Two dams upstream from Huonville in southern Tasmania are built on an active fault line. Hydro Tasmania has had modelling done to map the potential flood area if the dams failed in an earthquake. The dams were classified as high-risk assets in 2016 sparking a debate about the community's right to know.
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00:00It's a beautiful, still day on the Hewan River.
00:05The water here in Hewanville flows all the way from Lake Pedder, about 100 kilometres
00:10away, where there's two dams built alongside an active fault line.
00:15Edgar Dam and Scots Peak Dam were built in the 1970s, but recent research shows there
00:21have been three earthquakes on the fault line of up to magnitude 6.9 in the past 60,000
00:27years.
00:28It's not necessarily going to happen in a lifetime of mine, but the things do happen.
00:35Hydro Tasmania created flood modelling to show what would happen in the unlikely event
00:40of the dams failing, but chose to keep it under wraps to avoid causing unnecessary concern.
00:46Eight years later, it's been released under Right to Information to the Tasmanian Greens.
00:52The modelling suggests if Edgar Dam breaks, a flood peak of at least nine metres would
00:57flow down the Hewan, arriving at Hewanville after 12 hours, where it would start to spread.
01:03To put this into context, we're talking about a likelihood of one in 10,000.
01:07Buildings throughout the centre of the town would be inundated by metres of flood water,
01:12including the council offices, the police station and the SES headquarters.
01:18The council also called for the modelling to be released in the interests of emergency
01:22planning.
01:23It's no different than a bushfire or any of the events that we could have.
01:29It's those three things that you have to have your plan.
01:32Mock evacuations were carried out, but the flood mapping still wasn't publicly released
01:36by Hydro, meaning most residents are unaware.
01:39To actually inform them of what would happen if either of those dams were to fail, what
01:45the evacuation procedures would be.
01:47These maps, they're made really for emergency services response and scenario planning to
01:53be able to pull into action, so by nature then they look at the worst case, they're
01:57very pessimistic.
01:58Works to strengthen Edgar Dam have now been approved, and planning is underway to upgrade
02:04Scott's Peak Dam.
02:06But back in Hewanville, locals weren't letting something that has a one in 10,000 chance
02:10of happening per year ruin their day.
02:13Well if everything worries you like that, you know, have a big headache I suppose.
02:19You can spoil a lot of life by worrying about something that may never happen, and what
02:24can you do?