| Crotty Dam | |
|---|---|
| Location | West Coast Tasmania |
| Dam and spillways | |
| Impounds | King River |
| Reservoir | |
| Creates | Lake Burbury |
Crotty Dam also known earlier as the King River Dam is an 82metre high concrete faced rock and gravel fill dam in Western Tasmania.
It is one of two dams that contain Lake Burbury, which forms the headwaters for the King River Hydroelectric Power Development on Tasmania's West Coast. The other is Darwin Dam.
The dam is located in the upper reaches of the King River gorge where the river breaks through the West Coast Range. It captures the high rainfall in the catchment of the King River and allows diversion of water through a tunnel to the John Butters Power Station some 8 kilometres downstream of the dam.
Crotty Dam and Lake Burbury have been identified as Indicative places on the Register of the National Estate.[1]
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The dam was constructed in the 1980s following the abandonment of the Gordon-below-Franklin power development scheme (The Franklin Dam) of Hydro Tasmania. It was commissioned in 1991.
It is named after James Crotty, who founded the North Mount Lyell Copper Mine at the turn of the 20th century. A ghost town site of the same name Crotty was submerged by the waters of Lake Burbury.
In the 1910s the Mount Lyell Mining and Railway Company had investigated and surveyed a site very close to this dam for a proposed hydro electric scheme. Charles Whitham also wrote of the inevitability of the dam in 1927 and even proposed a name for the reservoir created - Lake Dorothy
In 2001, The Institution of Engineers Australia selected Crotty Dam as one of the 25 dams with the greatest Australian heritage value.
A unique feature of the Dam is its spillway. The spillway is located on the embankment, rather than on one of the rock abutments. This had never been successfully attempted before in the design of dams of any significant height, due to problems in making allowance for embankment settlements.
In the case of Crotty Dam, the embankment was partly composed of well graded gravels, and thus a very high modulus of embankment deformation was achieved. The high modulus limits embankment settlements. Additionally, the spillway was designed to articulate in order to accommodate any settlement that did occur.
The spillway has a capacity of 240 m³/s and is designed to allow sufficient time for a large jet flow valve located in the diversion tunnel to be opened so that larger floods can be safely handled.
The spillway designers, Sergio Giudici (the chief engineer on the Gordon Dam), Frank Kinstler, Steven Li, Tony Morse and Graeme Maher were acknowledged within the engineering community because the spillway was the first known to provide for articulation of the spillway structure so that movements in its foundations could occur without damage to the overlying structure. [1]
The water from Lake Burbury is conveyed through a 7km long unlined tunnel to the John Butters Power Station (installed capacity 144MW), which is located on the King River downstream of the dam, near the confluence with the Queen River.