Question

In context with Water Supply, working head is generally takes as _______ of the critical depression head.
1. three times
2. one - third
3. two - times
4. half

Answer 1

Correct Answer - Option 2 : one - third

Explanation:

(i) As the water in an open well is pumped out, the water level inside the well is lowered, the lowering of the water table to the prior water table is known as depression head. The flow discharge into the well is given as,

Q = K_oH

Q = discharge, Ko = Specific capacity, H = Depression head

(ii) As the depression head increases, the flow velocity also increases, so there is a critical depression head at which flow velocity is so high that it causes dislodging of soil particles.

(iii) The discharge corresponding to this critical head is called as critical yield and maximum yield.

(iii) The depression head is kept equal to one-third of the critical depression head.

(iv) We apply a factor of safety (normally 2-3) on the critical head to find out the working head. The discharge corresponding to this head is called as safe yield.