cross drainage works
DESCRIPTION
cross drainage workTRANSCRIPT
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CROSS DRAINAGE WORKS
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It is a structure carrying the discharge of a
natural stream across a canal intercepting
the stream.
Classification based on
Relative levels
Discharges
Type I (C D works carrying canal over the
drainage)
Aqueduct
Syphon aqueduct
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Type II (Drainage passes over the
irrigation canal)
Super passage
Syphon super passage
Type III (Drainage and canal intersect
each other at the same level)
Level crossing
Inlet and outlet
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TYPE I
Canal is carried over the natural drain.
Opened to Inspection
Damage done by flood is rare.
The drain is very big comparison to the
section of the canal
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AQUEDUCT
Irrigation canal is taken over the drainage Suitable when the bed level of canal is well
above the H.F.L of drainage Drainage water passes clearly below the
canal
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SYPHON AQUEDUCT
In this canal is taken over drainage, but
drainage water not clearly passes below the
highest flood level.
It flows under syphonic action
Suitable when the bed level of the canal is
below the H F L
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TYPE II
Drainage is carried over the canal
CD works are less liable to damage than the
earth work of the canal.
Disadvantages
Not open to inspection
If silt is deposited, it is difficult to clear it
out.
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SUPER PASSAGE
FSL of canal is lower than the underside of the trough carrying drainage water.
Canal water runs under gravity
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CANAL SYPHON
The drainage is taken over the canal but
water passes below the drainage under
siphonic action.
Suitable when bed level of the drainage is
below the FSL of the canal
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TYPE III Level crossing
Bed level of canal and drainage are approximately same.
The quantity of water in canal and drainage is not that much different
In this water in canal and drainage is allowed to mix
With the help of regulator both in canal and stream water is disposed in reqd quantity.
Components Crest wall Canal regulator Stream regulator
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DESIGN OF SYPHON AQUEDUCT
A. Hydraulic design Determination of max. flood discharge and
the HFL. Fixation of waterway of the drain Contraction of canal waterway Clearance and free board Head loss through syphon barrels Determination of uplift pressure on the roof
of trough Determination of uplift pressure on the floor Design of bank connections
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B. Structural design Design of c/s of syphon barrrel and aqueduct
trough Design of piers and abutments Design of foundations
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Determination of flood discharge
For small drains the high floood discharge
may be worked out from empirical
formulas.
Large drains- hydrograph analysis and
rational formula etc may be used.
Fixation of waterway of the drain
P = 4.75√Q
P- wetted perimeter of the river
Q- total discharge
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Clearance and freeboard
Clearance /headway- vertical distance b/w
u/s HFL inclusive of afflux, of the drainage
and the bottom surface of trough.
Freeboard
Canals – FSL to top levels of banks
Drainage – HFL including afflux and top of the
embankment or guide banks
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CONTRACTION OF CANAL WATERAY
Type I aqueduct – the canal cross section not
changed at crossing, so that the culvert
length is max. not economical on big drains
Type III- original width of canal is reduced.
Requires the provision of extra transition wings
for joining the flumed portion gradually to the
normal section.
Fluming is done in such a way velocity in the
trough is not more than 3 m/s.
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The approach transition wings shd not steeper
than 300 ( corresponding to a splay of 2:1)
The departure transition wings shd not steeper
than 22.50 ( corresponding to a splay of 3:1).
Transition consist of curved and flared wings