Research has accounted for the flow of water through the Murrumbidgee Catchment and established where it is economically feasible to save water.
As part of the Pratt Water Initiative: Murrumbidgee water efficiency study, Water for a Healthy Country researchers have been calculating:
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the amount of water in the 84 000 square kilometres of the Murrumbidgee catchment
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where it is economically feasible to save water
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where the water is going
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how much water is being lost to evaporation and seepage.
Where the water flows
The Murrumbidgee River is 1 600 kilometres long. On average, the total annual flow is approximately 4 300 gigalitres.
Around 295 gigalitres of water could be saved per year across the Murrumbidgee and Coleambally irrigation areas.
Almost two-thirds of this flows into the system upstream of Burrinjuck Dam and Blowering Dam (on the Tumut River), and one third is contributed by the catchment between dam walls and Wagga Wagga.
A team led by CSIRO’s Dr Shahbaz Khan took a two pronged approach to the task of accounting for the water.
First, they assembled and analysed every available piece of existing hydrological research into the area.
This not only saved the team from repeating work already done, but enabled them to calculate the average and seasonal flow, and the unaccounted flows and true losses, for the past century.
Secondly, this work was backed up by a suite of modern measuring technologies such as ultrasonic flow measurements, electro-magnetic and resistivity surveys which were used to locate areas of substantial ‘true’ water loss, and assess the quantities involved.
According to Dr Khan, it was important that the research team be able to distinguish between true water loss such as evaporation, or seepage into saline groundwater, and apparent water loss into good-quality aquifers, or back to the river, where the water is often recovered by water users further downstream.
Water savings possible
While the unaccounted flows in the main river system were over 500 gigalitres, there were also over 350 gigalitres of unaccounted flows in the irrigation areas.
The team estimates that total ‘true’ losses for the river and the major irrigation areas are approximately 345 gigalitres annually, made up of:
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evaporation from the river (80 gigalitres)
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seepage and evaporation in the Murrumbidgee Irrigation Area (100 gigalitres)
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on-farm losses in this area (90 gigalitres)
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seepage and evaporation in the Coleambally Irrigation Area (90 gigalitres)
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on-farm losses in the same region (45 gigalitres).
The potential true water savings across the two irrigation areas are around 295 gigalitres per year even if the present cropping systems are maintained.
Recommendations for water use
The research team has made a number of recommendations, which include:
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implementing engineering solutions to prevent build-up of salt in irrigated areas
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improving management of local sources of salt
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improving measuring and metering techniques
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recharging depleted aquifers with good quality water to prevent salinisation, and for evaporation-free underground storage
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spreading peak summer irrigation demand by diversifying crops
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targeted remediation of sites with high seepage rates.
Dr Khan says, 'Saving water is certainly possible but any decision should follow a full cost benefit analysis, including the impact of climate variability'.
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