1. Lec.16
Underground pipeline irrigation system - structures for underground pipelines.

2. UNDERGROUND PIPELINE IRRIGATION DISTRIBUTION SYSTEM
An underground pipeline water distribution system consists of buried pipes for conveying water to different points on the farm and allied structures required for the efficient functioning of the system.

3. ADVANTAGES
Cultivation can be done above the pipeline
No culverts or other structures are required
Saves land area.
The pipelines do not interfere with farming operations.
Long life and low maintenance costs.
Eliminates water loss by evaporation.
Operate under pressure and can be laid uphill or downhill, thus permitting the delivery of irrigation water to areas not accessible by open channels.
Wells need not be located at the highpoint of the farm but may be at a location that provides best water supply.
Water pumped from wells may be delivered directly into the pipeline system.

4. DISADVANTAGES
Under ground pipeline irrigation distribution systems have a higher initial cost
Difficult to locate leakages and repair is costly
Needs techanical man power for installation

5. PIPES TYPES
Reinforced concrete pipes
Factory-made reinforced concrete pipes
Vitrified clay pipes
Asbestos cement pipes
Plastic or PVC pipes

7. DISCHARGE CAPACITY = Q = AV
By re-writing the Darcy’s equation
V = (2Hdg / f L)1/2
In which
A = Area of cross section of the pipe in m2
V = velocity of flow of water through the pipe, m/sec.
H = available head causing flow in m
d = diameter of pipe in m
g = acceleration due to gravity m/sec2
L = length of pipe, m
f = Darcy’s roughness coefficient

8. PUMP STAND The inlet structure Minimum inner dia. = 60 cm
Foundation concrete = 15 cm
Free board = 30 cm
Buried pipe 10 cm above concrete and 45 cm below soil surface
Pipe inlet covered by mesh to prevent debris entry
It should be tall enough to create required hydraulic head

10. Air vent Provided to release the entrapped air from the system
The dia. of riser pipe should be minimum of d/2 as buried pipe upto 60 cm above soil surface
There after the dia. can be reduced upto 5 cm to reduce cost
60 cm free board should be given
Provided at all points of change of direction of flow
Provide at every 150 m on the straight line

12. Riser valve – alfalfa valve
Provided at outlet points
The structure has a threaded valve stem fitted on a bracket
The valve plate is raised or lowered with a handle
The valve plate seats on a rubber washer/ valve seat making a leak proof set up

14. End plug It is provided at all closing points of pipe line
The plug protrudes in side the pipe for about 10 to 15 cm
The end of the plug should be supported sufficiently to with stand the operating pressure

15. INSTALLATION OF CONCRETE PIPELINES
Proper installation of the pipe is the key to trouble-free service
The process of laying the pipeline
Selection of depth and grade of laying,
Digging to proper length and grade,
Lowering the pipe and squeezing,
Sealing the joints, and
Backfilling the trench.