Submerging farms, houses and roads may have to be the price of keeping Wairarapa watered in summer.
A shortlist of nine possible private land sites for dams and water storage for the Wairarapa Valley was announced yesterday by the Greater Wellington Regional Council.
The proposal outlines collecting around 270 million cubic metres of water during winter and discharging it in drier seasons to irrigate up to 60,000 hectares.
The largest suggested storage area near Kaituna, called Black Creek, would create a lake holding 78 million cu m.
It would flood 11 dwellings and a public road, and be about 4km long.
Wairarapa Water Use Project Leadership Group chairwoman Fran Wilde said the project could cost hundreds of millions of dollars and take about 10 years to put together, but stressed estimates were "extremely preliminary" due to a large number of assumptions and uncertainties.
So far, the 12-month investigation has been in 50/50 partnership with the Irrigation Acceleration Fund, under the Ministry of Primary Industries.
The nine sites, narrowed down from 243 locations, are mostly on privately owned land in south Martinborough, White Rock Rd, Mangatarere, Black Creek, Kiriwhakapapa, Te Mara, Te Ore Ore, Dorsets Rd and Mauriceville West.
Several more options may be considered in the upper Tauweru catchment area.
Ms Wilde said there was sufficient water available in winter running off the Tararua Ranges to refill dams for summer.
Their "whole of the valley" approach would require from 5 to 13 per cent of the average volume flowing from the valley in a 1-in-10 dry year, between 250-300 million cu m.
Users could be shareholders, or pay for the water use.
Analysis was at a very early stage, she said.
"We do not expect all these sites to be suitable, for a range of social, technical, economic, cultural or environmental reasons.
"The next step is to gather more in-depth information, which will provide greater confidence as to which sites are most suitable."
A pre-feasibility study will take about a year to finalise sites for a full feasibility study.
Around 200 landowners across the valley had been interviewed, with "really positive feedback".
The group had also contacted 80 landowners associated with the nine chosen sites, with eight responses.
Some had expressed concerns about effects on their future plans and wanted more discussions.
Ms Wilde was asked if the latest drought had helped their cause.
"It is a fact, we will be getting more extreme events, floods and droughts," she responded.
"We need to be aware of that."
She estimated irrigation benefits, over 20 years, could equate a $400 million GDP increase to the Wairarapa community.
"This has a huge economic impact for Wairarapa, a complete change on the economic landscape.
"People will be looking at land use change, not just dairying."
She said there was potential for investors but the cost was too big for locals.
"I would love to think there is a sense of ownership but we will need outside funding."
? More details can be found at www.wairarapawater.org.nz