Develop a Water Retention Curve from KSSL Data

Water retention curve modeling via van Genuchten model and KSSL data.

Usage

KSSL_VG_model(VG_params, phi_min = 10^-6, phi_max = 10^8, pts = 100)

Arguments

VG_params: data.frame or list object with the parameters of the van Genuchten model, see details
phi_min: lower limit for water potential in kPa
phi_max: upper limit for water potential in kPa
pts: number of points to include in estimated water retention curve

Value

A list with the following components:

VG_curve: estimated water retention curve: paired estimates of water potential (phi) and water content (theta)
VG_function: spline function for converting water potential (phi, units of kPa) to estimated volumetric water content (theta, units of percent, range: {0, 1})
VG_inverse_function: spline function for converting volumetric water content (theta, units of percent, range: {0, 1}) to estimated water potential (phi, units of kPa)

Details

This function was developed to work with measured or estimated parameters of the van Genuchten model, as generated by the Rosetta model. As such, VG_params should have the following format and conventions:

theta_r: saturated water content, values should be in the range of {0, 1}
theta_s: residual water content, values should be in the range of {0, 1}
alpha: related to the inverse of the air entry suction, function expects log10-transformed values with units of 1/cm
npar: index of pore size distribution, function expects log10-transformed values (dimensionless)

Note

A practical example is given in the fetchSCAN tutorial.

References

water retention curve estimation

Author

D.E. Beaudette

Examples


# basic example
d <- data.frame(
  theta_r = 0.0337216, 
  theta_s = 0.4864061, 
  alpha = -1.581517, 
  npar = 0.1227247
)

vg <- KSSL_VG_model(d)

str(vg)
#> List of 3
#>  $ VG_curve           :'data.frame':	100 obs. of  2 variables:
#>   ..$ phi  : num [1:100] 1.00e-06 1.38e-06 1.92e-06 2.66e-06 3.68e-06 ...
#>   ..$ theta: num [1:100] 0.486 0.486 0.486 0.486 0.486 ...
#>  $ VG_function        :function (x, deriv = 0L)  
#>  $ VG_inverse_function:function (x, deriv = 0L)