Until the recent flurry of publicity about the Lake Onslow proposal, pumped hydropower storage had not been seriously considered in New Zealand since the 1970s.
At that time the Tekapo canal was under construction to link the two main storage reservoirs (Lakes Tekapo and Pukaki) in the Upper Waitaki power development, and an obvious option was to design the canal to take pumped flow from Pukaki to Tekapo as well as gravity flow from Tekapo to Pukaki. The canal design was duly analysed, constructed and tested to have the required reverse flow capacity.
Instead, the newly developed Maui gas field was utilised and the Huntly thermal power station continues in use, and the importation of coal means that our thermal emissions have actually increased.
The disastrous outcomes of poor power planning have now been recognised, but the reaction seems to be one of panic, adopting the first scheme to come to mind while ignoring the alternatives, especially the final 10% of the Tekapo-Pukaki scheme.