Question

Saturated hydraulic conductivity is measured in the field by

• A. Constant head permeameter
• B. Tensiometer
• C. Infiltrometer
• D. Guelph permeameter

Hint:

Field Measurement = Guelph Permeameter.
Lab Measurement = Constant/Falling Head Permeameter.
Remember: $K_s$ is the "speed limit" of water through saturated soil.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify an instrument used for measuring the saturated hydraulic conductivity (\( K_s \)) specifically under field conditions, as opposed to laboratory conditions.
Detailed Explanation:

• Saturated Hydraulic Conductivity (\( K_s \)):
This property describes how easily water moves through soil pores when the soil is completely saturated. It is a vital parameter for designing drainage systems and predicting runoff.

• Guelph Permeameter:
The Guelph permeameter is a widely used field instrument based on the "constant head" principle.
It is used to measure in-situ saturated hydraulic conductivity in the unsaturated (vadose) zone.
It involves boring a hole into the soil and maintaining a constant level of water in that hole. The rate at which water flows out of the hole into the soil is measured to calculate \( K_s \).

• Analyzing other options:
Constant Head Permeameter: While it measures \( K_s \), it is usually a laboratory setup using soil cores.
Tensiometer: Measures soil moisture "tension" or "potential," not conductivity.
Infiltrometer: Measures the "Infiltration Rate" (the rate water enters the soil surface), which is related to but distinct from the hydraulic conductivity of the subsurface soil profile.

Step 2: Final Answer:
The Guelph Permeameter is specifically designed for determining the saturated hydraulic conductivity of soil in the field.