Changes to the scheme over time

Changes to the scheme over time


Broughton's Pass Weir after it was destroyed by a flood in 1898. It was rebuilt soon after on the original
foundations, but in concrete and it still stands today.

Features of the 1888 scheme

  • Pheasants Nest Weir - 3 metre high weir just below the junction of the Cordeaux and Nepean rivers.
  • Nepean Tunnel - 7km tunnel from the Nepean River under the town of Wilton to the Cataract River at Broughtons Pass.
  • Broughtons Pass Weir - 3.5 metre high weir across the Cataract River.
  • Cataract Tunnel - 3km tunnel from Broughtons Pass Weir to Brooks Point, near Appin.
  • Upper Canal - 64 kms of canals, tunnels and aqueducts to Prospect Reservoir.
  • Prospect Reservoir - Australia's first earth fill and rock embankment dam, designed to store 50,000 megalitres of water at Prospect, 35km west of the city.
  • Lower Canal - 7.7 km canal from Prospect Reservoir to a basin at Guildford, known as Pipe Head, where Nepean water is connected to the city's water supply system.
  • Potts Hill Reservoir - service reservoir built near Bankstown.
  • Petersham Reservoir - reservoir capacity increased from 3.6 to 9 megalitres.

Expansion of the scheme (1902-1935)

A Royal Commission after the Federation drought of 1901-02 recommends expansion of the Upper Nepean Scheme. Four dams are built above the original two weirs which do not alter the way the scheme works - they simply increase the amount of water the scheme can reliably supply, by storing water in upstream dams rather than relying solely on river flows.

Cataract Dam 1902-07

Created by damming the Cataract River, Cataract was the first of the four Upper Nepean dams. Together with Cordeaux Dam, Cataract supplies water to Camden, Campbelltown and Wollondilly council areas via the Macarthur water filtration plant as well as Prospect Reservoir.

Cordeaux Dam 1918-26

Created by damming the Cordeaux River, Cordeaux was the second of four Upper Nepean dams. Together with Cataract Dam, Cordeaux supplies the Camden, Campbelltown and Wollondilly council areas via the Macarthur water filtration plant as well as Prospect Reservoir.

Avon Dam 1921-28

Created by damming the Avon River, Avon was the third and largest of the four Upper Nepean dams. Today, it's main role is to supply the Illawarra region.

Nepean Dam 1925-35

Created by damming the Nepean River, Nepean was the last and smallest of the four Upper Nepean dams, but it has the largest catchment. Today it supplies nearby Bargo, Thirlmere, Picton and The Oaks, as well as the Macarthur and Prospect water filtration plants.

Improvements and maintenance (1935 to today)

The main features of the Upper Nepean Scheme continue to operate today just as they were designed.

To meet modern dam safety standards, Prospect Reservoir and the four Upper Nepean dams were upgraded between the 1970s and the 1990s. A tunnel linking Avon and Nepean dams, to enable the transfer of water between dams in either direction, was completed in 1973.

In 2008 a $56 million Raw Water Pumping Station was built at Prospect Reservoir to create greater flexibility in Sydney's water supply and to access an additional 28,000 million litres from the reservoir.

Prospect Reservoir wall was further upgraded in 2016 with the removal of the clay core and reshaping of the dam wall.


Wednesday 27 January
2,392,415 ML
2,581,850 ML
11,945 ML
1,707 ML
-12,079 ML
Wednesday 27 January