SSgard: 'Gardner' Water Retention Model for Grouped Data

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

'Gardner' Water Retention Model for Grouped Data

Description

This is a four-parameter function to determine water retention hydraulic parameters contained in the Gardner water retention model

Usage

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

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
scal	This is a parameter or index for the pore-size distribution

Details

A Gardner model is a type of self-starting nonlinear curve fitting model for fitting water retention characteristics using grouped experimental data. 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

Gardner WR. 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

SSomuto, SSvgm, Campbel

Examples

data(isric)
isric1 <- isric[1:32,]
library(nlme)
library(minpack.lm)
gardner <- nlsLM(y ~ SSgard(x,thr,ths,alp,nscal), isric1)
gardner
gard <- nlsList(y ~ SSgard(x,thr,ths,alp,scal) | Sample, isric1)
coef(gard)

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