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Banking water underground for our future

Storing surplus water underground will ease the hard times during drought. Tim J Keegan/Flickr

Australia should prepare now for dry times ahead by “banking” its water underground. This means storing surplus water underground during wet periods and bringing it up for use during dry times. Water storage and banking are the missing links in Australian water reform.

Historically Australians rely on large surface reservoirs to provide water for agriculture and cities, and encourage farmers to harvest and store water in farm dams. This strategy is not sufficient to cope with drought and increasing climate variability as demand for food and water grows. Underground water banking can help ensure that there is enough water for both irrigation and the environment when drought hits.

The benefits

Water banking has several advantages.

First, it augments the natural processes of water storage in the landscape, avoiding evaporative losses. In the Murray-Darling Basin up to 3000 gigalitres (GL or billion litres) of water a year evaporates from surface water storages.

Second, it helps to recharge aquifers during wet years, thus ensuring that rivers continue to receive flows of water from aquifers during dry times. It can also assist environmental water managers by allowing them to synchronise supply with specific environmental watering requirements.

Third, water banking helps communities adjust to climate variability and uncertainty, and enables irrigators to receive additional water during droughts.

Fourth, it can help to increase Australian agricultural exports. Water banking expertise and technology could also be a valuable new export industry in its own right.

What’s happening currently

We are already storing about 45GL of water underground in the Burdekin region of Queensland every year for use in agriculture and horticulture. Significant quantities of recycled stormwater and wastewater are being stored and used around Adelaide. In Orange County, California they store around 300 GL a year – enough for the annual household use of 2.3 million people. One water bank in California has held up to 800 GL for its members. The known capacity of aquifers to store additional water below Perth, Adelaide and Melbourne could meet the needs of 2.5 million people per year– and may be far larger.

The argument that there is no spare surface water to store underground, ignores hundreds of gigalitres per year in dam spills and floodwater, recycled stormwater and wastewater. This “spare” water can be stored by channelling water to sand or gravel beds where it can filter down into the aquifer. When infiltration is blocked by rock or clay injection drills can be used.

On the face of it storing water underground and extracting it costs more than storing it on the surface – but this fails to account for the high engineering and environmental costs of dams and reservoirs. Also surface storages lose a third or more per year due to evaporation, and this cost is rarely acknowledged. If we choose not to make water users pay the full cost of surface storage, including evaporative losses, there is a case for public intervention to reduce the cost of aquifer storage for users.

Where to from here

While this needs national leadership, the concept of water banking can be implemented at grassroots level by Landcare and catchment management groups, even by individuals, as well as by larger organisations and agencies.

It is important that water banking is consistent with national water management principles and guidelines, and that the broader impacts are assessed. Every decision to bank water underground needs to be based on careful analysis of local needs. It is important to ensure that aquifer structures are not damaged and that water quality is maintained. In some cases water quality may even benefit from increased groundwater storage.

Good management of groundwater banks also requires some changes to current water management practises. When Australians deposit water in an underground water bank they generally do not retain legal ownership rights, or have any guarantee that they can recover their water. These rights and guarantees need to be established. There are restrictions on how much water entitlement can be carried over from one year to another. This prevents Australians from saving enough water to buffer them against the next drought. Extended carryover could be developed, with rules to prevent excessive withdrawals from aquifers during droughts.

The Murray-Darling Basin Plan is a major step forward in planning the future use of surface water and groundwater. The basin plan provides a platform for the development of coordinated surface water and groundwater plans and water banks at regional scale. Meanwhile communities can start their own water banking initiatives.

We bank money so it is there when we need it. We stockpile many other things, like grain or minerals, so there is always a reliable supply on hand. Why should water be any different? We should start banking our water now – before another major drought arrives.

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