Zapata (2000) Estimation 
The Zapata (2000) estimation of the soilwater characteristic curve (SWCC) uses soil grain size properties to estimate the a, n, m, and h fitting parameters of the Fredlund and Xing (1994) equation. If a fine grained soil is selected then the wPI value is used to estimate the SWCC. If a coarse grained soil is selected then the D60 value is used to estimate the SWCC.
