Publication Date

6-2016

Publisher

Innovative Groundwater Solutions

City

Middleton

Abstract

The Department of Agriculture and Food Western Australia has undertaken a four-year Royalties for Regions funded project in the La Grange Groundwater Area south of Broome. The purpose of the project was to provide improved knowledge and confidence about soil suitability and water availability for potential expansion of irrigated agriculture in the region. A range of complementary techniques have been used to assess the groundwater resources in the Broome Sandstone aquifer, including contemporary approaches such as drilling and aquifer pumping tests, and state-of-the-art approaches such as airborne geophysical surveys and hydrochemistry investigations.

This report presents a synthesis of all hydrochemistry data collected from about 200 existing and recently drilled bores over three campaigns from 2013 to 2015. Major ion chemistry data, stable hydrogen and oxygen isotopes of the water molecule, chlorofluorocarbons and radiocarbon have all been used to address key knowledge gaps in the context of future irrigation development and water allocation planning.

Most groundwater in the Broome Sandstone aquifer is exceptionally good quality with salinity less than 500 mg/L as total dissolved salts. Major ion compositions are consistent with a source of solutes from aerosols in rainfall of marine origin, followed by minimal water-rock interaction including weathering of soil carbonates.

Stable hydrogen and oxygen isotope compositions of groundwater samples indicate that recharge to the aquifer only occurs after intense monsoonal rainfall events in the wet season.

Three different environmental tracer based methods for estimating recharge rates have produced remarkably consistent results, despite differences in the spatial and temporal scales over which they apply. There are no apparent spatial trends in recharge rate, which indicates that recharge is driven by large episodic events associated with tropical cyclones rather than mean annual rainfall.

Residence times of groundwater flow in the Broome Sandstone range from ‘modern’ for shallow bores to more than 20 000 years for deep bores in down-gradient parts of the aquifer. These residence times correspond to flow path lengths ranging from only a few kilometres for groundwater in the shallowest bores, to more than 150 km for groundwater in the deep bores near the coast.

Number of Pages

54

Keywords

Broome Sandstone aquifer, La Grange area, hydrochemistry, groundwater recharge, irrigated agriculture

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 hydrochemical assessment used all data analysed in:

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