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Approximation of Field Hydraulic Conductivity by Laboratory Procedures on Intact Cores¹

ABSTRACT

The utility of several laboratory procedures for approximating field values of unsaturated hydraulic conductivity over the suction range 30 to 100 cm of water was studied. Conductivity was measured at the 68-cm depth using neutron probe and tensiometer data taken during drainage of a bare plot of Ramona sandy loam. Conductivity was measured in the laboratory on 10- by 30-cm intact cores by the transient flow (TF) method of Richards and Weeks and was calculated by both the Marshall (M) equation and Millington and Quirk (M&Q) equation using moisture characteristic curves from laboratory measurements on intact cores and from the field data.

The TF values were all higher than field values but, when used with a matching factor, they satisfactorily approximated field conductivities. This study, the first test of this TF method against field data indicated that the method of calculating the flow velocity influenced the results and that the best results were obtained from a computer program which used a numerical differentiation subroutine.

When used with matching factors, conductivities calculated (for 33 pore classes) by the M equation and M&Q equation were good approximations of field conductivity, though less satisfactory than results from the TF computer calculations. The best M&Q values were calculated from a field moisture characteristic while the M values were satisfactory when calculated either from the field moisture characteristic or from one measured in the laboratory on intact 6 by 10-cm cores.

It is recommended that the conductivity value to be used in calculating the matching factor for any of these methods be measured in the field within the suction range being studied.

¹ Contribution of the Department of Soil Science & Agricultural Engineering, University of California, Riverside 92502. Presented in part at the Western Soil Science Society meetings, June 21–25, 1970, Berkeley, Calif.

² Associate in Soil Physics, Professors of Soil Physics, and Staff Research Associate, respectively, in the Department of Soil Science & Agricultural Engineering, Univ. of California, Riverside.

Received for publication March 10, 1971. Accepted for publication January 14, 1972.