WARRAGAMBA DAM

Facts and History

Located about 65 kilometres west of Sydney in a narrow gorge on the Warragamba River, Warragamba Dam is one of the largest domestic water supply dams in the world.

Created by damming Warragamba River and flooding the Burragorang Valley, the storage lake is four times the size of Sydney Harbour and stores around 80 percent of Sydney’s water.

How the dam works

Warragamba Dam supplies water to more than 5 million people living in Sydney and the lower Blue Mountains.

The best quality water is selected and drawn through screens on three outlets in the upstream face of the dam. Water flows by gravity through a valve house into two pipelines that feed the raw water to Prospect water filtration plant and via off-takes to smaller filtration plants at Orchard Hills and Warragamba.

Early history

A local Gundungurra Aboriginal creation story tells of two dreamtime spirits Mirragan – a large tiger cat, and his quarry Gurangatch – a part fish part reptile who lived in a lagoon where the Wollondilly and Wingecarribee rivers meet. During a long cross-country battle in the Dreaming (Gunyungalung), the deep gorges of the Burragorang Valley were gouged out. It was this valley that was flooded when Warragamba Dam was built.

The location of the dam was first suggested in 1845. The deep narrow gorge of the Warragamba River, at the exit to Burragorang Valley, was identified as an ideal place for a dam by Polish explorer Count Paul Strzelecki. More than a century and many droughts later, work finally started in 1948 to build a reliable new water supply for Sydney’s growing population. It took 12 years and 1,800 workers to build the dam, which opened in 1960. It was such a major undertaking that a town was built next to the site to house the dam builders.

Why the dam was built

The Warragamba River offered two important advantages as a site for a major dam – a large catchment area, and a river flowing through a narrow gorge. A tall and narrow dam capable of holding a vast amount of water could be built.

A population boom after World War I followed by the worst drought in recorded history, from 1934 to 1942, placed immense pressure on Sydney’s water supply. However, despite the first sketch plans for Warragamba Dam being drawn up in 1867, plans were deferred during the construction of the Upper Nepean dams (1907-35), the Great Depression (1929-32) and World War II (1939-45).

How the dam was built

Warragamba Dam was a major engineering feat of the mid-20th Century. In 1946 the Warragamba River was diverted so excavation for the dam could start. Trees were cleared from the Burragorang Valley, and two temporary (coffer) dams and a tunnel were built to keep the site dry. More than 2.3 million tonnes of sandstone was removed.

Concrete was mixed on site using 305,000 tonnes of cement and 2.5 million tonnes of sand and gravel. The sand and gravel was transported from McCann’s Island in the Nepean River via an aerial ropeway.

The dam was built in a series of large interlocking concrete blocks. Overhead cableways lifted 18 tonne buckets to place the concrete. Ice was mixed with the concrete to control heat generation and prevent cracks. One of the first pre-stressed concrete towers in Australia was built to house the ice-making plant.

To get to the work site from Warragamba township, the dam builders used two suspension bridges, one across Folly Creek, upstream of the dam wall, and the other across the Warragamba Gorge just downstream from the dam. The Folly Creek bridge was removed after the dam was built but the bridge over the gorge was kept and incorporated into the beautification works at the dam. In 2001 it suffered damage in a bushfire and was subsequently demolished.

Later improvements

To meet modern dam safety standards, in the late 1980s the dam wall was strengthened and raised by five metres. In the early 2000s an auxiliary spillway was built to divert floodwaters around the dam in a rare and extreme flood so as to protect the dam and ensure it remains safe in an extreme flood. A deep water pumping station was established in 2006 to allow water to be accessed lower down in the lake during times of drought.