Soil Hydraulic Models
where (also for the equations below):
θs - saturated water content [-]
θr - residual water content [-]
α, m, n - empirical parameters [1/L], [-], [-]
hs - air-entry value [L]
Se - effective water content [-]
KS - saturated hydraulic conductivity [L/T]
Kr - relative hydraulic conductivity [-]
Kk (hk) - unsaturated hydraulic conductivity at pressure head hk [L/T]
When the van Genuchten model is used, either a non-hysteretic description, a hysteretic description only in the retention curve, or hysteretic descriptions in both the retention curve and the hydraulic conductivity curve can be used.
When one of the hysteretic descriptions is selected, then users must specify whether the initial condition is associated with the main wetting or the main drying retention curve.
Kosugi [1996] suggested using a lognormal distribution model as follows:
Applying Mualem's model, the hydraulic conductivity function becomes:
Durner [1994] divided the porous medium into two (or more) overlapping regions and suggested to use for each of these regions a van Genuchten-Mualem type function [van Genuchten, 1980] of the soil hydraulic properties. Linear superposition of the functions for each particular region gives then the functions for the composite multimodal pore system [Durner et al., 1999]:
where wi are weighting factors for the two overlapping regions, and αi, ni, mi (=1-1/ni), and l are empirical parameters of the separate hydraulic functions (i=1,2).
The Dual-Permeability module is activated when the "Dual-Permeability" check box is selected in the Soil Hydraulic Model window (above). Once this check box is selected, the edit box "Fraction of Boundary Flux into Fracture" appears. The value of this parameter can be specified by a user and should vary between 0 and 1. When 0 is specified, all water at boundaries with a specified boundary flux will enter into the matrix. When 1 is specified, all water at boundaries with a specified boundary flux will enter into the fracture domain.