Groundwater Hydrology MCQ with answer and solution

Concept

Cone of depression and drawdown distribution around a pumping well in an unconfined aquifer.

Formula

h₀ - h = [Q / (π × K × (h₀² - h²))] × ln(R / r)

Step-by-step solution

1. Understand the concept of pumping from an unconfined aquifer. 2. When pumping occurs, water is drawn from the aquifer, creating a drawdown curve shaped like an inverted cone known as the cone of depression. 3. The maximum depth of the water table lowering (drawdown) occurs directly at the well face (r = r_w). 4. As the radial distance (r) increases, the drawdown decreases, eventually dropping to zero at the radius of influence (R).

Explanation

When water is pumped from a well in an unconfined aquifer, the water table is lowered, forming a cone of depression. The maximum drawdown occurs at the pumping well itself and decreases with radial distance from the well until it reaches the radius of influence.

Why the other options are wrong

B: Drawdown decreases as distance from the well increases. C: Drawdown is not uniform; it varies inversely with the distance from the well. D: Drawdown is heavily dependent on radial distance.

Shortcut

Drawdown is always maximum at the well and decreases with distance.

Common mistake

Confusing drawdown with the height of the water table itself; drawdown is the *drop* in water level, which is greatest near the well.