Measurement and Numerical Simulation of Hysteretic Flow in a Heterogeneous Porous Medium1

A finite difference solution of the Richards equation was tested experimentally for hysteretic flow in a nonuniform medium. The space-dependent hydraulic properties (water content-pressure head and hydraulic conductivity-water content) were determined experimentally on a laboratory column of sand and were represented in the numerical model by empirical equations. Boundary conditions resulting in hysteretic flow were applied to both the experimental column and the numerical model and the resulting water content and pressure head profiles were compared. Agreement was excellent between the measured and computed results. An additional simulation, in which the medium was considered to be nonhysteretic, gave good agreement between the measured and computed pressure head values but resulted in substantial error in the computed water content values.