Question

A 5 m diameter open well has a discharge of 40 cumecs under a depression head of 3 m. What will be the discharge (in cumecs) from a 8 m diameter open well in the same aquifer under a depression head of 2 m?

• A. 26.67
• B. 40
• C. 51.26
• D. 68.27

Answer 1

The correct option is D 68.27

Discharge Q=C'S
Where C'=specific capacity
S=depression head

Specific capacity is defined as well yield per unit drawdown

Specific capacity per unit area is a property of aquifer
$\therefore Q_1=\left(\frac{C^{\prime }}{A_1}\right)A_1{S}_1$

$Q_2=\left(\frac{C^{\prime }}{A_1}\right)A_2{S}_2$

$=\frac{Q_1}{A_1{S}_1}{A}_2{S}_2$

$=Q_1\left(\frac{A_2}{A_1}\right)\times \frac{S_2}{S_1}$

$=40\left(\frac{\frac{\pi }{4}\times 8^2}{\frac{\pi }{4}\times 5^2}\right)\times \frac{2}{3}$

$=68.27cumecs$