With more rain due, Plimmerton residents are continuing to face a big clean-up, a day after water surged through properties in the seaside suburb north of Wellington.
Plimmerton fire chief Carl Mills said it was an exceptional event and something he hadn't witnessed before during 25 years of service.
Plimmerton was hit by torrential rain leaving some residents ankle deep in water in their living rooms.
State Highway 1 on the Kapiti Coast between Paekakariki and the Plimmerton roundabout was closed for several hours, causing major delays for drivers.
NZTA spokesperson Mark Owen told Morning Report the volume of rainfall yesterday was too great for the "storage area", and "combined with the high tide, the water just could not get away."
"[The highway is] clear for now but there is more rain forecast for this afternoon so it is a concern. It just really highlights the vulnerability of our network in New Zealand with the weather events, particularly with these high intense rainfall events that can have a high impact over a short duration."
Owen said they were working with regional and local councils to on preventing this situation from occuring in the future, with one of the longer-term considerations being the Transmission Gully.
"That'll give the highway traffic an alternative route. But in that particular area [off the highway], it's obviously going to be an ongoing concern, so we need to work with the councils around what the options are for improving drainage when we get these high rainfall events.
"Even if you increase the drainage slightly, the sheer volume of water that arrived just could not get away, so you either have to retain it somewhere in very, very large ponds or get it out in the sea, and with a high tide, the water just can't get away so that's when it backs up and we have flooding."
The road clean up was continuning, he said, urging motorists to plan their journey ahead as more rainfall was forecast later today.
There was potential for more road closures, but that depended on how heavy the rain was and tide situation, he said.
The deluge caught Plimmerton local, Hazel Kale, completely by surprise. She woke up at 8am to the flooding and left the house to check on her father, Trevor, who was trapped by the rain.
"We were just surrounded by water. We got water off the road, coming down from the hills, on to our property. So we were absolutely surrounded by water."
He said it wasn't the first time flooding had occurred. "We've had a couple the last three or four years. Next door has been flooded out two or three times now, but this is probably the worst one that we had."
Resident Dave Anderson's home was also flooded. He told Morning Report his house was a mess, and that the floors were sodden with water.
"Outside on the road it's just full of slush, it's about knee-high deep. We're waiting on the contractors to come and pick it up."
He said the community response to the emergency had been incredible.
"People who we didn't know came down with wheelbarrows and shovels, cakes, fish and chips and we got it all cleaned-up outside. But now we have to sort out inside, which is going to be a challenge."
Porirua council crews are continuing with the clean-up this morning.
Emergency services said they couldn't stop a huge amount of debris from blocking drains and contributing to flash flooding in Plimmerton yesterday.
Fifteen homes were declared uninhabitable.
Plimmerton fire chief Carl Mills told Morning Report the clean-up had been an incredible community effort, meaning most of the roadways were passable, apart from one street.
But some homes had been severely flooded, with living rooms filled with water knee-high, he said.
"We were able to help six properties pump out residual water. The good thing is a lot of the water has gone, but now the sadness will set in with the internal property damage and with people recognising how this has impacted them."
Most of the water pooled around Karehana Park, which was in a narrow valley.
"The valley has a few more sub-valleys with houses going up and rain has literally been funnelled all down to this one location and in many cases there's been one house at the bottom of a kind of mini trough and they've born the brunt of, not just water, but silt and debris which has come right up against walls, blocked in cars."
He said existing drains just couldn't cope and debris cascading down the valley was too much for authorities to stop. A high-tide at 10am at the peak of the rainfall made matters worse, he said.
"From what I saw the amount of debris that had been washed down was something I haven't seen in 25 years, with trees stumps... and things we just couldn't stop. This was quite exceptional."
MetService is forecasting patchy periods of rain from midday that will intensify later in the afternoon. Heavy rain is forecast for this evening, starting at about 7pm.
Mills said local authorities would be looking closely to ensure drains remained unblocked and had capacity to deal with it.
Council crews have a big job on their hands today - clearing silt left by flash flooding.
Porirua Mayor Anita Baker said she was grateful to everyone who had offered to help with the clean-up. She denied the state of the drains were to blame for the damaging flood.
"We had a 7.1 high-tide, we had torrential rain and yes, our culverts got blocked because we had so many logs and branches coming down. Yes, we have issues with some of our pipes, but I think that it was the amount of rain that actually came through the valley that time.
"I think the residents and the council have done a fabulous job getting in there and helping out."