Type curves and effective parameters for unsaturated flow systems with structured heterogeneities

Unsaturated flow simulation requires identification of soil parameters at length scales that usually subsume smaller-scale heterogeneities. The standard two-parameter constitutive model performs well for predictions of moisture plume evolution in homogeneous soils but may not be as successful in capturing the flow and dispersion of soil water in heterogeneous domains. The first step in evaluating the limitations of this model is to develop a clear understanding of the effects of the constitutive parameters on moisture plume evolution. One approach is to define type curves derived from multiple homogeneous simulations. These type curves are based on bulk measures of system behavior, suitable for comparison to responses of heterogeneous systems. Simulation results for a range of heterogeneities defined on a specific test system indicate that some heterogeneity patterns allow definition of effective parameters for use in the two-parameter constitutive model, while others do not. For those heterogeneity patterns, the mathematical structure of the governing equations applied at the large scale must have a form that is different from the equation that underlies the type curves.