Storm Washes Away New Zealand Bridge

FRIDAY, MARCH 29, 2019

Heavy storms were named as a significant contributor to the collapse of a motorway bailey bridge, located near the town of Franz Josef, New Zealand, on Tuesday (March 26). Flooding of the Waiho River washed out the structure, resulting in one reported fatality.

According to the Australian Broadcasting Corporation, the river had been running as high as 7.6 meters (roughly 24.9 feet). One woman was reportedly found dead on the riverbank north of the town of Hokitika; she had tried to cross floodwaters on foot after exiting her vehicle.

Waiho River Bridge Collapse

A bailey bridge is a prefabricated truss structure known for being portable. According to the New Zealand Transport Agency, debris build-up, the force of the swollen river along the northern bank and the amount of rock impacting the bridge’s piers all contributed to a structural collapse that likely could not have been avoided. The bridge’s river protection system had just undergone maintenance two weeks prior, however.

Transport Agency System Manager Pete Connors noted that the river had also built up in the center over the course of recent months, which resulted in the main channel being pushed toward the north bank. All of this combined led to high water velocity that impacted the rock groins, which serve to protect the bridge, as well as the rock embankment protection at the northern abutment.

The northernmost pier was reportedly hit by a large boulder, which caused the pier to fail. Once the main northern span collapsed, other sections of the bridge also fell.

"This is a 100-year event, there is a huge amount of rain. I haven't seen all of the rivers impacted in Westland at exactly the same time," Westland Mayor Bruce Smith told Newstalk ZB.

Recent Maintenance Work

The Transport Agency reported that roughly two weeks ago, after some high water flows into the river, crews repaired the river bridge’s protective rock walls along the north side, which included patching and filling in gaps in the rock work and reinforcing groin ends. This was considered to be regular maintenance work.

“Once completed, the crew removed the top from the temporary [protective rock wall] which was built to access the [groins], so it would not influence where the river went later and would erode away quickly,” the Transport Agency stated on its website.

“That temporary stopbank was washed away by the time the river started to rise and push hard at the bank.”

According to RNZ News, the transportation agency was warned two days before the bridge collapsed that work ongoing upstream could make the structure unstable. Franz Josef businessman Logan Skinner noted that the work was redirecting the current toward the structure’s northern abutment, an abutment that failed 25 years ago.

"There was a temporary bank put in upstream of the bridge to divert the channel while they repaired the groins on the north bank and that is probably disappearing, which is what is supposed to happen to it," transportation agency network manager Colin Hey said.

Plans are to have the bridge replaced within seven to 10 days, which will reconnect the South Westland community and the South Island tourism loop. The replacement is slated to cost $1 million NZD ($678,600 in USD).

“Bailey bridges are usually fairly quick to put back up, so we're confident that we can get it back within a week or two anyway,” Hey told Newstalk ZB.


Tagged categories: Accidents; Asia Pacific; Bridges; Disasters; Health & Safety; Infrastructure; OC

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