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

UNDERGROUND PIPELINE IRRIGATION DISTRIBUTION SYSTEMAn 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.

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.

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

PIPES TYPES

• Reinforced concrete pipes• Factory-made reinforced concrete pipes• Vitrified clay pipes • Asbestos cement pipes • Plastic or PVC pipes

DISCHARGE CAPACITY = Q = AV

By re-writing the Darcy’s equation

V = (2Hdg / f L)1/2

In whichA = 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 md = diameter of pipe in mg = acceleration due to gravity m/sec2

L = length of pipe, mf = Darcy’s roughness coefficient

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

Air ventAir vent

Provided to release the entrapped air from Provided to release the entrapped air from the systemthe system

The dia. of riser pipe should be minimum of The dia. of riser pipe should be minimum of d/2 as buried pipe upto 60 cm above soil d/2 as buried pipe upto 60 cm above soil surfacesurface

There after the dia. can be reduced upto 5 There after the dia. can be reduced upto 5 cm to reduce costcm to reduce cost

60 cm free board should be given60 cm free board should be given Provided at all points of change of direction Provided at all points of change of direction

of flowof flow Provide at every 150 m on the straight lineProvide at every 150 m on the straight line

Riser valve – alfalfa valveRiser valve – alfalfa valve

Provided at outlet pointsProvided at outlet points The structure has a threaded valve stem The structure has a threaded valve stem

fitted on a bracketfitted on a bracket The valve plate is raised or lowered with a The valve plate is raised or lowered with a

handlehandle The valve plate seats on a rubber washer/ The valve plate seats on a rubber washer/

valve seat making a leak proof set upvalve seat making a leak proof set up

End plugEnd plug

It is provided at all closing points of pipe It is provided at all closing points of pipe lineline

The plug protrudes in side the pipe for The plug protrudes in side the pipe for about 10 to 15 cmabout 10 to 15 cm

The end of the plug should be supported The end of the plug should be supported sufficiently to with stand the operating sufficiently to with stand the operating pressurepressure

INSTALLATION OF CONCRETE PIPELINES

Proper installation of the pipe is the key to trouble-free service

The process of laying the pipeline1.Selection of depth and grade of laying,2.Digging to proper length and grade,3.Lowering the pipe and squeezing,4.Sealing the joints, and 5.Backfilling the trench.