Call for river mouth to be on flood opening list

Buller constituency regional councillor Chris Coll has asked for Westport’s Orowaiti River to be added to a list of river mouths that can be opened up at short notice when floods are looming.

The West Coast Regional Council is reviewing its rules for digging out blocked ocean outlets, at the urging of Cr Peter Ewen after last year’s Wairoa flood disaster.

The Hawke’s Bay Regional Council was accused of failing to open the Wairoa River bar in time to save the town from a one-in-250-year flood during Cyclone Gabrielle.

And an independent review recommended closer monitoring and preventive measures, including an overflow trench.

Cr Coll said the merits of an Orowaiti "cut" had been hotly debated over the years, but he believed it deserved another look.

"If we ever need to tweak the planned stopbanks, it could give us a bit of wiggle room in terms of water levels — a safety valve of sorts."

The Orowaiti and its lagoon act as an overflow for the Buller River, effectively turning the town into an island in large flood events.

A Niwa report in 2015 said the idea of a cut through the sandbar should be explored but warned it could also expose the town to the risk of flooding from tidal surges.

In a report to the council’s operations committee last week, catchment staff proposed work to rationalise the way the council managed river-mouth risks.

More than 40 rivers and creeks on the coast can have their ocean outlets opened as a permitted activity. No resource consent is needed.

Three more on the "permitted" list — Karamea, Pororari and New River — can have their outlets to the sea opened when floodwaters back up to a "trigger" level, threatening property.

But the council cannot dig out a new, more sustainable outlet without resource consent even when the current one is likely to be quickly choked again by sediment.

That rule was written after consultation with Doc and iwi some years ago, staff reported — but more flexibility could be helpful.

Cr Ewen said he supported Cr Coll’s suggestion the Orowaiti should be on the "permitted" list, and he would also include the Hokitika River.

"The biggest flood Hokitika ever had was in 1947 when the sand bar was choking the river mouth — the water was all through the town. We should be looking back at our history."

The committee approved the staff’s proposed work programme and noted the issues raised would be up for review shortly as work began on the new coastal plan.

— Lois Williams, Local Democracy Reporter

— LDR is local body journalism co-funded by RNZ and NZ On Air.