Description Usage Arguments Details Value Author(s) References See Also Examples

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

1 | ```
Brook(x, thr, ths, alp, nscal)
``` |

`x` |
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 |

`nscal` |
This is a parameter or index for the pore-size distribution |

A Brooks-Corey model is a type of nonlinear curve fitting model for fitting water retention characteristics using experimental data. It requires initial parameter estimates for the model to work. This can be obtained using Dstart function (e.g. thr=Dstart(data)[1]). 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

A list of objects returned by standard R regression functions such as nls and lm

Christian Thine Omuto

Brooks RH and Corey AT.1964. Hydraulic properties of porous medium. Hydrology Paper Number 3. Colorado State University, USA

SSvgm, SSgard, Campbel

1 2 3 4 5 | ```
##Attach sample data (isric data) from the package
data(isric)
pf= subset(isric, Sample=="Benin2")
brook.ns=nlsLM(y~Brook(x,thr,ths,alp,nscal),data=pf, control=nls.lm.control(maxiter=200),start=c(thr=Dstart(pf)[1],ths=Dstart(pf)[2], alp=Dstart(pf)[3], nscal=Dstart(pf)[4]-1))
summary(brook.ns)## To produce a summary of modelling results
``` |

```
Loading required package: nlme
Loading required package: minpack.lm
Formula: y ~ Brook(x, thr, ths, alp, nscal)
Parameters:
Estimate Std. Error t value Pr(>|t|)
thr -1.820e+01 1.432e+03 -0.013 0.99
ths 2.673e-01 1.035e+04 0.000 1.00
alp 2.106e-01 7.425e+04 0.000 1.00
nscal 1.589e-03 1.232e-01 0.013 0.99
Residual standard error: 0.09488 on 4 degrees of freedom
Number of iterations till stop: 94
Achieved convergence tolerance: 1.49e-08
Reason stopped: Number of calls to `fcn' has reached or exceeded `maxfev' == 500.
```

HydroMe documentation built on May 29, 2017, 2:58 p.m.

Embedding an R snippet on your website

Add the following code to your website.

For more information on customizing the embed code, read Embedding Snippets.