Parameter constraints on closed-form soilwater relationships

Modeling effect of initial soil moisture on sorptivity and infiltration

“…[18] The van Genuchten-Burdine model has been shown to be more accurate for fine-textured soils (with low values of m) [Fuentes et al, 1992]. However, the van GenuchtenMaulem model enjoys widespread usage, serving as the basis for equation (5) and for numerical simulation models such as HYDRUS-1D [Simunek et al, 2005].…”

“…[50] Again, we will focus on seven distinct soil types, whose properties were characterized by Fuentes et al [1992] (Table 3). Looking at initially dry soil conditions (Â 0 ¼ 0), subtle differences are seen in the wetting front potential contour lines predicted by equations (12) and (27) ( Figure A1).…”

“…For finetextured soils with wide pore size distributions (low values of m), however, the models begin to diverge, which can have significant consequences on predicted wetting front potential. The van Genuchten-Burdine retention model has previously been demonstrated to be more accurate in soils with low m values [Fuentes et al, 1992], while the van Genuchten-Maulem retention model has previously been more widely used, resulting in a number of relevant and practical applications. We will leave it to the reader, then, to decide which model to employ based on his/her specific intent and desired outcome.…”

“…For one-dimensional vertical infiltration, C is proportional to the soil's saturated hydraulic conductivity (K s ). The ratio C/K s is 1, depending on soil type and soil moisture [Philip, 1990], with proposed ranges of 1/3 C/K s 2/3 [Fuentes et al, 1992] or 0.3 C/K s 0.4 [Philip, 1990]. In the case of three-dimensional infiltration, C incorporates both saturated hydraulic conductivity and sorptivity [Smettem et al, 1995;Touma et al, 2007].…”

A Review of Approaches for Measuring Soil Hydraulic Properties and Assessing the Impacts of Spatial Dependence on the Results

“…Through an extensive study, Fuentes et al (1992) concluded that only the combination of the van Genuchten water retention equation (equation 2A), h(), based on the Burdine theory (m=1-2/n) together with the Brooks and Corey conductivity equation (Equation 5A) stays valid for all different types of soil encountered in practice without becoming inconsistent with the general water transfer theory. This is due to the rather limiting constraint which exists for shape parameter m when using the Mualem theory : 0.15 ≤m≤1 Even though the residual water content ( r ) has a well-defined physical meaning, the parameter  r , which enters in equations (1A) to (5A) is somewhat of a misnomer because it usually behaves as a pure fitting parameter without any physical meaning.…”