Question

Saturated hydraulic conductivity in situ is measured by:

• A. Guelph permeameter
• B. Infiltrometer
• C. Neutron probe
• D. Piezometer

Hint:

The Guelph permeameter is a widely used field instrument because it requires only a small auger hole.
It allows for rapid, localized measurements of subsurface hydraulic properties above the water table.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Hydraulic conductivity (\( K \)) is a measure of the soil's ability to transmit water under a hydraulic gradient.
Saturated hydraulic conductivity (\( K_{\text{sat}} \)) represents this ability when all soil pores are filled with water.
Measuring \( K_{\text{sat}} \) *in situ* (in the field) provides more realistic values than laboratory measurements because it preserves the natural soil structure and macropores.

Step 2: Detailed Explanation:
Various field methods are used to measure \( K_{\text{sat}} \) depending on the water table depth.
The Guelph permeameter is a constant-head well permeameter used to measure \( K_{\text{sat}} \) *in situ* in the unsaturated zone (above the water table).
It operates by maintaining a constant depth of water in an auger hole and measuring the steady-state rate of water flow into the soil.
This flow rate, combined with the well geometry, is used to calculate the field-saturated hydraulic conductivity using analytical equations.
In contrast:
- An infiltrometer (B) (like a double-ring infiltrometer) is used primarily to measure the surface infiltration rate, not \( K_{\text{sat}} \) within the subsurface profile.
- A neutron probe (C) is used to measure soil volumetric water content.
- A piezometer (D) is used to measure hydraulic head and water table depth in saturated zones.
Therefore, the Guelph permeameter is the instrument used to measure *in situ* saturated hydraulic conductivity.

Step 3: Final Answer:
The instrument used to measure saturated hydraulic conductivity *in situ* is the Guelph permeameter.