A massive irrigation scheme in Hawke's Bay could result in the influx of 106,500 dairy cows capable of producing more than 1.72 million litres of milk a day, a Hawke's Bay Regional Council report says.

The cows would be on the Ruataniwha Plains area, in central Hawke's Bay, which has traditionally been beef and sheep country.

The council has produced a report on the possible effects on groundwater and surface water, but this has yet to be made public. It has been issued to stakeholders only this week.

The council's $230 million Ruataniwha Water Storage scheme involves building a dam on the Makaroro River and increasing the amount of irrigable land on the plains, west of Waipawa, from 6000 hectares to 30,000ha.

The council is still carrying out studies on the scheme and expects to lodge a resource consent application with the Environmental Protection Agency with the aim of starting construction of the dam in 2014.

The council's own Regional Land Transport Strategy 2012-42, made public this month, discusses the possibility of 40,000ha being converted to dairy farming.

Previously the council has said the scheme would irrigate only up to 30,000ha. A council spokeswoman could not explain the variance.

The transport strategy says the scheme would drive land-use change through irrigation and "this would transform the intensity of agriculture on the Ruataniwha Plains and demands on road and transportation".

If all 40,000ha were converted to dairy farming, it would produce 1.72 million litres of milk a day.

Using Dairy New Zealand figures for milk production per cow in Hawke's Bay, this would equate to 106,500 cows.

"Irrigation of the Ruataniwha Plains is forecast to generate up to the equivalent of 86 milk tankers of 20,000-litre capacity on the roads a day," the strategy says.

If Fonterra took the milk, it would transport it to its depot at Oringi, south of Dannevirke, via state highways 2 and 50.

Alternatively, the milk could go to an "entirely new local dairy factory [at Waipukurau, for example], although no such factory exists at present", the strategy says.

"However, a small independent dairy factory could be established in the local area if there were a strong growth in dairying on the Ruataniwha Plains."

The strategy, which outlines future demands on the road network, says that some dry-stock farmers now on the plains might choose to convert to cropping.

The regional council did not respond to questions.

- © Fairfax NZ News