Question

In deriving the equations for confined and unconfined aquifers, which of the following assumptions are used?
A. Change in the drawdown with respect to time is negligible.
B. The well penetrates the entire aquifer.
C. The flow is vertical and uniform everywhere in the horizontal section.
D. The flow is laminar.
Choose the correct answer from the options given below:

• A. A, B and D only
• B. A,B,C only
• C. A,B,C,D
• D. B,C and D only

Hint:

The key Dupuit-Thiem assumptions are: 1. Steady-state flow (\(\Delta h/\Delta t = 0\)). 2. Aquifer is homogeneous and isotropic. 3. Flow is horizontal (radial). 4. Darcy's Law is valid (laminar flow). 5. The well is fully penetrating.

Answer 1

The Correct Option is B

Phase 1: Review the Dupuit-Thiem postulates concerning well hydraulics. These postulates are simplifications used to formulate the steady-state equations for flow toward a well.
Phase 2: Assess each assertion against the established postulates.
- A. Drawdown rate of change over time is insignificant: This defines steady-state flow, characterized by unchanging conditions over time. This postulate is applied in the Thiem equation and is valid.
- B. The well fully penetrates the aquifer: This describes a "fully penetrating" well, which simplifies flow to be exclusively radial. This is a standard postulate.
- C. Flow is vertical and uniform in all horizontal sections: This is inaccurate. The Dupuit postulate posits that flow is horizontal, and the hydraulic gradient equals the water table's slope, remaining constant with depth. Flow is not vertical. This assertion is false.
- D. Flow is laminar: This implies the applicability of Darcy's Law, a foundational requirement for deriving these equations. This is a valid postulate.
Phase 3: Determine the accurate combination.
Assertions A, B, and D are standard postulates utilized in the derivation of steady-state well equations. Assertion C inaccurately characterizes the flow.
Consequently, the correct combination comprises A, B, and D.