Find out the Discharge of a Siphon Spillway
Find out the discharge of a siphon spillway from following data:
- Number of siphon units = 4.
- Area at throat in m2 = 3.
- Full reservoir level = 150 m.
- R.L of centre of outlet = 128.
- Tailwater level on D/S side during rains = 130.
- Tailwater level during winter = 125.
- Discharge coefficient = 0.60.
In rainy days outlet remains submerged and hence discharge depends upon the tailwater level.
Working head = R.L of reservoir – R.L. or T.W.L. = 150 – 130 = 20 m.
Or, Q = 35.75 cumecs.
So, the discharge of four units = 4 × 35.75 = 143 cumecs.
In winter T.W.L falls down and spillways discharge free in the air.
Available head = Reservoir level – R.L of center of outlet = 150 – 128 = 22 m.
Or, Q = 37.5 cumecs.
Discharge of four units = 4 × 37.5 = 152 cumecs.