The bridge was closed in mid-July and work was scheduled to take about 14 weeks, but in early September it was found that rock under the northern abutment was too solid for piles to be driven to the depth specified by seismic requirements.
The northern abutment had to be redesigned with steel-encased piles below the road surface connected to the northern end of the bridge by concrete beams.
Waitaki District Council roading engineer Graeme Butler said the work had been completed one day ahead of the revised schedule, after the council had requested Breen Construction to ensure the bridge was completed before mid-January.
It had cost $220,000 more than the $600,000 originally estimated, he said.
The high water mark had prevented additional clearance being added to the bridge, which was designed to withstand a once-in-100-year rain event.
Humber St, used by many as an alternative route to Oamaru's main street, Thames St, had been more heavily used since traffic lights were placed on Thames St, and some business owners in the area had said the bridge closure had hurt trade.
Mr Butler paid tribute to local business owners who had put Oamaru's transport needs ahead of their own profit margins for about five months.
"It's been inconvenient for our townspeople and especially for the businesses in this section of Humber St," he said.
"They have been absolutely brilliant in their understanding and tolerance for the delays."
