Understanding the water table and capillary zone: Which of the following statements are correct regarding water table behavior and pore-water pressures?

Introduction / Context:
The water table separates saturated zones with positive pore pressures from the capillary zone where suction prevails. Recognizing these fundamentals is essential in irrigation design, drainage, and groundwater studies.

Given Data / Assumptions:

• Unconfined aquifer conditions.
• Open wells tapping the phreatic surface.
• Typical soil behavior in the vadose (unsaturated) zone.

Concept / Approach:
The water table (phreatic surface) is the locus of points with zero gauge pressure. Above it, capillary rise creates negative pore pressures. In plan, the water table tends to mimic land-surface undulations, smoothed by hydraulic conductivity contrasts and recharge/discharge patterns. Open wells in unconfined settings reflect the local water table elevation when static.

Step-by-Step Solution:
Statement A: True—though subdued compared with the ground surface.Statement B: True—well water level equals local water table in static equilibrium.Statement C: True—capillary tension above the water table causes negative pore pressure.Statement D: True—by definition, gauge pressure = 0 at the phreatic surface.

Verification / Alternative check:
Field piezometers and tensiometers verify these pressure regimes; soil–water characteristic curves quantify suction above the water table.

Why Other Options Are Wrong:
Each individual assertion is correct; therefore the comprehensive choice “All the above” is the best answer.

Common Pitfalls:

• Confusing piezometric head in confined aquifers with water table elevations.
• Assuming capillary rise is negligible in coarse sands; it can still be significant relative to root depths.

Final Answer:
All the above