Numerical simulations have been performed to study flow and solute tra
nsport phenomena in strongly heterogeneous, variably saturated porous
media. Different saturation scenarios were applied varying from fully
saturated to highly unsaturated conditions, corresponding to different
infiltration rates into the soil. It was found that the solute travel
s along preferred flow paths, which may be called channels. The degree
of channeling, the location of channels, and the hydraulic properties
along channels are a function of the mean saturation in the flow doma
in. Strong channeling effects were obtained in both fully saturated an
d in low-saturation cases. At intermediate saturation values, channeli
ng effects are less significant, and the system exhibits a more homoge
neous flow pattern. The dispersion of solutes as shown in the calculat
ed tracer breakthrough curves essentially reflects the degree of chann
eling and thus is saturation dependent; in cases when flow channeling
is less evident we observe much smaller dispersion than in cases with
strong channeling. The hydraulic properties of the channels appeared t
o be an invariant of the actual location and geometry, indicating that
they may be an intrinsic characteristic of the soil heterogeneity and
the water saturation.