Soil Water Retention, based on the van Genuchten's (1980) formula
Function to calculate the soil water content based on the van Genuchten's (1980) formula:
θ = θ_R + (θ_S - θ_R)(1 + (α x)^n)^{-m}
soilwater(x, theta_R, theta_S, alpha, n, m = 1 - 1/n,
saturation.index = FALSE)x |
the matric potential. |
theta_R |
the residual water content. |
theta_S |
the water content at saturation. |
alpha |
a scale parameter of the van Genuchten's formula. |
n |
a shape parameter in van Genuchten's formula. |
m |
a shape parameter in van Genuchten's Formula. Default is 1-1/n (Mualem, 1976). |
saturation.index |
logical; if FALSE (default) the outcome is the soil water content, otherwise the saturation index is returned. |
The the soil water content or the saturation index (a value between 0 and 1).
Anderson Rodrigo da Silva <anderson.agro@hotmail.com> (code adapted from the function swc(), package soilwater (Cordano et al., 2012).)
Genuchten, M. T. van. (1980). A closed form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Science Society of America Journal, 44:892-898.
Mualem, Y. (1976). A new model for predicting the hydraulic conductivity of unsaturated porous media. Water Resources Research, 12:513-522.
# example 1 soilwater(x = 0.1, theta_R = 0.06, theta_S = 0.25, alpha = 21, n = 2.08) curve(soilwater(x, theta_R = 0.06, theta_S = 0.25, alpha = 21, n = 2.08)) # example 2 (punctual predictions) p <- seq(0, 1, length.out = 10) m <- soilwater(x = p, theta_R = 0.06, theta_S = 0.25, alpha = 21, n = 2.08) points(m ~ p, type = "b", col = "red") # End (not run)
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