Canal falls and its classification

Types of canal falls [drop]

1. CANAL fall By Gnana Prakash P 315126508064

2. Contents Introduction Necessity Types of Falls : Conclusion References Ogee fall Rapid fall Trapezoidal fall Well type fall Vertical Drop fall Stepped Type Fall Montague Fall

3. Canal : An artificial waterway constructed to allow the passage of boats or ships or to convey water for irrigation provided with permissible slope.   Canal Fall : A Structure constructed to achieve the object of lowering the bed level of a canal suitably

4. introduction Canals are constructed with some permissible bed slopes so that there is no silting in the canal bed Ground surface may be steep and sometimes it may be very irregular with abrupt change of grade.

5. Necessity: When the slope of the ground suddenly changes to steeper slope.

6. When the slope of the ground is more or less uniform and the slope is greater than the permissible bed slope of canal

7. Considerations in selecting type of fall : The height of fall of water The discharge passing over the fall Topography of site location Type of soil in upstream and downstream of structure Economy

8. types Ogee fall Rapid fall Trapezoidal fall Stepped fall Montague fall Vertical drop fall Straight Glacis fall

9. Ogee fall an ogee curve (a combination of convex curve and concave curve) is provided for carrying the canal water from higher level to lower level.

10. It is limited to low depths Due to smooth transition, velocity of flow is not reduced since it may cause erosion in down stream It has high discharging efficiency

11. Rapid fall It is suitable when the slope of the natural ground surface is even and long. It consists of a gentle longitudinal slope which varies from 1 in 10 to 1 in 20.

12. These are expensive compared to others Commonly used at West Yamuna canal

13. Trapezoidal fall In this the body wall consists of several trapezoidal notches between the side piers and the intermediate piers. The sills of the notches are kept at the upstream bed level of the canal.

14. It may of Singular or number of openings constructed at high crested wall providing smooth entrance to downstream With this the depth to discharge value are less affected These are quite common and economical

15. Stepped fall It consists of a series of vertical drops in the form of steps.

16. This steps is suitable in places where sloping ground is very long and require a long gentle slope to connect the higher bed level at u/s with lower bed level at d/s.

17. Vertical drop fall In this Canal u/s bed is on the level of upstream curtain wall, canal u/s bed level is below the crest of curtain wall. In both the cases, a cistern is formed to act as water cushion.

18. Easy to construct and economical Losses may be high in case of higher depths For discharges upto 15cumecs vertical drop fall is used

19. Straight glacis fall It consists of a straight glacis provided with a crest wall. For dissipation of energy of flowing water, a water cushion is provided

20. Generally sloping will be 2 :1 These have Good performance Suitable upto 60cumecs and drop of 1.5m

21. Montague type fall In the straight steep type profile, energy dissipation is not complete. Therefore, montague developed this type of profile where energy dissipation takes place

22. For flumed conditions vertical type is not suitable because effective dissipation is difficult, at there Straight galcis falls are used When full energy dissipation does not take place on structure, baffle wall is used For un-flumed conditions the baffle design is well suited conclusion

23. references Talwani, B.S. et al (1952).Canal Falls. Journal of Irrigation & Power, April, 269–288. Naib, S.K.A. (1966). Hydraulic Design of Energy Dissipators. Water & Water Engineering, May, Vol. 70, 191–193 and (1967), Vol. 71, 336