Researchers who discovered brackish wateer 50m below the seabed 50km off the Canterbury Coast got a tantalising glimpse of a resource now proving to be much bigger than first thought.
“In New Zealand very little had been known about reserves of undersea freshwater, with the exception of the Waiwhetu aquifer below Wellington harbour,” Niwa researcher Joshu Mountjoy said.
The Wellington aquifer supplies the region with much of its drinking water and is the fifth largest aquifer in the country, extending out as far as Matiu/Soames Island.
The unexpected find off the Canterbury coast prompted researchers to seek and get European scientific funding to extend their work through the Marcan project, a five-year international programme investigating how offshore groundwater influences continental margins.
The Niwa research vessel Tangaroa was commissioned to do electromagnetic surveying capable of distinguishing between fresh and salt-water reserve.
That work established the volume and area of the reservoir that dates back across the last three ice ages when the sea level was more than 100 metres lower than today and the water became trapped in Canterbury’s large sedimentary plains that extend well out to sea.
“Ground water pressure on land in bores had indicated there may be something that extended out beyond the coast but this proved to be very significant in terms of volume.”
The reservoir might contain as much as 2000 cubic kilometres of water, the equivalent of half Canterbury’s groundwater volume.
Mountjoy said being an extension of the known groundwater volumes adds significantly to the knowledge of the region’s aquifers and how best to manage them.
“It has major implications for how we model and our onshore fresh water management.”
Replenishment of Canterbury’s known ground water aquifers tends to come from the Southern Alps.
Climate change research also done by Niwa scientists means snow loss in the Alps is already well understood and of concern.
“This is a large area of water reservoir that we did not include in past calculations.”
It is uncommon to find reserves of such scale anywhere in the world and the sedimentary nature of the east coast means there could be similar reserves further north around Pegasus Bay and off Hawke’s Bay.
“Hawke’s Bay is an example of a region needing to manage what they are dealing with onshore. They have got only half the picture if they do not know how far out the aquifer goes and how much is leading into the ocean.”
Another country known to have generous reserves of freshwater is Malta and researchers there have worked with Niwa staff on better understanding the potential for underwater ground water.
No one is tapping into such reserves to supply populations and the whole area of research remains very new.
“I think it could become a possibility. It is a big resource out there and countries like South Africa and India are facing problems in securing water supply. It will require step changes in technology to extract. That is likely to occur in years to come.”
The Canterbury research is only the second time such intensive surveying has been done, with the first on the east coast of the United States.
the work puts New Zealand at the forefront of a new research area and one so critical for NZ’s future.
“Our groundwater systems are a critical resource for society. They are increasingly under pressure and we need every bit of information we can get.”
