COMPARING EXACT AND NUMERICAL-SOLUTIONS OF RICHARDS EQUATION FOR ONE-DIMENSIONAL INFILTRATION AND DRAINAGE

Analytical solutions to Richards' equation are valuable in testing num erical models of water movement in soils, but few such solutions are a vailable, especially for general soil hydraulic properties. We present such a solution, valid for restricted boundary conditions during infi ltration and drainage, and illustrate its use by comparing numerical a nd analytic solutions. In the case of infiltration the solution is bas ed on an earlier result which is extended here to describe drainage fr om soil with a uniform initial water content. Accurate numerical solut ions could be obtained with a coarse spatial grid of eleven points.