A forced meeting between scientists has failed to resolve an impasse over key technical evidence submitted to the Board of Inquiry assessing the controversial Ruataniwha dam proposal.
Hawke's Bay Regional Council and opponents of its Tukituki Catchment Proposal remain at loggerheads over the validity of scientific models the council is relying on to predict changes in nitrogen and phosphorus levels across the catchment if the dam is built.
The TRIM models, developed by NIWA's principal freshwater scientist, Dr Kit Rutherford, had been challenged by expert witnesses engaged by Hawke's Bay Fish and Game and other groups concerned about the dam proposal.
The models predict the nitrogen and phosphorus levels in streams, the risk of nitrate toxicity and the effects of nutrients on periphyton growth if land in the Tukituki catchment is able to be used more intensively because extra water becomes available from the Ruataniwha dam.
When the board of inquiry begins sitting next month, the council will argue the models support its case that nutrient loss from farmland will not be significant if the dam goes ahead.
Last month Fish and Game challenged the lack of detail provided to the board about how the models worked. NIWA and the council argued those details were commercially sensitive but the board ordered a meeting between scientists from both sides where Dr Rutherford provided more information about how the model worked.
At a pre-hearing legal conference last week, Fish and Game lawyer Sue Simons said the organisation's expert witnesses came away from that meeting concerned there were "significant issues with regard to the TRIM modelling" which they considered "not fit for purpose".
Fish and Game's scientific experts include Associate Professor Russell Death of Massey University, and Dr Jonathan Abell. Massey senior lecturer Mike Joy, who has been engaged by the Hawke's Bay Environmental Water Group, the Royal Forest & Bird Protection Society and Ngati Kahungunu, was also at the meeting.
In a brief of evidence provided to the board last week, Dr Joy said he "came away from the meeting with more misgivings about the validity of the TRIM models".
Ms Simons said an independent expert should be appointed by the board to assess the models.
But council lawyer Trevor Robinson said claimed failings of TRIM were not fundamental to the proposal and bringing in an independent expert could create "a situation that is born to fail".
"The idea that another expert might create a model that will be accepted by the parties given the extent of the criticism of the existing model, I would submit is remote in the extreme," he told the pre-hearing conference.
Board chairman Lester Chisholm ordered the two sides to agree by Friday this week on one or more scientists who could independently assess the models, after which the board would decide whether such an assessment would be required.
The stoush over nutrient run-offs will be one of many environmental, economic and social issues related to the Ruataniwha proposal that will be hotly debated when the board begins hearing evidence in a little over three weeks' time.
The board has already begun wading through more than 6000 pages of written evidence and submissions from the council, expert witnesses and 384 interested parties.
It will sit in Hastings and Waipawa to hear oral evidence from November 18 to December 20. Hearings will also be held on local marae.