With Australia’s long dry periods, it make sense to Capture and store excess flood water in times of floods. But capturing and storing the water is only a small part of it. With high rate of evaporation and vast distances, economic and environmental factors struggle to warrant the viability of any water storage solution in our country.
One promising option that is being further investigated is to store the water underground. Not only can it eliminate evaporation and provide long-term storage, it can also replenish groundwater supply, prevent seawater from intruding, and protect ecosystems that depend on groundwater for their very survival.
The concept of ‘Managed Aquifer Recharge’ or MAR is the process of manually filling aquifers with groundwater runoff. MAR has two general approaches:
- Infiltration, whereby the water is gravity fed down into the aquifer via seepage.
- Injection, whereby the water is gravity fed or pumped into the aquifer via a well.
Managed Aquifer Recharge schemes in Australia
One of the oldest MAR schemes in Australia, and one of the largest, is in Northen Queensland, 45 gigalitres a year is stored underground in Burdkin Delta, near Townsville, through the use of infiltration basins allowing for sustainable groundwater levels for agriculture and has kept seawater at bay.
The Northern Territory has Australia’s first ‘soil aquifer treatment’ scheme which stores treated wastewater underground and augments groundwater resources at Alice Springs. Shallow groundwater has also been taken and stored in a deeper aquifers to supply the Goulburn Islands in NT with drinking water.
The Cloudbreak iron ore mine in the Pilbara uses an injection technique to recharge more than 20 GL/year of brackish and saline water. Its main use is for mine water management and to protect groundwater-dependent ecosystems.
On the Ashburton River in the Pilbara, mining magnate Andrew Forrest has built an underground dam on his family’s property, Minderoo Station, to store wet-season flows. The feat of engineering, which Mr Forrest refers to as an ‘upside-down weir’, is now supplying water year round for cattle and fodder.
“This MAR scheme is the first of its kind in Australia,” says Dr Joanne Vanderzalm, a senior research scientist at CSIRO. “Others were trialled but have not met with success.”
The Economics behind MAR
Dr Richard Evans, Principal Hydrogeologist with Jacobs Engineering Group, was involved in the Minderoo Station weir and is now investigating opportunities for Managed Aquifer Recharge in the Pilbara and in Katherine in the NT, under the National Water Infrastructure Development Fund.
“We are confident that underground dams will work in a technical sense in the right hydrogeological environment. It still has to be proven and we need to demonstrate it. But the challenge is to demonstrate that MAR schemes will work in an economic sense.
“For irrigation in northern Australia, if it’s not cheap it’s just not going to fly. The challenge is what does it cost relative to the alternatives? If the alternative is a big dam, that could cost many millions. Can irrigated agriculture pay that back? Usually not. Our thinking is in line with CSIRO’s—it’s all about cashflow and the ability to pay back the loan on the capital cost of the infrastructure.”
The main advantage of some MAR schemes, says Dr Evans, is that they are relatively cheap to run. Then there’s the obvious advantage of evaporation being “practically nil” underground.
Scalability is another advantage of Managed Aquifer Recharge schemes, he says. It’s possible, for example, to progressively add underground dams along the same river.
“These are significant hurdles”, says Dr Evans. “But if the hydrogeology is right and other factors, we believe it can be economic.”
Is MAR Cost effective?
CSIRO research Peter Dillon said.
“You’ve got to clean out the silt when it gets caught there. Otherwise the structure becomes ineffective not only because it has lost its storage capacity, but also because its infiltration rate has dropped,” Dillon said.
In terms of costs, surface infiltration has been the cheapest method of recharging aquifers, as it requires little capital investment in infrastructure, and often the water used requires no treatment.
“If you’re using infiltration schemes, it’s about 10 cents per kilolitre to recharge and recover water,” Dillon said.
Recharge schemes that use bores, such as Western Australia’s Groundwater Replenishment Scheme, can be more costly, especially if water treatment is required, but they are often still more cost effective than alternative supplies.
The WA scheme uses a thorough multi-stage treatment process, including reverse osmosis, to purify wastewater before injecting it into aquifers and carrying out sophisticated water quality management, yet Dillon said “CSIRO research showed it still had a cost saving of 40% on current seawater desalination operations.”