Clapp and Hornberger (1978) representative soil hydraulic parameters by texture.¶
Source¶
Clapp, R. B., & Hornberger, G. M. (1978). Empirical equations for some soil hydraulic properties. Water Resources Research.
Scope¶
Territory: United States
Dataset: Desorption data reported by Holtan et al. (1968) for soils collected at 34 United States localities; 1,446 soils remained from an initial set of more than 1,800 after the exclusions described by the paper.
Functions¶
calc_ptf_clapp1978¶
Return representative soil hydraulic parameters for a USDA texture class.
Status: implemented
Prediction target: Representative moisture-characteristic exponent, saturation suction, wetting-front suction, saturated water content, saturated hydraulic conductivity, and sorptivity for a soil textural class.
Models: \(h(\theta)\) — Power-curve moisture characteristic with a parabolic gradual-air-entry section near saturation; \(k(h)\) — Campbell relative-conductivity power relation
Inputs¶
| Name | Type | Unit | Domain | Description |
|---|---|---|---|---|
soil_texture | UsdaTextureClass | — | — | USDA soil textural class used to select a row of Table 2. |
Outputs¶
| Name | Unit | Domain | Description |
|---|---|---|---|
b | 1 | value > 0 | Mean exponent of the moisture-characteristic power curve. |
saturation_suction | cm | value > 0 | Representative saturation suction, calculated as the antilog of the mean logarithm of fitted saturation-suction values. |
wetting_front_suction | cm | value > 0 | Representative Green-Ampt wetting-front suction. |
saturated_water_content | 1 | 0 < value < 1 | Mean saturated volumetric water content, taken as total porosity. |
saturated_hydraulic_conductivity | cm/min | value > 0 | Mean saturated hydraulic conductivity reported by Li et al. (1976). |
sorptivity | cm/min^(1/2) | value > 0 | Representative sorptivity for the paper's single initial moisture deficit corresponding to 500-cm initial suction. |
Note
The representative wetting-front suctions use an inflection wetness of 0.92 to model gradual air entry near saturation.
Note
The sorptivity values use the average saturated hydraulic conductivities reported by Li et al. (1976) and one initial moisture deficit at 500-cm suction.
Warning
The paper states that these unverified average values should not be used blindly because saturation suction varies substantially within texture classes.
Warning
Sorptivity values must be treated cautiously because the conductivity averages may not represent the same average soils as the other parameters.