vg: R estimation of van Genuchten water retention curve and...

In gowusu/vadose: The estimation of saturated hydraulic conductivity and soil water retention Curves in the vadose zone

Description

This function estimate and optimise van Genuchten water retention and hydraulic conductivity.

Usage

vg(data = NULL, h, theta = NULL, thr = 0.1, ths = 0.1, alp = 0.1,
  n = 1, m = "m", Ks, para = NULL, group = NULL)

## Default S3 method:
vg(data = NULL, h, theta = NULL, thr = 0.1, ths = 0.1,
  alp = 0.1, n = 1, m = "m", Ks = "Nasta", para = NULL,
  group = NULL)

## S3 method for class 'vg'
predict(object, h = NULL, ...)

## S3 method for class 'vg'
plot(x, main = NULL, xlab = "Water Content",
  ylab = "Tension Head,h(cm)", ylab2 = "Hydraulic Conductivity, K (cm/day)",
  layout = NULL, kcol = "green", hcol = "black", hlog = NULL,
  klog = NULL, ...)

## S3 method for class 'vg'
summary(object, ...)

## S3 method for class 'vg'
print(x, ...)

## S3 method for class 'vg'
coef(object, ...)

Arguments

data	dataframe that contains pressure head "h" and the corresponding water content "theta"
h	character. The name of the pressure head as in the data parameter above.
theta	character. The name of the water content as in the data parameter above
thr	numeric. Residual volumetric soil water content. This can be calibrated.
ths	numeric. The saturated soil water content [m3/m3].
alp	van Genuchten water retention alpha parameter
n	numeric. A shaping parameter for water retention curve. This can be calibrated. If the parameter "PSD" is not set NULL lass3 will be automatically used to estimate it.
m	character. The water retention curve condition. It takes either "b" for Burdine condition or "m" for Mualem condition.
Ks	saturated hydraulic conductivity
para	character. This is useful if the function is used for estimation instead of optimisation. It can be combined with Ks parameter to retrieve hydraulic parameters from Carsel&Parrish (1988). If para is set to "soil" and Ks is set to "Clay", the parameters of clay soil from Carsel&Parrish (1988) will be used for estimation. see example below.
group	character. The name of the group variables if the data is from different areas.
object	Model output object
...	Any other graphical parameter
x	a return object of the function.
main	Title of the plot
xlab	x label of the plot
ylab	y label of the plot
ylab2	y label of the second plot (K)
layout	plot layout
kcol	colour of hydraulic conductivity
hcol	colour of pressure head
hlog	TRUE or FALSE. Whether metric potential should be log transformed
klog	TRUE or FALSE. Whether hydraulic conductivity should be log transformed

Value

optimised parameters

• Ks saturated hydraulic conductivity [LT^-1]

• mod_theta,mod_thetal,mod_thetay,mod_thetab: The estimated soil water content at different metric potentials

• theta: The observed soil water content at different metric potentials

• K: The unsaturated hydraulic conductivity [LT^-1]

• se: effective saturation

• thr optimised residual water content[LTLT^-1]

• ths optimised saturated water content[LTLT^-1]

• alp optimised alpha value

• n optimised n shaping parameter

• Kr The ratio of K and Ks

Author(s)

George Owusu

References

• van Genuchten, M. T. (1980). A Closed-form Equation for Predicting the Hydraulic Conductivity of Unsaturated Soils1. Soil Sci. Soc. Am. J., 44(5), 892-898. doi: 10.2136/sssaj1980.03615995004400050002x

• Carsel, R. F., & Parrish, R. S. (1988). Developing joint probability distributions of soil water retention characteristics. Water Resour. Res., 24, 755-769.

Examples

## Not run: 
 #optimisation with single data
datartc=read.csv(system.file("ext","sys","retentionVG.csv",package="vadose"))
modrtc<-vg(data=datartc,h="h",theta="theta",thr=0.1, ths=0.1, alp=0.1, n=1)
plot(modrtc)

#optimisation with group data isric

data=read.csv(system.file("ext","sys","isric2.csv",package="vadose"))
#optimisation with group data
#used public initials and multiple Ks
modisrc<-vg(data=data,h="x",theta="y",m="b",thr=0.1, ths=0.1, alp=0.1, n=1,group="Sample",
Ks=c("Sand","Clay","Silt","silty clay loam"),para="soil")
modisrc<-vg(data=data,h="x",theta="y",m="b",thr=0.1, ths=0.3, alp=0.01, n=2,group="Sample")
plot(modisrc)
mod=vg(h=200)

## End(Not run)

gowusu/vadose documentation built on May 17, 2019, 7:59 a.m.