Publication Date

2-2020

Series Number

413

Publisher

Department of Primary Industries and Regional Development

City

Perth

Abstract

Previous groundwater investigations had identified the presence of palaeochannel sediments under the Capitela Valley in the Perth Basin, about 25 kilometres south-west of Moora. The sediments of this Capitela Palaeochannel were thought to form a discrete aquifer of good quality groundwater suitable for agriculture.

To improve our understanding of the Capitela Palaeochannel, its distribution, water quality and potential as a groundwater resource, we undertook an airborne electromagnetic (AEM) geophysical survey of the area in December 2012. This led to the discovery of a palaeochannel located in the Darling Range between Gillingarra and New Norcia, and we named this the Gillingarra Palaeochannel.

The Gillingarra Palaeochannel warranted further investigation so we undertook a drilling program to validate the geophysical interpretation and to obtain information about the aquifer’s hydraulic and geochemical properties. As part of the program, we installed 16 monitoring bores and a production bore at nine sites, during October 2013 to February 2014.

Drilling results show that the Gillingarra Palaeochannel is up to 197 metres (m) deep, up to 1.18km wide and at least 18km long, and is mostly composed of coarse sand.

We conducted test pumping of the production bore to estimate the Gillingarra Palaeochannel’s parameters and potential bore yields. The bore produced about 700 kilolitres per day of brackish quality water — 307 millisiemens per metre electrical conductivity, or 1700 milligrams per litre total dissolved solids — suitable for livestock watering. We estimate the annual recharge to the aquifer to be about 0.85 gigalitres per year and the brackish groundwater in storage to be 4.6GL.

We discovered that, although they seem to be aligned, the Gillingarra Palaeochannel is not connected to the shallower Capitela Palaeochannel.

The rising groundwater levels and salinity developing along the Bindoon–Moora Road and Midlands rail line is due to discharge from the Gillingarra Palaeochannel.

Despite not being an extensive groundwater resource, this aquifer will be able to provide a valuable local source for livestock watering and some agriculture for the Gillingarra – New Norcia area.

Number of Pages

73

Keywords

hydrogeology, Gillingarra Palaeochannel, Capitela Valley, Capitela Palaeochannel, Perth Basin

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