Airborne electromagnetic survey for water supply planning – Cane River, Western Australia

Abstract

A SkyTEM airborne electromagnetic survey was flown in the Cane River area near Onslow, Western Australia in 2011, in order to assist groundwater investigation and borefield development. The survey yielded a range of information relevant to future groundwater investigations. The detailed geometry of the nearshore saline intrusion has been successfully defined in three dimensions. The intrusion occurs in the unconfined aquifer above the impermeable Muderong Shale. A broad zone of low conductivity has been mapped within the alluvium and Trealla Limestone, which has been interpreted to indicate the extent of relatively fresh groundwater. The low conductivity zone has greatest extent in the 10 – 20 m depth slice. Between 20 – 50 m depth, the low conductivities are confined to the downstream part of the Cane River. At these depths, the low conductivities extend further to the eastern side of the river than to the west. This result suggest that it may be possible to expand the existing borefield to the east in areas without clay cover, while retaining a reasonable buffer from the nearshore saline intrusion. A number of shallow granite bedrock highs have been identified in the northern and central parts of the survey area, many of which have not been intersected by existing drilling. The upper weathered and/or fractured parts of the granite may have potential as aquifers where they are not overlain by impermeable clays. However the margins of the granite should be avoided where they are in contact with the onlapping Muderong Shale, which is associated with poor water quality.