Bhagwan Mahavir College of

Engineering and Technology

PRESENTATION ON

Prepared by : Ankit Gangani : 140060106055

OUTLINE

Introduction

Necessity of CDWs

Types of CDWs

Classification of Aqueducts & Siphon Aqueducts

Selection of type of CDWs

Selection Of Site

How to avoid CDWs

Reference

Introduction

WHAT IS CROOS DRAINAGE WORK…

when the network of main canals, branch canals, distributaries, etc.. are provided, then these canals may have to cross the natural drainages like rivers, streams, nallahs, etc. at different points.The crossing of the canals with such obstacle cannot be avoided. So, suitable structures is constructed at the crossing point for the easy flow of water of the canal and drainage in the respective directions. These structures are known as cross-drainage works.

Irrigational Canals while carrying water have to cross few natural drainage streams, rivers, etc.. To cross those drainages safely by the canals, some suitable structures are required to construct. Works required to construct, to cross the drainage are called Cross Drainage Works (CDWs). At the meeting point of canals and drainages, bed levels may not be same. Depending on their bed levels, different structures are constructed and accordingly they are known by different names.

WHAT IS CROSS DRAINAGE WORK..

NECESSITY OF CDWs

TYEPS OF CDWs(1) Type I (Irrigation canal passes over the drainage)

(a) Aqueduct,(b) Siphon aqueduct.

(2) Type II (Drainage passes over the irrigation canal) (a) Super passage, (b) Siphon super passage.

(3) Type III (Drainage and canal intersection each other of the same level) (a) Level Crossing,(b) Inlet and outlet.

AqueductThe hydraulic structure in which the irrigation canal istaken over the drainage (such as river, stream etc..) isknown as aqueduct. This structure is suitable when bedlevel of canal is above the highest flood level of drainage.In this case, the drainage water passes clearly below thecanal.

Siphon AqueductIn a hydraulic structure where the canal is taken over the drainage, but the drainage water cannot pass clearly below the canal. It flows under siphonic action. So, it is known as siphon aqueduct. This structure is suitable when the bed level of canal is below the highest flood level.

Super PassageThe hydraulic structure in which the drainage is taken overthe irrigation canal is known as super passage. Thestructure is suitable when the bed level of drainage isabove the full supply level of the canal. The water of thecanal passes clearly below the drainage.

Siphon Super PassageThe hydraulic structure in which the drainage is taken over the irrigation canal, but the canal water passes below the drainage under siphonic action is known as siphon super passage. This structure is suitable when the bed level of drainage is below the full supply level of the canal.

Level CrossingsWhen the bed level of canal and the stream areapproximately the same and quality of water in canal andstream is not much different, the cross drainage workconstructed is called level crossing where water of canaland stream is allowed to mix. With the help of regulatorsboth in canal and stream, water is disposed throughcanal and stream in required quantity. Level crossingconsists of following components (i) crest wall (ii)Stream regulator (iii) Canal regulator.

Inlet and OutletWhen irrigation canal meets a small stream or drainat same level, drain is allowed to enter the canal asin inlet. At some distance from this inlet point, apart of water is allowed to drain as outlet whicheventually meets the original stream. Stone pitchingis required at the inlet and outlet. The bed andbanks between inlet and outlet are also protected bystone pitching. This type of CDW is called Inlet andOutlet.

Classification of Aqueducts & Siphon Aqueducts

Depending upon the nature of the sides of the aqueduct or siphon aqueduct it may be classified under three headings:

Type I:Sides of the aqueduct in earthen banks with complete earthen slopes. The length of culvert should be sufficient to accommodate both, water section of canal, as well as earthen banks of canal with aqueduct slope.

Classification of Aqueducts & Siphon Aqueducts

Type II : Sides of the aqueduct in earthen banks, with other slopes supported by masonry wall. In this case, canal continues in its earthen section over the drainage but the outer slopes of the canal banks are replaced by retaining wall, reducing the length of drainage culvert.

Classification of Aqueducts & Siphon Aqueducts

Type III:

Sides of the aqueduct made of concrete or masonry. Its earthen section of the canal is discontinued and canal water is carried in masonry or concrete trough, canal is generally flumed in this section.

SELECTION OF TYPES OF CDWs Relative Bed Level

According to the relative bed levels of the canaland the river or drainage, the type of crossdrainage work are generally selected which hasbeen discussed earlier.

The following points should be rememberedwhile recommending the type of work,(a) The crossing should be at right angle to

each other,(b) Well defined cross-section of the river or

drainage should be available.(c) At the crossing point the drainage should be

straight for a considerable length.(d) The width of the drainage should be narrow

as far as possible.

Availability of Suitable Foundation For the construction of cross drainage works suitable

foundation is required. By boring test, if suitablefoundation is not available, then the type of crossdrainage work should be selected to site Condition.

Economic Consideration The cost of construction of cross drainage works should

be justified with respect to the project cost and overallbenefits of the project. So, the type of works should beselected considering the economical point of view.

Discharge of the drainagePractically the discharge of the drainage is very uncertain inrainy season. So, the structure should be carefully selectedso that it may not be destroyed due to unexpected heavydischarge of the river or drainage.

Construction Problems Different types of constructional problems may arise at the

site such as sub soil water, construction materials,communication, availability of land etc. So the type of worksshould be selected according to the site condition.

water , water table Earthwork Materials Weather Land acquisition

Selection of Site

1. At the site, the drainage should cross the canal alignment at right angles. Such a site provides good flow conditions and also the cost of the structure is usually a minimum.

2. The stream at the site should be stable and should have stable banks.

3. For economical design and construction of foundations, a firm and strong sub-stratum should exit below the bed of the drainage at a reasonable depth.

Selection of Site

4. The site should be such that long and high approaches of the canal are not required.5. The length and height of the marginal banks and guide banks for the drainage should be small.

6. In the case of an aqueduct, sufficient headway should be available between the canal trough and the high flood level of the drainage.

7. The water table at the site should not be high, because it will create dewatering problems for laying foundations.

Selection of Site

8. As far as possible, the site should be selected d/s of the confluence of two streams, thereby avoiding the necessity of construction of two cross-drainage works.

9. The possibility of diverting one stream into another stream upstream of the canal crossing should also be considered and adopted, if found feasible and economical.

10. A cross-drainage work should be combined with a bridge, if required. If necessary, the bridge site can be shifted to the cross-drainage work or vice versa. The cost of the combined structure is usually less. Moreover, the marginal banks and guide banks required for the river training can be used as the approaches for the village roads.

How to avoid CDW

Change the alignment of canals

Diverting small drainage into large drainage.

Reference

http://uap-bd.edu/ce/Handouts/CE-461/Doc/Chapter-9.pdf

https://theconstructor.org/water-resources/cross-drainage-works-types/12051/

http://www.idc-

online.com/technical_references/pdfs/civil_engineering/Cross_Drainage_Works.pdf

http://www.aboutcivil.org/cross-drainage-works.html

http://nptel.ac.in/courses/105106114/pdfs/Unit1/1_3.pdf

http://civilpddc2013.weebly.com/uploads/2/2/5/5/22556782/14_-

_cross_drainage_works.pdf

Irrigation Engineering by Dr. R P Rethaliya