Design and application of a constant head well permeameter for shallow high saturated hydraulic conductivity soils

A new constant head well permeameter has been designed to measure saturated hydraulic conductivities (Ks) ranging from 10−6 to 10−3 ms−1. Application to shallow soils of Western Australia in this Ks range highlighted problems with different aspects of the borehole discharge response. Firstly steady‐state borehole discharge was only reached in 13 out of 50 tests conducted. This was a consequence of the constraint placed on the volume of water storage (40 L) of the permeameter. For some non‐steady‐state cases, techniques of estimating steady‐state discharge from the available data are examined. Secondly borehole discharge was observed to increase with time in 34 per cent of cases. A satisfactory physical explanation of this phenomenon is not presently available. Other limitations in the application of the constant head well permeameter are noted. Examination of a number of recent theoretical developments in the determination of Ks led to a preference of saturated‐unsaturated flow solutions by Philip (1985) and Reynolds et al. (1985). These solutions involve the ‘sorptive number’ to which the solutions were sensitive but not critically sensitive. The theory was used to establish design criteria for the permeameter and to identify an optimum application strategy in terms of well dimensions and heads. Error estimation indicated that the designed permeameter was a practically useful field instrument.