Subtopic: Steady and unsteady flow in confined and unconfined aquifers
Question Statement:
An unconfined aquifer extends over an area of 1 km² and has hydraulic conductivity, total porosity and specific retention of 20 m per day, 30% and 10%, respectively. After pumping some groundwater from this aquifer, the water table dropped to a depth of 20 m from the ground level. If the water table was initially at 14.5 m below the ground level, the change in groundwater storage in million cubic meters would be _______________
Official Answer Key:
1.1
Step-by-Step Solution & Explanation
Specific yield, S_y = total porosity − specific retention = 30% − 10% = 20% = 0.20.
Drop in water table = 20 − 14.5 = 5.5 m.
Change in storage = Area × drop × S_y = (1×10⁶ m²) × 5.5 m × 0.20 = 1.1×10⁶ m³ = 1.1 million m³.
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