Comparison of Fractal Geometry and Kriging Methods to Estimate the Effect of Length Scale on Dispersivity of Reactive Elements in Soil

Hydrodynamic dispersion rate of solutes in soil is considered as the major parameter for pollution and solutes transport in soil, which is related to pollutant transport distance. As fractal geometry theory and geostatistical theory are capable of explaining and predicting the distance-related phenomena, this research used fractal geometry and geostatistics method for determining dispersivity.
Solutes transport experiment was carried out at 16 points of soil vertical column with a diameter of 10 centimeters and a length of 1 meter and BTCs were extracted at the depth of 6, 12, 18, 24, 30, 36, 42, 54, 48, 60, 66, 72, 78, 90, 84, 96 centimeters from the model bottom. CDE equation was then fitted with the BTCs with respect to the fractal assumptions on dispersivity coefficients.
Findings: With respect to phosphorus absorption experiments in soil, phosphorus adsorption isotherm had the best fitting at 4, 12, 25, 50, 70 mg/l of phosphorus concentrations. The results showed that both methods are capable of predicting changes and increase of dispersivity coefficient in soil column after performing a mean-comparison test. However, fractal geometry method estimated values at a higher accuracy.
Discussion and Result showed that, dispersivity along the sample followed the exponential relation. The regression coefficients of the fractal and geostatistical models in predicting dispersivity values were 0.97 and 0.84, respectively.