He also said the iwi would be demanding a six-month extension of the board of inquiry process that is under way to consider resource consents for the Hawke's Bay Regional Council's proposed water storage scheme.
The extension would give it time to have evidence presented at the board of inquiry peer-reviewed by independent experts.
If the inquiry process was not extended, a decision that can only be made by Environment Minister Amy Adams and Conservation Minister Nick Smith, the iwi would take legal action on the grounds the council has failed to adequately consult with Maori on the project, Mr Tomoana said.
"We've asked to meet board-to-board with the regional council and we'll put it [the time extension] to them then. Otherwise the only other option is to go to judicial review, which is going to take that sort of time anyway, give or take a month or two." Either outcome would be a major blow to the council's plans to begin construction of the dam late this year.
Andrew Newman, the chief executive of Hawke's Bay Regional Investment Company, the council's commercial arm, told councillors last month the project was working to a tight schedule in order for construction to begin on the dam site in December. If that deadline was missed the project would need to be delayed until the following summer because some construction work is not possible during winter.
Regional council chairman Fenton Wilson said Ngati Kahungunu had first made the request for an extension to the hearing nine months ago and "from my point of view that's not going to happen. A lot of the information [put to the inquiry] has been on the table for a long time now. They should be right up to speed with the bulk of the information as far as a peer review goes."
Mr Tomoana's call for an extension came at the end of a rollercoaster week in the relationship between Ngati Kahungunu and the council regarding the dam. During the 29-day board of inquiry hearing the iwi accused the council of failing to meet its Resource Management Act requirements to adequately consult with Maori.
On Tuesday, the final hearing day, the council hit back, saying it had consulted extensively but had been caught up in iwi politics.
Later that day it emerged the two sides had been in behind-the-scenes discussions to thrash out their differences.
While some agreement was reached as a result of those discussions, they remained at odds over key issues such as the effect the dam would have on water quality in the Tukituki River.
Mr Tomoana said the iwi wanted environmental and other evidence put to the inquiry to be peer-reviewed because the dam project would affect future generations.
"It's incumbent on us to ensure that no stones are left unturned on something like this, the biggest project since the Endeavour landed to happen in our region. That's the sort of enormity we give it."
Mr Wilson said as a result of Tuesday's agreement the council and the iwi were now "shoulder to shoulder so I'm sure we can get through these issues without having to throw any extra and potentially unnecessary delay into the process".
Mr Tomoana said a year-long delay in the dam would not be significant in the long term but Mr Wilson said he "totally" disagreed.
"Ratepayers' money has been put against the scheme. The sooner we can make a decision to get on with things, the sooner we can start to pay that back. We need to know if this thing is a goer or not.
"The irrigators, the primary producers, the processors, all the people who have some skin in this game need a definite direction: yes, or no."
