A confined aquifer is 6 m deep and the coefficient of permeability in the soil is 2 m³/day-m². The wells are 100 m apart and the difference in the water elevation in the wells is 3·0 m. The superficial velocity through the aquifer is :
- A0·09 m/day
- B0·12 m/day
- C0·03 m/day
- D0·06 m/dayCorrect
Solution
Concept
Darcy's law
Formula
v = k i = k (Δh / L)
Step-by-step solution
1. Hydraulic gradient i = 3 / 100 = 0.03. 2. v = k i = 2 × 0.03 = 0.06 m/day.
Explanation
The superficial (Darcy) velocity is the product of permeability and hydraulic gradient. The thickness of the aquifer is needed only for the discharge.
Why the other options are wrong
0.09 and 0.12 m/day are 1.5 and 2 times the right value; 0.03 m/day is i alone (permeability not used).
Shortcut
v = k × Δh / L.
Common mistake
Multiplying by the aquifer thickness (that gives discharge per unit width).
Correct answer: D) 0·06 m/day