The New Zealand Transport Agency says SH1 at the Rangitata bridge will reopen on Wednesday afternoon - with the exact time will be confirmed at 3pm.
- Check highway conditions here
NZTA said floodwaters were coming under control, and while there was a small amount of surface water left at the SH1/SH79 Orari intersection, the highway was increasingly dry to the north.
A barrier upstream of the highway redirecting water away is expected to be completed by Thursday, and Chorus is also finishing essential repairs to its network.
After peaking at 2200 cumecs during Saturday's flood, the river has now dropped to 330 cumecs - still five times its average flow, Environment Canterbury said.
Given the pounding taken by the river’s protection systems at the weekend, it remains vulnerable in any future flood events, ECan said.
Road users can cross the Rangitata River via a bridge near Arundel on Route 72. However, due to speed restrictions and increased traffic volumes, delays are likely on this route.
On the other side of the island, NZTA says State Highway 6 between Franz Josef and Fox Glacier reopened on Wednesday morning after a slip closed the highway after the recent heavy rain.
NZTA says the journey will be slow in places while crews continue to remove and remediate the slip sites and road shoulder damage.
North of Franz Josef, SH6 will remain closed "until further notice".
NZTA says it hopes to have the road reopened by Christmas, but this is weather dependent.
The highway from Hokitika to Franz Josef has been closed since Saturday after heavy rain over the weekend caused several washouts and slips along the highway, leaving hundreds of tourists and locals stranded in the region.
