Detailed Presentation on dams Spillways. Includes: Types of spillways Component Parts of Spillways Energy Dissipators Spillway Gates

1. SPILLWAYS
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2. SPILLWAY
1.A passageway through which surplus water escapes from a
reservoir, lake, or the like.
2.Discharges the flood water to downstream of river without
overtopping the dam.
3.A structure which will not let the water rise above the
maximum reservoir level.
4.A spillway is essentially a safety valve for a dam.
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3. REQUIREMENTS OF SPILLWAY
1.Provide structural stability to dam under all conditions.
2.Able to pass the designed flood without raising the water
level above H.F.L.
3.Safe disposal of water without toe erosion.
4.Should have an efficient operation.
5.Should be economical.
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4. LOCATION OF SPILLWAY
1. Within the body of the dam
1. At one end of dam Or At both ends.
1. Entirely away from it, independently in a saddle.
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5. TYPES OF SPILLWAYS
1. Main Spillway
2. Emergency Spillway
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6. Main Spillway
1. Constructed within dam body or at one end of the
dam.
1. Constructed in masonry or in concrete.
1. It starts functioning when water rises above FRL.
1. Sub types:
Drop Spillway
Ogee Spillway
Shaft Spillway
Chute Spillway
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7. Drop Spillway
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8. Drop Spillway
In a drop spillway, the over flowing water falls freely and
almost vertically on the downstream side of the hydraulic
structure.
Suitable for weirs or low dams.
The crest of the spillway is provided with nose so that the
water jet may not strike the downstream base of the
structure.
To protect the structure from the effect of scouring
horizontal impervious apron should be provided on the
downstream side.
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9. Ogee spillway
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10. Ogee spillway
1. Ogee spillways are most commonly used in case of gravity
dams, arch dams, buttress dams, etc.
2.It is an improved form of a straight drop spillway. In this
case, the downstream face of the weir is constructed
corresponding to the shape of lower nappe of freely falling
water jet which is in ogee shape.
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11. Shaft Spillway
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12. Shaft Spillway
1.The shape is just like a funnel .
2. water drops through a vertical shaft in a the foundation
material to a horizontal conduit that conveys the water
past the dam.
3.Lower end of shaft is turned at right angle and then water
taken out below the dam horizontally.
4.Also called as glory hole spillway.
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13. Chute spillways
1. In this type water is conveyed from the reservoir to the
river or to nalla below the dam through an excavated open
channel, through fairly steep slope.
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14. COMPONENT PARTS OF SPILLWAY
1. Approach channel
1. Control structure
1. Discharge carrier
1. Discharge channel
1. Energy dissipators.
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15. 1. Approach channel
Entrance structure or the path to draw water from reservoir and
convey it to the control structure.
It may be straight or curved in plan. Its banks may be parallel,
convergent, divergent or combination of these and may be
vertical or sloping.
It may insure minimum head loss through the channel and to
obtain uniformity of flow over the control structure.
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16. Approach channel
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17. 2. Control structure
Major component of spillway provided with bridge and
gates.
Regulates and controls the surplus water from the
reservoir.
It does not allow discharge of water below the fixed
reservoir level.
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18. 3. Discharge carrier
It is the waterway provided to convey the flows released
from the control structure to the downstream side of
spillway.
The cross section may be rectangular, trapezoidal or of
other shape.
Waterway may be wide or narrow, long or short.
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19. 4. Discharge channel
Provided to convey the water from bottom of the
discharge carrier to the downstream flowing river.
It may be the downstream face of spillway itself.
The width of discharge channel depends on amount of
water to be conveyed.
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20. Energy dissipators
The water flowing down from the spillways possess a large
amount of kinetic energy that is generated by virtue of its
losing the potential head from the reservoir level to the level
of the river on the downstream of the spillway.
If this energy is not reduced, there are danger of scour to the
riverbed which may threaten the stability of the dam or the
neighbouring river valley slopes.
The various arrangements for suppressing or killing of the
high energy water at the downstream toe of the spillways are
called Energy Dissipaters.
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21. The following are the different types of dissipators:
1.Hydraulic Jump with stilling basin
2.Buckets
Solid Roller Bucket
Slotted Roller Bucket
Ski Jump Bucket
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22. 1.Hydraulic Jump with stilling basin
1.Water changes its states from super critical to sub critical.
2.Due to hydraulic jump turbulent roller is formed which
cause destruction of kinetic energy.
3. Most suitable method because energy loss is due to impact
of water against water.
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23. 2.Buckets
1.SOLID ROLLER BUCKET
1.Water flows over the bucket and 2 rollers are formed.
2.One on surface of bucket moves anti clock wise.
3. Other on d/s side moves clock wise.
4.Movement of these 2 rollers cause destruction of kinetic
energy.
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24. 2.SLOTTED ROLLER BUCKET
1.It is provided with slotted deflector lip.
2. Suitable for low tail water.
3. Bucket roller and ground roller are formed and they
helps to destruct kinetic energy.
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25. 3.SKY JUMP BUCKET
1.When sufficient depth is not available to form hydraulic
jump , Sky jump bucket is provided.
2.Water deflects in the form of free jet in the riverbed away
from the spillway.
3.For safety purpose river bed portion protected by boulder.
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26. SPILLWAY WITH GATES
1.Sometimes spillways are provided with gates on top of the
crest of spillway.
2.Gates are fitted with steel frames fixed in pier.
3.Operated manually or automatically.
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27. NON AUTOMATIC GATES
Vertical Lift Gate
1.Gates are made with steel plates, They are rectangular in
shape.
2.Fixed in the piers on both ends.
3.Through which gates can moved vertically in their own
plate.
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28. Vertical Sliding Gate
Slides in a groove and heavy frictional resistance is
developed while lifting gates against water pressure.
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29. Rolling Gate
1.Wheel are attached on the gates along each side.
2.Due to wheels friction is reduced.
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30. Radial Gate
1. Curve shape and useful for spans varying from 4m to15m
and height varying from 3m to 10m.
2. Gates are lifted by using ropes and chain.
3. Due to circular shape, thrust of water passes in radial
direction.
4. It requires less efforts
for lifting the gates.
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