For the first time in 26 years, Dartmouth Dam in north-eastern Victoria has water flowing over the spillway thanks to recent rainfall. It is only the fifth time since construction of the Dam was completed in 1979 that it has spilled.
Such a rare occurrence provides us with an opportunity to consider the unique structure of this vital piece of Basin infrastructure, and the role it plays to support communities, industries, and First Nations across the Murray–Darling Basin.
And its pivotal role should not be underestimated.
Dartmouth Dam – which is jointly managed by the Murray–Darling Basin Authority and Goulburn-Murray Water – has the largest capacity of any dam in the Basin (almost 4,000 GL) and its 3,600 square kilometre catchment delivers almost 10% of the inflow into the Murray system.
When the Dam is full, it holds 40% of the Murray system’s total storage capacity. It is a deep reservoir in a narrow valley – some may even suggest it’s shaped like a bathtub. The benefit of the Dam’s shape is that for such a large body of water, the percentage loss of water to evaporation is considerably less than other structures, such as Hume Dam. When it is available, reserve water is therefore stored in Dartmouth Dam.
Australia’s Governor-General, His Excellency the Honourable Sir Paul Hasluck KG GCMG GCVO, formally opened construction of the Dam in February 1973. Completed 6 years later, Dartmouth Dam boasts an earth and rock-filled wall that measures 180 metres from the wall foundation to the roadway across the top of the dam. It is the highest dam wall in Australia.
The spillway – the current centre of attention at Dartmouth Dam – is located where the rock used for the Dam’s construction was quarried. The spilling water flows for 80 metres down a concrete chute and then onto the cascades before reentering the Mitta Mitta River downstream.
The Dam is now spilling because it has been effectively ‘operationally full’ at approximately 99% capacity since August.
Dartmouth Dam was primarily built to conserve water during wetter periods as ‘insurance’ against future dry times and drought. Today it is a vital source of water for domestic, industry, irrigation, and stock use in Victoria and New South Wales, and South Australia.