Woronora Dam is the fifth dam built as part of Sydney’s water supply network, and the final one to be built before World War II. Because of this, there are workers’ cottages and remnants of old platforms, plant and machinery (such as large pipes, roller gate, stopboards and penstocks) used in the dam’s construction in the 1930s.
Located about 50 kilometres south of Sydney, Woronora Dam was built specifically to supply water to communities south of the Georges River. Created by damming the Woronora River, the dam today supplies water to nearby communities such as Helensburgh and Engadine, and parts of the Sutherland Shire and northern Wollongong.
Woronora Dam is a mass gravity dam, which means it remains in position under its own weight. Its lower levels are built of cyclopean masonry – massive sandstone blocks quarried on site. The main wall is made from blue metal and gravel concrete. It is quite tall (almost 70 m) and nearly 400m in length, with an operating capacity of over 70 gigalitres from a catchment area of 75 km2 collected by a lake with a size of 4 km2.
The dam has a separate, serpentine spillway that discharges floodwater through a concrete lined cutting into the river downstream of the dam. Construction began in 1927 but stopped for four years during the Great Depression of the 1930s, forcing workers to look elsewhere for employment until the project started again. The dam was finally completed in 1941. There are some Sydney families that have a long association with Sydney dams, with multiple generations involved in building the Upper Nepean dams, Woronora Dam and then moving onto Warragamba Dam after World War II.
The dam today is virtually unchanged from when construction was finished, apart from an upgrade in 1988 to incorporate a system of drains in the wall and foundations.
We visited the dam on 13 April 2021 in the morning. Sadly, the spillway looks like it’s recently was active but no longer. The valley downstream looked spectacular, and there are multiple levels of picnic areas and a water filtration plant nearby.