An unexpected river rise of more than 679 cubic metres in two hours trapped eight people and two dogs in two vehicles on the Waimakariri River on Wednesday.
That wall of water sparked an urgent rescue of the group from emergency services and the coastguard, north of Christchurch, shortly after 4pm.
"We were on the rocks and then we got stuck," rescued passenger Kayla Watts says.
"We got bellied out and then, within five minutes, we were under water up to our shoulders."
Some of the group managed to scramble to the rooftops of their trucks, where they waited for an hour until rescue, after spending the afternoon in the riverbed.
The coastguard was called in and rescued the group - one person was taken to hospital with moderate injuries.
Data from Environment Canterbury (ECan) shows the Waimakariri River flow had risen from 147 cubic metres to 826 cubic metres in little more than two hours in the afternoon.
'Wrong spot, wrong time' - coastguard
The local coastguard needed three trips to rescue all of those involved.
"They were very lucky," says coastguard volunteer Glenn Scott. "The water was up to their chests and the river was rising, so they possibly could have got in to really deep trouble.
"There were warnings about river levels and high-country rain. Whenever there is a norwest [weather] system, the [Waimakariri River and] Rakaia River all rise.
"This time, it just rose very, very quickly."