spillwayalvand.basu.ac.ir/~j.sadeghian/courses/hydraulics... · 2016-10-17 · appreciable increase...

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Spillway: One of the most important structural component of a dam

• Spillway evacuates the flood wave from reservoir to

river at the downstream.

• It is normally composed of three major components:

• The approach facility admits flow to the spillway.

• The discharging conduit evacuates the flow from the

approach facility to an outlet structure.

• The outlet structure (tailwater channel) dissipates the

excessive energy of the flow from the discharging

conduits and conveys tranquil flow to the downstream.

• For safety, spillways should have sufficient capacity to

discharge floods, likely to occur during the lifetime of

the dam.

• Spillway Design Flood (SDF) can be selected using

some prescribed guidelines or from a risk-based

analysis.


Types of Spillways 1. Overflow(Ogee) Spillways

2. Chute Spillways

3. Side Channel Spillways

4. Shaft (Morning Glory) Spillways

5. Tunnel Spillways

6. Labyrinth Spillways

7. Siphon Spillways

8. Baffled Chute Spillways

9. Over fall or Free Spillways

10. Stepped Spillways

11.Cascade Spillways

12.Fuse plug Spillway


Overflow spillways also called

ogee-shaped (S-shaped)

spillways.

• This type of spillways allows the

passage of the flood wave over its crest.

• Widely used on

• Gravity dams,

• Arch dams, and

• Buttress dams.


Uncontrolled (ungated, free)

Ogee Spillway


Ogee Spillway

Almost all recently constructed dams are installed

with crest gates to store more water in the reservoir

Controlled (gated, guided)


Gated Spillway


Ogee Spillway


Chute Spillway

In case of having sufficient stiff

foundation conditions at the spillway

location, a chute spillway may be used

in stead of overflow spillway due to

economic consideration.


Chute Spillway


Chute Spillway

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Chute Spillway


Side Channel Spillway

If a sufficient crest length is not

available for an overflow or chute

spillways in narrow valleys,

floodwater is taken in a side channel


Side Channel Spillway


Morning Glory Spillway

If a sufficient space is not available for

an overflow spillway, a shaft spillway

may be considered. In the site of shaft

spillway

Seismic action should be small,

Stiff geologic formation should be

available,

and Possibility of floating debris is

relatively



When the shaft is completely submerged,

further increase in head will not result in

appreciable increase in discharge.

This type of spillway is not suitable for

large capacity and deep reservoirs because

of stability problems.

Special designs are required to handle

cavitation damage at the transition between

shaft and tunnel.

Repair and maintenance of shaft spillways

are difficult.


Tunnel Spillway


Labyrinth Spillway


Siphon Spillway A siphon spillway may be constructed in the

body of

a concrete dam when space is not available for

an overflow spillway. It has a limited capacity.

• Discharge Q = Cd A (2gh)1/2

where

Cd: discharge coefficient (≈0.9)

A: flow area of siphon

h : the elevation difference between the upstream

water level and end of the barrel. When the

downstream end is submerged, h is elevation

difference between the upstream and

downstream

water levels.


Siphon Spillway


Siphon Spillway

Disadvantage of siphon spillway:

• A the siphon is primed the flow would result excessive

vibrations in the dam body which may cause expansion

problems in the joints.

• There is a possibility of cavitation for negative

pressures, which is affected by the head between

upstream and downstream water levels.

• Repair and maintenance of siphon spillways are

difficult.


Baffled Chute Spillway


Baffled Chute & Labyrinth Spillway


Over fall or Free Spillway



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Stepped Spillway


Cascade Spillway

A cascade spillway consists of a cascade

of falls, with a stilling basin at each fall.

It is ideally suited for very high dams in

which the energy cannot be dissipated

by a hydraulic jump or a bucket. In the

case of a high rockfill dams, already

excavated quarry benches on d/s may be

utilized for the formation of cascades.


Cascade Spillway


Fuse plug Spillway

A fuse plug is a collapsible dam installed on

spillways in dams to increase the dam's capacity

http://en.wikipedia.org/wiki/Spillways

http://en.wikipedia.org/wiki/Dams

spillwayalvand.basu.ac.ir/~j.sadeghian/courses/hydraulics... · 2016-10-17 · appreciable increase...

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