Measurements of riverbed hydraulic conductivity in a semi-arid lowland river system (Murray–Darling Basin, Australia)

Abstract

Riverbed hydraulic conductivity (Kr) was measured along one river reach in four tributaries of the Murray–Darling Basin (MDB) in south-eastern Australia. Two techniques were trialled: in-river falling-head tests in high Kr sediments, and laboratory evaporation tests on intact riverbed cores for low Kr sediments. In-river falling-head tests were conducted using two types of permeameter: a steel-base permeameter or a stand-pipe permeameter. Kr was found to range from 10–10 to 10–3 m s–1, corresponding to a range in riverbed sediment textures from clay to silty gravels, respectively. Although the within-reach variability in Kr was also large, in general the river reaches could be divided in two groups, those with a low Kr (<10–8 m s–1) or a high Kr (>10–5 m s–1). The low Kr reach (Billabong Creek) was a clay-lined bed, whereas the others had silty sand or silty gravel beds. Thus, regional-scale assessments of Kr in the MDB could be made using a stratified sampling process in which reaches would be first classified into low or high Kr classes, and then Kr measurements made in a subsample of low and high Kr reaches. This would be an improvement over the current practice whereby riverbed Kr is estimated either from regional soil maps or through the calibration of groundwater models.