cross drainage m

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CROSS DRAINAGE WORKS


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INTRODUCTION

These structural elements are required forconveying the canals across natural drainagewithout interrupting the continuous canalsupplies.

These are costly structures and therefore acanal should be made to reach watershed orridge line as shortly as possible.


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Types Of Cross Drainage Works:Depending upon the relative bed levels, maximum water levels and relative discharges of canalsand drainages the cross drainage works may be of following types,1. Type1-Irrigation Canal passes over the drainage:

In this type of C.D work, an irrigation canal is taken over the drainage


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Advantages of Type1:1.The canal running perennially is above ground and isopen to inspection.

2.Damage done by floods is rare.

Disadvantages of Type1:1.During high floods, the foundationcan be scoured or the water way ofthe drain may be chocked with trees .


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2. Type2-Drainage passes over the irrigation canal:In this type of cross drainage work, drainage is taken over thecanal

This condition involves the construction of thefollowing ,


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Advantages of Type2:1. C.D works are less liable to

damage then the earthwork ofcanal.

Disadvantages of Type2:1. Perennial canal is not open toinspection.

2. It is difficult to clear the siltdeposited in the barrels of the C.D.work.


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3. Type3-Drainage and Canal intersection at the same level:In this type of work, the canal water and drainage water are

permitted to intermingle.


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a) Level Crossing:When the beds of the drainage and canal are practically at the

same level, then a hydraulic structure is constructed which isknown as level crossing. This is suitable for the crossing oflarge drainage with main canal.


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The level crossing consists of the followingcomponents.1 . Crest Wall: It is provided across the drainage just atthe upstream side of the crossing point. The top levelof the crest wall is kept at the full supply level of thecanal.

2. Drainage Regulator: it is provided across thedrainage just at downstream side of the crossingpoint. The regulator consists of adjustable shutters at

different tiers.3. Canal Regulator: it is provided across the canal justat downstream side of the crossing point. Theregulator consists of adjustable shutters at differenttiers.


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b) Inlet and Outlet:In the crossing of small drainage with small channel no

hydraulic structure is constructed. Simple openings areprovided for the flow of water in their respective directions. Itis not necessary for the number of inlets and outlets to besame. There may be one outlet for two or three inlets. A canal

inlet is constructed when the cross drainage flow is small andits water may be absorbed into the canal without causingappreciable rise.


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Advantages of Type3:1. Low initial cost

Disadvantages of Type3:1. Regulation of such work is difficult & requires

additional staff2.The canal has to be designed to carry theincreased flood discharge of drain.

3. The faulty regulation of the gates maydamage the canal.4. There is additional expenditure of silt

clearance.


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PROPER SITE FOR DRAINGE CROSSING:The site selected for the cross drainage works should have thefollowing main characteristics,

1. It should be such that it requires minimum disturbanceregarding the approach and tail reaches of the drainagechannel.

2. Suitable foundation soil should be available at reasonabledepth.

3. Sufficient headway is available for the super structure ofthe aqueduct over the H.F.L of the natural stream.

4. Suitable existing topography, geological and hydraulicconditions for the cross drainage works at reasonable costs

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