Managing dams and reservoirs

A key responsibility for WaterNSW is to effectively manage water storages in NSW.

In regional NSW, WaterNSW captures and stores water in weirs and dams, including 18 large dams. A dam is a wall-like structure that is built across a creek or a river to block the flow of water through the landscape. When it rains, water builds up behind the dam creating an artificial lake or reservoir.

This captured water is used to fulfil customer orders, via the river system the storage is located on. It is also used to provide environmental flows for the river system.

In times of flood, our regional dams are permitted to be used for flood mitigation, where water is released in anticipation of rain to allow additional airspace to capture inflows.

Managing the supply system in Greater Sydney

In Greater Sydney, we operate 21 dams with 11 being major supply dams, transporting water between storages via a network of rivers, pipes and canals.

Warragamba system

Warragamba Dam is Greater Sydney's major supply dam.

From Warragamba Dam, water flows by gravity through two pipelines, 27km to Prospect water filtration plant, which supplies 75% of Sydney. The dam also supplies Warragamba, Penrith and the lower Blue Mountains via water filtration plants at Warragamba and Orchard Hills. Water is released into the Warragamba River to provide a secure water supply to the people of North Richmond and as environmental flows to keep the river healthy. The Warragamba system can be topped up by water from the Shoalhaven system. Water from Wingecarribee Reservoir can be released into the Wingecarribee River, which flows into the Wollondilly River and Warragamba Dam.

Woronora system

The Woronora system supplies water to residents in southern Sydney and northern Wollongong. Rainfall in the catchment area, located in bushland about 40 kilometres south-west of Sydney, flows to Woronora Dam, which lies in a narrow gorge on the Woronora River upstream of its junction with the Georges River. The dam supplies water to parts of the Sutherland Shire, Helensburgh and Stanwell Park. Water is also released into the Woronora River as environmental flows, to keep the river healthy.

Upper Nepean system

The Upper Nepean system, comprised of Nepean, Avon, Cordeaux and Cataract dams, supplies water to Sydney, the Macarthur and Illawarra regions.

A tunnel between Avon and Nepean dams allows the transfer of water to the Illawarra from the Shoalhaven system. Water is also released from the four dams into the Upper Nepean rivers as environmental flows to keep the rivers healthy. Water from Avon, Cordeaux and Nepean dams can be released to Pheasants Nest Weir, while water from Cataract Dam can be released to Broughton Pass Weir. The 7km Nepean Tunnel under Wilton connects Pheasants Nest Weir with Broughtons Pass Weir. The Macarthur Water Filtration Plant extracts water from Broughtons Pass Weir to supply the Camden, Campbelltown and Wollondilly council areas. From Broughtons Pass Weir, water can be released to the Upper Canal, a series of tunnels, aqueducts and open canals, which flows by gravity 57 km to Prospect Reservoir to supplement Sydney's water supply. Water is also released from Broughtons Pass and Pheasants Nest weirs as environmental flows, to keep the lower Nepean River healthy.

Shoalhaven system

The Shoalhaven system supplies water to parts of the Shoalhaven and Southern Highlands, and tops up Sydney, Goulburn and Illawarra water supplies.

Water from Wingecarribee Reservoir can be released into the Wingecarribee River, which flows into the Wollondilly River and Lake Burragorang to top up Sydney's main water supply at Warragamba Dam. Water can also be released from Wingecarribee Reservoir via canals and pipelines, collectively known as Glenquarry Cut, into the Nepean River which flows into Nepean Dam.

Wingecarribee Reservoir can top up Goulburn's water supply during drought, via an 84km pipeline. Water is also released into the Shoalhaven and Wingecarribee rivers as environmental flows, to keep the rivers healthy.

Blue Mountains system

The Blue Mountains system sources water from within and outside the Blue Mountains catchments, a small group of bushland valleys that feed water to Lake Medlow, Greaves Creek and the three Cascade dams. These five dams provide water for the Cascade water filtration plant at Katoomba, which supplies the middle and upper Blue Mountains. Supplies can be topped up when needed with water from Oberon Dam or Duckmaloi Weir via a pipeline from the Fish River Scheme, west of the Great Dividing Range at Oberon.

To ensure the best quality raw water is available for treatment we monitor the water quality in our storages at different depths, allowing us not only to choose the best storage but the best water available in a storage.

We have a system of movable chambers and screens that can be set at varying levels to ensure we take the best raw water available.