group ppt

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

17. THANK YOU