Comparison of Fractal and Rosetta Approaches for Estimation of Soil Water Retention Curve

The van Genuchten (vG) function is often used to describe the soil water retention curve (SWRC) of unsaturated soils. The objective of this study was to evaluate a method to determine the vG model parameters m and α of 100 soil samples of Guilan province from the fractal dimension of SWRC. Also, we used two models introduced by Lenhard et al and vG for estimating m from pore size distribution index of Brooks and Corey (BC) model. In both of the mentioned methods, the relationship between pore size distribution index of BC and SWRC fractal dimension was used. Also, vG parameters using Rosetta software were estimated and then, the amounts of vG parameters from the Rosetta, fractal method and RETC were compared. Results showed that Rosetta software had a better estimation of vG parameters than the Rosetta. The estimated vG model parameters m and α obtained with the above-mentioned different methods, in conjunction with measured saturated water contents, were used to estimate water contents at different matric potentials and compared with determined values by RETC via fitting of vG model on the measured values. The estimated SWRC data via fractal method were compared with those obtained with the Rosetta model. Results showed that fractal method had more accurate performance for prediction of SWRC than the Rosetta. Even though, the Rosetta software could lead to better estimates of the vG model parameters than the fractal approach, it was not capable of predicting SWRC as accurately as the fractal approach. This is due to the fact that estimation of the water content is a result of an interaction between the estimated vG model parameters, α and m.