GATE 2021 CE (CE1) – Question 34

Hydrology · Ground water hydrology, well hydraulics and aquifers · 1 mark · Numerical answer

Two reservoirs have heads 30 m and 10 m above a common datum and are connected by a confined aquifer over a 2 km flow path. K=25 m/day and effective porosity=0.3. Find contaminant travel time in days, to one decimal.

see the reproduced source diagram and its labels.

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: 2400 to 2400

Explanation

The hydraulic gradient is $(30-10)/2000=0.01$. Darcy flux is Ki=0.25 m/day; actual pore velocity is $Ki/n=0.25/0.3=0.83333$ m/day. Travel time is distance divided by pore velocity: $2000/0.83333=\mathbf{2400.0}$ days. Aquifer thickness cancels from this velocity calculation.