Warragamba Dam
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Warragamba Dam
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.
Water is collected from the catchments of the Wollondilly and Coxs River systems covering an area of 9,050 square kilometres to form Lake Burragorang and Warragamba Dam.
Lake Burragorang is the largest urban water supply in Australia, containing four times the volume of water of Sydney Harbour. It accounts for about 80 per cent of the water supply for nearly four million people in the Sydney region.
Why Warragamba Dam was built
The Warragamba River offered two important advantages as a site for a major dam. Firstly, it had a large catchment area and secondly the river flowed through a long, narrow gorge. A comparatively tall and narrow dam capable of impounding a vast amount of water could be built.
Its potential was identified as early as 1845 but plans were deferred during the construction of the Upper Nepean dams between 1907 and 1935. An increasing demand for water from expanding population, and a record drought from 1934 to 1942, forced the development of Warragamba Dam to ensure a reliable water supply.
How the dam was built
Constructed between 1948 and 1960, Warragamba Dam was a major engineering feat of the mid 20th Century. More than 2,300,000 tonnes of sandstone was removed from the site. Concrete was mixed on site using 305,000 tonnes of cement and 2,500,000 tonnes of sand and gravel.
The dam was built in a series of interlocking concrete blocks. A system of overhead cableways lifting 18 tonne buckets was used to place the concrete.
Ice was mixed with the concrete to control heat generation and to prevent cracks from forming. One of the first pre-stressed concrete towers in Australia was built to house the ice-making plant.
How the dam works
Warragamba Dam supplies bulk water to three Sydney Water filtration plants (Prospect, Orchard Hills and Warragamba), where it is filtered and distributed to 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 the smaller filtration plants at Orchard Hills and Warragamba.
Eraring Energy owns and operates the 50 megawatt hydro-electric power station which generates power only when there is a high level of water in the lake.
How the dam is monitored
SCA officers inspect and monitor Warragamba Dam through a network of more than five kilometres of galleries. They monitor water pressure, seepage and any physical changes in the dam structure and its foundations to ensure they fall within acceptable limits.
Warragamba Dam was designed to deflect slightly as the lake level rises and falls. These deflections are measured regularly using precise surveying techniques. Sensitive seismic equipment located in the dam and surrounding catchment monitors earth movements. Crest gates, valves, pipelines, and associated equipment are regularly inspected and maintained.
Safeguarding the dam
When rainfall and flood event studies showed that the dam could experience floods much larger than originally estimated, the height of the dam wall was increased by five metres as the first step in a two-stage solution to make the dam meet international dam safety standards. Work took place between 1987 and 1989 as the dam wall was raised and strengthened using post-tensioned steel cables, tying the upper portion of the wall to its base.
In late 1998, work began on stage two of the dam safety program, involving the construction of an auxiliary spillway located on the east bank of the dam. Construction of the auxiliary spillway was completed in June 2002.
During rare and extreme floods, the auxiliary spillway will allow floodwaters to pass safely around the dam, reducing the pressure on the dam wall. This will protect the areas downstream of the dam from the devastating effects of a dambreak, and will safeguard Sydney’s water supply.
