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CROSS-DRAINAGE
STRUCTURES
CROSS DRAINAGE WORKS
• when the network of main canals, branch canals,
distributaries, etc. are provided, then these canals may
have to cross the natural drainages like rivers, streams,
nallahs, etc. at different points. The crossing of the canals
with such obstacle cannot be avoided. So, suitable
structures is constructed at the crossing point for the easy
flow of water of the canal and drainage in the respective
directions. These structures are known as cross-drainage
works.
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CROOS DRAINAGE WORKS
• Irrigational Canals while carrying water have to cross few
natural drainage streams, rivers, etc.. To cross those
drainages safely by the canals, some suitable structures are
required to construct. Works required to construct, to cross
the drainage are called Cross Drainage Works (CDWs). At
the meeting point of canals and drainages, bed levels may
not be same. Depending on their bed levels, different
structures are constructed and accordingly they are known
by different names.
NECESSITY OF CDWs
• The water-shed canals do not cross natural drainages. But in
actual orientation of the canal network, this ideal condition
may not be available and the obstacles like natural drainages
may be present across the canal. So, the cross drainage
works must be provided for running the irrigation system.
• At the crossing point, the water of the canal and the
drainage get intermixed. So, far the smooth running of the
canal with its design discharge the cross drainage works are
required.
• The site condition of the crossing point may be such that
without any suitable structure, the water of the canal and
drainage can not be diverted to their natural directions. So,
the cross drainage works must be provided to maintain their
natural direction of flow.
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TYPES OF CDWs
(1) Type I (Irrigation canal passes over the drainage)
(a) Aqueduct
(b) Siphon aqueduct
(2) Type II (Drainage passes over the irrigation canal)
(a) Super passage
(b) Siphon or Canal siphon or Inverted siphon
(3) Type III (Drainage and canal intersection each other of the
same level)
(a) Level Crossing
(b) Inlet and outlet
• Aqueduct
The hydraulic structure in which the irrigation canal is taken
over the drainage (such as river, stream etc..) is known as
aqueduct. This structure is suitable when bed level of canal
is above the highest flood level of drainage. In this case, the
drainage water passes clearly below the canal.
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• Siphon Aqueduct
In a hydraulic structure where the canal is taken over the
drainage, but the drainage water cannot pass clearly below
the canal. It flows under siphonic action. So, it is known as
siphon aqueduct. This structure is suitable when the bed
level of canal is below the highest flood level.
• Super Passage
The hydraulic structure in which the drainage is taken over
the irrigation canal is known as super passage. The structure
is suitable when the bed level of drainage is above the full
supply level of the canal. The water of the canal passes
clearly below the drainage.
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• Canal Siphon
The hydraulic structure in which the drainage is taken over
the irrigation canal, but the canal water passes below the
drainage under siphonic action is known as canal siphon.
This structure is suitable when the bed level of drainage is
below the full supply level of the canal.
Level Crossings
When the bed level of canal and the stream are
approximately the same and quality of water in canal and
stream is not much different, the cross drainage work
constructed is called level crossing where water of canal and
stream is allowed to mix. With the help of regulators both in
canal and stream, water is disposed through canal and
stream in required quantity. Level crossing consists of
following components (i) crest wall (ii) Stream regulator
(iii) Canal regulator.
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Inlet and Outlet
When irrigation canal meets a small stream or drain at
same level, drain is allowed to enter the canal as in inlet.
At some distance from this inlet point, a part of water is
allowed to drain as outlet which eventually meets the
original stream. Stone pitching is required at the inlet and
outlet. The bed and banks between inlet and outlet are also
protected by stone pitching. This type of CDW is called
Inlet and Outlet.
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