CROSS DRAINAGE WORKS AND THEIR FUNCTIONS

education

1. CROSS DRAINAGE WORKS AND THEIR FUNCTIONS

2. Group Members Fatima Anjum 15PWCIV4291 Muhammad Nadeem 15PWCIV4288 Muhammad Zaheer Khan 15PWCIV4278 Muhammad Muzzamil 15PWCIV4294 Azeem Ullah Shah 15PWCIV4277

3. Contents Introduction Necessity of Cross drainage works Types Selection criteria for cross drainage type

4. Cross Drainage Work Cross drainage works is a structure constructed when there is a crossing of canal and natural drain, to prevent the drain water from mixing into canal water. . Canal comes across obstructions like rivers, natural drains and other canals. The various types of structures that are built to carry the canal water across the above mentioned obstructions or vice versa are called cross drainage works.

5. Necessity of Cross Drainage Works 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. 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

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

7. Types of Cross Drainage Works Type I (Cross drainage work carrying canal over the drain ) Aqueduct Syphon Aqueduct Type II (Cross Drainage work carrying Drainage over the canal) Super passage Canal Syphon

8. Type III (Cross drainage works admitting canal water into the canal) Level crossing Inlet and outlet

9. Type-I Cross Drainage Work Carrying Canal Over The Drainage The structures that fall under this type are when ( HFL< FSL): Aqueduct Syphon Aqueduct

10. AQUEDUCT In an aqueduct, the canal bed level is above the drainage bed level so canal is to be constructed above drainage. A canal trough is to be constructed in which canal water flows from upstream to downstream. This canal trough is to be rested on number of piers. The drained water flows through these piers upstream to downstream . The canal water level is referred as full supply level (FSL) and drainage water level is referred as high flood level (HFL). The HFL is below the canal bed level.

11. AQUEDUCT This structure is suitable when bed level of canal is above the highest flood level of drainage. In this case, the drainage water passes clearly below the canal .

12. AQUEDUCT

13. SIPHON AQUEDUCT In a hydraulic structure where the canal is taken over the drainage, but the drainage water cannot pass clearly below the canal. The drainage water flows under syphonic action and there is no presence of atmospheric pressure in the natural drain . Syphonic aqueducts are more often constructed and better preferred than simple Aqueduct, though costlier . This structure is suitable when the bed level of canal is below the highest flood level.

14. SIPHON AQUEDUCT

15. Type-II Cross Drainage Work Carrying Drainage Over The Canal The structures that fall under this type are when ( HFL > FSL ): Super passage Canal syphon or called syphon only

16. SUPER PASSAGE Super passage structure carries drainage above canal as the canal bed level is below drainage bed level . A super passage is similar to an aqueduct, except in this case the drain is over the canal. The water in canal flows under gravity and possess the atmospheric pressure. This is simply a reverse of Aqueduct structure . This structure is suitable when the bed level of drainage is above the flood surface level of the canal. The water of the canal passes clearly below the drainage

17. SUPER PASSAGE

18. CANAL SYPHON In a canal syphon, drainage is carried over canal similar to a super passage but the full supply level of canal is above than the drainage trough.so the canal water flows under syphonic action and there is no presence of atmospheric pressure in canal . Flooring of canal is depressed and ramp like structure is provided at upstream and downstream to form syphonic action. This structure is a reverse of Syphon aqueduct . This structure is suitable when the bed level of drainage is below the full supply level of the canal.

19. CANAL SYPHON

20. Type III Cross Drainage Works Admitting Canal Water Into The Canal The structures that fall under this type are when ( HFL = FSL ): Level crossing Inlet and outlet

21. LEVEL CROSSING When the bed level of canal is equal to the drainage bed level, then level crossing is to be constructed. This consists of following steps : Construction of weir to stop drainage water behind it Construction of canal regulator across a canal Construction of head regulator across a Drainage With the help of regulators both in canal and stream, water is disposed through canal and stream in required quantity.

22. LEVEL CROSSING Level crossing consists of following components ( i) Crest wall (ii) Stream regulator (iii) Canal regulator This structure is suitable when in peak supply time of canal water parallel to drainage, both the regulators are opened to clear the drainage water from that of canal for certain time interval. Once the drainage is cleared, the head regulator is closed down

23. LEVEL CROSSING

24. INLET AND OUTLET When irrigation canal meets a small stream or drain at same level, drain is allowed to enter the canal as in inlet. At some distance from this inlet point, a part of water is allowed to drain as outlet which eventually meets the original stream. Stone pitching is required at the inlet and outlet. The bed and banks between inlet and outlet are also protected by stone pitching. This type of Cross Drainage Work is called Inlet and Outlet.

25. INLET AND OUTLET

26. Selection Of Suitable Site For Cross Drainage Works The factors which affect the selection of suitable type of cross drainage works are: Relative bed levels and water levels of canal and drainage Size of the canal and drainage. The following considerations are important When the bed level of the canal is much above the HFL (high flood level) of the drainage, an aqueduct is the obvious choice .

27. Cont.…. When the bed level of the drain is well above FSL (Full supply level) of canal, super passage is provided. The necessary headway between the canal bed level and the drainage HFL can be increased by shifting the crossing to the downstream of drainage. If, however, it is not possible to change the canal alignment, a siphon aqueduct may be provided. When canal bed level is much lower, but the FSL of canal is higher than the bed level of drainage, a canal siphon is preferred. When the drainage and canal cross each other practically at same level, a level crossing may be preferred. This type of work is avoided as far as possible.