The discovery of part of Rotorua's original water supply system - along with rain and soft ground - has delayed the completion of the Hemo Rd intersection redevelopment.
Work on the $8.1m intersection was scheduled to finish in the middle of this year but is now expected to be finished by October.
Soft ground in some areas, significant rainfall, and the discovery of two colonial water tanks on Old Taupo Rd, dating back to 1897, meant more time was needed, according to the NZ Transport Agency.
The Transport Agency regional relationships director Parekawhia McLean said they put a hold on works near the tanks last year while they worked through the discovery and got it added to the historical record.
"This work should add some valuable material for people studying colonial civic history in Rotorua," she said.
The tanks have been recorded on the New Zealand Archaeological Association register and have been preserved below the ground.
The tanks were discovered last July near 451 Old Taupo Rd. One is a rectangle structure measuring 2.3m by 3.6m with 28cm concrete walls and the other is a trapezoid shape 21m long and up to 6.4m wide.
Work near the tanks was put on hold for around two months while they were studied.
Despite the delays Ms McLean said significant progress had been made.
"The crews have been working hard, however the weather has not been on our side and there were also some areas of soft ground that we had to stabilise before being able to lay service pipes."
Work will now focus on the roundabout formation over the three underpasses, formation of Mokoia Drive, and construction of the State Highway 30 pavement, barriers and lighting, landscaping, line marking and signage.
The roundabout will boost safety at the high-risk intersection, provide cycle and pedestrian access and create a gateway to Rotorua.
A timeline for completion of the 12m sculpture to be installed on the roundabout is expected to be finalised this month.
The sculpture is being funded by the Transport Agency, Rotorua Lakes Council, and Te Puia with potential for others to contribute.
More than $17m worth of transport projects are under way in Rotorua including the Hemo roundabout, walking and cycling connections and safety work. Last year the Government also announced $24m in funding to transform the central and eastern corridors in the Connect Rotorua project.
The preferred options for both corridors are expected to be announced later this year.
The concrete settling tanks
•The tanks have been recorded on the New Zealand Archaeological Association register and have been preserved below the ground.
•They were discovered in July 2016 near 451 Old Taupo Road.
•One is a rectangle structure measuring 2.3 metres by 3.6 metres with 28 cm thick concrete walls and the other is a trapezoid shape and is 21 metres long and up to 6.4 metres wide.
•Work near the tanks was put on hold for around two months while they were studied.
•Finding old water supply isn't unusual in New Zealand but the tanks that are found are associated with goldmining sites rather than civic sites.
•The find offers a chance to understand the early water supply for Rotorua and assist in understanding how the tanks functioned.