2. SPILLWAY
• A spillway is a structure used to provide for the
controlled release of flows from a dam or levee
into a downstream area, typically being the river
that was dammed.
• To prevent overtopping and possible failure of the
dam.
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8. Components of spillway
• Straight head spillway
• Ogee spillway
• Side channel spillway
• Chute spillway
• Tunnel spillway
• Siphon spillway
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Free overfall or straight drop spillway
•In this type, water drops freely from the crest.
•Occasionally the crest is extended in the form of overhanging lip to direct
small discharges away from the face of overfall section.
10. Straight head spillway
1. It should be consists of lower height.
2. Narrow crested weir at the downstream side.
3. The overflow of water pass though free nappe or crest weir
4. It should be consists of lower dams and rock fill and
earthen dams
5. It is not suitable for weak type of foundations
14. Ogee or overflow spillway
•The Ogee spillway is generally provided in rigid dams and forms a part of the main dam itself
if sufficient length is available.
•The overflow type spillway has a crest shaped in the form of an ogee or S-shape.
•The upper curve at the crest may be made either larger or sharper than the nappe.
29. Chute spillway
•chute spillways are used in flow ways where water is to be lowered from one level to
another and where it is desirable to avoid a stilling basin.
•These are mostly used with earth dams and have the following merit.
It can be provided on any type of foundations.
Simplicity of design.
However this type of spillway should not be provided where too many bends are
to be given as per topography.
Baffle apron or chute spillway
41. Siphon spillways
• Instead of allowing water to spill over the crest of a dam the
surplus water may be discharged d/s through siphon spillways
consisting of one or more units.
Types of siphon spillways
1. Saddle siphon spillway
2. Volute siphon spillway
42. Saddle spillways
•A siphon spillway is a closed conduit system formed in the shape of an inverted U.
•This type of siphon is also called a Saddle siphon spillway.
•Siphonic action takes place after the air in the bend over the crest has been exhausted.
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