NZTA project manager Jason Forbes said the flood-prone section of the main highway has had $3 million of engineering improvements made in recent months.
The aim of the project was to keep the road open and above water level, even in a one-in-50-year flood.
The project, built by Oamaru-based Whitestone Contracting, took seven months and was part of the government’s nationwide works to reduce the risk of natural disasters closing key highway.
But not everyone is happy with the changes.
Last November, local residents and Waitaki District Mayor Gary Kircher did not want the roadworks to go ahead because they were concerned the increased road height would act as a dam and make flooding worse in Maheno township when the river rose.
Mr Kircher said not all options were considered.
Mr Forbes said modelling showed that culverts would not be effective and alternative routes were not viable.
Keeping communities and businesses connected during flood events was the aim of the completed project, he said.
"The most effective, efficient, and affordable option of those investigated to reduce the flood risk at this location, was retaining the existing highway layout, and raising the road height by slightly over a metre.
"NZTA modelling showed this would reduce the amount of floodwater covering the highway and result in little if any increases in water on nearby property."
Mr Forbes said the Whitestone team completed the project ahead of schedule and under budget.
