A leading hydrologist says there is potential for another mega reservoir, on par with Lake Tekapo (above), in Central Otago. He says such a storage facility could solve farmers’ irrigation woes and alleviate power shortages.
Potential exists in Central Otago for the world’s largest pumped-storage reservoir, linked to the Clutha River by a 15km tunnel.
In summer the reservoir would supply farm irrigation water and in winter power generation at Roxburgh, says Waikato University hydrologist Earl Bardsley, associate professor in the department of earth sciences.
Along with storing a vast reserve of farm irrigation water, the scheme would at least treble the total national hydro-power energy storage capacity, producing an energy storage capacity of 10,200GWh of realisable potential energy, Bardsley says.
‘This would be a significant engineering scheme but the cost would be offset by benefits to farmers and others,’ Bardsley told Rural News. ‘We’re lucky in New Zealand with our topography, which enables such schemes.’
Commenting on recent spilling of water from the Benmore Dam on the Waitaki River, Bardsley says the lost generating potential highlights the need for a large pumped storage scheme in the region.
He proposes turning the Onslow-Manorburn depression into one gigantic reservoir – it already contains the Upper Manorburn, Greenland and Lake Onslow reservoirs – 800m above sea level. This is about about the same elevation as Lake Tekapo, New Zealand’s highest major hydro storage lake.
The Manorburn reservoir, 40km south-east of Alexandra, is one of the largest areas of natural ice in New Zealand, attracting thousands of visitors to skating and curling.
The scheme would allow hydro generation rivers to revert to natural summer/winter flows. Water flow is naturally low in summer and high in winter, but the hydro-power dams neccesitate dumping in summer and conservation in winter. These are currently reversed by, for example, the Benmore hydro scheme.
Reverting to natural flows would benefit farmers on both the Clutha and Waitaki rivers, Bardsley says.
Winter flows would drive generators powering pumps that sent the water through the rock tunnel to the new reservoir. In summer the water would flow back down the tunnel to the river, available for farm irrigation.
Bardsley says the scheme’s viability has been verified using a pumped storage simulation coupled with past Clutha River flow records. The river would be maintained within its normal discharge scheme because ‘water release for electricity supply tends to coincide with times of low Clutha flow, while river water for pumping would be extracted during times of high flow’.
The reservoir could be located entirely within the Onslow basin, or the Onslow and Manorburn basins could function as a single reservoir if they were connected by a cut or tunnel.
