EVALUATION OF THE EFFECT OF MORPHOLOGICAL FEATURES OF FLOW PATHS ON SOLUTE TRANSPORT BY USING FRACTAL DIMENSIONS OF METHYLENE-BLUE STAINING PATTERN

Fractal dimensions of methylene blue staining patterns in five undisturbed soil columns were used to explain solute transport in five soils. Columns, 15 cm in diameter and 15 cm in height, were taken from each B or BC horizon of a Brown Forest soil (BFS), a Dark Red soil (DRS), a Pseudogley (PSG), a Brown Andosol (ADO) and a Volcanogenous Regosol (VRS). Fractal dimensions of stains were related to Brenner numbers of chloride breakthrough measured under a saturated steady-state condition in each column. The Brenner number was smaller in columns showing the most rapid initial elevation of concentration. The degree of the effect of the macropore was in the order of DRS>PSG>VRS>BFS>ADO. The fractal dimension of the internal structure of staining patterns (D(s)), decreased with an increase in depth, ranging from 0. 59 to 2.0. A value less than 1 was obtained for stains found in parts of cracks and in root channels in the deeper layers of DRS and PSG columns, while a value greater than 1.7 was obtained for large stains found throughout the ADO column. On the other hand, the fractal dimension of the perimeter of stains (D(pe)) was estimated to be almost the same through each column; the depth average ranged from 1.30 for ADO to 1.64 for VRS. Smaller values of D(pe) indicated that the stained parts had smoother boundaries. An empirical equation, which explains the Brenner number (B) for chloride breakthrough as a function of depth averages of both fractal dimensions and macroporosity (theta(m)), was obtained as follows: B=a-theta(m)-DsBAR+bD(pe)BAR + c When D, was taken to be the average value of D(s) obtained in the lower half of each column, the relation regressed with a correlation coefficient of 0.9995. This equation suggests that the macropore flow contributes significantly to miscible displacement and that this contribution depends on the internal structure of the stains and on the smoothness of their boundaries.