GATE AG 2021 • Q60 NAT • 2 Marks

Section 5: Irrigation and Drainage Engineering

Groundwater Hydrology

Subtopic: Steady and unsteady flow in confined and unconfined aquifers

Question Statement:

Two fully penetrating wells are dug 1.4 km apart in a homogenous confined aquifer. The difference in their piezometric levels is 4.0 m. The groundwater flow is steady and unidirectional. If the aquifer has a hydraulic conductivity of 3.5 m·day⁻¹ and effective porosity of 40%, the time taken for water to move from one well to the other in days is ______. [in integer]

Official Answer Key:

56000 to 56000

Step-by-Step Solution & Explanation

Darcy (specific discharge) velocity, v = K×i = K×(ΔH/L) = 3.5 × (4.0/1400) = 3.5×0.002857 = 0.01 m/day. Actual (seepage) pore velocity, v_seepage = v/porosity = 0.01/0.40 = 0.025 m/day. Time = Distance/v_seepage = 1400/0.025 = 56,000 days. Section 6 — Agricultural Process Engineering

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