The significance of hysteresis in modeling solute transport in unsaturatedporous media

Previous investigations disagree as to the appropriateness of neglecting hy steresis with regard to predicting solute transport under transient conditi ons, primarily because of the unique porous media and conditions used in th ese studies. In the present study, the significance of hysteresis in predic ting solute transport in the near-surface region is investigated using one- dimensional, homogeneous numerical experiments with a fully hysteretic now and transport model. The experiments involve introduction of a solute pulse , followed by intermittent cycles of infiltration, redistribution, and evap oration. Comparisons are made between transient hysteretic simulations and simulations ignoring hysteresis. Hysteretic and nonhysteretic simulations c onducted with porous media that have large differences between netting and draining characteristic curves exhibited the greatest variation in solute m igration behavior. Larger differences between maximum and minimum water con tents also produced greater impacts when hysteresis was considered However, the results indicate that the magnitude of the deviations between hysteret ic and nonhysteretic simulations is not a simple function of each independe nt parameter, but rather depends on the combined values of many or all of t he hydraulic parameters. As the solute travels further into the vadose zone , the effects of hysteresis are reduced. In general, hysteresis had a minor effect on solute transport in the systems considered in this work.