Diversion Headwork in Canal

Concept of Headworks in Canal Regulation

1. Topic 05- Diversion Headworks - Mr. Hole G.R. Lecturer-Civil Department, JSP,HADAPSAR

2. The works which are constructed at the head of the canal in order to divert the river water toward the canal, so as to ensure a regulated continuous supply mostly silt free water with certain minimum head into the canal, are known as diversion headworks. Diversion Head-Works

3. Storage Headwork : A storage Headwork is structure( Dam) which is constructed across river to store water during excess inflow and used to supply during less inflow and high Demand. Diversion Headwork: It is structure which constructed across river (Weir) to raise the water level in river so that it can diverted in to canal system. Types of Diversion Headwork

4. The Following are the objective of Diversion Head works To Raise the water level at the head of canal. To form a storage by construction of dykes on both side of banks of the river so that water is available throughout the year. To control the entry of silt into the canal and to control the deposition of silt at the head of canal. To control the fluctuation of water level in the river during different seasons. Objectives of Diversion Head Works

5. The following points should be considered to select a site for this diversion headworks. The river should be straight and narrow at the site The elevation of site should be higher than the area to be irrigated for gravity flow. River banks at site should be well defined and stable. Valuable land upstream of the barrier like weir or barrage should not be submerged . Selection of Site for Diversion Head Works

6. Material of construction should be locally available. Roads or railway communication to the site is essential to carry the material of construction. Site should be close to the cropland to minimize loss of water due to seepage and evaporation of canal. The site should provide a good foundation for construction of weir or barrage.

7. Components of Diversion Headworks

8. The components of diversion headworks are: Weir or barrage Canal head regulator Divide Wall Fish Ladder Scouring Sluices Under sluices Silt excluder Silt ejector. Marginal embankment or dikes Guide bank Silt pocket or trap. Components of Diversion Headworks

9. 1.Weir It is a solid obstruction placed across the river. Its main function is to raise the water level so that water can be diverted by canal to crop field due to difference of head. 1.Weir or Barrage

10. Weir

11. 2.Barrage Barrage is practically a low weir with an adjustable gate over this low weir. Heading up of water is affected by gate .

12. Barrage

13. Comparison Between Weir & a Barrage

14. 1.Vertical Drop Weir(Masonry Weir) A crest gate may be provided to store more water during flood period. At the upstream and downstream ends of impervious floor cut off piles are provided. Launching apron are provided both at upstream and downstream ends of floor to safeguard against scouring action. A graded filter is provided immediately at the downstream end of impervious floor to relieve the uplift pressure. This type of weir is suitable for any type of foundation. Types of Weir

15. Vertical Drop Weir

16. This type is suitable for soft sandy foundation. It is used where difference in weir crest and downstream river bed is not more than 3 m. Hydraulic jump is formed when water passes over the sloping glacis. Suitable for soft soil foundation. 2.Sloping Weir ( Concrete Weir)

17. In rock fill type weir, there are no of core wall on D/S of main weir wall and space between weir wall is filled with rock fragments that’s why it is called as Rock fill Weir. Requires large quantity of rock fragments so it is economical when rock are available easily in surrounding region. Suitable for fine sand foundation. 3.Rockfill Weir

18. Structure at the head of canal taking off from a reservoir may consist of number of spans separated by piers and operated by gates . Regulators are normally aligned at 90° to the weir . These are used for diversion of flow. Silt reduces carriage capacity of flow. II. Canal Regulator:

19. Functions of Canal Head Regulators Provides platform for bridges for communication facility. To maintain constant supply in off tacking canal during low Discharge Period. To cut off the Discharge of parent canal during maintenance on D/S side.

20. The Divide Wall is a long wall constructed at right angle to the weir or barrage, it may be constructed with stone masonry or cement concrete. On the upstream side, the wall is extended just to cover the canal regulator and on the down stream side, it is extended up to the launching apron. The functions of the divide wall are as follows, 1. To form a still water pocket in front of the canal head so that the suspended silt can be settled down which then later can be cleared through the scouring sluices from time to time. 2. It controls the eddy current or cross current in front of the canal head. 3. It provides a straight approach in front of the canal head. 4. It resists the overturning effect on the weir or barrage caused by the pressure of the impounding water. III. Divide Wall

21. The Scouring sluices are the openings provided at the base of the weir or barrage at lower level. It is provided at same side on which off tacking canal is located. The crest of under sluices is kept lower than crest of weir due to which water is attracted towards sluice which helps to easy diversion of water in to canal. IV. Scouring Sluices or Under Sluices

22. The Fish Ladder is passage provided adjacent to divide wall for the movement of fishes from U/S to D/S and vice-versa. I n general, the tendency of fish is to move from upstream to downstream in winters and from downstream to upstream in monsoons. This movement is essential for their survival. In the fish ladder, the baffle walls are constructed in the zigzag manner so that the velocities of flow within the ladder does not exceed 3 m/s V. Fish Ladder

23. Fish Ladder

24. Silt excluder is the structure provided in still pocket to pass silt content water in D/S . This is helps to allow clear water entry in canal. Water contains silt is having high density so it is always near to bed level. The tunnel nearest to the head regulator is longest, and the successive tunnels decrease in length, the tunnel nearest to the divide wall is shortest . The tunnels are covered by R.C.C. Slab. The top level of the slab is kept below the sill level of the head regulator. So , the completely clear water is allowed to flow in the canal through the head regulator. VI. Silt Excluder

25. Silt ejectors, also called silt extractors, are those devices which extract the silt from the canal water after the silted water has traveled a certain distance in the off-take canal. These works are, therefore, constructed on the bed of the canal, and little distance downstream from the head regulator. It consist of tunnels parallel to flow of canal and turns in to 90 to eject silt. The length provided may be different. Silt Ejectors

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