Avon Dam

The Upper Nepean Scheme is a series of dams and weirs in the catchments of the Cataract, Cordeaux, Avon and Nepean rivers of New South Wales, Australia. The scheme includes four dams and two weirs and provides water to the Macarthur and Illawarra regions, the Wollondilly Shire, and metropolitan Sydney.

By 1867, Sydney was outgrowing the water supply available from Botany Swamps and the Governor (Sir John Young) appointed a Commission to recommend a future water supply. In 1869, the Commission recommended the Upper Nepean Scheme. This comprised weirs on the Cataract and Nepean rivers, a storage reservoir at Prospect and 63.25 miles (101.79 km) of pipelines, tunnels, canals and aqueducts to bring water from the 347 square miles (900 km²) catchment area to Sydney. Work on the Scheme began in 1880 and was completed in 1888. The Scheme was a significant feat of engineering at the time of construction.

In June 1885 Sydney was in the grip of a severe drought and the Upper Nepean Scheme was incomplete. The Government accepted an offer from Hudson Brothers to bridge the gaps and deliver 3 million imperial gallons (14 ML; 3,600,000 US gal) of water per day into Botany Swamps. Duplicating the entire length of the half built permanent scheme this became known as Hudsons' Temporary Scheme and was turned into the swamps on 30 January 1886. This emergency work was dismantled as the main scheme was completed.

As originally built, the Upper Nepean Scheme was capable of supporting an estimated population of 540,000. By 1902, Sydney had a population of 523,000 and was again in the grip of a severe drought. A Royal Commission appointed to report on Sydney's water supply recommended a dam on the Cataract River and construction commenced in the same year. Dams were subsequently built on each of the Cordeaux, Avon and Nepean rivers, with the last being completed in 1935. Each dam includes a public picnic area. In total, the four dams hold 483,600 ML (1.064×10¹¹ imp gal; 1.278×10¹¹ US gal) and can safely provide 353 megalitres per day.

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