South Wairarapa District councillor and chair of its infrastructure committee, Colin Olds, confirmed the council would follow engineers' advice to close Lower Valley Bridge on Kahutara Rd whenever the Waihenga Bridge on State Highway 53 into Martinborough closed.
Both bridges cross the Ruamahanga River.
During October last year alone, the Waihenga bridge closed three times due to flooding, on the 12th, the 23rd and 28th.
The Waihenga Bridge would typically close for safety reasons whenever the river height reached 4.5 metres.
With both access routes closed, the only roads in and out of the part of the district serving Martinborough, Ngawi, Lake Ferry, Te Awaiti - among others - in severe flooding would be through Carterton and Ponatahi Rd.
A fourth minor route through Longbush Rd was narrow and itself vulnerable to closure due to slips and falling trees.
Olds acknowledged the effect on the community.
"It will have a huge impact."
"When we get those floods, it will be pretty tricky," he said. "It's another option cut off."
Hawkins said if Ponatahi Rd closed, the only route out would be Longbush Rd.
"The risk with the other roads being closed is [that] it could get dangerous if there's a lot of traffic pushed onto Longbush Rd."
Olds said a recent audit of the district's bridges had raised concerns about some, including the Lower Valley bridge.
A report tabled at a council infrastructure committee meeting on Thursday said full inspections had been done and issues with the capacity to carry loads identified for the bridge.
The council subsequently engaged a specialist diving consultancy to do further investigations.
"Council has further engaged another dive team to clear out the river debris, which is entangled around the bridge piers and updated the maximum speed limit to 10km/h as an immediate response," the report said.
"Council has also engaged a surveying team to monitor the bridge after each flood event. Closure of SH53 will trigger the closure of Lower Valley Bridge."
Olds said of the bridges identified with concerns, Lower Valley Bridge was a key priority.
"The foundations of the bridge, and the spars that support it, have been undermined to a large extent.
"From what the engineers have told us, it's generally caused by a build-up of slash around the piers. That has a tendency to wash out the material under those foundations and cause problems."
Councillor Aidan Ellims, the deputy chair of the council's infrastructure committee, said the slash was probably willow debris washed down the Ruamahanga.
Olds said addressing the issues would be a priority.
"The reality is, there has to be some work done on the bridge. Ultimately, council will need to make a decision on the extent of that work."
He explained why the two bridges would need to close simultaneously.
"In the event of SH53 being closed as a result of flooding, that water would be flowing down the Ruamahanga rapidly. Ultimately, from what I gather from the engineers, there is a risk those piers could fail if they were to have further damage."
Following every closure event, the engineers would inspect the bridge before allowing it to reopen.
He said the council would be prioritising addressing the issue for both Lower Valley and other bridges affected, and a decision would soon be made on what the next steps would be.
"It's important the public are aware of the state of our bridging network, but it's also important we don't over-react."
- By Sue Teodoro, Local Democracy Reporter
LDR is local body journalism co-funded by RNZ and NZ On Air.
