- Cross Drainage work is a structure constructed for crossing canal water safely over or under the drainage water.
- It is expensive and one should avoid it if possible.
- One can avoid it by diverting one stream to another or changing the alignment of the canal.
Necessity of cross drainage work is as follows:
- Firstly, it is a structure constructed on a canal where it crosses a natural drain like a stream, nala or river.
- It is essential so as to dispose of the drainage water and hence one builds it in such way that canal supply remains uninterrupted.
- One generally takes the Canal at a cross-drainage work (C. D. work) over the drainage or below the drainage.
- At the crossing point of canal and C. D. work, the intermixing of the water of canal and the drainage takes place. Hence for the smooth running of the canal with its design discharge, the cross drainage works is necessary.
- Lastly, the site condition of the crossing point may be such that without any suitable structure, it is very difficult to divert the water of canal and drainage. To avoid this, One should provide the C. D. works to maintain natural direction of natural drainages.
Types of Cross Drainage work:
The various types of cross drainage work are as follows:
- Super Passage
- Level Crossing
- Inlet and Outlet
- One constructs this irrigation structure for passing canal water over the drainage work.
- An aqueduct is consist of masonry or concrete trough of rectangular section supported on abutment and piers and stream flows below the trough through abutment and piers.
- One aligns the aqueduct normal to the canal and under the following situation, one constructs an aqueduct:
- When discharge of stream is more as compared to discharge through canal.
- And sufficient clearance is available i.e. bed level of canal is at higher level than high flood level of stream.
- One constructs the structure at point of crossing where this structure takes drainage water over the canal.
- In this case stream passes at higher level than FSL of canal.
- The main object of super passage is to take stream discharge safely across canal and at higher level.
- In this case stream passes over the canal through masonry trough which is supported on supporters. (e.g. abutment, piers etc.).
- Stream is always flumed by providing suitable wing wall.
- One adopts this type of cross drainage work when bed level of canal and drainage is same.
- In this case both water allows to mix with each other.
- One provides the regulators on downstream side of drainage and canals to regulate discharge. Regulators are provided with lift gates.
4.Inlet and Outlet:
- Inlet admits water of stream into the canal and it flows mixed with canal water and then excess discharge is allow to pass through outlet.
- The capacity of inlet and outlet must be same and sides and beds of canal must be protected by stone pitching.
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