Updated inversion of SkyTEM data using downhole a-priori for new conceptual model and GW management targets at Toolibin Lake

Abstract

Toolibin Lake is located southeast of Perth in the WA Wheatbelt. Due to land clearing that altered the hydrologic balance depth to groundwater has risen from around ten meters below ground level to being at the land surface in the 1990s. For vegetation to survive at Toolibin Lake pumping groundwater has become an important management tool, to reduce groundwater levels and if possible stored salt. To achieve this pumping bores need to be installed in aquifers that allow water (and salt) to be drawn down from the root zone. Different geological and hydrogeological information was available for drilling investigations in the late 1980s and 1990s and as a result not all bores are installed in aquifers that achieve the management goal. A number of different AEM systems have acquired data over the lake and catchment. Results from the SkyTEM survey reported by Reid et al (2007) modelled a relatively homogeneous palaeochannel from 20 to 28 meters below ground level. Recent data collected using the Javelin borehole NMR tool (VistaClara Inc) have allowed for the mapping of a more complex sequence of channels and valley fill deposits. In this study we present updated geophysical results and groundwater conceptual model. They were obtained by i) reprocessing and re-inverting the SkyTEM data using borehole conductivity and hydrogeological surfaces as a-priori, and ii) inspecting again the correlation between AEM and MRS, and iii) producing new hydrogeological units to build a robust numerical model. The updated conceptual and numerical allows the fine tuning of management targets.