"We can't chain people to the desk and say they can't leave," he said.
He said the board discussed giving retention bonuses to staff who worked until the end to encourage them to stay.
But that idea was rejected.
"It would be an extra cost to the programme and it is a dangerous precedent to set," he said.
Senior staff were also being moved from incomplete SCIRT projects to work on private ones within the five contracting companies, he said.
But he said the companies had agreed not to do that unless they could provide a suitable replacement.
As of August, SCIRT had spent $2.08 billion of its total $2.2 billion budget for almost 700 infrastructure projects.
Of the spend, 70 per cent was on wastewater system repairs, with just 10 per cent spent on roads.
As each project is finished, all the files and information is handed over to the city council, which plans to continue repairs and upgrade roads gradually.
It is expected to take at least 20 years to return the roads to the state they were in before the earthquakes.
The city council has budgeted $4.6 billion over the next 10 years for capital works. Of that, each year about $150 million would be put into transport budgets and $150 million into "Three Waters" infrastructure, city services general manager David Adamson said.
That would pay for the remaining earthquake repairs to roads, footpaths and underground networks, as well as the normal replacements and upgrades.
City council Infrastructure, Transport and Environment Committee chairman Phil Clearwater said the city councillors were due to get a behind closed doors briefing on the situation at the council meeting today.
They would have a better understanding of how much work the city council would have to do after that, he said.
