Scaling Factors

HYDRUS implements a scaling procedure designed to simplify the description of the spatial variability of the unsaturated soil hydraulic properties in the flow domain (only for two-dimensional applications). The code assumes that the hydraulic variability in a given area can be approximated by means of a set of linear scaling transformations which relate the individual soil hydraulic characteristics θ(h) and K(h) to reference characteristics θ*(h*) and K*(h*). The technique is based on the similar media concept introduced by Miller and Miller [1956] for porous media which differ only in the scale of their internal geometry. The concept was extended by Simmons et al. [1979] to materials which differ in morphological properties, but which exhibit 'scale-similar' soil hydraulic functions. Three independent scaling factors are embodied in HYDRUS. These three scaling parameters may be used to define a linear model of the actual spatial variability in the soil hydraulic properties [Vogel et al., 1991] in which, for the most general case, aθ, ah and aK are mutually independent scaling factors for the water content, the pressure head and the hydraulic conductivity, respectively. Less general scaling methods arise by invoking certain relationships between aθ, ah and/or aK. For example, the original Miller-Miller scaling procedure is obtained by assuming aθ=1 (with θr* = θr), and aK=ah-2. A detailed discussion of the scaling relationships and their application to the hydraulic description of heterogeneous soil profiles, is given by Vogel et al. [1991].

The scaling factors can be randomly generated using the Stochastic Distribution of S.F. command from the Edit menu.