The loop used to carry out the electromagnetic survey, seen here with Rogier Westerhoff from GNS Science and Susie Osbaldiston from the Northland Regional Council, consists of copper wire within a hexagonal fibreglass frame. It is suspended under a helicopter flying at about 100m. Photo / supplied
The loop used to carry out the electromagnetic survey, seen here with Rogier Westerhoff from GNS Science and Susie Osbaldiston from the Northland Regional Council, consists of copper wire within a hexagonal fibreglass frame. It is suspended under a helicopter flying at about 100m. Photo / supplied
An aerial survey starting today in the Far North aims to find out exactly how big a vital aquifer is and where it risks being infiltrated by seawater.
The aerial electromagnetic survey of the Aupōuri aquifer will involve a helicopter flying over the Aupōuri Peninsula, north of Kaitaia, witha large wire loop suspended underneath it.
The chopper will fly in parallel lines 200-300m apart at a height of 100m. The loop will be about 35m above the ground.
The survey is expected to take about six weeks with the helicopter flying every day weather allows.
Transmitters on the loop send electromagnetic signals underground while sensors measure the returning signals.
The technique is similar to radar in that it allows scientists to "see" what's under the ground.
Water from the aquifer, which stretches roughly from Awanui to Ngataki, is under increasing demand as land is converted to dairy farms and avocado orchards.
With no major streams in the area, it's also a vital source of water for the area's growing population.
Last year independent commissioners for the Northland Regional Council granted 22 parties, known as the Aupōuri Aquifer Water Users Group, consent to take 4.5 million cubic metres of water a year.
That was, however, appealed by the Department of Conservation, which argued not enough was known about the effect on some of Northland's biggest and most precious wetlands.
The aerial electromagnetic survey equipment is tested prior to the Aupōuri aquifer study. Photo / supplied
Earlier in the consenting process it was revealed that data used to estimate the amount of water in the aquifer was wrong, with the result that the water level in parts of the aquifer — especially around Houhora — was 2.5m lower than previously thought. In other areas it was higher.
It is hoped the survey will clarify exactly how large and deep the aquifer is.
The survey also aims to find out how and where the aquifer is connected to wetlands, lakes and streams; to identify the boundary between groundwater and seawater; and improve understanding of how groundwater recharges.
The new information will help identify how to balance environmental protection with increasing demand for water.
The $3.3 million survey is a part of a wider Te Hiku Water Study and will be funded mainly by Aqua Intel Aotearoa (AIA), a collaboration between Kānoa and GNS Science.
Kānoa, a government agency, is the delivery arm of what used to be called the Provincial Growth Fund (PGF).
AIA programme director Jane Frances said the helicopter would fly about 6500km in total.
The survey method was safe and had been used in other parts of New Zealand, including Hawke's Bay and Wairarapa.
The low-frequency, long-wavelength electromagnetic waves used were less harmful than those emitted by a blowdrier or big-screen TV. They would not interfere with electrical equipment.
The method could "see" as far as 300m underground but definition decreased the deeper it went.
Frances said locals initially approached the PGF to help fund the survey.
It was the most cohesive community she had dealt with.
"Local iwi, growers and the two councils have come together to do this. It's a real credit to the Far North," she said.
The aerial electromagnetic survey involves a helicopter flying over the Aupōuri Peninsula with a transmitting loop suspended underneath it. Photo / supplied
The Northland Regional Council, Far North District Council, Ngai Takoto and Te Aupōuri have also contributed funding. The survey will be carried out by specialists from SkyTEM Australia.
The project is overseen by the Te Hiku Water Study Project Team, which includes representatives of iwi, landowners and district and regional councils. DoC is also collaborating with the study.
