Question

The boundary between the unsaturated and saturated water zones in the underground is called:

• A. vadose zone
• B. ground water table
• C. phreatic line
• D. capillary zone

Hint:

Water table = top surface of the saturated zone, below which groundwater completely fills pore spaces.

Answer 1

The Correct Option is B

To determine the correct term for the boundary between the unsaturated and saturated water zones underground, we analyze the given options and their definitions in hydrology.

1. Understanding the Key Terms:
- Vadose Zone: The unsaturated zone above the water table where soil pores contain both air and water.
- Ground Water Table: The top surface of the saturated zone where water pressure equals atmospheric pressure (correct answer).
- Phreatic Line: The line representing the top flow boundary in seepage analysis (e.g., in earth dams).
- Capillary Zone: The transition zone just above the water table where water rises due to capillary action.

2. Identifying the Correct Boundary:
The boundary between the unsaturated (vadose) and saturated zones is specifically called the ground water table. This is where pore water pressure equals atmospheric pressure, marking the start of full saturation.

3. Why Other Options Are Incorrect:
- Vadose Zone: Refers to the unsaturated zone, not the boundary.
- Phreatic Line: A seepage flow term, not the general boundary.
- Capillary Zone: A sub-region above the water table, not the boundary itself.

Final Answer:
The correct term is \( \boxed{\text{ground water table}} \).