Horizons Regional Council beginning flood resilience projects on Whanganui and Rangitīkei river

The Horizons Regional Council is installing a gate on the stopbanks of Kōwhai Park to more quickly release water if floodwaters breach the bank. Photo / Bevan Conley

Horizons Regional Council staff are planning to start work on major flood resilience projects in the Whanganui and Rangitīkei districts in the next few weeks.

Catchment operations manager Dr Jon Roygard said work was about to begin on the installation of an egress gate on the stopbanks of Kōwhai Park to allow for the faster release of floodwaters in the event of the Whanganui River cresting over the banks.

“During a flood that we’ve had in the past at Kōwhai Park, obviously the water’s over-topped and got in there and has had a lot of trouble getting out,” Roygard said.

The gate would allow the water to get out of the area faster to provide easier and better access for residents and emergency services after a flood.

The gate was part of a longer-term Horizons project to address areas along the river where staff have previously had to install temporary structures when there has been a possibility of flooding.

“What we’ve been doing is putting things in so they’re permanent but we haven’t inconvenienced people... so we’re not having to send staff out and put structures in place that are perhaps less reliable than a permanent solution,” Roygard said.

He said the council aimed to get the project under way in mid-May and have the majority of the work finished in around three weeks.

Horizons will do flood prevention work in the Rangitīkei River. Photo / Bevan Conley

Minor follow-up work, such as re-establishing grass in the area around the gate, would follow but would be weather dependent.

The council also plans to do channel management work in the Rangitīkei River to make it more resilient in flood conditions.

The work, co-funded by the Government as a climate resilience project, will involve removing vegetation such as weeds from the river to allow water to move more freely.

“[It’s] giving the river a corridor to move in so that it can shift more of its own gravel through and cause less damage during floods,” Roygard said.

This would allow the river to be a more natural and freer system.

“The river system has become a lot more enclosed or a lot narrower because vegetation has built up around it so the river becomes restricted and then during a flood it sort of forces itself outside of that,” Roygard said.

Doing this work would give the river a wider corridor, which would help keep it within its stopbanks in flood conditions.

Currently, the project is programmed to be completed by the end of June 2024 but the schedule may have to be extended due to work being undertaken to repair damage caused by Cyclone Gabrielle.

Horizons recently had $9 million in funding approved to enact cyclone-related repairs in the region, some of which will be put towards the damage in the Rangitīkei district.

Roygard said the council hoped to get the major clean-up work completed before winter.

“We’re really focusing on those places that might cause damage to key infrastructure or homes or those sorts of things in the first instance because we know we can’t get it all done prior to winter but we want to make sure that real priority stuff is done.”

However, it would take between two and three years to have the damage fully repaired.

He said it had been a busy time for council staff, but he was pleased to have the funding approved after assessing the damage to the region post-cyclone.