New data gathered from 20 years research has identified hundreds of Masterton properties as being at risk of flooding and homeowners are being alerted as to what measures they should take.

Greater Wellington Regional Council (GWRC) gathered the new data using aerial photos and surveys, electronic flood mapping tools and a range of analytical techniques to update a flood plain model dating back to 1995.

From a flood plain map just released, estimating a one in a 100-year-flood spread - it appears the new data greatly upgrades the risk from flooding especially from the Waipoua River and the previously risk area is enlarged to incorporate huge chunks of Masterton's housing area stretching from Akura Road and upper Oxford Street north of town to the Homebush sewage ponds and Lees Pakaraka Road in the south.

Landowners are being sent information packs explaining the flood risk to their properties which includes some of the "practical issues" they need to look at such as the impact on insurance policies and property development.


They will also be told how GWRC and Masterton District Council plan to manage the wider flood risk to the community.

Apart from sending letters to people directly affected by the updated flood data GWRC is also holding an open day on the Te Kauru Upper Ruamahanga Floodplain Management Plan.

This will be held next Saturday in the Frank Cody Lounge, Masterton, between 10am and 4pm.

Chairman of the floodplain management subcommittee Bob Francis said no one is at greater risk of flooding as a result of the new information.

"It simply pinpoints where flooding is likely to occur, if it happens.

"By arming people with knowledge about their specific circumstances we are helping them make smarter decisions on matters such as the development and insurance of their properties.

'We want them to be able to manage some of the potential, personal impacts of a flood," he said.

Subcommittee member Barbara Donaldson, who is also deputy chairwoman of GWRC, said people would be concerned but she wanted to reassure them the subcommittee was working to find a solution which would reduce future risks to property.

In its letter to property owners affected GWRC explains research into the impact of flooding in the Upper Wairarapa Valley has been done as the first step towards a flood protection programme.

It was initiated "given increasingly extreme weather in New Zealand and therefore a growing risk of flooding in Wairarapa."

A map is attached showing homeowners the difference between the previous flood model dating back to 1995 and the new one.

"What it shows is that your property appears to be at risk of flooding in the rare event of a major flood."

"GWRC and your district council are working with a committee of local people on development of flood risk solutions - which will include consideration of stop-banks, house raising, edge protection, and river management - over the next two years, and we will consult with you to help determine which options will be the best for you and others living in your area."

The new data is expected to have an effect on information required on Land Information Memorandums, commonly known as LIM reports, which are available to potential home and property buyers.

The GWRC map showing the flood hazard area is not strictly limited to Masterton and does impinge to some extent on rural Carterton, namely the Ponatahi and Gladstone districts.