A Method for Simultaneous In Situ Measurement in the Vadose Zone of Field-Saturated Hydraulic Conductivity, Sorptivity and the Conductivity-Pressure Head Relationship

The Guelph Permeameter (GP) method for simultaneous, in situ measurement in the vadose zone of field-saturated hydraulic conductivity (KfS), sorptivity (S) and the conductivity-pressure head relationship [K(Ψ)] is described and discussed. The method involves measuring the steady-state liquid recharge, Q, necessary to maintain a constant depth of water, H, in an uncased, cylindrical well of radius, a, finished above the water table. An “in-hole” Mariotte bottle device is used to maintain H and to measure Q. Step-by-step procedures with example calculations are given for obtaining KfS, S and K(Ψ). Techniques for assessing the results are also given. Although detailed field verification of the GP method is still incomplete, the studies conducted so far are quite encouraging. Theoretical and practical advantages afforded by the GP method make it a desirable and cost-effective means for in situ measurement of Kfs, S and K(Ψ), which are three of the most important parameters governing the flow of water and other wetting liquids in the vadose zone.