As. Elhames et Ks. Richards, TESTING THE NUMERICAL DIFFICULTY APPLYING RICHARDS EQUATION TO SANDY AND CLAYEY SOILS, Journal of hydrology, 167(1-4), 1995, pp. 381-391
In this paper numerical tests are performed to assess the numerical di
fficulty, defined as the number of iterations per time increment, when
using the Richards' equation to determine infiltration and moisture r
edistribution in the unsaturated zone. The results suggest general gui
delines for researchers dealing with these problems, although specific
examples are employed in the tests.