Reversed longitudinal salinity profile of a major river in the south-west of Western Australia

Abstract

Water samples, 51 in October 1973 and 44 in February 1974, were taken from riverine and tributary localities extending for 475 km inland from the estuary over the course of the major Blackwood River System of south-western Australia. Each of the two series of river conductivity (K₂₀) values was positively correlated with distance upstream, but the slopes of the spring and summer regressions were not significantly different. Salinity increased by approximately 10.9 mg/l and 16.6 mg/l, respectively, per km in the upstream direction. Only the lower river and adjacent tributaries could be classified as freshwater (<3000 mg/l). The loads of total dissolved salts passing a Stream Gauging Station, 70.8 km upstream from the estuary, during the spring and summer samplings were 29.57 kg/sec and 0.28 kg/sec, respectively. The reversed longitudinal salinity profile could be explained by reference to the reversed sequence of valley forms, the pattern of clearing of catchments, decreasing rainfall inland, and the release of cyclic salts, accumulated in groundwater, by clearing.