- To explain the dynamic behavior of the matric potential at the wetting front of gravity
driven fingers, we take into account the pressure across the interface that is not continuous
and depends on the radius of the meniscus, which is a function of pore size and the dynamic
contact angle θ[subscript d] • θ[subscript d] depends on a number of factors including velocity of the water and can
be found by the Hoffman-Jiang equation that was modified for gravity effects. By assuming
that water at the wetting front imbibes one pore at a time, realistic velocities are obtained
that can explain the capillary pressures observed in unstable flow experiments in wettable
and water repellent sands.