Hydraulic conductivity of deeply weathered materials in the Darling Range, Western Australia

Abstract

The hydraulic conductivity (K) of unconsolidated, deeply weathered material was measured by the slug test method In 214 boreholes distributed over five distinct areas in the Darling Range of Western Australia. Most of the measurements were made in the zone 0-3 m above hard rock. Theory of the method was extended to include a layer of material with lower K about the slotted pipe. The frequency distribution of K in each area was well fitted by the log-normal function. Parameters of the linear regression of logK against the inverse Gaussian function of cumulative frequency differed significantly (P<0.001) between areas. In one area of 134 ha, measurements were made in 54 boreholes located on a grid. There was a very poor correlation between values of K at the smallest separation of grid points (100 m), which suggests that there is an essentially random spatial variation of K measured by this method in this study area. Assuming log-normal frequency distributions and random spatial distributions, bulk conductivities were estimated for each area. On the basis of these investigations, it is concluded that the bulk hydraulic conductivity of the weathered material in the Darling Range is slow to moderately slow, and relatively uniform on the broad scale.