Question

An unconfined aquifer of porosity 30% permeability 35m/day and specific yield of 0.20 has an area of $100{\text{km}}^2$. If the water table falls by 0.25 m during a drought, the volume of water lost from storage, in million cubic metres, is

• A. 2.0
• B. 5.0
• C. 1.0
• D. 4.0

Answer 1

The correct option is B 5.0

The actual volume of water that can be extracted by the force of gravity from a unit volume of aquifer material is known as the specific yield ($S_y$).
Volume of water lost during drought
$=S_y\times \text{Area}\times \text{drop in water table}$
$=0.2\times 100\times {10}^6\times 0.25$
$=5\times {10}^6{\text{m}}^3$