The document discusses spillways, which are structures used to safely discharge water from reservoirs when the water level rises too high. Spillways typically have several key components, including an approach channel, control structure, discharge carrier, discharge channel, and energy dissipators. The control structure regulates water flow and prevents discharge below a fixed level. Energy dissipators, like bucket or baffle types, reduce the water's velocity and kinetic energy before it reaches downstream areas. Spillways must provide stability, safely pass flood waters, operate efficiently, and do so economically.

1. Subject- WRE-II
By
Mr. Denish Jangid
Assistant Professor
Civil Engineering Department
Topic- SPILLWAYS

2. SPILLWAYS
• When the water in the reservoir increases, the large accumulation of
water endangers the stability of the dam structure. To avoid this a
structure is provided in the body of a dam or near the dam or
periphery of the reservoir. This structure is called as spillway.
• Mainly used to discharge water during flood period.
Requirements:
• Provide structural stability to the dam under all condition
• Should able to pass the designed flood without raising the reservoir
level above H.F.L.
• Should have an efficient operation
• Should be economical

3. FUNCTION
• The spillway has the function of
discharging all the water not utilized for
generation. The maximum discharge
capacity of the spillway is 62.2 thousand
m3/s; 40 times greater than the mean
discharge of the Iguaçu Falls.

4. LOCATION OF SPILLWAY
• Generally, the spillways are provided at
the following places
• Spillways may be provided within the
body of the dam.
• Spillways may sometimes be provided at
one side or both sides of the dam.
• Sometimes by-pass spillway is provided
which is completely separate from the
dam.

5. Component parts of
Spillway :
Approach channel
Control structure
Discharge carrier
Discharge channel
Energy dissipators.

6. APPROACH
CHANNEL

7. 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.

8. Control
structure

9. 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.

10. Discharge
carrie
r

11. 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.

12. Discharge
channel

13. Energy
dissipators
At the end of discharge carrier, the water released from
control structure has great velocities enough to cause scour.
Thus, energy dissipators are provided to avoid the scouring
of downstream side of spillway.
These are to be provided before water entering the discharge
channel.
The following are the different types of dissipators:
1. Bucket type energy dissipators
2. Stilling basin type dissipators
3. Baffle type dissipators.

14. Bucket type
dissipators
 The high kinetic energy of water is reduced by providing
a hydraulic jump at the end of spillway.
The hydraulic jump can be achieved by providing bucket
type dissipators.
By hydraulic jump of water some part of energy is
dissipated by aeration.

15. Bucket type
dissipator

16. Stilling
basin
Stilling basins are usually provided after the buckets.
Due to the hydraulic jump of water, the water falling on
the ground may cause cavitations on the ground.
These cavitations can be avoided by providing the stilling
basin.
The stilling basin consists of water which reduces some
part of energy of water.

17. Stilling
basin

18. Baffle type
dissipators
After passing the stilling basin water has still some energy.
If any amount of energy exist, it can be fully dissipated by
providing baffle dissipators.
In this, baffle type structures are provided in a number of
series depending on the amount of energy.

19. Baffle type dissipators

20. TYPES OF SPILLWAYS
 Overfall spillway
 Chute spillway
 Saddle spillway
 Shaft spillway
 Side channel spillway
 Emergency spillway
 siphon spillway

21. FIGURES
Overfall spillways
Chute spillways:
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
Overfall spillway:
• that allows water to pass over its crest
widely used on gravity, arch, &
buttress dam
• This is a simplest type

22. SADDLE SPILLWAYS
This type is mainly used when other types are not
favourable.
In some basins formed by a dam, there may be
one or more natural depressions or saddles in the
rim of the basin, which can be used as spillway.
It is essential that the bottom of the depression should
be at full reservoir level.
It is usually necessary for the saddle to be on firm
rock.

23.  The shape is just like a funnel .
 water drops through a vertical shaft in a the foundation material toa
horizontal conduit that conveys the water past the dam.
 Lower end of shaft is turned at right angle and then water taken out
below the dam horizontally.
 Also called as glory hole spillway.
SHAFT SPILLWAY

24. SIDE CHANNEL SPILLWAY
 When the dam is not rigid and it is undesirable to pass flood water
over the dam , this type of spillway is used.
 After passing crossing over the spillway crest ,water flows parallel to
the crest.

25. SIPHON SPILLWAYS
It is designed by the principle of a siphon.
When water rises over the FRL then water startspilling.
There is a air vent for removing the entrapped pressure from the
water.

27. EMERGENCY SPILLWAY
• This type is rarely used .
• Extra spillways provided on a project in rare case of
extreme floods(emergency)
• Used to convey frequently occurring outflow rates.

28. ADVANTAGES
• Very stable. The likelihood of serious structural
damage is less than for other types of structures.
• The rectangular weir is less likely to be clogged
by debri,s than the openings or other structures
of comparative discharge capacities.
• They are relatively easy to construct. The
concrete block type can be built with farm labor,
while the reinforced concrete or steel sheet
piling type usually requires the services of
a contractor.

29. DISADVANTAGES
• It is more costly than some other types of
structures where the required discharge
capacity is less than 100 c.f.s. and the
total head or drop is greater than 10 feet.
• It is not a favorable structure where
temporary spillway storage is needed to
obtain a large reduction in discharge.
• A stable grade below the structure is
essential.

30. ENERGY DISSIPATION
• As water passes over a spillway and down
the chute, potential energy converts into
increasing kinetic energy capacity of its
power plant.
• The energy can be dissipated by
addressing one or more parts of a
spillway's design

31. ENERGY DISSIPATION

32. SAFETY
• Spillway gates may operate suddenly without warning, under remote
control. Trespassers within the spillway run the risk of drowning.
Spillways are usually fenced and equipped with locked gates to
prevent casual trespassing within the structure. Warning signs,
sirens, and other measures may be in place to warn users of the
downstream area of sudden release of water. Operating protocols
may require "cracking" a gate to release a small amount of water to
warn persons downstream.
• The sudden closure of a spillway gate can result in the stranding of
fish, and this is also usually avoided.