Cross Drainage Work 2v2v69

Term Paper CIV 039 Irrigation Engineering Topic: - Cross drainage works

Submitted To Mr. Nipen Kumar Das

Submitted By Atish Kumar Roll No.:- 15 Class: - Diploma Civil Semester: - 6th

Acknowledgements I Am Heartily Thankful To My Teacher Mr. Nipen Kumar Das, Whose Encouragement, Guidance And From The Initial To The Final Level Enabled Me To Develop An Understanding of The Subject. Lastly, I Offer My Regards And Blessings To All Of Those Who ed Me In Any Respect During The Completion Of The Term Paper. And also Thanks GOOGLE.COM.

2

CONTENTS S.N.

Description

Page No.

1.

Cross Drainage Work

4

2.

Necessity Of Cross Drainage Works

4

3.

Types Of Cross Drainage Works

5

4

Type1-Irrigation Canal es over the drainage

5

5

Type2-Drainage es over the irrigation canal

7

6

Type3-Drainage and Canal intersection at the same level

9

7

Suitability of Cross-Drainage Works

11

8

Proper Site For Drainage Crossing

12

9

Reference

13

3

Cross Drainage Works: A “cross drainage work” is a hydraulic structure which needs to be constructed at the crossing of a natural stream and an irrigation canal flowing normally at right angles underneath or over the natural stream. It is generally a very costly item and should be avoided by, i. ii.

Diverting one stream into another. Changing the alignment of the canal so that it crosses below the junction of two streams.

Necessity of Cross- Drainage Works: The following factors justify the necessity of cross drainage works, 1. 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. 2. At the crossing point, the water of the canal and the drainage get intermixed. So, for the smooth running of the canal with its design discharge the cross drainage works are required.

3. The site condition of the crossing point may be such that without any suitable structure, the water of the canal and drainage cannot be diverted to their natural directions. So, the cross drainage works must be provided to maintain their natural direction of flow.

4

Types Of Cross Drainage Works: Depending upon the relative bed levels, maximum water levels and relative discharges of canals and drainages the cross drainage works may be of following types,

1. Type1-Irrigation Canal es over the drainage: In this type of C.D work, an irrigation canal is taken over the drainage

This condition involves construction of following, a) Aqueduct: The hydraulic structure in which irrigation canal is ing over the drainage is known as aqueduct. This structure is suitable when bed of canal is above the highest flood level of drainage. In this case, the drainage water es clearly below the canal.

5

b) Siphon Aqueduct: The hydraulic structure in which irrigation canal is ing over the drainage, but the drainage water cannot clearly below the canal is known as siphon aqueduct. It flows under siphoned action. This structure is suitable when the bed level of canal is below the highest flood level of the drainage.

Advantages of Type1:  

The canal running perennially is above ground and is open to inspection. Damage done by floods is rare.

Disadvantages of Type1: 

During high floods, the foundation can be scoured or the water way of the drain may be chocked with trees.

6

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

This condition involves the construction of the following, a) Super age: The hydraulic structure in which the drainage is ing over the irrigation canal is known as super age. This structure is suitable when the bed level of drainage is above the flood surface level of the canal. The water of the canal es clearly below the drainage.

7

b) Siphon Super age: The hydraulic structure in which the drainage is taken over the irrigation canal, but the canal water es below the drainage under siphonic action is known as siphon super age. This structure is suitable when the bed level of drainage is below the full supply level of the canal.

c) Canal Siphon: If two canals cross each other and one of the canals is siphoned under the other, then the hydraulic structure at crossing is called “canal siphon”. For example, lower Jhelum canal is siphoned under the Rasul-Qadirabad link canal and the crossing structure is called “L.J.C siphon”

Advantages of Type2: 

C.D works are less liable to damage then the earthwork of canal.

Disadvantages of Type2:  

Perennial canal is not open to inspection. It is difficult to clear the silt deposited in the barrels of the C.D. work.

8

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.

a) Level Crossing: When the beds of the drainage and canal are practically at the same level, then a hydraulic structure is constructed which is known as level crossing. This is suitable for the crossing of large drainage with main canal.

The level crossing consists of the following components. 1. Crest Wall: It is provided across the drainage just at the upstream side of the crossing point. The top level of the crest wall is kept at the full supply level of the canal. 2. Drainage Regulator: it is provided across the drainage just at downstream side of the crossing point. The regulator consists of adjustable shutters at different tiers. 3. Canal Regulator: it is provided across the canal just at downstream side of the crossing point. The regulator consists of adjustable shutters at different tiers.

9

b) Inlet and Outlet: In the crossing of small drainage with small channel no hydraulic structure is constructed. Simple openings are provided for the flow of water in their respective directions. It is not necessary for the number of inlets and outlets to be same. There may be one outlet for two or three inlets. A canal inlet is constructed when the cross drainage flow is small and its water may be absorbed into the canal without causing appreciable rise.

Advantages of Type3:



Low initial cost

Disadvantages of Type3:

   

Regulation of such work is difficult & requires additional staff The canal has to be designed to carry the increased flood discharge of drain. The faulty regulation of the gates may damage the canal. There is additional expenditure of silt clearance.

10

Suitability of Cross-Drainage Works: The factors which affect the selection of the suitable type of cross drainage works are: 1. Relative bed levels and water levels of the canal and drainage 2. Size of the canal and the drainage The following considerations are important, 1. When the bed level of the canal is much above the highest flood level (H.F.L) of the drainage, so that sufficient headway is available for floating rubbish etc and also for the structural elements of the work. An ‘aqueduct’ is the obvious choice. Similarly, if the bed level of the drain is well above the Flood surface level (F.S.L) of the canal, ‘Super-age’ is provided. 2. The necessary headway between the canal bed level and the drain H.F.L can be increased by shifting the crossing to the downstream of the drainage. If, however, it is not possible to change the canal alignment or if such a shifting does not give sufficient headway between the two levels, a ‘siphon aqueduct’ may be provided. Thus in case of siphon aqueduct, the H.F.L of the drain is above channel (canal) bed. 3. When the canal bed level is much lower but the F.S.L of the canal is higher than the bed level of drainage, a ‘canal siphon’ is preferred. 4. When the drainage and the canal cross each other practically at the same level a ‘level crossing’ may be preferred. This type of work is avoided as far as possible.

The considerations governing the choice between aqueduct and siphon aqueduct (or a super age and siphon-super age) are, (i)Suitable canal alignment (ii)Suitable soil available for bank connections and (iii) Nature of available foundation As discussed earlier, the relative difference between the bed level of the canal and the H.F.L of the drainage can be suitable altered by changing the canal alignment so that the point of crossing is shifted upstream or Downstream of the drainage.

11

For example, if the canal alignment is such that headway is not available between the H.F.L of the drain and the bed of the canal, a siphon aqueduct is to be constructed at the crossing. But if the other conditions are not favorable for the construction of the siphon aqueduct, the canal alignment may be changed so that the crossing is shifted to the downstream and sufficient headway required for the construction of an aqueduct is available.

PROPER SITE FOR DRAINGE CROSSING: The site selected for the cross drainage works should have the following main characteristics, 1. It should be such that it requires minimum disturbance regarding the approach and tail reaches of the drainage channel. 2. Suitable foundation soil should be available at reasonable depth. 3. Sufficient headway is available for the super structure of the aqueduct over the H.F.L of the natural stream. 4. Suitable existing topography, geological and hydraulic conditions for the cross drainage works at reasonable costs.

12

Reference website  

http://web.iitd.ac.in/~chahar/Courses/CEL351/CEL351%20Hydraulic%20S tructures.htm www.idoub.com

Book 

Irrigation Engineering by N.N. Basak

13