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Diversion head works
- 3. Definition • It is a structure constructed across the river so as to raise water level on u/s side so that it can be diverted towards canal • Ideal site for diversion head works- 1. Good foundation should be available 2. The site should be such that weir can be aligned at right angle to the diversion of water in the river 3. The site should be such that there should be sufficient space for regulation of head regulator and other component of the diversion head works 4. The overall cost should be less 5. Proper approach way should be near by site 6. On the u/s side where water is retained, should not include costly land 7. While construction of weir or barrages river should be available near the site.
- 4. • The materials and labours should be available near by site. • The river should be perennial • The river should have non erodible as well as non submersible banks • The site should be narrow and well defined
- 5. Layout of diversion head works • Weir • Under sluice • Fish ladder • Divide wall • Canal head regulator • Silt excluder • Guide bank • Marginal bund
- 7. Weir • A structure constructed across river to raise water so as to divert this raise water into canal and this raising of water is mostly done by the crest wall constructed across river and very small part or nil part is by shutter sometimes if provided on its top is called as weir and • when storing of water is done by gates or shutters and small part of water is by raised crest then such structure constructed is known as barrage.
- 10. Types of weir • Gravity weir the wt. of weir balances the uplift pressure caused by seepage water 1. Vertical drop weir 2. Rock fill weir 3. Concrete weir • Non gravity weir uplift pressure is largely resisted by wt. of concrete slab with the wt. of divide piers
- 11. Vertical drop weir • It consist of horizontal floor and a masonry crest with vertical or nearly vertical d/s face and the shutters are provided at the crest • Most storage is done by weir crest and some storages by shutters
- 13. Rock fill weir • Called as dry stone slope weir • Suitable for sandy foundation • Requires large quantity of stones
- 14. Concrete weir • Suitable for permeable foundation • Sheet piles are provided for both u/s & d/s floors to destroy the energy of the water
- 16. Classification of weir • According to use & function- 1. Storage weir 2. Pick up weir 3. Diversion weir 4. Waste weir
- 17. Storage weir • High weir for storing water called as diversion weir • Shutters may or may not provided Pick up weir- • Constructed when command area is far away from reservoir due to rolling topography or no culturable land • Water from main storage is released and carried through same river up to pick up weir from which it is diverted into canal Diversion weir- • A weir is constructed to divert the river water into the canal is called as diversion weir • Constructed at 90⁰ to the flow of river. Waste weir- • Constructed in continuation of dam • Known as escape channel or spillway
- 18. Diversion weir Pick up weir
- 19. Under sluice • Opening provided in the body of weir at low level • Located at same side from which canal is taking off • Functions- 1. Control entry of silt into canal 2. Lower the HFL 3. Helps in passing the low river floods without lifting shutters 4. Helps to pass silt on d/s side of weir
- 20. Divide wall • Wall constructed between under sluices & the weir at right angle to the axis of weir to divide the river channel. • Functions- 1. Separate the under sluices from weir 2. Also helps in reducing velocity of flow near head regulator due to which silt is deposited and clear water passes into canal 3. Prevents vortices means flow in circular motion.
- 21. Fish ladder • It is passage provided adjacent to divide wall for movement of fish from u/s to d/s and vice versa called as fish ladder • Normally fish moves from colder water to warm water
- 22. Silt exclusion devices • Device which are constructed at the main head of canal which prevent entry of silt called as silt exclusion devices
- 23. Silt ejectors • The structure which is constructed across the canal to eject the silt accumulated in canal section are called as silt ejectors • It consist of tunnel with sufficient slope so that silt not to be deposited
- 24. Silt excluder • It is structure in under sluices to pass water containing silt on d/s through under sluices so that only clear water enters into the head regulator • These are parallel to the axis of head regulator silt excluder prevent entry of silt into the canal • Consist of no. of small tunnels with their roof slab at same level.
- 26. Guide bank • Provided on either side of diversion head works • Function- 1. Prevent oblique approach to the head regulator 2. Protect regulator from river attack 3. Increases max. discharge at all points 4. Prevent out flanking of structure 5. Create reasonable water way for a weir
- 28. Component parts of weir • Body of weir • u/s apron • u/s curtain wall • d/s apron • d/s curtain wall • Crest • shutter
- 29. Barrage • Component of barrage 1. Crest wall 2. Gate Advantages- 1. As small afflux is caused above hfl, the area under flooding is less 2. Low cost flood bank 3. More safe due to less afflux 4. Economical as preventive and energy dissipations work is less 5. Control of flood with gates 6. Preferred in flat longitudinal area and low silt Disadvantages- 1. Storage capacity is less 2. Maintenance and initial cost is more
- 30. Sr. no. Weir Barrage 1 Initial cost low More 2 More area of submergence Less 3 Silting problem No 4 Rising and lowering of shutters are not convenient as it is operated by manually By mechanically and easy 5 No control over flood Possible 6 Difficult to inspect and repair Easy 7 Roadway is not possible Possible 8 Storage is by crest By gates/shutters