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

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