Cross Drainage Works – Necessity and Types

What is Cross Drainage Work?

In an irrigation project, when the network of main canals, branch canals, distributaries etc. are constructed then these canals may have to cross the natural drainage like rivers, streams, etc. at different locations within the command area of the project. The crossing of the canals with such obstacles cannot be avoided. Therefore, suitable structures must be constructed at crossing points of canal and natural obstacle such that the easy flow of water of the canal and drainage can be allowed in their respective directions. These structures are known as cross drainage works.

But the nature of cross drainage works may be different at different locations. Sometimes, the bed level of canal may be below the bed level of drainage and sometimes it may be higher than that of the drainage. The bed levels of canal and drainage may be nearly same also. So the structures are different at different places and the designation of the structures are also different.

Necessity of Cross Drainage Works :

The following factors justify the necessity of cross drainage works –

1. To maintain the smooth running of water and prevent intermixing of water for both canal and drainage.

2. At site locations of crossing point, the natural flow direction of canal and drainage cannot be diverted. Therefore, to maintain their flow in respective directions cross drainage structures are provided.

3. 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.

Types of Cross Drainage Works :

Type 1 – Irrigation Canal passes over the Drainage

1. Aqueduct

i) Aqueduct is the hydraulic structure in which the irrigation canal is taken over the drainage (river, stream etc.).

ii) It is suitable when bed level of canal is above H.F.L (Highest Flood Level) of drainage.

iii) Drainage passes clearly below the canal.

Aqueduct

2. Siphon Aqueduct

i) Siphon Aqueduct is a hydraulic structure in which canal is taken over the drainage, but the drainage water cannot pass clearly below the canal i.e. flows under siphonic action.

ii) It is suitable when bed level of canal is below the H.F.L of the drainage.

Siphon Aqueduct

Type 2 – Drainage passes over the Irrigation Canal

1. Super Passage

i) Super Passage is the hydraulic structure in which the drainage is taken over the irrigation canal.

ii) It is suitable when the bed level of drainage is above the full supply level of canal.

iii) The canal water passes clearly below the drainage.

Super Passage

2. Siphon Super Passage

i) Siphon Supper Passage is the hydraulic structure in which the drainage is taken over the irrigation canal, but the canal water cannot pass clearly below the drainage.

ii) It is suitable when the bed level of drainage is below the full supply level of the canal.

iii) The canal water passes under siphonic action below the drainage.

Siphon Super Passage

Type 3 – Drainage and Canal intersect each other at the same level

1. Level Crossing

i) Level Crossing is provided where the bed levels of both drainage and canal are same.

ii) Level Crossing for the crossing of large drainage with main canal.

Level Crossing

2. Inlet and Outlet

The site where crossing of small drainage with small canal channel exist, no hydraulic structure is constructed. In such case, openings are provided for the flow of water in their respective directions.