SSbrook {HydroMe}R Documentation

Selfstarting function for estimating hydraulic parameters in the Brooks-Corey model

Description

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

Usage

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

Arguments

input A numeric vector of natural logarithm of the suction potentials.
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 product of alp and input is less than or eaual to unity and when this quantity is geater than unity

Value

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

Note

If the model returns negative values for the residual moisture content, a zero value should be dopted for this parameter. One may need to adjust the nls controls incase of convergence problems.It is also important to note that some datasets do perform poorly with this function

Author(s)

Omuto, Christian Thine

References

Brooks, R.H., Corey, A.T., 1964 Hydraulic properties of porous medium Hydrology Paper, Nr. 3 Colorado State University: fort Collins

See Also

SSvan, SSgard, SScamp

Examples

##---- Obtaine the data----
x <-c(0,log(10),log(31),log(100),log(200),log(500),log(2500),log(15000))# get log (x)
y <-c(0.362,0.353,0.294,0.230,0.206,0.182,0.148,0.136)
Brookdata <-data.frame(x,y)# make data frame
Brook.nls <-nls(y~SSbrook(x, Thr, Ths, alp, scal), Brookdata)# model for whole dataset
summary(Brook.nls)

[Package HydroMe version 1.0 Index]