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Abstract The hydraulic function of three types of macropores during saturated flow through four swelling fine clayey and very fine clayey soil horizons was characterized with methylene blue as a tracer, and was quantified in large thin sections with the Quantimet 720. All three types of macropores, described as channels, vughs, and planar voids, contributed to flow. Distinction between “smooth” and “rough” ped faces in field structure descriptions proved meaningful for three soils with high linear extensibility values, because vertical flow did not occur along interconnected planar voids adjacent to “smooth” peds, whereas it did occur along “rough” peds. However, flow did occur along “smooth” ped faces in the fourth soil, which had significantly lower extensibility values. Calculations of hydraulic conductivity K sat , based on the observed dye patterns, are difficult because the dye solution flowed in interrupted patterns along the walls of the macropores without apparently filling them, due to the occurrence of smaller pore “necks” in overlying soil. But the number and percentages of colored pores for each of the three macropore‐types showed (with one exception for planar voids) consistant differences among the four soils, which corresponded with differences in measured K sat values.
Bouma et al. (Thu,) studied this question.