Environmentalists have blasted the move as "doubling down" on inappropriate land use in the driest part of the country.
But Manuherekia Catchment Group (MCG) co-chairman Andrew Paterson said increased water storage had been investigated since at least 2017 — and the dam ran dry this year.
Falls Dam was safe, but in order to meet new dam safety regulations brought in earlier this year the nearly 100-year-old dam needed an estimated $20m to $40m of work, he said.
"We know that we have a repair bill under the new dam safety regulations of in excess of $20m.
"The opportunity has come up to enter the fast-track application and we considered that it might be timely to look closer at a new replacement dam, which would have increased storage.
"That would then allow for higher reliability in irrigation and potentially increased minimum flows in the Manuherikia catchment," Mr Paterson said yesterday.
"The dam is perfectly safe — it’s just the change in regulations puts increased scrutiny on it."
The proposal was to build a new dam slightly south of Falls Dam, he said.
The reservoir at present could store 10,000,000cum but the proposal was to quadruple the storage at the new dam.
With a reservoir that size there would be increased reliability for water users and enough water to meet higher minimum flows, but not enough water to allow for any substantial increase in irrigation area, Mr Paterson said.
After the group applied for its project to be included in schedule 2 of the Fast-track Approvals Bill, MCG general manager Clare Hadley told members the group had spoken to affected landowners and engaged with interested parties.
She said the group’s proposal had taken a whole-of-catchment approach, focused on a new flow regime for the river, and included a range of other measures.
The group had shied away from commenting on specific dam size, reservoir level, minimum flows and the like because there had not been the time for detailed design or hydrological modelling.
The fast-track approvals process was separate from funding considerations "and we’ll be looking at all options for that", she said.
"We feel this is a unique opportunity to achieve a sustainable water resource bringing economic and environmental benefits for the whole community," Ms Hadley said.
"We know this may be the beginning of a long journey with a lot of unknowns at this stage — but a journey we need to start."
At this week’s Otago Regional Council meeting Central Otago Environmental Society chairman Phil Murray said building a new dam, or raising the existing one, would have "unavoidable ecological consequences".
The area had the driest climate in the country and the plan was aimed at facilitating a land-use more suited to Southland or the Waikato "where it rains a lot".
The public were not being informed about what more water storage would mean to their river, he said.
"To our group this is simply doubling down on an economically and ecologically irrational farming model in this catchment.
"We’re the driest part of the country, where water is scarce.
"We need to make the best possible use of the water we have without stuffing our natural environment, one that has huge value to most of our community."
