06 September 2024
Header image: Devils Gate Dam in North-West Tasmania 'on spill'
A spillway is a common feature of hydroelectric dams. They are designed to let excess water leave the dam when the lake is full – we call this water 'spill'.
Trevallyn Dam in Northern Tasmania 'on spill'
While Hydro Tasmania manages a few lakes that can hold water for years (Lake Gordon, Lake Pedder and yingina/Great Lake), most of our 52 lakes are part of “run of the river' hydropower schemes.
Run of the river hydropower schemes harness the natural flow of the river, generating electricity through a series of power stations as the water flows downstream and eventually out to sea. This means we can generate electricity using the same water as it travels through each power station, one after the other.
Hydropower lakes, often called ‘storages’, don’t hold much water and can fill up very quickly in winter and during heavy rainfall. Spilling is a normal part of how our dams operate and it’s what they’re designed to do!
Graphic showing the 'run of the river' lower half of the Derwent hydropower scheme: After moving through Tarraleah Power Station, the same water will flow through five more hydropower stations before making its way down the River Derwent!
Run of the river storages do not increase the risk of flooding downstream. The incoming water either goes through the machine or over the spillway, so the amount of water downstream remains the same. In some run of the river schemes, some water is diverted between storages via tunnels or penstocks, like in our Mersey-Forth Scheme in Tassie's North-West - but these are still considered to be run of the river systems.
During the recent heavy rains, more than half our dams were 'on spill'. Our teams mobilised across the state, working 24/7 alongside emergency services to keep people safe, monitor and maintain infrastructure, and keep the power on.
We also give important hydrological data to the Bureau of Meteorology and State Emergency Services so they have all the information they need to plan during extreme weather events.
The silver lining is the increase in water storages across our system, including in the major lakes, after what has been the second-driest year in the last century. Total energy in storage rose by over 5% in the last week!
You can stay up to date with how full our storages are by checking our lake levels page, and learn more about the different hydropower schemes across Tasmania by clicking here.
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