Discrete Water Content Solution of the Infiltration Problem

Efficient and accurate simulation of the exchange between atmospheric, surface, and ground waters is essential in large-scale hydro-climatic models where high-resolution computational grids are not practical. This objective is met with a new and innovative method for simulating the entry and redistribution of water in the vadose zone using a discrete water content solution. Unlike infiltration predictors such as the solution of Richards' equation or approximations thereof, our method employs a novel discretization in terms of water content. An explicit relationship is used to describe water movement in each discrete water-content region of the pore space. Water is advanced according to capillary drive, and is re-distributed according to the capillarity of each region of discrete water content. Evapotranspiration removes water from the profile according to a root distribution. The linear-explicit nature of the computations provides for computational efficiency in both speed and the required resolution for numerical stability and accuracy. The finite volume solution methodology guarantees conservation of mass for all soil types and wetting front conditions.