Groundwater investigations to support irrigated agriculture at La Grange, Western Australia: 2013–18 results

Authors

Robert J. PaulFollow
Gregory Paul RaperFollow
Richard J. George DrFollow
Nicholas J. WrightFollow
Adam M. LillicrapFollow
Peter S. GardinerFollow

Publication Date

12-2019

Series Number

398

Publisher

Department of Primary Industries and Regional Development

City

Perth

Abstract

The Broome Sandstone aquifer is the main aquifer and groundwater resource in the La Grange area, near Broome in the West Kimberley, Western Australia. Land use is dominated by cattle grazing on pastoral stations, dispersed mining and tourism. Irrigated agriculture has developed at a small scale, with about 470 hectares under cultivation in 2014. Groundwater abstraction is licensed under the La Grange groundwater allocation plan (Department of Water 2010) and managed by the Department of Water and Environmental Regulation. The La Grange groundwater allocation area is split into the La Grange North subarea and La Grange South subarea, with groundwater allocation limits of 35 gigalitres per year (GL/y) and 15GL/y, respectively. The volume of water licensed, committed and requested as of October 2016 was 13.15GL/y.

The Department of Agriculture and Food, Western Australia (DAFWA), now part of DPIRD, conducted the four-year La Grange project to help determine the level of irrigated agriculture the aquifer can sustain. This report describes the methods, data analyses and outcomes of a project designed to give a better understanding of the hydrogeological processes of the Broome Sandstone aquifer at La Grange, the interactions between all of its users, and its environmental and cultural assets. As part of the project, DPIRD coordinated development of a bore monitoring network and developed a water balance model to run irrigation scenarios.

Number of Pages

257

Keywords

Broome Sandstone aquifer, La Grange area, hydrogeology, water balance modelling, irrigated agriculture

Disciplines

Agriculture | Geochemistry | Geology | Hydrology | Water Resource Management

Comments

The following commissioned reports provide supporting data and information:

• Broome Sandstone Aquifer La Grange Groundwater Area: A preliminary report on the hydrochemistry and groundwater recharge rates, with recommendations for future drilling and environmental tracer sampling - analysis of groundwater chemistry data collected in the bore inventory to assist in planning the DPIRD drilling and subsequent groundwater sampling programs.

• Preliminary isotope assessment, La Grange Groundwater Area - analysis of chemical and isotope techniques to determine the age of Broome sandstone groundwater: groundwater sampled from the top of the aquifer is modern (old), groundwater at the base of the aquifer may be as old as 12 000 years. Isotope analyses also showed that recharge only occurs after heavy rainfall events during the wet season. The annual recharge rate of 5-15mm/y was estimated.

• A hydrochemical assessment of groundwater recharge and flow in the Broome Sandstone Aquifer, La Grange Area, Western Australia - analysis of all data in previous 2 reports plus more recently acquired data. Main conclusions are: most Broome sandstone groundwater is of good quality for irrigation at <500mg/L, the estimated annual recharge rate was refined to between 11 and 16mm/y, and groundwater ages varied from modern to 20 000 years.

• The application of AEM to mapping the aquifer and groundwater characteristics of the La Grange groundwater area, WA - the products of AEM survey include definition of the top and base of the Broome Sandstone plus inland extent of the saltwater interface and its depth. This information was used to plan the DPIRD drilling program, which was then used to refine the products derived from the AEM, in particular the base of the Broome Sandstone.

• Pumping tests, La Grange Region, Western Australia - results of aquifer test pumping on Roebuck Plains, Shamrock, Frazier Downs and Nita Downs stations. The test results support the assumption made following the DPIRD drilling program that the top of the Broome Sandstone is moderately permeable with a significantly more permeable layer below. The hydraulic conductivity of the lower, more permeable layer ranges from 10 to 30m/d. Estimates of storage coefficients and specific yield are also presented.

Recommended Citation

Paul, RJ, Raper, GP, George, RJ, Wright, NJ, Lillicrap, AM & Gardiner, PS 2019, ‘Groundwater investigations to support irrigated agriculture at La Grange, Western Australia: 2013–18 results’, Resource management technical report 398, Department of Primary Industries and Regional Development, Perth.

Maps

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