# 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/cm^{3} |
cm^{3} |
cm^{3} |
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:**

- Bulk Density for the VIC model should be in kg/m
^{3}(g/cm^{3}* 1000 = kg/m^{3} - 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 cm
^{3}/cm^{3}by dividing the values by the fractional porosity in the table. - Saturated Hydraulic Conductivity for the VIC model is in mm/day (cm/hr * 240 = mm/day)
- 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`