Fig. 4. The van Genuchten function of Eq. [9]. This function has exactly zero slope at x = 0 and at x = 
. The dashed straight lines represent the limiting case of d = 0.
Fig. 4. The van Genuchten function of Eq. [9]. This function has exactly zero slope at x = 0 and at x = . The dashed straight lines represent the limiting case of d = 0.