Drainage of Soil Profiles

The scaled approximations of Brooks and Corey for water content versus capillary pressure and capillary conductivity versus water content were used to obtain a scalded diffusion function that was dependent only upon the pore-size distribution index, λ. A predictor-corrector finite difference scheme was used to obtain numerical solutions for the scaled differential equation for drainage from vertical soil columns. Results of several numerical solutions were presented for two soil profiles and for two greatly different pore-size distributions. The effects of soil hydraulic properties upon drainage were discussed and used to interpret the term field capacity. Experimental data obtained by several independent investigators were compared with theoretical solutions of discharge as a function of time using the Brooks-Corey approximations. The comparisons between experiment and theory were reasonable and some explanations for lack of agreement were presented.