rocks may be
avoided
iv. Dams built on one uniform formation is preferred
DAMS : Choosing a suitable location of dam
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Submergence possibilities
Availability of a suitable spillway site
Hydrologic adequacy : it should satisfy1. The average quantity of water available in the river through out
year.
2. The minimum flow of the river
3. The maximum flow that has been recorded and estimates of whatmight occur in future.
Reservoir : deep reservoir is preferred over shallow one to minimize cost of submerged land per unit capacity, evaporation losses
and weed growth
Possibility of river diversion during construction
Sedimentation possibilities
Communication
Locality
DAMS : Choosing a suitable location of dam
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DAMS : CLASSIFICATION
Based on use:i. Storage dams
ii. Diversion dams
iii. Detention dams :
Water spreading dams / dikes
Debris dam
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DAMS : CLASSIFICATION
Based on hydraulic structure:
i. Non overflow dams
ii. Overflow dams
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DAMS : CLASSIFICATION
Based on materials:
i. Rigid dams
i. Gravity dam (masonry / concrete)
ii. Arch dam (masonry / concrete)
iii. Buttress dam (concrete)
iv. Steel dam
v. Timber dam
ii. Non-rigid dams
i. Earth fill damii. Rock fill dam
iii. Combined earth and rock fill dam
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Embankment ams constructed of natural materials excavated or obtained from the
vicinity of the dam site
The natural fill materials are placed and compacted without the
addition of any binding agent
Earth-fill or earthen embankmentsuse compacted soil for
constructing the bulk of the dam volume.
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Rock-fill embankments
impervious core of compacted earth fill or a slender concrete
or bituminous membrane
bulk of the dam volume is made of coarse grained gravels,
crushed rocks or boulders.
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Gravity dams
External forces are resisted by weight of the dam
Masonry or concrete
Permanent
Less maintenance
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The basic shape of a concrete gravity dam is triangular in section
A gravity dam should also have an appropriate spillway for
releasing excess flood water
energy dissipating structure : stilling basin
spillway is provided with a gate
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Advantages (over earth dams)
Strong and stable than earth dams
Suitable for across gorges having very steep side slope
Can be used as an overflow spillway crest
Suited for the areas having heavy downpour Least maintenance
No sudden failure
Deep-set sluices can be used to retard sedimentation in
reservoir
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Disadvantages
Sound rock foundation, impermeable rock strata
High initial cost
More time to construct
Skilled labour Difficult to allow subsequent rise in height
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ARCH DAMS
Curved in plan
Carries major part of the water load horizontally to the abutments (arch
action ) The balance of the water load is transferred to the foundation by cantilever
action
Strong side walls
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Advantages (over gravity gravity dams)
Suited for gorges where length is small in proportion toheight
Section is less when compared with gravity dam of same
height
Less material
Less base width
Limited problems due to uplift pressure
Can be constructed on moderate foundations
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Disadvantages
Skilled labour
More time
Very strong abutments
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BUTTRESS DAM
buttresses dividing the space into a number of spansm
Multiple arch type
Deck type buttress dam
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Advantages (over gravity dam)
Less massive
Less material
Less foundation pressure, can be constructed on moderate
foundations
Water load acts normal to deck: vertical components
stabilizes dam against overturning and sliding
Subsequent raising of height is posiible
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Disadvantage
Skilled labour
Deterioration of upstream concrete surface is fatal
More susceptible to damage
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Gravity dam: Structure
Heel
Gallery
Toe
Spillway(inside dam)
Crest
NWL
Normal
water level
MWL
Max. level
Free boardSluice way
Upstream Down stream
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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 checkingoperations.
Diversion tunnel: Tunnels are constructed for diverting water before theconstruction of dam. This helps in keeping the river bed dry.
Spillways: It is the arrangement near the top to release the excess water of thereservoir to downstream side
Sluice way: An opening in the dam near the ground level, which is used toclear the silt accumulation in the reservoir side.
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GRAVITY DAM : Forces
Water pressure
Weight of dam
Uplift pressure
Earth quake pressure Ice Pressure
Wave Pressure
Silt Pressure
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GRAVITY DAM : Failure Overturning
Sliding
Compression / crushing
Tension
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Safety against overturning
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safety against sliding
FS against sliding = actual coeft of friction / sliding factor
Sliding factor = tan = H/ (V U)
FS = /tan
Greater than 1
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Safety against compression and tension
Normal stress =Direct stress + Bending stress
Direct stress =FV/b*1
Bending stress = 6
FV.e/b2