Two appeals on an Environment Court decision allowing a landfill in Auckland's Dome Valley to go ahead have begun.

Ngāti Whātua and Forest and Bird have both taken separate appeals to the Auckland High Court against the decision, which allowed the landfill consent to go ahead, with conditions to its proposal which aimed to mitigate negative impacts.

The landfill consent was given conditional approval in 2021, kicking off opposition to the 60-hectare mega-dump from iwi and community groups in the Environment Court.

Representing Te Rūnganga o Ngāti Whātua lawyer Rob Enright said the Court wrongfully assessed its relationship to the landfill site and the downstream Kaipara flats.

"The wrong and unlawful approach and the process followed by the Environment Court was to prefer Ngāti Manuhiri's position of support of the proposed landfill, without first reaching determinations needed to resolve competing tikanga and strength of relationship," he told the Court.

Ngāri Manuhiri Settlement Trust originally opposed the landfill - but mid-way through Environment Court hearings last year, changed their position to support the landfill, with waste management providing them with $2 million for the construction of nearby homes, a $10m environment fund, the promise of jobs and return of land once the site was no longer needed.

Enright said the landfill would have significant effect on Ngāti Whātua way of life and kaitiakitanga activities, which could not be avoided with the conditions provided to Ngāti Manuhiri.

"It is vitally interested in the question of iwi tribal boundaries, and the active protection of the whenua, waters and tribal taonga of the iwi. It is a common cause that transcends acknowledged differences and nuances in tikanga within Ngāti Whātua and between hapu. There is a unanimous position opposing the landfill at the site selected. The stakes could not be higher."

He said adverse affects caused by the landfill, at the headwaters of the Hotea awa, would be both irreparable and intergenerational.

The hearing continues with submissions from Ngāti Manuhiri, Waste Management and Auckland Council this week.