The Transport Agency is confident the newly repaired Wanganui River bridge on the West Coast will be able to withstand more heavy rain in the catchment.
Forty metres of the approach to the bridge, near Harihari, washed away when the river broke its banks last Wednesday, forcing travellers to take long detours.
The bridge reopened on Monday evening but MetService is warning 300 - 400 millilitres could fall in the ranges south of Otira before 9am on Thursday.
Transport Agency West Coast asset manager Mark Pinner says the river should be contained by its newly strengthened banks.
"We've put further protection in by basically putting rocks at the side of the river bank, to basically make sure the river doesn't get behind it and start eating the way into the ground."
Mr Pinner says there are about 450 bridges on the West Coast's highways, which are inspected and upgraded regularly.