Dartmouth Dam

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Dartmouth Dam is a large dam on the Mitta Mitta River in the north-eastern portion of the Australian state of Victoria. The dam creates the artificial Lake Dartmouth (36°34′S 147°33′E), storing water from the Victorian "High Country" for summer release into the Mitta Mitta (and the downstream Lake Hume) and subsequently into the greater Murray River for irrigation.

Construction was started in 1973 and completed in 1979 at a cost of $139 Million. The dam is constructed with an earth core and rock filled walls, rising to a height of 180 metres making it Australia's highest dam. It has a capacity of 3906 gigalitres.^[1] It can release a maximum outflow of approximately 10,000 megalitres per day in normal operation. The dam's inflow and outflow capacity is quite small considering its size, meaning that its levels vary little compared to some other dams on the Murray and their tributaries.^[2]

The dam is a popular recreational trout fishery, being regularly restocked by the Victorian Department of Primary Industries.

Since its completion in 1979, the dam has spilled over only twice - once in 1998, and again in 1999. The 1998 overflow came, largely coincidentally, soon after a major accident in which two steel beams entered the turbines of the (unattended) 200 MW hydroelectric generators installed in the dam. The resulting force ruined the power station and the dam's control systems, making it impossible to gradually release water from the near-capacity dam by conventional means. An improvised system, placing large pipes over the spillway to siphon water over it, was soon installed, but the inflow from an unusually wet spring was such that the dam would have overflowed anyway, leading to a spectacular cascade over the huge rock steps formed when the rock used for the dam itself was quarried from the valley walls.

A subsequent investigation could not find any explanation for the presence of the steel beams.