Poster Presentation Australasian Groundwater Conference 2017

The use of airborne EM/3d modelling to reinterpret the carbonate aquifer, and its relationship to seawater intrusion/sustainable yield in Exmouth. (#57)

Mal McGivern 1 , Karen Gilgallon 2
  1. Water Corporation, Leederville, WA, Australia
  2. Southern Geoscience, Belmont, WA

Exmouth is a regional centre located 1260km north of Perth, Western Australia that relies entirely on groundwater for its water supply. The Exmouth bore field extracts groundwater from an unconfined carbonate limestone aquifer within the Cape Range Group. Groundwater flows easterly from the Cape Range to Exmouth Gulf where it discharges above a saline wedge at the base of the aquifer. The current extraction from the bore field does not have capacity to meet increased water demand due to population growth and the influx of tourists in holiday periods.

In 2016-2017, the Water Corporation decided to undertake an investigation to optimize bore field performance through improved production from existing infrastructure. A desktop review, an Airborne Electromagnetic (AEM) survey, 3D modelling, and pumping tests, helped define the extent/geometry of the saltwater interface and karstic features within the aquifer.

The AEM survey effectively mapped the location of saline water. It identified existing bores screened in areas with lower salinity and twenty four hour pumping tests of these was undertaken at rates much higher than their current extraction rate. The survey also identified existing bores in areas of higher salinity where increased extraction was not recommended.

A new conceptual 3D model was created using Leapfrog Hydro tm from all historic and recently acquired data. The new model identified the major karstic features within the aquifer system, as well as detail about the screened lithology for each bore, and their proximity to these karstic features.

The new model and the AEM survey have established a clear relationship between the extent of the saltwater interface and the location of the karstic features. Importantly bores have been identified which could accommodate additional sustainable extraction, and other bores where extraction rates should be not be increased, or should be reduced.

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