The aim of this year's post-flood talk fest is to find out whether Whanganui people are willing to pay for more protection, Horizons Regional Council river manager Ramon Strong says.

Some have pointed at Palmerston North's protection from 500-year floods - provided by Horizons - and asked why Whanganui's Anzac Pde only has 30-year protection.

The answer is simple, Whanganui Horizons councillor David Cotton said.

"Manawatu ratepayers said they would pay for it."

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Horizons has been talking to Whanganui people about what they want. Mr Strong gave a short presentation to about 45 in the Whanganui Girls' College hall on Monday night.

He gave rough estimates of the costs of various options.

The 600 ratepayers affected by flooding in the Matarawa Stream will be asked to contribute to a scheme to keep it clear of vegetation, he said.

The district can expect five to 10 per cent more rain because of climate change. There are likely to be more and larger floods, with sea level rising and more moisture in the atmosphere.

The Anzac Pde stopbank would need to be raised another 1.5m to withstand a 200-year flood. There's a 0.5 per cent chance of a flood that size happening in any year - but there can always be one next year and the year after.

Horizons has surveyed the Whanganui River since the 2015 June flood, and discovered it has the same capacity to carry floodwater as 20 years ago. Fine silt from the flood is still being flushed out.

"A large flood event like that mobilises a substantial amount of silt and it will keep moving through the river system for a number of years," Mr Strong said.

Jim Ennis said it was important for people to be able to see the river. He didn't like the idea of high stopbanks and supported raising and floodproofing houses instead.

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Residents needed more warning in the June 19-20 flood, and the Horizons website fell over. Mr Strong said a lot of work has been done to improve it.

Sara Dickon suggested storing floodwaters upriver, on flood plains. Mr Strong said the volume of water was too great.

"In June the river was carrying two Olympic-size swimming pools of water a second. We couldn't store that much."

One man said his Horizons rate had risen 208 per cent over 12 years.

"We can't afford to continue at that rate."

But Marie McKay said it took her a year to fix her two Taupo Quay buildings after the June flood. She applauded what had been done so far, wanted more protection and was willing to pay more in rates.

Former Whanganui Mayor Annette Main was annoyed Horizons had done no flood consultation last year, despite Whanganui District Council asking for it.

"It's now looking like three years before anything gets done."

She said the council had wanted 200-year stopbanks for Anzac Pde, Taupo Quay and Putiki and it was a small group "riled up by a councillor" that opposed them. If stopbanks had been started earlier they would have cost less and the town would have been protected.

Mr Strong said the council got 1500 submissions about flood protection for its 2012-22 Long-Term Plan, most of them strongly opposed to more stopbanks. The council hadn't wanted to push the matter.
Mr Cotton said he had asked around and it was more than a small group that opposed adding stopbanks.

There's no deadline for feedback. Horizons staff will be at the River Traders' market again this weekend and more formal consultation will be done in a year's time.

PROTECTION FROM A 200-YEAR FLOOD
Anzac Pde - raise and extend stopbanks, cost $6-$7million
Taupo Quay - 2.5km stopbank or floodwall, cost $4 million
Putiki - 600m stopbank, cost $1 million
Total cost $10 -$12 million

COST TO RATEPAYERS OVER THREE YEARS
People most affected $50-$60/year per $100,000 capital value of property
People less affected $25 to $30/year per $100,000 capital value of property

THE MANAGED RETREAT OPTION AT ANZAC PDE
No new building in flood zone
100 houses moved off, cost $23 million
Some houses raised and some houses moved off, cost $15 million
Still problem with SH4 flooding
Could set precedent for moving Whangaehu and Scotts Ferry houses

THE DO NOTHING OPTION
Cost to repair June 2015 flood, $7-$15 million
Cost to repair future flood damage
Cost to business, transport and reputation