Meridian overturns conventional wisdom on hydro costs

By RICHARD BRADDELL utilities writer

Meridian Energy chief executive Keith Turner has big plans - billion-dollar plans to turn the conventional view of hydro power costs on its head.

Dr Turner's dream is to build six dams, connected by a series of canals, alongside the South Island's Waitaki River. Together they would generate electricity equivalent to the output of the Clyde Dam, supplying 8 per cent of New Zealand's needs and providing irrigation to farms.

The proposal is remarkable for several reasons. One is that Dr Turner reckons it will produce electricity at less than 4c a kWh, a third to a half less than conventional wisdom says hydro schemes should cost.

The savings lie in the design of the scheme. In the past, hydro schemes have typically involved expensive dams strung across river valleys to form lakes.

Project Aqua, as Meridian's scheme is known, has a big lake. But it is behind existing dams on the upper reaches of the Waitaki. The new dams would simply channel water out of the Waitaki into canals running alongside.

The canals would run at a shallower gradient than the river, so after a few kilometres there would be sufficient fall to drive a turbine in a small power house.

In combination, the six power houses would generate 570 MW or 3200 GWh of electricity.

Computer simulations suggest the network of canals and dams would have nothing like the visual and ecological impact that might be expected. One reason is that, instead of constructing the canals out of tonnes of concrete, they would be created by bulldozing gravel into 2.5m-high stopbanks.

Another is that the dams and their powerhouses would be much smaller than traditional hydro installations. Each dam would have only one turbine, and it would be remote controlled, eliminating the need for local support facilities. Furthermore, in contrast to large dams that boost their bulk with large crane infrastructures, Project Aqua's six dams would share one mobile crane.

But visual impact is just one improvement. Hydro schemes typically interrupt water flows, making life difficult for spawning salmon and eels. They can also disturb river mouth ecologies by blocking normal silt deposits carried downstream.

Dr Turner says that would not be the case with his scheme, because although up to two-thirds of the Waitaki's water would be drawn off into the canals, there would always be water flowing through channels without dams, following a natural course to the sea.

He says the scheme would leave water in the Waitaki at no less than the minimum the resource consents for the existing dams specify.

The scheme aims to avoid the overbuilding of traditional hydro dams, which have to withstand one-in-a-thousand-year floods. Project Aqua's tolerance would be one in five years. And then, if its stopbanks were breached, they could be rebuilt even as flood waters recede.

But Dr Turner's scheme is only a proposal, and, if it gets off the ground (it would be operational in six years), who would use this electricity?

Meridian has already made its views known about constraints on Transpower's transmission lines, which prevent it getting power to Auckland at peak times.

Dr Turner brushes that concern aside. Comalco has stepped up consumption by 800 GWh since 1995, an amount equal to New Zealand's annual consumption growth.

Otago and Southland have been booming on the back of horticulture, viticulture and energy-demanding dairy farm conversions. Downstream processing from those alone will demand new electricity sources. And demand can only increase from the boost to production from improved irrigation.