Six of the seven Hamilton families whose properties were damaged by flash flooding cannot return home for another night.

The families are waiting for Hamilton City Council to carry out the final property assessments and are expected to be able to return tomorrow.

Civil Defence deemed the homes uninhabitable due to contamination from a water supply after flash flooding on Sunday afternoon.

One family has returned home, while three families placed in temporary accommodation and three who made their own accommodation arrangements face a second night away.

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Council's incident response controller Andre Chatfield said power was turned off to the properties as a precaution during the flooding, and electrical assessments are being completed as part of safety checks.

Community Development staff have spoken with all evacuated residents.

Hamilton City Council says its stormwater system worked as it was designed during a deluge in the city which saw 40mm of rain fall in less than an hour.

This incident was a localised and very heavy downpour affecting just one area, receiving more than 40mm of rain in less than an hour – almost half the average monthly rainfall for December.

The city's stormwater and wastewater services operated as designed – they were simply overwhelmed by the volume of water in such a short time. The network was not damaged, was operating normally within an hour or two and is operating as expected now.

When asked about yesterday's ferocious, yet brief, storm council's incident Response controller Andre Chatfield described it as a "highly unusual event, and could happen anywhere in the city or in New Zealand".

"It is a reminder of our Civil Defence messaging that unexpected events can, and do, happen."

Whatawhata Rd resident Peter Cague had lived in his house since 1984. It was the first time he'd had to be evacuated - and he hoped it would be the last.

He was unimpressed the storm water system was unable to cope and said ever since there had been recent, nearby developments in the area the street was prone to more flooding.

Residents were today waiting to be assessed by council staff and packing up sodden belongings as they awaited news about when their power and water would be reconnected.

Water levels were nearly knee high along Whatawhata Rd on Sunday after approximately 40mm of rain fell in less than an hour. Photo / NZME
Water levels were nearly knee high along Whatawhata Rd on Sunday after approximately 40mm of rain fell in less than an hour. Photo / NZME
Peter Cague, left, and son, Scott, were evacuated from their home yesterday due to a sewage pipe contaminating floodwaters. Photo / Belinda Feek
Peter Cague, left, and son, Scott, were evacuated from their home yesterday due to a sewage pipe contaminating floodwaters. Photo / Belinda Feek

However, Chatfield defended the system.

"The system worked as designed, and was back to normal in an hour or so after the deluge but it is simply not designed for this amount of water in such a short time."

As for the amount of water that fell, he said there was 40mm in less than an hour, with the majority in a 45-minute period.

Asked when affected residents would get back into their homes, Chatfield said the properties were still being assessed.

"The properties are being assessed today and we can provide information to families when we have the results of that assessment."

However, the city's wet weather would not impact the work carried out by council staff, he said.

Chatfield reminded residents that natural events or disasters could happen "anywhere, anytime".

"We encourage people to have their own emergency response plans and talk with their families about how they can be prepared for an unexpected event of any kind."