Publication Date

7-2017

Publisher

CSIRO

City

Perth

Abstract

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.

Number of Pages

382

Keywords

Broome Sandstone aquifer, La Grange area, hydrogeology, airborne electromagnetic survey, irrigated agriculture

Disciplines

Agricultural Science | Agriculture | Geology | Hydrology | Soil Science

Comments

The Department of Agriculture and Food, Western Australia, now part of DPIRD, conducted the four-year La Grange project to help determine the level of irrigated agriculture the Broome Sandstone aquifer can sustain. The project included investigating the hydrogeological processes of the aquifer, the interactions between all of its users, its environmental and cultural assets, and developing a water balance model to run irrigation scenarios. These investigations are reported in 'Groundwater investigations to support irrigated agriculture at La Grange, Western Australia: 2013–18 results'.

This final report on applying AEM to the La Grange Groundwater Area builds on the milestone 1 report in the individual parts below.

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