part ii_intake structures

Intake Structures
Unit I
Chapter 2

Definitionof intakes
• A structure placed in a water source to permit the
withdrawal of water from the source and discharge it
into an intake conduit through which it flows to the
treatment plant, or into an intake well from where
water is pumped to treatment plant is called intake.
• Intake consist of two sections First, intake conduit with
the screen at the inlet end and valve to control the
flow of water. Second, a structure permitting the
withdrawal of water from source and housing and
supporting intake conduit, valves, pumps etc.

• The structure may be of stone masonry or
brick masonry, R.C.C, or concrete blocks. The
structure is constructed watertight and is
designed to resist all forces likely to come
upon it including the pressures due to water,
wave action, the wind, floating debris, annual
rainfall, geological formations.

Factors governing the selection of site for the
location of an Intake
1. Site should be as nearer to the treatment plant as
possible, so that cost of conveyance of water is less
2. Located in pure water zone-reduces load on
treatment plant
3. Should not be located at the d/s or in the vicinity of
sewage disposal point
4. As far as possible not located in or near the navigation
channel- may be polluted due to discharge of refuse
and wastes from ships and boat

5. Located so as to ensure the supply of water even
under worst conditions – when water level is min.
sufficient quantity should be available . Thus in the
case of rivers, intake should be located in deep
waters, sufficiently away from coast line
6. There is sufficient scope for future expansion
7. Should remain easily accessible even during floods
and it should not be flooded
8. Well connected by good approach road
9. Sit should be free from the attacks of heavy currents

Design considerations
a) Reliability of operation:
Intake should ensure safety of design & reliability of
operation. A failure here would mean shutting off,
of entire supply
a) Quality of water:
Located carefully to obtain best quality of water;
In large rivers this should preferably submerged and
several meters above to bed level to prevent entry of
silt;
In areas of large variations in water level, intake should
be so located to draw water from several depths, so
that excess of turbidity & microorganisms are
prevented from entering the conduit;
Far off from settlement, sewage disposal points and
other pollution sources

c. Structural strength:
Strong enough to resist such forces as caused by
floods, impact of boats, floating debris etc.
d. Economy of construction:
If intake conduit is short, it may be merely an
extension of suction side of the pump
If however, too long, it would be advisable to
interpose a wet well or chamber near the pumps
and draw water from there, instead of having a
long suction pipe.
The latter arrangement may prove to be
comparatively costly involving greater head losses

Types of intakes:
1. Based on no of ports:
Single port & multiple ports
2. Based on source of supply:
Canal intake, river intake, reservoir intake
and lake intake
3. Based on location:
Submerged intake & exposed intake
4. Based on intake condition:
Dry intake & wet intake

Important Features:
• Canal intake is comparatively a simpler arrangement
consisting of a brick-masonry chamber built particularly in
canal bank.
• It has side opening fitted with coarse screen which excludes
floating matter, silt etc from entering the intake well.
• Withdrawal conduit is covered with a fine screen to avoid
entry of silt, sand etc, into the conduit.
• The entry of water is controlled by gate valves which is
operated from top.
• Pitching on both U/S & D/S to avoid scouring as it reduces
the area and velocity of water is increased.

• Wet well type – single port
Coarse screen: MS bars – 15 to 20 mm dia
• Opening : 25 to 50 mm
• Flow velocity: 0.15 m/s or less
Fine screen: Wire mesh type
• Opening size: 6mm x 6 mm or less
• Velocity: 0.3 m/s
Intake conduit (withdrawal conduit): Flow velocity –
1.0 to 1.5 m/s

Important features:
• Wet well type – multiple ports
• It is the structure constructed with an objective of
withdrawing water from the rivers.
• It is generally constructed when water is required in
large amount for a large community.
• River intakes are so located that even during the low
water level in the river water remains available at the
intake in sufficient quantity.

• It consists of masonry or RCC inlet tower which is
provided with several inlets called penstocks.
• The penstocks are provided with valves to control
the entry of water through them.
• The penstocks are provided at different water
levels to permit the withdrawal of water when
the water level in the river drops.
• The penstocks discharge water into intake tower.
Pumping is required when the level of intake is
lower than community.

Important Features
• In the case of the reservoir, the type of intake to be
provided depends on the type of dam constructed to
create the reservoir.
• The reservoir intake for gravity dam consists of an
intake conduit or intake well constructed within the
dam itself
• In the case of a reservoir created by constructing an
earth dam, the intake consists of a masonry or R.C.C
intake tower (or intake well) placed near the upstream
toe of the dam. The intake tower is connected to the
top of the dam by a foot bridge.

Key feature of intake for earth dam
• The intake pipes are at different levels with the common
vertical pipe.
• The intake pipe has the fine screen to permit entry of clear
water.
• Pipes at different levels maintain continuous withdrawal of
water from the of reservoir.
• Intake pipes are provided with valves to control the flow of
water.
• The control room is at the top to operate valves.
• Common vertical pipe enters the conduit which carries
water to the treatment plant.
• The dry intake tower has pipes fitted inside.

part ii_intake structures

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part ii_intake structures