The Ka Huanui a Tahuna Alliance started upgrading services to lower Ballarat St on October 14 last year.
That section was supposed to have been finished by December 20.
The work includes construction of a new "outfall feature" into Horne Creek, by the Village Green. It is now understood that it will take about 12 weeks to build.
However, the Alliance said it was returning to the site on February 10.
That means lower Ballarat St, between Stanley and Camp Sts, will be closed until May 16.
There will be no general access to or from Athol St from lower Ballarat St for the duration.
Then, from February 19 until April 24, the Stanley-Ballarat St intersection will close to allow crews to connect the piped stormwater network.
Public bus stops will be relocated to the Stanley St carpark during that period and carparks will be closed.
Queenstown Lakes District Council commercial and procurement manager Geoff Mayman said while crews did install "a lot of utilities" last year, "they are considerably behind where we thought they’d be".
"It was more complex than anticipated."
Mr Lewers said that, similarly to the CBD street upgrades and the arterial road construction, crews had found many services they were not aware of or that were not mapped correctly.
"I think the average was a new one every 90mm when we did the street upgrades in the CBD."
The stormwater upgrades form a critical part of the overall 1.1km arterial road budget — which now sits at $128.02million.
When asked if the delays would have a further financial impact on ratepayers — the Alliance has asked the council for more money several times already — Mr Mayman said "it’s always [been] planned, and the project is going to carry on".
"I don’t know the detail, but if it is, it is minor in the scheme of things."
Mr Lewers said "put it this way, it’s a watching brief from my point of view."
As part of the next phase, the Alliance is planning night works from 10pm to 10am, from February 19 to March 17, Sundays to Thursdays.
That follows engagement with affected businesses and ensures access to Brazz and Speight’s Ale House will remain clear and accessible during the day.
Council property and infrastructure general manager Tony Avery said special conditions were imposed on the Alliance to ensure heritage features such as Wellingtonia trees, the historic courthouse building, the Ballarat St bridge and Horne Creek, were protected.
