Whether or not there is a future for the Taieri spill gates tampered with during last month's flood is being investigated by the Otago Regional Council.
At a meeting this week, councillors asked why dropping the gates during the flood had become such a contentious issue with affected farmers.
The propping up of the gates by an unauthorised person after the regional council dropped them is being investigated by police at the request of the council.
The gates provide a 75m-long unhindered flow path into the upper ponding area on the Taieri while flood waters flowed freely over the rest of the spillway.
Cr Gerry Eckhoff asked engineering and natural hazards director Gavin Palmer whether the need to drop the gates so early was a design fault that could be fixed.
Dr Palmer said the benefit or risk of removing the gates, to which this flood gave "impetus", was being considered.
"The fundamental question is: Should they be there at all?, rather than: Should we tinker with the design?."
The true benefit of the gates, given they only operated during a narrow band of flows, begged the question: "Is it worth it", given the spillway was predominantly ungated, he said.
Farmers had been critical of the council's decision to drop the gates before the Taieri River at Outram reached 1360cumecs.
Dr Palmer said knowledge gained from floods in 2006 and 2007 showed the 1360-cumec level was theory and in practice water flowed over the uncontrolled portion of the spillway at a lower level.
"It's simplistic to say only drop it at 1360. In practice, it is only effective in a narrow band of flows between 1050 and 1360," he said.
The river could pass through those levels within three or four hours.
Cr David Shepherd said the question was: Why had the effectiveness of the gates dropped back?.
Dr Palmer said they were not certain why it had, and were looking into it.
Taieri farmer Colin Scurr, who farms the land on which the spill gates are located, attended the meeting. He said the gates were an integral part of the overall scheme to protect West Taieri from floodwater, so their removal could have an impact on protection for that area.
"It's complicated. There would have to be a lot of modelling done before a decision was made."
It would also depend on what works the council decided to install in the gate's place, he said.
There also seemed to be a misunderstanding in the community about the policy around the dropping of the gates and farmers were expecting to meet the council soon to discuss the floodgates.
The council had already removed spill gates on the Clutha Delta after a similar investigation.
