SSgard {HydroMe}R Documentation

A selfstarting function to estimate hydraulic parameters in the Gardners retention model

Description

This selfstarting function estimates the water retention parameters contained in the Gardners function. It has an initial attribute that creates initial estimates of the parameters Thr, Ths, alp, and scal

Usage

SSgard(input, Thr, Ths, alp, scal)

Arguments

input A numeric vector of the suction potential
Thr A numeric parameter representing the residual moisture content
Ths A numeric parameter representing the saturated moisture content
alp A numeric parameter representing the inverse of air-entry potential
scal A numeric parameter representing the pore-size distribution index

Details

The dataset should contain a column for logarithm of suction potential, taking care to place a very small numer for log (x) whenever x is zero. The function estimates the parameters in two parts: when the product of alp and input is less than or eaual to unity and when this quantity is geater than unity

Value

numeric vector of the same length as input. It is the value of the expression Thr+(Ths-Thr)/(1+(alp*input^scal)) . It represents the fitted estimates of moisture contents using the Gardners model

Note

If the model returns negative values for residual moisture content, a zero value should be dopted for that residual moisture content. Also, if the model fails to converge, one may need to adjust the controls. It is also important to note that some datasets do perform poorly with this function

Author(s)

Omuto, Christian Thine

References

Gardner, W.R., 1958 Some steady state solutions of the unsaturated moisture flow equation with application to evaporation from a water table Soil Science, 85, 228-232

See Also

SSvan, SSbrook, SScamp

Examples

##-- Load pfdata--
data(pfdata)
gard.nlis <-nlsList(y~SSgard(x, Thr, Ths, alp, scal)|Level, data=pfdata)
cor(fitted(gard.nlis),pfdata$y, use="complete")^2 # To compute r^2

[Package HydroMe version 1.0 Index]