In 1957 a decision was made to stop water flowing south from the Great Lake through the Shannon and Waddamana Power Stations and take it north to use the much bigger drop down the face of the Great Western Tiers. A fall of 830 metres was achieved using some of the most advanced engineering techniques available at the time. A six kilometre tunnel was drilled under a ridge to the northern edge of the Great Western Tiers. From here the water flows down a large, high-pressure steel penstock and vertical shaft into Tasmania's first underground power station at Poatina.
The Poatina Power Station is a huge underground excavation, as wide as a city street, as long as a city block and as high as a seven storey building. It houses six, 50 MW generators and is the State's second largest power station.
A variety of works was undertaken to increase the amount of water available for use at Poatina. A dam and small levee created Arthurs Lake from two smaller bodies of water. A pumping station was constructed on its western shore and water is pumped up 140 metres to a five kilometre flume. The water flows along the flume and down through the small automatic Tods Corner Power Station on the shore of the Great Lake. The energy used in the pumping station is recovered in part at Tods Corner and many times over at Poatina.
Penstock at Poatina
The storage capacity of the Great Lake was increased to 2300 million cubic metres with the completion of a 22 metre high rockfill dam at Miena (the third Miena Dam) in 1967. This dam was raised another six metres in 1982 to provide a further 700 million cubic metres of storage capacity. Because of its high head and large volume, the Great Lake represents 48% of Tasmania's total hydropower storage capacity.
Water leaving the Poatina Power Station flows through a 4.5 kilometre tailrace tunnel to a canal and eventually into the South Esk River via Brumby's Creek and the Lake River.
Inside Poatina Power Station