The first major dam built for irrigation in New South Wales was Burrinjuck Dam. It is situated in the upper catchment of the Murrumbidgee River, approximately 60 kms from Yass. The name Burrinjuck comes from the Aboriginal words “Booren Yiack”, meaning “Precipitous Mountain”.
Early Days:
In 1891, the drought-ravaged Murrumbidgee Valley was nominated as an ideal location for irrigation development. After devastating droughts in 1901 and 1902 State Parliament approved the establishment of the Murrumbidgee Irrigation Scheme. Burrinjuck Dam was constructed to provide water for the scheme.
Construction started in 1907, but due to delays caused by the shortage of labour and materials during World War 1, the original design was not completed until 20 years later, although it was able to provide water for irrigation in 1912.
With the dam largely completed, a massive flood in the Murumbidgee Valley in 1925 sent water more than a metre deep pouring over the crest of the main wall. Although Burrinjuck was barely damaged by the torrent, the size of the spillways was increased and the height of the main wall raised to prevent future devastation. Work on these alterations and other improvements began in the 1930’s. Again, construction was delayed by a world war but finally, Burrinjuck Dam was completed in 1956. It was the first major dam built for irrigation in NSW and when construction began in 1907, it was the fourth largest dam in the world.
The Structure:
Burrinjuck is a ‘mass gravity dam’. This type of dam holds back stored water by using its own weight to withstand the pressure from the water. The basic structure of the dam wall is similar to a gigantic brick wall. It is made of massive concrete blocks, which were cast in situ and contains huge granite boulders.
Following an analysis of the largest possible flood that could occur, the spillway capacity of Burrinjuck Dam was re-evaluated and the spillways were upgraded and enlarged. One hundred and fifty steel cables were inserted into the structure at bedrock level (at maximum length of 130 metres) and each cable was post tensioned to 1,100 tonnes each.
Burrinjuck is one of the first dams in NSW to have environmental flow releases based on inflows.
Facts:
Holding capacity: 1,025,000 million megalitres, (almost half the volume of water in Sydney Harbour).
Surface area: 5,500 hectares (more than 8,000 football fields.
Catchment area: 13,953 square kilometres, larger than the catchment area of the whole of the Snowy Mountains.
Height of the wall: 97.8 metres (taller than the highest sail on the Sydney Opera House).
Length of crest: 233 metres.
Width of base: 58 metres.
Weight of concrete: Approximately 950,000 tonnes.
Irrigation: 1.2 million ML per year for crops in the MIA.
