Question

Optimum yield of a well is arrived at by conducting a “step drawdown test” in the well. Arrange the steps in sequence for conducting a "step drawdown test" from the below statements.
A. Bore is first pumped at a very low and constant discharge rate for a fixed period of time in such a manner that the water level stabilizes at a shallow depth.
B. The pump discharge is then increased to a medium rate of pumping so that water level falls further down but eventually stabilized at an intermediate depth.
C. The pump discharge is further increased higher so that the water level again stabilizes at a lower level further down.
D. When the discharge versus steady state drawdown of the different steps is plotted, a parabolic curve is obtained.
Choose the correct answer from the options given below:

• A. C, B, A, D
• B. A, B, D, C
• C. A, B, C, D
• D. C, A, B, D

Hint:

To remember this sequence: any step-drawdown test must progress from the lowest discharge rate to the highest discharge rate in sequence. Plotting and data analysis (D) are always done last after all measurements are complete.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
A step-drawdown test is a single-well pumping test designed to evaluate the hydrogeometric characteristics of an aquifer and determine the optimum yield of a well.
The test is conducted by pumping the well at a series of progressively increasing, constant discharge rates (steps).
The drawdown measured during each step is used to calculate the well loss and aquifer loss components of total drawdown.

Step 2: Detailed Explanation:
Let us arrange the operational steps of a step-drawdown test in their logical chronological sequence:
1. First Step (A): The well is pumped at a low, constant discharge rate ($Q_1$) until the water level stabilizes and reaches a steady state at a shallow depth. This establishes the baseline step.
2. Second Step (B): The pump discharge is increased to a medium, constant rate ($Q_2$). The water level drops further before stabilizing at a deeper, intermediate depth.
3. Third Step (C): The pump discharge is increased to an even higher, constant rate ($Q_3$). The water level falls again, stabilizing at a deeper level. This process can be repeated for additional, higher steps.
4. Data Analysis Step (D): Once the steady-state drawdown ($s_w$) is recorded for all discharge steps ($Q$), the relationship is plotted.
The relationship between total drawdown and discharge is given by Jacob's equation: \[ s_w = BQ + CQ^2 \] This quadratic relationship produces a parabolic curve when plotted, allowing engineers to calculate the optimal operating yield.
This chronological sequence follows the order: A $\rightarrow$ B $\rightarrow$ C $\rightarrow$ D.

Step 3: Final Answer:
The correct sequential order of steps for conducting a step-drawdown test is A, B, C, D.
Hence, the correct option is (C).