Cross Drainage
(CD) Works:
Cross Drainage Works are
hydraulic structures built to carry the water from a natural stream across a
canal or vice versa. The purpose of these structures is to ensure that both the
canal and the natural stream can pass across each other without disturbing the
flow of the other. The type of CD work chosen depends upon the relative levels
of the canal and the natural stream, and the importance and discharge of both.
Here are some types of
CD works:
- Aqueduct: An aqueduct is a bridge-like structure
that carries a canal over a river or another canal, allowing the two to
cross without mixing their waters. The water of the natural stream flows
under the canal in a channel or pipe. This structure is used when the
canal has to cross a natural stream and the bed level of the canal is
above the high flood level of the stream.
- Siphon Aqueduct: This is a structure that is used when the
canal and the river have to cross each other at nearly the same level. In
this case, the canal crosses over the river, but there is also a siphonic
action created that allows the river water to flow under the canal when
the river's flow is higher than the canal's.
- Super Passage: A super passage is a structure that carries
a canal over a drainage channel or another canal. It is similar to an
aqueduct, but in a super passage, the drainage channel is artificially
constructed and the canal water flows in a conduit or pipe over the
drainage channel. This is used when the bed level of the drainage channel
is above the high flood level of the canal.
- Level Crossing: In a level crossing, both the canal and
the natural stream cross each other at the same level. The waters of the
two are allowed to mix at the crossing. A regulator is provided on both
sides of the crossing in the canal to control the flow of water. This type
of structure is usually avoided due to the potential for sediment and
pollution exchange between the canal and the stream, but it may be used in
cases where the discharge of the stream is relatively small or in case of
emergency.
Each of these
structures requires careful design to ensure that it can handle the expected
flow rates and that it will not disrupt the flow of either the canal or the
natural stream. Regular maintenance is also necessary to prevent blockages,
leaks, or other problems.