River planting probed for making flood damage worse

The review will investigate if flood damage was made worse by the plants. Photo/ Unsplash

A review of Taranaki's riverside planting scheme will investigate if flood damage was made worse by shrubs and flaxes meant to protect streams from pollution.

In February western Taranaki from Ōpunakē and Ōkato saw record-high flows in rivers and streams, causing widespread erosion of their banks.

Plants were washed away including shrubs and flaxes planted under Taranaki Regional Council's riparian programme.

Vegetation blocking water flow was blamed for increasing damage to culverts and bridges and councillors called for a review.

Since 1996 more than six million plants have been used keep stock out of streams and help trap and filter farm runoff.

On Tuesday councillors unanimously voted for an independent reviewer to look into storm damage including examples where it had been made worse by vegetation.

The reviewer will weigh the risks and benefits of planting close to waterways.

Council staff, contractors and landowners will be interviewed, and a sample of existing plantings audited to see how they might affect stream flows.

The reviewer will scope climate change impacts and recommend possible changes to the planting programme.

At a TRC meeting on Tuesday, chairman David MacLeod said the reviewer did not need to assess the benefits of riparian planting.

"We've got plenty of evidence scientifically to prove that it's doing a great job."

He said the review was more about "having riparian margins planted with certain types of plants … and maybe even the type of mechanical structures that clearly gave problems".

"If you've got small culverts that are easily blocked, whether there's a mechanical solution as much as a change to the riparian element."

Councillor Tom Cloke said it was good to question whether the council was doing the right thing in regards to planting streams and rivers.

"I agree it was never [about] the effectiveness of the riparian plan, but it doesn't do any harm just to question is that correct or not."

Local Democracy Reporting is Public Interest Journalism funded through NZ On Air.