## Find out the Discharge of a Siphon Spillway

**Mathematical Problem:**

Find out the discharge of a siphon spillway from following data:

- Number of siphon units = 4
- Area at throat in m
^{2}= 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

**Solution:**

**Case 1**

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,

Or, Q = 35.75 cumecs.

So, the discharge of four units = 4 × 35.75 = 143 cumecs.

**Case II**

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,

Or, Q = 37.5 cumecs.

Discharge of four units = 4 × 37.5 = 152 cumecs.

*Read Also:*

How to Calculate Annual Runoff – Problem & Solution

How to Calculate Discharge of the Water if the Depth and Crop Period are Given