1.0 INTAKE STRUCTURES
Surface sources of water are subject to wide variation in flow, quality, and temperature and
structures must be designed so that required flow can be withdrawn despite these natural
fluctuation. The intake itself normally consist of an opening (frequently screened in some
manner ) and a conduit which conveys the flow to a sump(open structure where water will flow)
from which it may be pumped to the treatment plant .
In design of intakes, one must consider the following points:
1. Source of water supply (collection basin, river, or lake ) …..etc
2. Surroundings characteristics of intake (water depth, or variation of water level,
navigation requirements, local currents and patterns of sediment deposition and scour,
spatial and temporal variation in water quality, and the quantity of floating debris.
3. The intake must be located at upstream of the water source as much as possible where
there is less pollution.
4. Prevent floating materials like plants to enter to the intake
5. The entrance of intake must be located in place with no fast currents.
6. The floor near intake must be stable enough.
7. The suction pipe should be located below water surface in order to convey water and to
preventing floating materials from been sucked in.
8. The entrance of intake should be located at suitable distance offshore of water source to
prevent pollution.
TYPES OF INTAKES
a)Submerged Intake Structures( used in lakes)
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It is the one which is constructed entirely under water.
It is commonly used to obtain supply from a lake.
Simple concrete block supporting the starting end of the withdrawal pipe
Covered by screen to prevent the entry of debris
Elevated 2 to 2.5m above the lake bed level to avoid entry of silt
They are cheap and do not obstruct navigation
Widely used for small water supply projects drawing water from streams or lakes
having a little change in water level throughout the year
Limitation: not easily accessible for cleaning and repairing
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b)Intake towers
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They are widely used on large water supply projects drawing water from rivers or
reservoirs having large change in water level
Gate controlled openings called ports are provided at various levels in these concrete
towers to regulate the flow.
There are two major types of intake towers
Wet intake towers
Dry intake tower
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ii) Wet intake towers
It consists of a concrete circular shell filled with water upto the reservoir level and has a
vertical inside shaft which is connected to the withdrawal pipe
The withdrawal pipe may lie over the bed of the rivers or may be in the form of tunnels
below the river bed
Openings are made in to the outer concrete shell as well as in the inside shaft
Gates are usually placed on the shaft and the withdrawal conduit
The water coming out of the withdrawal pipe is taken to treatment plant
Dry intake towers
The water is directly drawn into the withdrawal conduit through the gated entry ports
It has no water inside the tower if its gates are closed
When the entry ports are closed,a dry intake tower will be subjected to additional
buoyancy forces
Hence it must be of heavier construction than wet intake tower.
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c) River intake
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They are generally constructed for withdrawing water from almost all rivers
They can be classified into two types
i.
Twin well type of intake structure
ii.
Single well type of intake structure
Twin Well Type of Intake Structure
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They are constructed on almost all types of rivers, where the river water hugs the river
bank.
A typical river intake structure consists of 3 components
a) An inlet well
b) An inlet pipe
c) A jack well
Inlet well is usually circular in cross section, made of masonry or concrete
Inlet pipe connects inlet well with jack well. It has a minimum dia. of 45cm,laid at a
slope of 1 in 200.Flow velocity through it < 1.2m/s
Water entering jack well is lifted by pumps and fed into the rising main
Jack well should be founded on hard strata having bearing capacity ≥450KN/M2
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Single well type intakes
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No inlet well and inlet pipe in this type of river intake
Opening or ports fitted with bar screens are provided in the jack well itself
The silt entering the jack well will partly settle down in the bottom silt zone of jack well
or may be lifted up with the pumped water since pumps can easily lift sedimented water
The jack well can be periodically cleaned manually by stopping the water entry into the
well
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Canal Intake Structures
1. In some cases, source of water supply to a small town may be an irrigation canal passing
nearer or through the town. Then it will be constructed.
2. Generally it consists of masonry or concrete intake chamber of rectangular shape,
admitting water through a coarse screen.
3. A fine screen is provided over the bell mouth entry of the outlet pipe.
4. The intake chamber may be constructed inside the canal bank if it does not offer any
appreciable resistance to normal flow in the canal.
5. It’s preferred to provide lining to the canal near the intake chamber.
FSL- Flood water surface level
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Reservoir Intake Structures
1. When the flow in the river is not guaranteed throughout the year, a dam is constructed
across it to store water in the reservoir so formed.
2. These are similar to river intake, except that these are located near the upstream face of
the dam where maximum depth of water is available.
3. Design of intake may vary based on the type of dam
Or
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