Geothermal systems in Rotorua are used for a range of activities, including for tourism, health spas or powering large facilities like hospitals. Photo:
The Bay of Plenty Regional Council is considering "tweaks" to allocation rules for commercial users of geothermal systems in Rotorua, but is holding fire on a region-wide plan to manage the natural resource.
Late last year, the regulator went out for public consultation with updated draft management plans for the systems in Rotorua, Tauranga and the wider region, in efforts to greater streamline the consenting process.
The geothermal resources are of cultural, social and economic significance to the region that has 12 geothermal systems. The systems are used for a range of activities, including for tourism, health spas or powering large facilities like hospitals.
Furthermore, other uses for geothermal resources include drying timber at saw mills or using water for irrigation or frost protection in horticulture - in addition to generating electricity, heat or water.
Bay of Plenty Regional Council's geothermal programme leader Penny Doorman said the resource was a taonga that was generally well managed, and there was even scale for greater use at some sites.
But she said ongoing reform to the Resource Management Act - legislation which ordered "outdated" management plans be reviewed - resulted in the regional council pausing the wider regional management plan for the systems.
"We've had to pivot a little bit because with the resource management reforms that are underway, council decided not to progress the regionwide plan change, they thought it would be better to wait until there's a bit more certainty about that.
"But they have agreed to still go ahead with the changes to the Rotorua part of that regional plan change."
Visitors at Te Puia explore Whakarewarewa Geothermal Valley. Photo: Supplied / Te Puia
Up to 29 percent of overall use of geothermal water in Tauranga system was for horticulture, and made up 96 percent of geothermal water allocated to non-geothermal activities.
In a submission, fruit and vegetable growers raised concerns that changes to geothermal systems management might result in further costs and compliance for users.
However, Doorman said access to water for horticultural irrigators in Tauranga was not changing and the plan was progressing, however it would consider changes to allocation limits in Rotorua.
"We have made some recommendations for changes to the allocation [in Rotorua]. There's always been a limit to how much geothermal water can be taken from the system and not reinjected, and that limit has just been reviewed through some careful monitoring," she said.
"We're basically saying if you're taking geothermal water out of the system to take heat, then you've got to re-inject it."
She said it identified a system-wide cap to the amount of heat that could be taken off the system.
"The reason for that is that because it's really important to keep your water levels and your geothermal aquifer high but also hot because that's what our geyser system relies on," she said.
"If we can keep heat within this safe operating space, then we know that we can protect the mauri or the health of the geothermal system."
Meanwhile, in its submission, industry group Horticulture New Zealand said consent conditions should be reasonable and proportional to the environmental risks at the key Tauranga site.
"The council's science has shown that the water quantity will run out before heat in the Tauranga system, so volume is the limiting factor rather than the heat source," it said.
"Given that this is the case, non-geothermal uses of water such as irrigation should not be restricted on the basis of retaining the heat source."
It said consent conditions should also be "mindful of cumulative compliance cost on users."
It added that there was significant potential for low-temperature geothermal water to be used with ground source heat pumps for zero-carbon greenhouse vegetable growing in future.
Growers were also exploring new heat sources for their greenhouses in areas like geothermal, due to the rising cost and limited availability of gas.
GNS Science, now the Earth Sciences New Zealand with NIWA, developed a geothermal and groundwater interactive map to help greenhouse growers switch to geothermal heating.
Doorman said investigations were ongoing, including into the potential of Tauranga's low temperature geothermal system.
She said collaboration with mana whenua was key to managing the natural resources.
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