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Source: New Zealand Transport Agency

A one metre square culvert will be replaced by a much larger one with increased flood-carrying capacity north of Roxburgh (SH8) in the New Year.

Work is expected to get underway early in 2021 on the replacement of the culvert, known as Pumphouse Creek, under SH8 half a kilometre north of Roxburgh, says Waka Kotahi NZ Transport Agency Senior Network Manager John Jarvis.

“The new concrete culvert measuring four metres wide and two metres high is being manufactured offsite in precast sections and will replace the existing culvert that measures only one square metre,” he says.

“Following a series of floods over recent years in the Roxburgh area, a catchment study was conducted by Otago Regional Council, and Waka Kotahi  has been working closely with council staff to help improve the resilience of this section of SH8.”

Pumphouse Creek was identified as a waterway with ongoing risk of flooding, says Mr Jarvis. “Gravel was accumulating and blocking this undersized culvert following heavy rain in the hills which has occurred more frequently over recent years.

“Not only is the existing culvert unable to deal with these heavy rain events, an existing water treatment pumphouse owned by Central Otago District Council immediately downstream also becomes vulnerable to damage and possible outages to the residents of the town when it floods. The larger culvert will help channel flood waters and gravels under the road and below the pumphouse to the Clutha River once it is operational.”

Teviot Valley Community Board Chairman Raymond Gunn says this is very good news for Roxburgh and the wider community.

“With the fragile nature of the creeks behind Roxburgh since the major rain event in November 2017, we have seen even moderate events cause serious problems at SH8. This significant culvert upgrade will safeguard not only the Central Otago District Council infrastructure and private property but will provide reassurance to the community and businesses that they will not be cut off for extended periods in the future.”

Waka Kotahi has also been working on improving two other waterway culverts at the south end of Roxburgh at the Golf Course and Black Jacks Creek, which also suffer from flooding in large rainfall events. The design work to replace these has now been completed and funding will be applied for over the next few years.

“While Pumphouse Creek is the first priority, Waka Kotahi has already made some improvements to the flow of the other two waterways and will continue to monitor and maintain these so that further road closures are minimised,” says Mr Jarvis.

Once on-site work starts on Pumphouse Creek in the New Year, there will be some disruption to motorists on this section of SH8 with one option being a detour over the Roxburgh Dam for several days in order to accelerate the construction. Waka Kotahi will consult with Central Otago District Council and other stakeholders to discuss the detour and disruption options, before any work starts.

The total cost of the works is expected to be approximately $575,000.

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