Work undertaken by the Northland Regional Council has revealed inaccuracies in bore survey data used to assess the Aupōuri aquifer and set allocation limits to prevent saltwater intrusion.
Acting CEO Bruce Howse said water levels in north-eastern parts of the aquifer may be up to 2.5m lower than thought, but up to 1.8m higher in the northwest.
That survey datum recorded between 1987 and 1991, and which was used in groundwater assessments and recent allocation modelling, was inaccurate had come to light when council staff were undertaking preliminary surveys of bores to establish 'trigger' levels for resource consents in parts of the aquifer south of Houhora.
The bore datum was also used to assess the effects of 24 current consent applications by avocado growers seeking groundwater from the aquifer.
"In a nutshell, this discovery potentially means there's less water available in the north-eastern part of the aquifer than previously thought, although there may actually be more available on the northwestern side," Mr Howse said.