Waitaki Mayor Gary Kircher also feared flooded stormwater pipes connected to, and inundating, the town’s sewerage system were causing raw sewage to escape. After the July 21 storm, when Oamaru received 161.2mm of rain in a 24-hour period, he told the Otago Daily Times he had asked staff to report back "on the situation around where it’s been into people’s basements ... and what needs to happen there".
This week, he said it was now understood that flooded gully traps, or basins in the ground that collect piped household grey water before it is emptied into the sewer, had instead been the "major contributor", especially in low-lying areas in the North End.
"This was a major rain event, something we haven’t seen ... for some 30 years.
"You end up with this inundation into these gully traps, and so that then fills the pipes, and then the pipes back up, and then you end up with it coming out of some of those gully traps. And then, in some cases, it was pushing lids off ... manhole covers. So there was all this mixing going on, all this backflow."
To guard against a repeat would be "an expensive operation and it would be a personal cost to people".
"Like anything, you’ve just got to weigh up the chance of these things happening, or the regularity of these things happening, versus the costs of doing something. And also you’re not going to be able to fix them all."
Waitaki District Council acting chief executive Neil Jorgensen said "quite a comprehensive review" was completed about 20 years ago and had identified "a phase" when stormwater pipes being connected to the town’s sewerage system was not well regulated — "a lot of historical connections" were discovered and all were addressed at the time.
"There’s still a few that sneak through as someone connects to the wrong pipe," Mr Jorgensen said.
"It’s not end-of-the-world stuff, it’s not like the whole street is connected to the sewer system."
One of the major items of the clean-up from the storm had been the repairs to the Humber St bridge, which was now expected to reopen before August 25.
After it was learnt the Alps 2 Ocean cycle trail had sustained about $250,000 in damage, the clean-up was now expected to cost $1.37million. Funding sources had not been finalised, he said, but would be a "mix of insurance, government contributions ... maintenance budgets, some reserve funds and finally consideration of the disaster fund".
Mr Kircher said assessing the cost to clean up from the flood had been "a moving feast".
"We’ll see where we end up," he said.
"We hadn’t wanted to be mucking around, trying to get accurate costs when actually we need to get on and fix these things."
