One of the saturation from resistivity models:
| (1) | \frac{1}{R_t} = \frac{\phi_e^m \, s_w^n}{A R_w (1-V_{sh})} + \frac{V_{sh}}{R_{sh}} s_w^{n/2} \quad \Rightarrow \quad s_w^{n/2} = \frac{A R_w (1-V_{sh})}{2 \phi_e^m} \, \left( \sqrt{ \left( \frac{V_{sh}}{R_{sh}} \right)^2 + \frac{4\phi_e^m}{a R_t R_w (1-V_{sh}) } } - \frac{V_{sh}}{R_{sh}} \right) |