Avon Dam history
Located about 100 kilometres south of Sydney, Avon Dam was the third and largest of the four dams constructed to collect water from the Illawarra Plateau. Created by damming the Avon River and completed in 1927, Avon Dam's main role today is to supply water to the Illawarra region. It is Sydney's second largest dam after Warragamba, but has a small catchment.
Water from Nepean Dam and water transferred via Nepean Dam from the Shoalhaven can be sent to Avon to secure water for the Illawarra.
Together, the Nepean, Avon, Cataract and Cordeaux dams also provide an additional supply of water for Sydney, via Pheasants Nest Weir, Broughtons Pass Weir and the Upper Canal.
Why the dam was built
The Upper Nepean catchment south of Sydney is in one of the highest rainfall zones on the mid-NSW coast, and the area's rivers, located in narrow gorges, provide ideal dam sites.
As early as 1888, two weirs were built on the Cataract and Nepean rivers to capture this rainfall as part of the Upper Nepean Scheme to help meet Sydney's growing needs. Tunnels, canals and aqueducts - known as the Upper Canal - diverted the water 64 kilometres to Prospect Reservoir.
The scheme provided only temporary relief, and the 1901 - 1902 drought brought Sydney perilously close to a complete water famine. After two Royal Commissions, authorities agreed that a dam be built on Cataract River. The successive building of Cataract, Cordeaux, Avon and Nepean dams between 1907 and 1935 greatly increased the Upper Nepean Scheme's capacity.
How the dam was built
Work on Avon Dam began in 1921 and was completed in 1927. The curved dam wall was built using cyclopean masonry. This consisted of sandstone blocks, quarried from the site, fitted into an irregular pattern and packed with sandstone concrete. The blocks were lifted into place by electric powered cranes.
The rock was quarried to make a deep cut through a ridge to a neighbouring creek to provide the dam's spillway, which discharges into the Avon River 800 metres downstream.
A 9.6 kilometre road was built from Bargo railway station to transport construction materials. The dam builders lived near the construction site in single-storey barracks for single men. Land was placed at the disposal of the married men who were assisted in constructing temporary houses for themselves and their families.
To meet modern dam safety standards, Avon Dam was strengthened in 1971 by buttressing the downstream face with a rockfill embankment.
A tunnel linking Avon and Nepean dams, to enable the transfer of water between dams in either direction, was completed in 1973.
In the 1980's the downstream face of the dam was strengthened. In 2005 the access road was upgraded for safety purposes, and in 2006 works were undertaken above the operating level of it's gravity fed outlet.