Canberra's Main Outfall Sewer is a significant component of the original engineering infrastructure associated with the development of Canberra as the national capital. It enabled healthy conditions to be maintained as the population grew when the transfer of Federal Government functions commenced in the 1920s and still remains in service today more than 80 years later.

Construction of the sewer commenced in 1915 but ceased following a Royal Commission held during World War I. After further Parliamentary approval excavation recommenced in 1922 and the system with its treatment works at Weston Creek, was completed in 1926 in time for the opening of Parliament House in 1927.

The Sewer which commences in front of the Hyatt Hotel on Commonwealth Ave consists of an egg shaped concrete lined tunnel 1.68 metres high by 1.12 metres wide. It runs underground a distance of about seven kilometers to the former site of the treatment works at Weston Creek where it now connects with a newer tunnel which conveys its contents to the Lower Molonglo Water Quality Control Centre.

The depth below surface of the tunnel varies from zero where it crosses Yarralumla Creek to 30 metres under Stirling Ridge. Three ventilator shafts with ornate brick chimneys above ground are located on Stirling Ridge, in the Royal Canberra Golf Course and in the Weston Creek area off Cotter Road.

Hundreds of miners and other workers carried out the excavation of the tunnel and its shafts using pneumatic drills, explosives and hand tools. The spoil was removed by horse drawn drays and used for road making. Workmen lived in tents at three locations along the route during the construction period.

A vent for Canberra's Main Outfall Sewer with old municipal incinerator in background.

Canberra's Main Outfall Sewer crossing Yarralumla Creek.
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