Efficient calculation of solute transport in heterogeneous soils exhibiting non-Richards-type unsaturated flow

Soil heterogeneity hampers our ability to calculate field-scale solute leac hing, Many of the existing field-scale modeling attempts are laborious, tim e consuming, and computationally demanding. Non-Richards-type flow (e.g., f ingering) cannot be handled by methods based solely on the heterogeneity of the soil hydraulic properties. We developed a time- and cost-effective app roach that starts with a plot-scale solute transport model that must incorp orate any special flow features in the field of interest. The field was mod eled as an ensemble of plot-scale columns with random properties. The compu tational demand was reduced by: (i) simplifying the plot-scale model; (ii) keeping only the most influential parameters stochastic; (iii) replacing a full Monte Carlo simulation by systematic parameter sampling; and (iv) tran sforming the model output for one column to that of another where possible. The method was demonstrated for a field exhibiting fingered flow in the to psoil. A recently developed model to calculate solute leaching front a sing le finger served as the column-scale model. Three parameters appeared to be key for solute leaching to the groundwater. For two of them, the breakthro ugh curve for one value of the parameter could be transformed to approximat e the curve for all other values. Consequently, field-scale solute leaching could be computed with <20 model runs.