Sensitivity Analysis of Infiltration, Exfiltration, and Drainage in Unsaturated Miller‐Similar Porous Media

The effects of soil heterogeneity on the transport of moisture in the unsaturated zone are studied by means of functional sensitivities, which are more suitable than elementary (or conventional) sensitivities for analyzing continuous systems. The earlier described algorithm is applied to three problems, drainage, infiltration, and exfiltration, for two Miller‐similar soils (a randomly generated heterogeneous Yolo light clay and a homogeneous one). It reveals the difference between drainage, on the one hand, and both infiltration and exfiltration on the other. The scaled flux sensitivity profiles, i.e., the functional derivatives of fluxes with respect to Miller‐similarity parameter λ( x ), are flat for drainage, demonstrating that drainage is equally sensitive to changes in λ( x ) at all points of the profile and hence that the similarity parameter has to be modeled well in the whole soil column. Analogous sensitivity profiles for infiltration and exfiltration problems show, significant delay in propagation of functional sensitivities in the soil column (with respect to the moisture front), allowing thus for less stringent modeling of the similarity parameter for the bottom of the column. Infiltration problems seem to be most difficult to deal with, because they are most sensitive to the similarity parameter.