Abstract
The soil-water characteristic curve (SWCC) is the basis for obtaining the hydraulic conductivity parameters of a soil as well as for using soil water and heat transport models. At present, the curve can be obtained by two methods: by direct measurement and by empirical formula. Direct measurement is both difficult and time-consuming. By contrast, fitting the SWCC with a suitable empirical formula is stable and convenient. The van Genuchten (VG) model has the advantage of universal applicability due to its use of a statistical aperture distribution model for estimating hydraulic conductivity. This study selected the Mu Us Bottomland as a study area. Data on the water content and water potential of undisturbed soil from this site were obtained with a Ku-pF instrument and a self-designed soil column experiment with temperature settings of 13 °C, 18 °C, 23 °C, 27 °C, and 30 °C. The variation of four main parameters in the VG model with temperature was analyzed based on thermodynamic theory and considering the effect of temperature on soil capillary pressure via its effects on surface tension and contact angle. A prediction model for the soil-water characteristic curve of the Mu Us Bottomland was then constructed, and its applicability was further analyzed. The temperature dependence of the SWCC demonstrated here provides an important scientific basis for agricultural production, farmland water conservancy, and the design of soil and water conservation engineering projects.
Highlights
The soil moisture characteristic curve (SWCC) indicates the moisture retention and transport characteristics of a soil
The objectives of this study were : (i) to acquire the soil-water characteristic curve (SWCC) of soil at different temperatures by two types of experiment, a soil column experiment and Ku-pF unsaturated hydraulic conductivity measurement; (ii) to analyze changes to the various parameters in the van Genuchten (VG) model that resulted from the effects of temperature on soil capillary pressure via its effect on both the surface tension and the contact angle and construct a prediction model for the Mu Us bottomland; (iii) to evaluate the SWCC model for unsaturated hydraulic conductivity at different temperatures
Since the SWCC cannot be directly derived from theory, scholars have generally used various empirical formulas to describe it such as the Brooks–Corey model [28], Gardner model [29], van Genuchten model [30], Russo model [31], and Fredlund and Xing model [32]
Summary
The soil moisture characteristic curve (SWCC) indicates the moisture retention and transport characteristics of a soil. Changes in soil temperature and water content can lead to the occurrence of frost heave, bank collapse, masonry cracking, and other diseases in a water conservancy project [6,7,8,9,10]. It is of great theoretical and engineering significance to study the effect of temperature on the SWCC of unsaturated soil. Philip and de Vries [13] established a relationship between suction and temperature change based on the Laplace equation, and Wang et al [14] and Tong [15] derived the effect of temperature on a SWCC model theoretically.
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