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

Toolibin Lake is located southeast of Perth in the WA Wheatbelt. Land clearing since the early 1990’s changed the hydrologic balance, which has produced rises in groundwater levels, water logging and salinisation. To manage this and to protect the environmental values of the lake system, pumping bores were installed in aquifers to allow water (and if possible salt) to be drawn down from the root zone. Whether these have been optimally located and whether others could be installed to greater effect has been the subject of more recent investigation. To assist with that SkyTEM data acquired over Toolibin Lake in October 2006 were reprocessed and re-inverted using borehole elevation and conductivity data as a-priori information, with the aim of improving the accuracy of the interpretation. These data were combined with information from a borehole NMR survey across the lake, allowing for the mapping of a more complex sequence of channels and valley fill deposits. A new understanding of the palaeohydrology of the Toolibin Catchment shows a complex palaeovalley sedimentary package with higher yielding aquifers located beneath Toolibin Lake. The present distribution of pumping bores suggests that they do not appear to tap these aquifers as effectively as possible. The updated hydrogeological conceptual model, resulting from a re-interpretation of the geophysics, will be employed to build a new numerical model to test management scenarios that include the installation of new groundwater pumping bores on the floor of Toolibin Lake