A "good dollop of rain" over parts of the Waikato has caused the Waipa River to flood and raised the likelihood of a once-in-20-year flood event.
Farmers were yesterday urged to remain vigilant and move stock to higher ground if needed after Waikato Regional Council warned days of steady rain would cause the Waipa River to flood.
The downpour also caused havoc on the region's roads with a spate of car crashes and road slips.
Adam Munro, regional council's regional hazards programme manager, said up to 245 millimetres of rain fell in parts of the Waikato since Saturday, with the region west of Te Kuiti hardest hit.
He said a further 40mm of rain between 8am and 3pm yesterday had raised expectations of a once-in-20-year flood.
"It's not a civil defence concern at this point it's more a river user heads-up and we want to make people aware that rivers are going to be very dangerous over the next few days," he said.
"At the moment the Waikato River is coping pretty well, it's really the Waipa River that's reacted to all this rain which is not surprising given all the rain that's fallen in the Waipa and west coast catchment.
"It's been a good dollop of rain."
After liaising with the regional council, Mighty River Power yesterday began releasing extra water from Lake Karapiro to allow it, if necessary, to keep water back from the lower Waikato over the coming days.
The regional council has warned of potential flooding of the lower Waikato River when the Waipa flood waters join the Waikato River at Ngaruawahia in the next two days.
"The peak will probably take a few days to run through the system to Ngaruawahia and by the time it gets to Mercer it could be the end of the week. It's going to be a long, slow flat peak so we're going to have above normal levels for quite a few days."
Christine Baldock, who owns a lifestyle block on Otewa Rd, south-east of Otorohanga, said there had been moderate flooding on surrounding farmland.
Parts of Otewa Rd, which runs adjacent to the Waipa River, had also flooded in the downpour, she said.
"It's been steady rain here but it hasn't been heavy. For it to be flooding as much as it has, it must be pouring down in the mountains."
Meanwhile, heavy rain caused a 60 metre-long slip on State Highway 3 near Awakino with road crews working late last night to clear the debris.
NZ Transport Agency acting state highway manager Karen Boyt said the slip, east of the Awakino Tavern, blocked both lanes and would likely take several days to clear completely.
She advised motorists travelling between the Waikato and New Plymouth to take alternative routes. In other parts, Ohura township, west of Taumarunui, was cut off after Ohura Rd flooded.
RIVER FLOWS SINCE MIDDAY SUNDAY
Waipa River (at Whatawhata): Has increased from 50 cubic metres per second to 255 cubic metres per second and rising.
Waikato River (at Ngaruawahia): Has increased from 320 cubic metres per second to 500 cubic metres per second and rising.
- © Fairfax NZ News