Collecting vital data on underground water resources

Aqua Intel Aerial Mapping helicopter pilots and Hinetapora Kōhanga Reo and Hiruharama School students at a public information day in Ruatōria. Picture by Liam Clayton

A major aerial mapping project is under way to gather information on the  region’s underground water resources.

The project is being carried out by Aqua Intel Aotearoa (a partnership between GNS Science and Kānoa, funded by the Provincial Growth Fund) which is working with Gisborne District Council to plan the survey, in discussion with Te Runanganui o Ngāti Porou, Tāmanuhiri Tūtū Poroporo Trust, Te Aitanga a Māhaki Trust and Rongowhakaata Iwi Trust.

The surveying will be undertaken by helicopter, using aerial electromagnetic (AEM) technology to “see” under the ground. On Tuesday Ruatōria residents got a chance to check out the gear and meet the helicopter pilot tasked with the mission, which will last until next month.

“The helicopter will fly at 80-120 kmh in parallel lines, generally 175 - 200 metres apart, and at a height of approximately 100 metres,” Aqua Intel Aotearoa programme director Jane Frances said.

“The measurement instruments are suspended under the helicopter and will be about 30 – 50 metres above the ground.”

The main  challenge was the weather, especially the wind, she said.

“Flights can’t go ahead if it’s too windy, above approximately 15 knots, or more than ‘sea breeze’ strength. The weather’s been generally  favourable over the past week but on Friday the wind limited the number of flights the team could do.”

AEM surveying involves flying over the land with a loop system suspended from beneath a helicopter. Transmitters on the loop send electromagnetic signals underground, and sensors measure the behaviour of the returning signals.

“Similar to radar, this method allows us to ‘see’ what’s under the ground by looking at and interpreting the way the signals return.

“It is sensitive to rock type, porosity, permeability, clay content, moisture content, and properties of water such as salinity — all of which help in understanding aquifers and contribute to mapping and characterisation of aquifers.

“Alongside the aerial surveying, we are also working with Gisborne District Council to drill a number of bores that will provide more detailed information in specific locations, to help build up understanding of the geology and groundwater resources.”

Once collected, the raw data will be analysed by GNS scientists, with processing expected to take 12 months.

GNS Science hydrology and geophysics team leader Dr Stewart Cameron said the survey would build understanding of the depth and extent of groundwater in the region.

“This is vital knowledge to ensure that this precious resource can be appropriately managed and protected.”