This document summarizes the key components and design considerations for chute and siphon spillways. It describes that a chute spillway consists of an open channel called a chute that carries water from the spillway crest to the river below. It also discusses the entrance channel, side walls, chute channel profile, and hydraulic design factors like discharging capacity and priming depth. Siphon spillways operate using siphonic action and come in hood/saddle and volute designs, with precautions taken to maintain vacuum without cavitation. Hydraulic factors like flow regulation and wave effects on the reservoir are also addressed.

1. Design Chute and Siphon Spillway
Group members:
Chencho Dema
Kuenzang Dorji
Tenzin Kezang
Gobin Rai
Sonam Tshering
Nima Dorji

2. Chute Spillway
• A chute spillway consists of a
steep sloped open channel
called a chute or trough, which
carries the water passing over the
crest of spillway to the river
downstream

4. Entrance Channel
• An approach channel is required to draw water from the reservoir and
convey it to the control structure.
• The friction head lost in the entrance channel upto the spillway crest
can be calculated by:
Hf= Sf*L= (n2 V2L)/(R4/3)
Where n=manning coefficient of roughness
v=velocity in channel
R= hydraulic mean depth
L= length of channel
Sf = mean energy slope b/w two point

5. Side Wall of Chute
• The side wall of chute should be of such height that water doesnot
spill over them
• A sufficient freeboard must be provided
FB= 0.61+0.04Vm . (dm )1/3
Where Vm= mean velocity of water in the chute
dm= mean depth of water in the chute

6. Chute Channel
• The profile of discharge channel should usually be selected to confirm
to topographic and geological site conditions and should be provided
with uniform slope in reaches joined by vertical curves
• When slope of chute changes from steeper to mild a concave vertical
curves shall provided. The radius should be less than 10d, where d id
depth of water
• When slope of chute changes from mild to steeper a convex vertical
curves shall provided.

7. • The curvature should be parabolic in shape given by:
q= -xtanø- (x2/(k(4(d+hv ) cos2ø))
Where ø= slope angle of the floor upstream
(d+hv )=specific energy of flow at junction point
K= constant which is ≥ 1.5

8. Siphon Spillway

9. • A siphon spillways operates on the principle of siphonic action.
• There are basically two types of siphon spillways
• Hood or Saddle siphon (as shown in Figure 1)
• Volute siphon(as shown in Figure 2)
• All necessary precautions must be taken to ensure that the vacuum is
maintained and that it does not become so excessive as to cause
cavitation
• The maximum negative pressure at the spillway crest is theoretically
10 m of water at sea level

10. • Allowing for the vapor pressure of water, loss due to turbulence, etc.,
the maximum net effective head is rarely more than about 7.5 m
• Which means that the initial velocity in any siphon cannot exceed
about 12 m/s at the inlet

11. Hydraulic Design Consideration
Discharging capacity
Priming depth
Regulating flow
Effect of waves in the reservoir
Cavitation Vibration

12. Discharging Capacity
• The flow in the throat section of a saddle siphon can be idealised as a
free vortex, so that

14. This velocity should be the same at all sections along the siphon
barrel unless there is expansion or contraction of the section

15. • when the siphon is running full, the velocity is given by the total head H
• Total head H (from reservoir level up to the tail water level)

16. Cont…..
Energy Equation (Enterance and Exit)
The required outlet area Ao can then be calculated from Vo

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