January 27, 2020
by

### Soil Hydraulic Functions in R

#### Goodness of fit

#### Water Retention Functions

The *van Genuchten* (1980) model is the most widely used water retention curve function:

\[\Theta = \left( 1 +(\alpha \psi)^n\right)^{-m}\]

where the effective saturation is defined as: \(\Theta = (\theta - \theta_{r}) / (\theta_{s} - \theta_{r})\)

```
vG = function(h,a,n,ths,thr){
m = 1-1/n
Se = (1+(a*(h))^n)^(-m)
theta = thr+(ths-thr)*Se
# uncomment on the following two
#return(Se)
return(theta)
```

## NEw

**Fit parameters of van Gnuchten Model**