Spatial variability of soil texture fractal dimension and its application in sponge city construction

Accurate characterization of spatial variability of soil textures and their relationships with hydraulic properties is essential for the planning, design, and construction of sponge cities. This study explored effective approaches for characterizing the spatial variability of soil textures and determining the soil hydraulic parameters in the sponge cities by using fractal theory and geostatistics. The results show that soil particle sizes in the study area are mainly distributed between 0.002 and 0.5 mm, with silt being the dominant fraction. The fractal dimensions (D values) of soil particle size distribution (PSD) ranged from 2.07 to 2.71, with an average of 2.50. The Semi-variogram models, including the spherical and Gaussian models were found suitable for soil D values at different depths. The spatial distribution of soil D values was illustrated in a three-dimensional model, and the fractal model of soil water characteristic curves was established to understand the soil infiltration and storage capacities. Overall, this research demonstrates that fractal theory provides an efficient approach to characterize the spatial distribution of soil PSD and establish the relationship between soil D values and hydraulic parameters, offering a scientific basis for planning and construction of sponge city not only in China, but also in similar regions worldwide.