Development of regional-scale relationship between fractal dimension and soil physical properties in the hetao irrigation district of China
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The soil water retention curve (SWRC) is the basic information for analyzing hydrologic processes in the vadose zone. In practice, however, it is very costly and time-consuming to develop this function experimentally. Empirical models have been developed to describe the SWRC. Applications of the fractal theory have provided a useful tool to fill the gap between the use of empirical models and physical interpretation of their parameters. Especially a more generalized model for the SWRC has been developed based on the pore-solid fractal (PSF) distribution. The PSF model covers several existing models as its special cases and theoretically provides a direct way to estimate the SWRC fractal dimension from particle size distributions (PSD). The field study was conducted in the 2.16105 ha Jiefangzha Irrigation Scheme (JFIS) of the Hetao Irrigation District (HTID) of Inner Mongolia, China. Across the JFIS, 110 undisturbed soil samples were randomly collected. The first objective of this study was to evaluate the SWRC estimation with the PSF distribution using the 110 PSD data sets collected from the HITD. The second objective was to establish a relationship between the fractal dimension and soil texture, saturated soil water content ( s), residual water content( r) and Van Genuchten model parameters ( and n) .Linear regressions of the predicted and measured SWRC showed good agreement. The results indicated that the fine-textured soils had higher values for PSF, while the coarse-textured soils had smaller values. This will provide a reliable method to determine soil properties and parameters of SWRC at regional scale in Hetao Irrigation District, which are very important for understanding the regional water and salt transport as well as for developing water management scenarios.
