soilphysics (version 5.0)

soilwater: Soil Water Retention, based on the van Genuchten's (1980) formula

Description

Function to calculate the soil water content based on the van Genuchten's (1980) formula: $$\theta ={\theta }_R+({\theta }_S-{\theta }_R)(1+(\alpha x{)}^n{)}^{-m}$$

Usage

soilwater(x, theta_R, theta_S, alpha, n, m = 1 - 1/n,
    saturation.index = FALSE)

Arguments

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.

Value

The the soil water content or the saturation index (a value between 0 and 1).

References

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.

See Also

fitsoilwater

Examples

# NOT RUN {
# 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)
# }