Alluvial ground waters used for irrigation in the southwest Lockyer Valley, Queensland, experience varying salinity problems. Samples were taken on three occasions along transects in the valleys of the Tenthill and Ma Ma creeks during the dry season (August 1984), the wet season (February 1985), and during a period of drought (January 1987). The waters are categorized by chemical type, and hydrochemical sections are plotted for major cation data (magnesium, calcium and sodium). The interpretation of the sections permits the identification of recharge areas for the alluvial aquifers, and the location of saline intrusions into the alluvium from underlying sandstone aquifers. It is also possible, with the assistance of chemical type, to correlate some saline intrusions in adjacent valleys as issuing from the same sandstone aquifers. A diagram to summarize the locations and magnitudes of salinity changes along transects is given.
