The structure constructed to cross the canal water safely above or below the drain water is called cross drainage work.
C-D work is a structure that carries the discharge of a natural stream or river across a canal, intercepting a stream or river.
The work of a cross drainage is usually costly and should be prevented as much as possible by isolating a stream or changing the alignment key-canal.
Here we will learn about cross drainage work, types of cross drainage work & much more.
Introduction to cross drainage work:
In an irrigation project when a network of main canals, branch canals and distributaries is provided, these canals may have to cross natural drainage such as rivers, rivers, drains at various points.
The crossing canals with such a barrier cannot be avoided, so for easy flow of canal and drainage water, suitable structures must be constructed at the crossing point in the respective directions.
These structures are known as cross-drainage, the artificial canal is usually combined with ridgeline call watersheds.
Factors influencing the selection of a suitable type of cross drainage works as follows:
- Relative bed level, canal and drainage water level.
- Canal and drainage dimension.
Types of cross drainage work:
It is a structure built at the point of crossing where drainage water is carried over the canal.
In this case, the stream passes at a higher level than the FSL of the canal.
The main purpose of super passage is to safely carry stream discharges across the canal at high levels.
In this case, the stream passes over the canal through the masonry trough which is supported on the supporters.
The stream is always timed by providing a suitable wing wall.
It is an irrigation structure built for passing the canal water over the cross drainage work.
An aqueduct consist of masonry or concrete trough of rectangular section supported on abutment and piers and flows below the trough through abutment and piers.
It is adopted when the bed level of the canal and drainage is same.
In this case, water permits mixing with one another, the regulators are supplied on the downstream side of drainage and canals to manage discharge, regulators are provided with raise gates.
In order to protect the bed from eroding action suitable stone pitching is provided on bed and sides of the canal on the upstream and downstream side.
During dry season downstream drainage regulator is kept closed and canal regulator is kept open, so that canal water flows smoothly during floods, drainage regulator is opened to pass flood water.
Inlet and outlet in cross drainage work:
The inlet accepts the stream water into the canal, it is mixed with the canal water then allows additional discharge to pass through the outlet.
The capacity of the inlet and outlet should be the same and the sides and beds of the canals should be protected by stone pitching.
Inlet admits water of stream into the canal and it flows mixed with canal water and then excess discharge is allowed to pass through the outlet.
The capacity of inlet and outlet must be same and beds of canal must be protected by stone pitching.
When two canals cross one another and one of the canals is syphoned under the other, then the hydraulic structure on the crossing is termed as canal syphon or canal siphon.
In the case of canal siphons, the F.S.L of the canal is very high from the bed level to the drain.
In this type, the canal bed is lowered, the canal runs under symphonic action down the trough.
Necessity of cross drainage works:
- The cross-drainage work is important to eliminate the drainage water, therefore C. D. work built in such way that canal provided remains uninterrupted.
- Canal at a cross-drainage work is usually taken over the drainage or under the drainage.
- On the crossing point of the canal and C. D. work, the canal’s water and drainage are mixed, hence it is designed to keep the canal running smoothly.
- The watershed canals don’t cross natural drains comparable to stream or river, however within the actual practice of the canal network.
- The site condition of the crossing point should be without any suitable structure, it is very difficult to divert the water of the canal and drainage.
- To avoid this the C. D. works should be provided to maintain the natural direction of natural drainages.
Cross drainage work are required for the canal to run smoothly with its design requirement.
The position of the site may be such that the canal and drainage water cannot be sent in their natural directions without any suitable structure.