Direct determination of the Brooks–Corey hydraulic functions by fitting an extended power function to the outflow method data

A method is developed for the direct determination of the parameters characterizing the Brooks and Corey closed-form hydraulic functions (water retention curve and hydraulic conductivity function) using data obtained only from one-step outflow experiments. Simple algebraic equations are derived to calculate directly the Brooks and Corey model parameters. The only parameters involved in these equations are empirical parameters obtained by a simple curve-fitting procedure applied to the experimental outflow data for a simple three-parameter power form equation. In addition, the method requires the value of the water content obtained at the pressure head of −150 m. The suggested method is verified numerically by simulating a one-step outflow experiment of a hypothetical soil. The proposed method was also verified from one-step outflow experimental data. The predicted soil water retention curve is compared favorably with measured water retention data. The coefficient of determination R2 is greater than 0.87 in all cases examined.