The Relationship Between Bulk Electrical Conductivity and Dryland Salinity in the Narrabri Formation at Breeza, Liverpool Plains, New South Wales, Australia

Abstract

Dryland salinity occurs in some areas of the Liverpool Plains in northern New South Wales, Australia. Soils on the Plains comprise deep self-mulching Black Earths and form some of the country's most productive agricultural land. A survey of bulk electrical conductivity using an EM-31 was carried out over parts of the Plains with the intention of identifying areas at risk of developing salinity due to rising saline groundwater. Large variations in bulk electrical conductivity were identified by the EM-31 work, but interpretation of the data was uncertain. A trial site was selected for detailed study and a programme of additional surface geophysics, borehole geophysics, coring, laboratory measurements of chemical and physical properties of the cores, and chemical analysis was carried out. The results indicate that the ground associated with high values of bulk electrical conductivity is dominated by smectite clay containing high levels of entrained salts. Ground associated with low bulk electrical conductivity contains a fine-to-medium sand mixed with smectite clay. The data set demonstrates that clay content, and the salt entrained in the clay, is the dominant factor determining the bulk electrical conductivity in this area. The area may not, therefore, be a risk of developing dryland salinity.