The flooded farmland at lake Wairarapa prior to the Lower Valley Scheme. PHOTO/WAIRARAPA ARCHIVE

BECKIE WILSON and DON FARMER

A radical idea that could result in redirecting the Ruamahanga River back into Lake Wairarapa has been floated at a Greater Wellington Regional Council meeting.

Although only in its infancy, the idea has prompted a feasibility study and may result in more detailed investigations into its viability.

Redirection of the river back to the lake, it is claimed, will greatly improve its poor water quality and restore its mana.

It was discussed at a meeting of the regional council’s Wairarapa Committee on Thursday.

In 1963, work on an ambitious flood protection project known as the Lower Valley Development Scheme began which diverted the Ruamahanga River away from Lake Wairarapa.

It was one of New Zealand’s largest and most ambitious flood protection projects involving a land area of 31,500 hectares and was not finally completed until 1983.

The barrage gates under construction on the diversion. PHOTO/WAIRARAPA ARCHIVE

The scheme’s present-day value is $86 million and it has an annual maintenance budget of $500,000.

Ruamahanga Whaitua team leader Alastair Smaill said the idea was proposed by people in the community and local iwi.

While still in the early stages of feasibility, the Ruamahanga Whaitua committee has done modelling work to see if the redirection of the river would improve the lake’s water quality.

“The results we have are certainly encouraging to the point I think the whaitua will recommend to the regional council that further investigations are under taken in terms of feasibility,” Mr Smaill said.

He said redirecting the river back to the lake may improve the E.coli situation.

The lake’s health is monitored according to the Trophic Lake Index.

Mr Smaill said returning the river to the lake would complement the role of the wetlands in the moana.

The aim, decades ago, of diverting the river away from the lake was to manage floods in the lower valley.

Mr Smaill said an option that will be researched is to continue the flood flows down the diversion into the sea, and allow the smaller flows to be diverted into the lake.

“There are a range of options and it is quite early days, how you would design that and what flows go where, and what that does to lake levels, are still unknowns.”

Mr Smaill said there was no estimation of the time frame, and cost and funding would be the big questions.

South Wairarapa District councillor and previous Wairarapa Catchment Board chief executive Colin Wright said if the proposal resulted in improved water quality and maintained flood protection, it was a positive step.

“The way it used to be, before the catchment board did all this work years ago, was flood levels would often be a couple of metres higher than what they are nowadays,” he said.

“Today, there is also not only an emphasis on that, of course, but there is an emphasis on water quality and so on, which basically got little consideration back then.”

Mr Wright said he was optimistic about the plan to partially return water at times of low flows.

“From what they have explained, they are only talking about the low flows into the lake. If they can keep the higher flood flows out to sea, that lessens any concerns I have got.”

Mr Wright worked for the Wairarapa Catchment Board as an officer, then chief engineer, and later as its chief executive.

Joseph Potangaroa, of Rangitane o Wairarapa, said he had heard some suggestions around the diversion of the river back into the lake.

Mr Potangaroa said from a Maori perspective, there should be no altering of the natural course of water ways.

“From the beginning there was a fight to stop it from being altered — a number of reasons for that, one being it was going to reduce the ability to gather food.”

Mr Potangaroa said the lake had been a staple-food source “probably for centuries”.

He hoped that any further changes would not affect the large amount of planting done by surrounding farmers and the community.

“Perhaps in terms of the health of the lake if the Ruamahanga goes back in there to help circulate more water, it must be a good thing.”

Ra Smith, of Ngati Kahungunu ki Wairarapa, said he fully supported returning the river to the lake.

The plan to continue using the diversion for flood flows and to divert low flows, or cleaner water, to the lake was sensible.

“We are trying to keep sediment out of the lake so letting floodwater into the lake would only increase sediment,” Mr Smith said.

He said one of the principal features of the Ruamahanga was Mauri, or its connecting essence.

Rivers such as the Waiohine, Waingawa and Waipoua along with a range of other waterways connected to the Ruamahanga.

“There is only connection missing and that is the connection of the Ruamahanga to the lake.

“In Maori terms if the two biggest water passages can come together, then wow,” Mr Smith said.