Horizontal infiltration into wet soil

We obtain the long‐time asymptotic similarity solution for the wetting front for water absorption from a constant source into a homogeneous layer of soil with a preexisting moisture distribution. The presence of the initial water distribution in the soil introduces a time shift that advances the position of the wetting front. The time shift can be explicitly calculated for any form of diffusivity. A dynamic time shift is derived to yield a very efficient means for estimating the water content distribution and front position for all times in Brooks‐Corey‐type soil models.