This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Groundwater – Specific Capacity”.

1. What is the specific capacity of a well?

a) Volume of water corresponding to unit head drop

b) Discharge corresponding to safe yield

c) Discharge per unit area of well

d) Discharge per unit drawdown in a well

View Answer

Explanation: Specific capacity is an important property of well and it denotes the discharge that can be pumped from the well per unit drawdown inside the well. It is a measure of performance of the well.

2. Which of the following is a suitable unit for specific capacity?

a) m/s

b) hr^{-1}

c) m^{2}/hr

d) litre/s

View Answer

Explanation: \(Specific capacity = \frac{Discharge}{Drawdown}=\frac{volume/time}{length}=\frac{Area}{time}=[L^2 T^{-1}]\)

Therefore, the unit of specific capacity is m

^{2}2/hr.

3. It is given that for a well, the specific capacity is directly proportional to the transmissibility under equilibrium conditions. For which of the following cases is this true?

a) Confined aquifer with well losses

b) Confined aquifer without well losses

c) Unconfined aquifer with well losses

d) Unconfined aquifer without well losses

View Answer

Explanation: For a confined aquifer neglecting the well losses, from Dupit’s equation,

\(Q=\frac{2πST}{ln \frac{R}{r}}⇒\frac{Q}{S}=\frac{2πT}{ln \frac{R}{r} ⇒\frac{Q}{S}∝T\)

Therefore, specific capacity is directly proportional to transmissibility.

4. For a well discharges at a constant rate under steady state conditions, the specific capacity of the well is a constant.

a) True

b) False

View Answer

Explanation: The steady state discharge for a well is governed by Dupit’s equation. For a confined aquifer, taking the aquifer properties and conditions to not change over the time of pumping, which is generally the case, the specific capacity of the well does not change.

5. For a well in a confined aquifer, accounting for well loss with steady state conditions, what will be nature of specific capacity of the well?

a) It remains constant

b) It changes with time

c) It increases with increase in discharge

d) It decreases with increase in discharge

View Answer

Explanation: The term account for the well loss is directly proportional to discharge and it appears in the equation of specific capacity such that it is inversely proportional to it. Therefore, as the discharge increases, the specific capacity of the well decreases.

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