Otago Regional Council chief executive Richard Saunders said the report presented to councillors yesterday was an important milestone ahead of consultation on the council’s land and water plan.
The report, requested by councillors two years ago, provided information to support forthcoming staff recommendations on flow options and it would help inform council decisions, he said.
The "science recommendation" in the 47-page summary of hydrology modelling and ecological evidence was for the river to eventually have a minimum flow of between 2000litres and 2500litres per second at the Campground site in the lower Manuherikia.
Matakanui Station owner and Manuherikia Catchment Group interim chairman Andrew Paterson said minimum flows at those levels would force farms into drought.
The flow levels suggested could devastate the economy of the community that relied on the river.
"There’s a lot of worried farmers.
"There’s been a concerted campaign against the Manuherikia leading up to this — and against farming in the Manuherikia — and that’s very disappointing.
"There’s a lot of good work going on in the community to look after the river.
"It’s our lifeblood, the river, and essentially that’s going to be cut off from us.
"It’s going to have a huge effect.
"It seems very much that the cards are stacked against us."
At yesterday’s briefing, council biodiversity team leader Pete Ravenscroft said the irrigators’ voluntary minimum flow of 900litres per second at Campground was "definitely not looking after the river".
Despite the strong belief in the community that without Falls Dam at the top of the Manuherikia Valley the river would dry up, the hydrology suggested that would "never" naturally occur.
While it was quite possible locals had seen the river dry up in the past, it would have been because of abstraction, he said.
The hydrology modelling in the report showed that in a natural state, the river at Campground would have never dropped below 2000litres per second from 1974 to 2020.
It would have dropped to 2500litres per second once about every 25 years.
Forest & Bird Dunedin branch committee member and Otago Fish & Game environmental officer Nigel Paragreen said the report showed just how much pressure the river was under.
Deputy chairman Cr Lloyd McCall, who chaired yesterday’s briefing, said the report findings would be used alongside cultural and economic impacts to inform council policy decisions.
"It will be essential to support the communities involved and provide an adequate transition period to meet any increased level of protection for the health of the river."
Cr Andrew Noone said he was comfortable councillors had received "robust defendable science" to be used in council policy.
Crs Alan Somerville and Alexa Forbes said they were comfortable with the report as a basis for decision-making.
Cr Kevin Malcolm said by the time minimum flows were set, the council would need a "very clear plan in place" to ensure the affected communities had support to reach those levels.
Cr Gary Kelliher, who lives in the Manuherikia and has declared a conflict of interest, said he chose to not be in the room for the briefing, but his phone had "been running hot" with distressed and frustrated farmers as the detail of the report filtered out.
Cr Michael Laws said he believed a change in government after the October election could change the national freshwater management directive "which really sets the agenda on this issue".
Nevertheless, the work outlined in the report was important.
"I think it’s inevitable, whichever side of this argument you’re on, that this is going to end up in the Environment Court and potentially in the High Court."
