SSvgm: A five-parameter van Genuchten water retention model

In HydroMe: Estimating Water Retention and Infiltration Model Parameters using Experimental Data

A five-parameter van Genuchten water retention model

Description

This is a five- parameter function to determine water retention hydraulic parameters contained in the van Genuchten water retention model

Usage

SSvgm(input, thr, ths, alp, nscal, mscal)

Arguments

input	Suction potential/head as contained in the x-column of the xy water retention table or data
thr	This is the residual moisture content. It's the moisture content when suction potential is very high (almost at the drying point)
ths	This is the saturated moisture content. It's the moisture content when suction potential is very low (almost at the saturation point)
alp	It's the inverse of air-entry potential or bubbling pressure
nscal	This is a parameter or index for the pore-size distribution
mscal	This is a scaling parameter which is also related to index for pore-size distribution

Details

Van Genuchten model is a type of self-starting nonlinear curve fitting model for fitting water retention characteristics using experimental data. In this model, the restriction of m=1-1/n has been relaxed so that m is estimated as an independent parameter of the water retention characteristics. If warnings are given during the estimation process, try to increase the iteration limit using control function. Sometimes the warnings can be suppressed using (warn=-1)/ignored since they do not terminate the process

Value

A list of objects returned by standard R regression functions such as nls and lm

Author(s)

Christian Thine Omuto

References

van Genuchten MT. 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Science Society of America Journal 44: 892-898

See Also

SSomuto, Brook, Campbel

Examples

data(isric)
library(minpack.lm)
pf1=subset(isric,Sample=="Nicaragua21")
suppressWarnings(
vn.ns <- nlsLM(y ~ SSvgm(x,thr,ths,alp,nscal,mscal),
               data = pf1,
               control = nls.lm.control(maxiter=200)))
coef(vn.ns)
plot(fitted(vn.ns)~pf1$y)
abline(a=0,b=1,lty=20, col="blue")

HydroMe documentation built on May 29, 2024, 9:35 a.m.