A train crossing the Rangitata Rail Bridge on 25 April during testing following temporary repairs made after flooding washed away a pier. Photo: Supplied/ KiwiRail
A flood damaged rail bridge has been reopened after a concrete support pier was swept away in high waters, leaving the 610m-long structure sagging, but a mayor says more investment is needed for crucial infrastructure.
The bridge over the braided Rangitata River in Canterbury is an important rail transport link for much of the South Island, and would normally be crossed by about 45 freight trains each week.
It was hit by flooding during storms that lashed much of the country on 12 April and washed out part of SH6 on the West Coast, between Franz Josef and Fox Glacier.
KiwiRail chief infrastructure officer André Lovatt said these repairs were temporary, and a design was being drawn up for a permanent solution.
Ashburton Mayor Neil Brown said KiwiRail had done a great job to get the bridge reopened in less than a fortnight - albeit with a temporary fix, but he was concerned about the resilience of ageing infrastructure in the district.
The Rangitata rail bridge was the second bridge to have a significant support pier fail in the last three years, he said.
The 610m-long bridge was left sagging after one of its 34 piers was washed away on 12 April. Photo: Supplied / Allied Press / Connor Haley
"This infrastructure is getting up to a hundred years old and is it fit for purpose today or is it worn out? [We] don't know, but these bridges are owned by government, they need to be looked at and have a program in place for repair or replacement looking into the future," Brown said.
The Canterbury region was not seeing adequate funding to safeguard road and rail routes, he said.
"We in the South Island pay a lot of road user charges and petrol excise tax and we know what heads to Wellington and we just need to have our fair share coming back to keep our roads in the condition they need to be in."
The temporary repairs had been "a significant undertaking" for KiwiRail, Lovatt said. "First we had to divert the river away from where the pier was, then install a structure to ensure the bridge spans didn't sag further or collapse and damage the adjacent road bridge.
"We built a temporary support for the rail bridge, using a 250-tonne crane to push the four caissons [watertight chambers] deep into the river bed and install and weld cross bars into place. Finally we replaced the tracks across the two spans, which were warped when the bridge sagged."
A test train was run over the bridge on Anzac Day, with freight services expected to resume the next day.
Lovatt said "road-bridging options" had been provided to freight customers while the bridge was out of action, but the line being reopened meant there would be less heavy trucks moving between Timaru, Ashburton and Christchurch.
Initial work on the permanent repairs were expected to begin next week, and to take between 10 and 12 weeks.
They include driving new casings surrounding the bridge's support columns deeper into the river bed, and building a new steel and concrete pier.
Meanwhile, Lovatt said a search was on for the missing concrete pier, which could be buried in the river bed.