This report describes the interpretation of a large airborne electromagnetic data survey that was designed to aid characterisation of groundwater systems in the La Grange groundwater allocation area which lies south of Broome, Western Australia. Characterisation of these systems is critical to developing policy around water use in the region, especially for the development of agriculture. This report is the second of two reports and it is designed to refine surfaces which are used as inputs to groundwater models. The volume defined by these surfaces viz. the seawater intrusion in the west, the top of the Jarlemai siltstone and the top of the Broome sandstone describes the portion of the Broome sandstone aquifer that is able to store water that can be used for human purposes, agriculture and mining. With the identification of palaeochannels in the La Grange groundwater allocation area and an improved analysis of geological structure from AEM results, most objectives of the survey have been realised. Palaeochannels were identified in the north of the La Grange groundwater allocation area, around La Grange Bay, and also in the south. Also in the south, faults were identified. It is hypothesised that these faults permit groundwater movement between the Broome sandstone, which is the important aquifer in the La Grange groundwater allocation area, and the Wallal sandstone which is the important aquifer south of the allocation area. Objectives relating to delineation of freshwater zones, and of water quality were not addressed. Although the top of the seawater intrusion was mapped, as was the top of the Broome sandstone near the coast, because freshwater and the sandstone matrix have similar electrical resistivities, it is difficult to map freshwater specifically.
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Broome Sandstone aquifer, La Grange area, hydrogeology, airborne electromagnetic survey, irrigated agriculture
Annetts, D, Munday, T, George, R, Wright, N, Raper, GP & Cahill, K 2017, The application of AEM to mapping the aquifer and groundwater characteristics of the La Grange groundwater area, WA: final report, report EP165299, CSIRO, Perth.
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