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Factors Important in the Calculation of Hydraulic Conductivity¹

ABSTRACT

The calculation of hydraulic conductivity by a modified Millington-Quirk method with a matching factor gave conductivity values closely approximating experimentally measured values. The technique requires knowledge of the moisture characteristic and the saturated conductivity. A number of factors that affect the calculated values and improve the computational results were investigated. Calculated conductivity values decreased with an increasing number of pressure classes at low moisture contents. For all soils tested the calculated conductivities were less than the experimental values at the terminal point of the moisture characteristic. This discrepancy was partially corrected by a small change in the Millington-Quirk equation, by extending the moisture characteristics to higher suction values, and by reducing the number of pressure classes to approximately 10. A matching factor, the ratio of measured over calculated saturated conductivity, was found necessary for obtaining the best fit of calculated and measured data. Two conductivity functions calculated separately from each moisture characteristic forming a hysteresis loop, converged as the hysteresis loop was translated to higher tensions. All computations were done by computer.

¹ Michigan Agr. Exp. Sta. Journal Article no. 4315. The work upon which this article is based was supported in part by funds provided by the US Department of Interior as authorized under the Resources Research Act of 1964, Public Law 88-379.

² Associate Professor of Soil Science, Michigan State University; Associate Professor of Agronomy, University of Hawaii; and Research Technician in Soil Science, Michigan State University, respectively.

Received for publication March 1, 1968. Accepted for publication July 29, 1968.