Subtopic: Steady and unsteady flow in confined and unconfined aquifers
Question Statement:
An unconfined aquifer is pumped at a constant rate of 10 l s⁻¹. Steady state drawdowns measured at radial distances of 30 m and 60 m are 0.80 m and 0.70 m, respectively. Original thickness of aquifer is 30 m. Transmissibility of the aquifer is
Options:
(A) 19 m² d⁻¹
(B) 760 m² d⁻¹
(C) 952 m² d⁻¹
(D) 982 m² d⁻¹
Official Answer Key:
C
Step-by-Step Solution & Explanation
With drawdowns small relative to the 30 m saturated thickness, the Thiem equation reduces to the confined-aquifer form: T = Q·ln(r₂/r₁) / [2π(s₁−s₂)]. Q = 10 l/s = 864 m³/d. T = 864×ln(60/30)/[2π(0.80−0.70)] = 864×0.6931/(0.6283) = ≈952 m²/d.
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