Edgar Dam

The Edgar Dam is an earth-fill embankment saddle dam, located offstream in the South West region of Tasmania, Australia.

Completed in 1973 as part of the Gordon River Power Development Scheme, the resultant reservoir, Lake Pedder, formed with the Scotts Peak Dam and the Serpentine Dam, was established for the purpose of generation of hydroelectricity via the Gordon Power Station, a conventional hydroelectric power station located to the northwest of the dam wall. The impoundment flooded Lake Edgar, a naturally-forming fault scarp pond.

The Edgar Dam, together with the Scotts Peak and Serpentine dams, are some of the few dams and reservoirs owned and operated by Hydro Tasmania that do not have an adjacent hydroelectric power station. The dam draws its name from the flooded Lake Edgar.

Dam overview Location The Edgar Dam, completed in 1973 by the Hydro Electric Corporation (TAS), together with the Scotts Peak and Serpentine dams, are three major dams that form the headwaters for the Gordon River Power Development Scheme. The dam is located near Lake Pedder's most easterly point where the Huon River descends from the Marsden Range into what is now known as the Huon Basin. In a straight line, the Gordon Power Station is to the north west of the dam wall; or approximately by road.

Also at the southern end of the Lake Pedder, the Scotts Peak Dam impounds the Huon River. At the northwestern end of the lake, the Serpentine Dam across the Serpentine River is impounded into Lake Pedder.

Technical details The earth-filled dam wall is high and long. When full, Lake Pedder has capacity of and covers , drawn from a catchment area of . The dam wall does not have a spillway.

Water use The water in Lake Pedder provides around 40% of the water used in the Gordon Power Station. This non-hydroelectric dam helps retain water in the new impoundment, that is diverted to Lake Gordon (formed by the Gordon Dam) via the McPartlan Pass Canal. Water from Lake Gordon then exits through the Gordon Dam and into the Gordon River.

History In early 1967, Eric Reece, the Premier of Tasmania, announced plans to flood the natural Lake Pedder and the legislation was debated in the Tasmanian Parliament several days later. A small environmental movement was formed, which mobilised in the 1980s to stop the proposed Franklin River Dam. In 1972, Reece controversially approved the three dams and hence, the flooding of Lake Pedder, which proceeded despite a determined environmental protest movement and a blank cheque offer from his Labor colleague, Prime Minister Gough Whitlam, to preserve the area. Reece refused Whitlam's offer, stating that he would 'not have the Federal Government interfering with the sovereign rights of Tasmania.' Reece retrospectively commented: Environmental protests and political lobbying continued. It was claimed that the Tasmanian Government had contravened the National Parks and Wildlife Act (TAS), resulting in the passage of retrospective legislation that confirmed construction of the three dams could continue. Reece commented at the time, "As far as Lake Pedder is concerned, the sooner they fill it up the better."

Lake Edgar Fault The Lake Edgar Fault is a north–south trending scarp that occurs within the boundary of the Southwest National Park. The scarp traverses the button grass of the Huon Plains and is notable because faulting resulted in the defeat of westerly flowing drainage and the consequent formation of the fault-bound sag pond of Lake Edgar. In January 2001 a tremor measuring 3.2 on the Richter magnitude scale occurred near the Lake Edgar fault, which runs adjacent to the Edgar Dam, however damage was negligible.

In 2002 it was reported that a dam safety manager from Hydro Tasmania, was confident that the eventuality of the Edgar dam being destroyed by an earthquake was an extremely remote possibility, with a University of Tasmania geophysicist agreeing that the risk of collapse was remote.

In 2024 planning began for a strengthening project designed to improve Edgar Dam's earthquake resilience.

In 2025 there was a magnitude 4 earthquake in the area and, under pressure from the Greens, released modelling as part of a freedom of information request which showed that in the event of dam failure, Huonville would be inundated by waters up to 9m. The annual risk was estimated at 1 in 10,000 before dam upgrades, and 1 in a million after.

Dam strengthening works In 2025, Hydro Tasmania began dam strengthening works, scheduled to be completed in mid-late 2026.

Edgar Dam

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