Subtopic: Steady and unsteady flow in confined and unconfined aquifers
Question Statement:
A 150 mm diameter well is driven fully in a confined aquifer of thickness 12 m. When pumping is done at a constant rate of 150 L min⁻¹ for 10 h, the steady-state draw-downs are found to be 2.20 m and 0.02 m at distances of 14 m and 50 m, respectively from the centre of the well. The hydraulic conductivity of the aquifer in m day⁻¹ is ___________.
Official Answer Key:
1.20 to 1.70
Step-by-Step Solution & Explanation
Thiem equation (steady radial flow to a well in a confined aquifer):
K = Q·ln(r₂/r₁) / [2π·b·(s₁−s₂)]
Q = 150 L/min = 150×60×24 L/day = 216,000 L/day = 216 m³/day.
b (aquifer thickness) = 12 m; s₁−s₂ = 2.20−0.02 = 2.18 m; ln(50/14) = ln(3.5714) = 1.2726.
K = 216 × 1.2726 / (2π × 12 × 2.18) = 274.88 / 164.37 = 1.67 m/day, within the accepted range.
Wells and Pumps
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