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STORAGE HEAD WORKS
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ANIRUDHAN K M
LECTURER IN CIVIL ENGINEERING

DAMS
? Hydraulic structure
? Solid Impervious (or fairly impervious) barrier
constructed at a suitable location across a natural
stream (river), to store water in its upstream side.
? A reservoir is formed due to its construction
? The water in the reservoir is utilised as and when it is
needed
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TYPES OF DAM
? Classification according to use
�C Storage Dam
�C Diversion Dam
�C Detention Dam
? Classification by hydraulic design
�C Overflow Dam
�C Non Overflow Dam
? Classification by Materials
�C Rigid Dams
�C Non �C Rigid Dams
? Classification By Mode of Stability
�C Gravity Dam
�C Non Gravity Dam
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TYPES OF DAM
? Classification according to use
�CStorage Dam
? Constructed to store water during the rainy season, when water is
available in the river.
? Released gradually for intended purposes.
? They may store water for hydroelectric power generation, irrigation or
for Water Supply.
�CDiversion Dam
? Used to raise water level and divert water.
? No Reservoir is formed.
? No or a little Storage.
�CDetention Dam
? Flood mitigation.
? Stores water in the time of flood and released after flood at safe rate.
? Another type allows water to enter slowly to the ground water.
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TYPES OF DAM
? Over flow dam
�C Designed to carry Surplus
discharge
�C Crest is lover than High Flood
Level
�C Used along with Non
Overflow Dam as Spillway
Section
? Non Overflow Dam
�C Top of the dam kept higher than
Maximum expected high flood
level
�C Water not permitted to overtop
the dam
Classification by hydraulic design
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TYPES OF DAM
? Rigid Dam
�C Constructed of Rigid
Materials
? Solid Masonry or
Concrete Gravity Dam
? Arched Masonry or
Concrete Dam
? Concrete Buttress Dam
? Steel Dam
? Timber Dam
? Non Rigid Dam
�C Constructed of Non Rigid
Materials
? Earth Dam
? Rockfill Dam
? Combined Earth and
Rockfill
Classification by Materials
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TYPES OF DAM
? Gravity Dam
�C Self Weight of the Dam
the major Stabilization
Force
? Solid Masonry or
Concrete Gravity Dam
? Earth Dam
? Rockfill Dam
? Combined Earth and
Rockfill
? Non Gravity Dam
�C Stabilises against
mobilising forces using
Non Gravity Methods
? Arch Dam �C Load Transfer
by Arch Action
? Buttress Dam �C Load
Transferred to Supporting
Buttresses.
Classification by Mode of Stability
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SITE SELECTION
Factors governing site selection
? Foundation conditions
? Topography
? Site for spillway
? Material availability
? Reservoir capacity
? Communication
? Healthy Locality
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SITE INVESTIGATION FOR DAM
CONSTRUCTION
? Reconnaissance
? Preliminary Surveys
�C Engineering Surveys
�C Geological Surveys
�C Hydrologic Surveys
? Detailed Investigations
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CAPACITY OF RESERVOIRS
? Prismoidal Formula
? Trapezoidal Formula
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STORAGE ZONES OF RESERVOIRS
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EVAPORATION LOSSES IN RESERVOIRS
? Losses in Reservoirs are mainly due to evaporation and seepage
? The depth of water evaporated per year from the reservoir surface may
vary from about 400 mm in cool and humid climate to more than 2500
mm in hot and arid regions.
? Water budget method, Energy budget method etc are used for estimation
of Evaporation Losses
? Accurate estimation is done by using data from pan-evaporimeters or pans
exposed to atmosphere with or without meshing in or near the reservoir
site and suitably adjusted.
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FORCES ACTING ON A GRAVITY DAM
? Water Pressure
? Self Weight
? Uplift Pressure
? Silt Pressure
? Earthquake Pressure
? Wave Load
? Snow Load
? Wind Load
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FAILURES OF GRAVITY DAM
? Due to Overturning
? Due to Development of Tension at the Base
? Due to Sliding
? Due to Crushing or Compression
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ELEMENTARY PROFILE OF A DAM
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FREE BOARD AND TOP WIDTH
? Practical Considerations
�C Roadway at top
�C Load due to Roadway
�C Freeboard
? Top width is provided about 14% of the total height of dam
? Free Board
�C Margin provided Between KFL and Top of dam
�C Prevent waves, unforeseen floods
�C Provided equal to 3/2 x Height of Waves
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DRAINAGE GALLARY
? A gallery is an opening provided in the body of a dam for
various purposes
? Drainage gallery is a gallery extends only through the deepest
portion of the dam serving purpose of drilling and draining
the downstream portion of the foundation.
? Inspection gallery is provided for inspection purpose
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SPILLWAYS
? Free Overfall (Straight Drop) Spillway
? Overflow (Ogee) Spillway
? Chute (Open Channel/Trough) Spillway
? Side Channel Spillway
? Shaft (Drop Inlet/Morning Glory) spillway
? Tunnel (Conduit) spillway
? Siphon spillway
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EARTH DAMS
? Earth dams are the oldest type of dams, as well
as the most common ones.
? They are always most economical type that can
be constructed on soil foundations.
? Can be constructed using locally available soils.
? No special foundations are required for the
construction of these dams.
? Skilled labour is not required.
? Modern earth moving equipments can be used
to construct such type ofdams.
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SITE SELECTION OF EARTH DAM
? Topography - A wide valley with deep overburden
? Geology and Foundation Conditions
�C Gravel foundations, if well compacted is suitable for earth
dams.
�C Silt or fine sand foundations can be used for earth dams,
the main problems include settlement, prevention of
piping, excessive percolation losses.
�C Clay foundation may be used for each dams but require
flat side slopes
? Material availability
? Environmental Considerations
? Economy
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CAUSES OF FAILURES OF EARTH DAM
? HYDRAULIC FAILURES
�C Overtopping
�C Erosion of Upstream (Wave
Erosion)
�C Toe Erosion
? SEEPAGE FAILURES
�C Piping
�C Sloughing
? STRUCTURAL FAILURES
�C Upstream and downstream
slope failure due to
construction pore pressure
�C Upstream slope failure during
sudden drawdown
�C Downstream slope slide during
full reservoir condition
Upstream slope failure during sudden drawdown
Downstream slope slide during full reservoir condition
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