VIC Model - Soil Texture

Sample Index of Soil Hydraulic Properties*

USDA Class Soil Type % Sand % Clay Bulk Density Field Capacity Wilting Point Porosity Saturated Hydraulic Conductivity Slope of Retention Curve (in log space) b
g/cm3 cm3 cm3 fraction cm/hr
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