Measuring unsaturated sorptivity and hydraulic conductivity using multiple disc permeameters

SUMMARY A new field method of obtaining, with minimal disturbance, the unsaturated hydraulic conductivity ( K 0 ) and sorptivity ( S 0 ) from unconfined disc permeameter measurements is introduced. Conventionally, the sorptivity is obtained from the initial square‐root‐of‐time behaviour of discharge from the disc permeameter. In some cases this can be difficult to measure, in part because multi‐dimensional flows approach quasi‐steady state very rapidly. As an alternative we extend the ponded twin‐ring method to unsaturated discs of several radii. This method has the advantage that only long‐time, quasi‐steady discharges are needed to obtain K 0 and S 0 . In the present study, the two methods are tested using data obtained for a fine sandy loam at a supply potential ( Ψ 0 ) of – 35 mm and agreement is good.