Improved Prediction of Unsaturated Hydraulic Conductivity with the Mualem‐van Genuchten Model

Abstract

In many vadose zone hydrological studies, it is imperative that the al., 1998). Far fewer alternatives exist for unsaturated soil's unsaturated hydraulic conductivity is known. Frequently, the Mualem-van Genuchten model (MVG) is used for this purpose be-hydraulic conductivity. Although some pedotransfer cause it allows prediction of unsaturated hydraulic conductivity from functions are available (Saxton et al., 1986; Schuh and water retention parameters. For this and similar equations, it is often Bauder, 1986; Vereecken et al., 1990), pore-size distriassumed that a measured saturated hydraulic conductivity (K s) can bution models by Burdine (1953) and Mualem (1976), be used as a matching point (K o) while a factor S L e is used to account among others, are more popular. for pore connectivity and tortuosity (where S e is the relative saturation Generally speaking, the Burdine and Mualem models and L ϭ 0.5). We used a data set of 235 soil samples with retention infer the pore-size distribution of a soil from its water and unsaturated hydraulic conductivity data to test and improve preretention characteristic. By making assumptions about dictions with the MVG equation. The standard practice of using K o ϭ continuity and connectivity of pores, integral expres-K s and L ϭ 0.5 resulted in a root mean square error for log(K) sions can be derived that describe unsaturated conduc-(RMSE K) of 1.31. Optimization of the matching point (K o) and L to the hydraulic conductivity data yielded a RMSE K of 0.41. The fitted tivity in terms of water content or pressure head. A K o were, on average, about one order of magnitude smaller than general expression can be given as (after Hoffmannmeasured K s. Furthermore, L was predominantly negative, casting Riem et al., 1999): doubt that the MVG can be interpreted in a physical way. Spearman rank correlations showed that both K o and L were related to van

A simple model for describing hydraulic conductivity in unsaturated porous media accounting for film and capillary flow

“…In the Mualem model [Mualem, 1976a] t = 0.5, k = 1, and b = 2, whereas in the model of Alexander and Skaggs [1986] t = 1, k = 1, and b = 1. The parameter t in the Mualem model is often treated as a free fitting parameter [Hoffmann-Riem et al, 1999] that is frequently negative, and thus its physical meaning is questioned [Schaap and Leij, 2000]. These models were all derived to describe the capillary fluid flow in porous media.…”

A Modified van Genuchten-Mualem Model of Hydraulic Conductivity in Korean Residual Soils

“…On the other hand, many studies examined a range of values of the tortuosity parameter in the fit of the actual data [4,[22][23][24], which is frequently negative [25]. The parameter, q, was estimated to be −1.5-−4.3 (−3.2 in average) in Table 2, which was obtained directly from the experimental data for Korean residual soils.…”

Research Note:Determination of soil hydraulic properties using pedotransfer functions in a semi-arid basin, Turkey

“…Since in contrast to Type 2, Type 3 PTFs usually predict parameters in models describing the complete q-h-K relationship. The determinations were performed using the PTFs provided by Rosetta (Schaap and Leij, 2000); this package offers five pedotransfer functions (PTFs) that allow the prediction of the hydraulic properties from limited or more extended sets of input data (Schaap et al, 1998). The first model (H1) uses USDA soil textural classes.…”

“…The other four models (H2 to H5) are based on neural network analyses and provide more accurate predictions when measurements of more input variables are available. In addition to the hierarchical approach, a model (Schaap and Leij, 2000) that allows the prediction of unsaturated hydraulic conductivity parameters from fitted van Genuchten (1980) retention parameters was used to explore the variation of K with q. It is also possible to estimate the van Genuchten (1980) water retention parameters (q r , q s , a, n), the saturated hydraulic conductivity (K s ) and the unsaturated hydraulic conductiva:ity K (h) based on Mualems pore pressure distribution model.…”