Simultaneous scaling of soil water retention and unsaturated hydraulic conductivity functions assuming lognormal pore-size distribution

Using simultaneous scaling, soil spatial variability of hydraulic functions can be described from a single set of scaling factors. The conventional sc aling approach is based on empirical curve fitting, without paying much att ention to the physical significance of the scaling factors. In this study, the concept of simultaneous scaling of the soil water retention and unsatur ated hydraulic conductivity functions is applied to a physically based scal ing theory. In this approach, it is assumed that soils are characterized by a lognormal pore-size distribution, which leads directly to lognormally di stributed scaling factors. To test this concept, a total of 143 undisturbed soil samples were collected from two soil depths (25 and 50 cm), with each depth divided into two subsets based on the median soil capillary pressure head value, as determined from the lognormal pore-size distribution assump tion. Moreover, the theory was compared with the conventional simultaneous scaling method. Both the conventional and physically based simultaneous sca ling method performed equally well for all four subsets, as determined from the reduction in weighted root mean squared residual (WRMSR) values after scaling. We showed that the theoretical interpretation of the lognormal sca ling factor distribution was applicable to simultaneous scaling of soil hyd raulic functions. (C) 2001 Elsevier Science Ltd. All rights reserved.