In an area of 200 hectare, water table drops by 4m. If the

In an area of 200 hectare, water table drops by 4m. If the porosity is 0.35 and the specific retention if 0.15, change in volume of storage in the aquifer is

Porosity, η = Specific yield + Specific reference
⇒ η = S_y + S_R
⇒ 0.35 = S_y + 0.15
S_y = 0.2

S_y =	Volumeof water extracted
	Unit Volume of aquifer

⇒ 0.2 =	Volumeof water extracted
	200 × 10⁴ × 4

∴ Change in volume = 0.2 × 200 × 10⁴ × 4
= 1.6 × 10⁶ m³