Original Articles

Characterizing the hydraulic properties of a semi-arid catchment by means of sorptivity measurements and scaling theory

Published in: South African Journal of Plant and Soil
Volume 5, issue 4, 1988 , pages: 173–181
DOI: 10.1080/02571862.1988.10634980
Author(s): J.H. MoolmanDepartment of Soil and Agricultural Water Science, Republic of South Africa


The variability of soil sorptivity within a semi-arid catchment was investigated on a macro- (28 ha) and microscale (16 m2). In the macroscale study, sorptivity was measured at 176 sites using a falling hydraulic head technique. The mean sorptivity of the left slope (98 observations) was significantly higher than the mean of the right slope (77 observations). The sorptivity data were scaled according to the concept of similar porous media, and a scaling factor was calculated for each observation site falling on the intersections of a 50-m × 50-m grid of the catchment. The frequency distributions of these scaling factors on both slopes were lognormal with means of 1,085 and 1,073 and standard deviations of 0,594 and 0,630 for the left and right slopes respectively. A reference sorptivity value for each slope was obtained with a more rigorous study of cumulative infiltration in two 16-m2 areas. Twelve and 16 measurements were made on the left and right slopes respectively using a 120-mm constant hydraulic head and within this small area, the S and A terms of the two-parameter Philip infiltration equation were calculated. Contrary to the theory of similar porous media assumed in this study, the scaling factors of the S and A terms were not equal, but linearly related.

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