Why were these maps produced and what do they show?

Hydro Tasmania created flood maps for the Huon Valley region as part of mandatory requirements set by the regulator, the Department of Natural Resources and Environment Tasmania. They show the worst-case scenario of flooding if the Edgar Dam was to fail suddenly and are part of standard emergency management preparations.

We shared the maps with the regulator in 2016 and with emergency services, Tasmania police, and the Huon Valley Council Emergency Management Committee.

What is the chance of these floods occurring?

The scenarios shown in the maps are extremely unlikely a 1 in 10,000 or 0.0001 chance in any year. The risk at Edgar Dam is associated with a major earthquake (6.8 magnitude or greater) on the Lake Edgar Fault.

The upcoming strengthening project will reduce the risk even further to one in 1 million or 0.000001 in any year. We have more information on what risk means in the context of dams here.

What do these maps mean?

The flood maps show the worst-case scenario of what might happen in the very unlikely event of Edgar Dam failing suddenly. They cannot be used to provide certainties because the models used to produce these maps were based on data that was available at the time of production as well as a range of variables that would alter through time, such as catchment and river inflows, tides and river channel shape.

The maps show expected peak flood height and time to reach 'peak' flood at Judbury, Huonville, Glen Huon, Franklin, and Port Huon. This information was produced specifically to inform the regulator and for emergency management preparations by the State Emergency Service, Tasmania Police and the Huon Valley Council.

HRD Inundation Mapping - Edgar Dam - Earthquake Failure - Sheet 1 of 2

HRD Inundation Mapping - Edgar Dam - Earthquake Failure - Sheet 2 of 2