A new method for determining subsurface unsaturated hydraulic conductivity
in situ was developed. Steady state flow conditions were established from s
pheroidal cavities under subatmospheric pressure. Several borehole tension
permeameter devices were constructed and field tested in four different soi
ls. While the capillary length parameter (alpha) values were generally cons
istent with previously reported values, the estimates for saturated hydraul
ic conductivity (K-s) were, in some cases, 1 order of magnitude lower than
reported values for the test soils. In part, this can be traced to the rigi
d log linear shape of conductivity to pressure head used by the Gardner [19
58] model, which produces overly small intercept values (K(0) = K-s) when m
easured for drier conditions. Transformation of the estimated parameters to
the Brooks and Corey [1964] model seems to extend the useful range of the
parameters. A potential combination of near-saturation measurements [Shani
and Or, 1995] with the proposed method could lead to improved characterizat
ion of subsurface K(h).