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design of chute and syphonspillway

  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
  3. 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
  4. 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
  5. 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.
  6. • 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
  7. Siphon Spillway
  8. • 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
  9. • 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
  10. Hydraulic Design Consideration Discharging capacity Priming depth Regulating flow Effect of waves in the reservoir Cavitation Vibration
  11. Discharging Capacity • The flow in the throat section of a saddle siphon can be idealised as a free vortex, so that
  12. This velocity should be the same at all sections along the siphon barrel unless there is expansion or contraction of the section
  13. • 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)
  14. Cont….. Energy Equation (Enterance and Exit) The required outlet area Ao can then be calculated from Vo