The Tasman District Council says emergency work to the Aorere River has passed its first test.
The river reached its highest level in 150 years following torrential rain on 28 December and changed its course after breaking one of its banks.
The council says a work team has since cut a new channel to re-direct the river from the damaged rock wall.
Acting engineer manager Gary Clark says the emergency work was tested on Thursday and is working.
He says the emergency work on the Aorere River could cost as much as $800,000 while the district-wide repair bill, which includes significant damage in Murchison, could reach $2 million.