Well hydraulics – flow fields and controlling areas in different well types Choose the correct overall statement about flow patterns and controlling flow areas for common well types used in water-supply practice.

Introduction / Context:
Understanding how water approaches a well screen or a developed cavity is essential for predicting head losses and sand control. Introductory groundwater texts present idealized patterns for different well designs.

Given Data / Assumptions:

• Strainer (screen) wells in unconsolidated formations.
• Cavity wells in coarse formations where a natural cavity is developed.
• Steady radial flow assumptions around a vertical well in a homogeneous aquifer.

Concept / Approach:
For a vertical screened section in a uniform aquifer, far-field flow to the well is radial in plan. For a localized cavity, approach flow is often visualized as quasi-spherical near the cavity. The hydraulic entrance area that governs entrance losses depends on the active screen length for strainers and on cavity surface area for cavity wells.

Step-by-Step Solution:
Evaluate (a): Radial inflow to screen → conceptually correct.Evaluate (b): Cavity well inflow → frequently idealized as spherical near the cavity.Evaluate (c): Entrance area is proportional to active screen length → correct.Evaluate (d): Entrance area controlled by cavity size → correct.Since all (a)–(d) are correct, the only consistent choice for a single-answer question is “None of these” (none are incorrect).

Verification / Alternative check:
Classical well-loss relationships include a term associated with entrance velocity over the screen or cavity area, highlighting dependence on length (screen) or surface (cavity).

Why Other Options Are Wrong:

• Selecting any one of (a)–(d) would imply the others are wrong, which is not the case.

Common Pitfalls:
Confusing far-field radial flow with near-well entrance effects; both views are used at different spatial scales.

Final Answer:
None of these