Unprecedented rainfall, landslips likely on saturated Waikato region catchments

Continuing downpours over the rest of the long weekend on top of unprecedented rainfall are increasing the risk of more landslips in some areas of the region, warns Waikato Regional Council.

The council’s Regional Flood Response Team activated on Thursday and continues to liaise closely with the MetService around its forecasts for the region.

“MetService has told us there will continue to be localised downpours in the Coromandel Peninsula, Waitomo and South Waikato areas,” said Regional Flood Coordinator Derek Hartley.

“These weather systems can be notoriously hard to predict, so there’s a high degree of uncertainty around timing, rainfall volumes and location, but some downpours could be as high as 40mm an hour. This intensity of rain can cause surface flooding, as well as rivers and streams to rise rapidly, so people should consider travelling only if they need to,” Mr Hartley said.

“We have our teams in the field inspecting our stopbanks, pump stations and flood gates to ensure they continue working as they should.”

Consistent rainfall over much of the region in recent days has resulted in elevated river flows and localised surface flooding around the region.

Waikato Regional Council and power company Mercury are working together to manage flows in the Waikato Hydro System in response to the rain. To create storage through the system, the Karāpiro dam is starting to discharge an increased volume of water and outflows from Lake Taupō are being reduced for the next 12 to 24 hours.

“This situation will continue to be reviewed, taking into account rainfall over this period. Our flood protection scheme is expected to manage the higher flows, but there will be a rise in water levels downstream on the Waikato River which may result in some flooding on low-lying land.”

The rainfall total at the Pinnacles rain gauge for January has so far recorded 1224mm, which is more than the 1133.5mm that fell in July 1998, making it the wettest month since records began in March 1991.

Yesterday Te Kūiti rain gauge recorded rainfall greater than a 100 year average return interval for 12 and 24 hour durations.

The council was working to understand “what the impacts of this rainfall on already sodden catchments is likely to be and where”, Mr Hartley said.

Based on MetService forecasts for further rain over the remainder of the long weekend, Mr Hartley said, there is a high likelihood of further landslips impacting the Coromandel Peninsula, in particular. 

“We’re taking a precautionary approach in our advice because of the unprecedented rainfall we’ve already received and the unpredictability of what’s to come,” Mr Hartley said.

“There may be futher landslips which have the potential to be quite damaging. So as well as being aware of the potential for rapid rises in river levels, people need to be alert to possible land movement and either contact 111 if you are in immediate danger or otherwise call your local council.”

The Regional Flood Response Team has been regularly briefing its partner agencies across the region to ensure preparedness, including local civil defence, Waka Kotahi NZ Transport Agency and the Department of Conservation.

The team is also working closely with the Waikato Civil Defence Emergency Management Group as it coordinates local and regional response activities to provide the best outcomes for the community.

People are urged to keep up-to-date with MetService forecasts, as well as updates from their local council, Waka Kotahi, local civil defence and power providers.

For the latest information, including links, visit waikatoregion.govt.nz/flood-room.