New dam plans for Clutha River released

Contact's Clyde Dam on the Clutha River. Photo/ Stephen Russell

Plans for up to four new hydro-electric dams on the Clutha River have been released by power company Contact Energy.

Contact has started a public consultation process around a variety of options, which include large new storage lakes and dams on a similar scale to the Clyde Dam, currently New Zealand's biggest.

A consultation website with information and "discussion boards" was launched this morning.

By next year the company hoped to be in a position to announce a preferred option.

The four dam options were originally investigated by the Electricity Corporation of New Zealand and inherited by Contact when the company was formed in 1995.

Indications of the possible costs of the options range from $300 million to $1.5 billion.

Contact said its modelling showed a role for new hydro developments in the coming 15 years as electricity demand continued to grow and existing large-scale coal-fired generation was phased out.

It preferred to put hydro developments on rivers that had already been modified.

The Clutha already had two large hydro dams on it and was big enough to enable further development, Contact said.

"We think the plans that have already been developed for the Clutha are likely to represent the country's best options for new hydro development."

The largest and furthest downstream option is for a dam about 2km upstream from Tuapeka Mouth on the Clutha.

It would be similar in size to the Roxburgh Dam, 40m wide at the base, 10m wide at the crest and 520m long, with an above-ground dam face 50m high.

The dam would create a lake in the Clutha Valley of about 3400ha extending some 50km upstream from the dam, with the lake level almost 50m above the existing river level at the dam site.

The current Beaumont township would be inundated along with much of the Rongahere Gorge.

Contact said the power station would have an estimated capacity of around 350 megawatts (MW) and be capable of generating around 1950 gigawatt hours (GWh) of electricity a year.

In comparison, the Roxburgh dam had a capacity of 320MW and an output of 1650GWh a year, while Clyde's capacity was 432MW with output of 2100GWh a year.

Another option is for a dam about 4km upstream from the Beaumont township. It would have a 30m tall concrete gravity dam and a powerhouse in the existing river bed with diversion and spillway structures on the eastern bank.

A lake about of about 620ha would be created, extending about 23km upstream with the lake level about 27m above the existing river level. Estimated capacity would be around 185MW with generation of around 1070GWh a year.

An option for a 14m concrete gravity dam located in the Queensberry Hills area would include a 9.5km or 12km canal linking the dam to a powerhouse downstream.

The Queensberry option would have a 220ha lake extending about 8km up the Clutha valley to near Luggate. It would have an estimated capacity of around 160MW and be capable of generating 850GWh a year.

The fourth option is for a 25m-tall concrete gravity dam about 2km downstream from the Luggate Bridge, creating a lake of about 230ha extending about 15km to near Albert Town.

It would have an estimated capacity of about 86MW and be able to generate about 500GWh a year.

- NZPA