Which instrument is right for you? Soil hydraulic conductivity is the ability of a soil to transmit water in saturated, nearly saturated, or unsaturated conditions. But measuring hydraulic conductivity can be confusing. Which measurement is right for your application: saturated or unsaturated hydraulic conductivity? And which instrument should you use? Make the right choice In Soil Moisture 302, Leo Rivera, Research Scientist at METER, teaches which situations require saturated or unsaturated hydraulic conductivity and the pros and cons of common methods used to measure both parameters. Find out: • When to measure saturated hydraulic conductivity • When to measure unsaturated hydraulic conductivity • Instruments that measure each parameter • The technology behind each instrument • Advantages vs. disadvantages of each method

2. SOIL MOISTURE 302
HYDRAULIC CONDUCTIVITY—
WHICH INSTRUMENT IS RIGHT FOR YOU?
Leo Rivera
METER Group, Inc. USA

3. INTRODUCTION
ABOUT ME
Background in Soil Physics & Pedology
12 years of experience measuring and
interpreting soil hydraulic properties and soil
moisture release curves

4. QUESTION:
I NEED TO MEASURE HYDRAULIC
CONDUCTIVITY FOR MY RESEARCH.
WHAT TYPE OF MEASUREMENT APPROACH
SHOULD I USE?

5. WHAT IS
HYDRAULIC CONDUCTIVITY?

6. WHAT IS
HYDRAULIC CONDUCTIVITY?
Hydraulic Conductivity:
A measure of the ability of a porous medium to transmit water

7. HYDRAULIC CONDUCTIVITY
WHAT DETERMINES
HYDRAULIC CONDUCTIVITY?
Soil texture
Soil structure
Biopores
Compaction/bulk density
Water content/potential

8. HYDRAULIC CONDUCTIVITY
A POROUS MEDIUM CAN BE
SATURATED OR UNSATURATED

9. SATURATED VS. UNSATURATED
HYDRAULIC CONDUCTIVITY

10. K-SAT VS. K-UNSAT
WHAT IS RIGHT FOR ME?
Saturated Hydraulic Conductivity
All pores are contributing to fluxes
Primarily driven by gravitational forces
Less common state of flow in soil
Applications:
Soil structure and macropore effects
Groundwater flow
Green Infrastructure Assessment
Unsaturated Hydraulic Conductivity
Varies depending on pore sizes which are able to contribute
to water fluxes
Primarily driven by matric forces
Most common state of flow in soil
Applications:
Understanding unsaturated water movement in the vadose
zone
Modeling fluxes
Repellency/hydrophobicity

11. METHODS FOR MEASURING
HYDRAULIC CONDUCTIVITY

12. METHODS
SATURATED HYDRAULIC CONDUCTIVITY
Laboratory (Ks)
Flow Cells
KSAT
Field (Kfs)
Ring Infiltrometers
Borehole Permeameters
Pressure Infiltrometers

13. Core samples collected from field or
repacked
Steady state flow rate measure as water
passes through saturated sample
Constant- & falling-head technique
Automated devices simplify the
measurements
LABORATORY METHODS
Flow Cells KSAT

14. Advantages
Simple calculations
No corrections for 3-dimensional flow
Separate different horizons
Multiple samples can be stored
Fairly easy setup
Disadvantages
Expansive soils are confined
Values may differ from field methods
Requires additional equipment to automate
Dedicated lab space
Small surface area
LABORATORY METHODS
PROS & CONS

15. Thin-walled, open-ended cylinders
Various cylinder arrangements
Constant- and falling-head techniques
FIELD METHODS
RING INFILTROMETERS

16. Double-ring configuration is the most
common
Single measuring cylinder placed inside
larger buffer cylinder
Intention of buffer cylinder is to prevent flow-
divergence from measuring cylinder
FIELD METHODS
RING INFILTROMETERS
Single-ring Double-ring

17. FIELD METHODS
DUAL HEAD METHOD
OVERCOMING 3-DIMENSIONAL FLOW
Multiple ponded head analysis measures
α-value for each site
How does it work?
Water level is controlled at constant head
Air pressure imposes higher pressure heads

18. FIELD METHODS
DUAL HEAD METHOD
0.00E+00
2.00E-03
4.00E-03
6.00E-03
8.00E-03
1.00E-02
1.20E-02
1
4
7
10
13
16
19
22
25
28
31
34
37
40
43
46
49
52
55
58
61
64
67
70
73
76
79
82
85
88
91
94
97
100
103
106
109
112
115
Flux(cm/s)
Time (min)

19. Constant-head method
Several permeameter designs
Single- and multiple-head analysis
Can also determine α
FIELD METHODS
BOREHOLE PERMEAMETER

20. FIELD METHODS
PROS & CONS
Advantages Disadvantages
Measurement of (𝛂𝛂) improves analysis
of Kfs
More complex measurement
apparatus
Can also be used to determine
sorptivity and matric flux potential
Multiple-head technique requires
more time
Not automated—requires more work
Advantages Disadvantages
Larger rings encompass more spatial
variability
Time consuming
Results represent field conditions Requires estimation of soil properties (𝛂𝛂)
to correct for 3-dimensional flow
Buffer cylinder often is not effective
Ring
Infiltrometers
Borehole
Infiltrometer

21. METHODS
UNSATURATED
HYDRAULIC CONDUCTIVITY
Laboratory
Tempe Cells
Evaporation Method
Field
Tension Infiltrometers

22. LABORATORY METHODS
FLOW CELLS
Steady flow rate into column
Flow rate maintained until both tensiometers
read same suction
Flow rate is increased in steps to obtain
different Kψ points

23. First Introduced by Wind (1968)
Saturated soil core allowed to evaporate
Constant evaporation rate
Simultaneous measurements of matric
potential and volumetric water content
LABORATORY METHODS
EVAPORATION METHOD

24. Simplified approach with two tensiometers at
different heights
Hydraulic Conductivity calculated
Using Inversion of Darcy-Equation
LABORATORY METHODS
SIMPLIFIED EVAPORATION METHOD
HYPROP

25. LABORATORY METHODS
PROS & CONS
Advantages Disadvantages
Simultaneous water transmission and
retention properties
Unreliable K(Ψ) data near saturation
Automated measurement Learning curve
Excellent measurement resolution Only desorption characteristics
Advantages Disadvantages
Simultaneous water transmission and
retention properties
Requires a method of maintaining a
constant flow
Estimation of saturated and
unsaturated flow parameters on the
same soil column
Complex operation
Flow Cells
Evaporation
Method

26. Porous plate is placed on the soil
Infiltration under imposed suctions
Suction is controlled by bubble tower
Analysis for 3-dimensional flow using
transient and steady-state methods
Also used for determining repellency
FIELD METHODS
TENSION INFILTROMETER

27. FIELD METHODS
PROS & CONS
Advantages Disadvantages
Controlled suction Steady-state methods are time
consuming
Larger disks account for more spatial
variability
Requires estimation of soil properties
to correct for 3-dimensional flow
Estimation of sorptivity and repellency
Tension
Infiltrometer

28. FIELD METHODS
SUMMARY
Strengths Limitations
Lab
Instrumentation
Controlled conditions
Run samples directly
Automated and relatively
fast analysis
Defined procedure
Accuracy
Doesn’t take into account field conditions
Complicated setup with some systems
Field
Instrumentation
Understand variability and
real time field conditions
Easy installation and setup
Automated measurements
Variability requires more measurements
More data to analyze
Uncontrolled conditions
Unpredictable weather can cause delays
and damage unprotected equipment
Poor installation can cause inaccuracy

29. COMMON QUESTIONS &
THINGS TO CONSIDER
How long do I have to take measurements?
Are you more interested in field scale effects or individual parts of the soil?
How many measurements do I need to take?

30. QUESTIONS?