Abstract
Analytical solutions are usually easy to apply and useful to understand processes. Unfortunately the non-linearity of Richard's equation restricts exact solutions to a few soil-water diffusivities. A general superposition principle is presented here which can be applied for any appropriate soil-water diffusivity. The resulting solutions are, however, approximate and are applicable in general to describe processes lasting a short time only. For this reason the method seems ideally suited to describe the interaction of abrupt fronts with surfaces. Two examples are considered; one involving a plane front, the other a curved front, to illustrate the simplicity and accuracy of the method.