World-renowned soil physicist, Dr. Gaylon S. Campbell, teaches the basics of soil infiltration, how to measure it correctly, and compares common measurement methods. Make the right decisions Soil infiltration impacts almost everything soils are used for. Infiltration rates impact irrigation, drainage, and how well water flows to crop roots. Infiltration measurements are used to predict erosion and determine soil health. And, in urban settings, stormwater systems and landfills need soil infiltration measurements to maximize or minimize water movement in soil. If you’re working in these situations, it’s critical to understand how to measure infiltration correctly, or you’ll risk inaccurate calculations that could lead to wrong decisions. Master the basics In this 30-minute webinar, world-renowned soil physicist, Dr. Gaylon S. Campbell, teaches the basics of soil infiltration and how to measure it correctly. Learn: - What is soil hydraulic conductivity? - How does soil infiltration vary from one porous medium to another? - What determines hydraulic conductivity? - Why you should care about the infiltration rate of water into soil - How to measure soil infiltration in the lab and the field - How different measurement methods compare

2. SOIL INFILTRATION 101
WHAT IT IS. WHY YOU NEED IT. HOW TO
MEASURE IT.
Gaylon S. Campbell, PhD
METER Group, Inc. USA

3. INFILTRATION RATE
Definition: The volume of water entering a unit area of soil in unit time [m3 m-2 s-1]
or [m/s]
Infiltration rate is the product of two factors:
1. Hydraulic Conductivity (K) – the ability of the soil to transmit water
2. Water potential gradient (dh/dz) – the forces moving water into the soil
Water potential has two components:
1. Matric – forces that attract water to mineral and organic surfaces (depend on
nature of matrix and its water content)
2. Gravitational – a constant vertical force

4. INFILTRATION RATE
Behavior with time
𝑖 = 𝐾
𝑑ℎ
𝑑𝑧
= 𝐾
𝑑ℎ'
𝑑𝑧
+ 𝐾
𝑑ℎ)
𝑑𝑧
𝑑ℎ)
𝑑𝑧
= 1
𝑎𝑡 𝑙𝑜𝑛𝑔 𝑡𝑖𝑚𝑒
𝑑ℎ'
𝑑𝑧
→ 0
𝑠𝑜, 𝑎𝑡 𝑙𝑜𝑛𝑔 𝑡𝑖𝑚𝑒 𝑖 ≈ 𝐾

5. MEASURING INFILTRATION
RATE & ITS COMPONENTS
METER makes instruments to
measure:
• Soil water content (field)
• Soil matric potential (lab and
field)
• Soil water potential (lab)
• Soil saturated hydraulic
conductivity (lab)
• Soil unsaturated hydraulic
conductivity (lab)
• Infiltration rate in field to
determine K (field)
TEROS 12
TEROS 21 TEROS 31
WP4C
KSAT
HYPROP SATURO

6. HYDRAULIC CONDUCTIVITY
WHY DO WE CARE ABOUT IT?
It impacts almost everything
soil is used for
• Crop production
• Irrigation and drainage
• Hydrology (native and urban)
• Landfill performance
• Storm water system design
• Soil health

7. HYDRAULIC CONDUCTIVITY
WHAT FACTORS DETERMINE ITS
VALUE?
• Soil texture
• Soil structure
• Biopores
• Compaction/bulk density
• Water content/potential

8. HYDRAULIC CONDUCTIVITY
Depends on whether the soil is saturated or unsaturated

9. KSAT
SATURATED CONDUCTIVITY
• Uses soil cores
• Steady saturated flow
at a known head

10. HYPROP
UNSATURATED CONDUCTIVITY
• Uses soil cores
• Tensiometers measure water potential
and gradient during evaporation
• Gives both moisture release curve
and unsaturated hydraulic
conductivity function

11. HYPROP
UNSATURATED HYDRAULIC
CONDUCTIVITY DATA

12. HYPROP
MOISTURE RELEASE DATA

13. MEASURING K IN THE FIELD
SINGLE-RING INFILTROMETER
• Single measuring cylinder
• Diameter: 10 to 50 cm
• Constant or falling head

14. MEASURING K IN THE FIELD
DOUBLE-RING INFILTROMETER
• Concentric cylinders;
outer cylinder provides a buffer
• Assumed one-dimensional flow
from inner cylinder
• Can do constant or falling head

15. FIELD STUDY
USING DOUBLE-RING
Research Project
• Semi-automated double-ring
infiltrometer system
• Made ~200 Kfs measurements
• Typical measurement times between
90 to 120 min
• Typically used over 2,000 L of water

16. IMPROVEMENT
OBSERVATIONS AND OPPORTUNITIES
• K is spatially and temporally variable
• Double-ring takes a lot of time and water
• Why not use math to eliminate the need for the second ring?
• It is hard to measure infiltration and control head.
Why not do that electronically?
• Sorptivity must be taken into account to get accurate conductivity
measurements. Automate that too.

17. IMPROVEMENT
• Fully automate measurements and control
• Reduce water requirements
• Be portable
• Have a wide flux rate range: 0.03 cm hr-1 to 115 cm hr-1
• Automatically calculate Kfs
We wanted an infiltrometer to:

18. ANALYSIS
Kfs is defined as:
F is a function that corrects for sorptivity and geometrical factors
Nimmo et al. (2009) gives F as:
D
+
+
=
+
+
+
=
D
b
C
d
C
D
F
l
l
1
1
2
1
D = ponding depth
d = insertion depth
b = infiltrometer radius
l = porous matrix characteristic length
C1 = 0.993
C2 = 0.578

19. ANALYSIS
For two ponding depths we can write:
Solving to eliminate l we get:

20. DUAL-HEAD MEASUREMENTS
Head
-25
-20
-15
-10
-5
0
5
10
15
20
0 20 40 60
Pressure,
cm
Time, Min
Flux
0.00E+00
5.00E-03
1.00E-02
1.50E-02
2.00E-02
2.50E-02
3.00E-02
3.50E-02
0 20 40 60
Flux,
cm
s-1
Time, Min

21. MEASURING KFS
DUAL-HEAD ANALYSIS METHOD
SATURO
• Water level is electronically
controlled
• Stepper motor pump accurately
measures infiltration rate
• Controlled air pressure in chamber
simulates different ponding depths

22. SATURO
AUTOMATED, ACCURATE SATURATED
HYDRAULIC CONDUCTIVITY
Pressure Infiltrometer
• Fully automated measurements
• Vastly reduced water requirements
• Improved portability
• Allows broad range of infiltration rates
• Automatically calculates Kfs
Enter
BACK
POWER / MENU

23. SATURO
FIELD SETUP
INSTALL RING

24. SATURO
FIELD SETUP
ATTACH CHAMBER

25. SATURO
FIELD SETUP
CONFIGURE TEST

26. MEASURING KFS
SATURO – FLUX DATA
0.00E+00
2.00E-03
4.00E-03
6.00E-03
8.00E-03
1.00E-02
1.20E-02
1
5
9
13
17
21
25
29
33
37
41
45
49
53
57
61
65
69
73
77
81
85
89
93
97
101
105
109
113
Flux
(cm/s)
Time (min)
Kfs =
Δ(i1 −i2 )
D1 − D2

27. COMPARISON STUDY
METHODOLOGY
METER Group soccer field
• Soil Type: Palouse silt loam
• NRCS infiltration values
• 7 measurement locations

28. COMPARISON STUDY
INSTRUMENTS
Double-ring infiltrometer SATURO infiltrometer

29. COMPARISON STUDY
RESULTS
Location Double Ring Kfs SATURO Kfs Δ Kfs
cm/hr cm/hr cm/hr
SF 1 21.27 18.1 -3.19
SF 2 20.43 11.4 -9.05
SF 3 1.23 62.6 61.41
SF 4 1.49 44.3 42.79
SF 5 6.07 7.6 1.48
SF 6 2.82 1.3 -1.50
SF 7 1.69 3.4 1.67

30. COMPARISON STUDY
RESULTS
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0
DOUBLE-RING
INFILTROMETER,
CM/HR
SATURO INFILTROMETER, CM/HR

31. CONCLUSIONS
• METER makes soil physics easier
• Infiltration measurement is now easy and accurate
• Both saturated and unsaturated hydraulic conductivity are now
easily and accurately measured in the lab and in the field

32. QUESTIONS?
Gaylon S. Campbell, PhD
Senior Scientist
METER Group, Inc.
2365 NE Hopkins Ct, Pullman, WA 99163
T 509.332.5600
E support.environment@metergroup.com
W www.metergroup.com