SAMPLE INDEX OF SOIL HYDRAULIC PROPERTIES*

USDA Class

Soil Type

% Sand

% Clay

Bulk Density

g/cm3

Field Capacity

cm3/cm3

Wilting Point

cm3/cm3

Porosity

fraction

Saturated Hydraulic Conductivity

cm/hr

Slope of Retention Curve (in log space) b**

1

s

94.83

2.27

1.49

0.08

0.03

0.43

38.41

4.1

2

ls

85.23

6.53

1.52

0.15

0.06

0.42

10.87

3.99

3

sl

69.28

12.48

1.57

0.21

0.09

0.4

5.24

4.84

4

sil

19.28

17.11

1.42

0.32

0.12

0.46

3.96

3.79

5

si

4.5

8.3

1.28

0.28

0.08

0.52

8.59

3.05

6

l

41

20.69

1.49

0.29

0.14

0.43

1.97

5.3

7

scl

60.97

26.33

1.6

0.27

0.17

0.39

2.4

8.66

8

sicl

9.04

33.05

1.38

0.36

0.21

0.48

4.57

7.48

9

cl

30.08

33.46

1.43

0.34

0.21

0.46

1.77

8.02

10

sc

50.32

39.3

1.57

0.31

0.23

0.41

1.19

13

11

sic

8.18

44.58

1.35

0.37

0.25

0.49

2.95

9.76

12

c

24.71

52.46

1.39

0.36

0.27

0.47

3.18

12.28

* Source is "Average hydraulic properties of ARS soil texture classes," draft dated February, 2000 by J. Schaake. This expanded the work of others and included a total of 2128 soil samples. Wilting point is the fractional water content at 15 bar tension; field capacity is the fractional water content at 1/3 bar tension.

**b is as used in Campbell's equation. ref: Cosby et al., A Statistical exploration of the relationships of soil moisture characteristics to the physical properties of soils, Water Resources Research 20(6): 682-690, 1984.

Note that units in this table differ from those used in the VIC model. In particular:

  1. Bulk Density for the VIC model should be in kg/m3 (g/cm3 * 1000 = kg/m3)

  2. Field Capacity and Wilting Point for the VIC model are described as a fraction of the maximum moisture, where the maximum moisture for each soil layer is the depth times the porosity. This can be obtained from the above data in cm3/cm3 by dividing the values by the fractional porosity in the table.

  3. Saturated Hydraulic Conductivity for the VIC model is in mm/day (cm/hr * 240 = mm/day)

  4. By default, VIC uses the Brooks-Corey relationship for unsaturated flow. The Brooks-Corey exponent, n, can be estimated from the slope of the Retention Curve (in log space), b, in the table above by: n = 3 + 2b