Crotty Dam
Crotty Dam (at right) aerial shot from the east
Location of the Crotty Dam in Tasmania
Country	Australia
Location	West Coast Tasmania
Coordinates	42°09′35″S 145°37′00″E / 42.15972°S 145.61667°E / -42.15972; 145.61667
Purpose	Power
Status	Operational
Opening date	1991 (1991)
Owner(s)	Hydro Tasmania
Dam and spillways
Type of dam	Embankment dam
Impounds	King River
Height	83 metres (272 ft)
Length	245 metres (804 ft)
Width (crest)	300 millimetres (12 in)
Dam volume	770×10^3 m3 (27×10^6 cu ft)
Spillways	1
Spillway type	Controlled and uncontrolled
Spillway capacity	245 m3/s (8,700 cu ft/s) chute on dam face 190 m3/s (6,700 cu ft/s) valve in tunnel
Reservoir
Creates	Lake Burbury
Total capacity	1,081,420 ML (38,190×10^6 cu ft)
Active capacity	1,065,000 ML (37,600×10^6 cu ft)
Catchment area	559 km2 (216 sq mi)
Surface area	53,250×10^3 m2 (573.2×10^6 sq ft)
John Butters Power Station
Coordinates	42°09′21″S 145°32′04″E / 42.15583°S 145.53444°E / -42.15583; 145.53444
Operator(s)	Hydro Tasmania
Commission date	1992 (1992)
Type	Conventional
Hydraulic head	184 metres (604 ft)
Turbines	1 x 144 MW (193,000 hp) Fuji Francis turbine
Installed capacity	144 megawatts (193,000 hp)
Capacity factor	0.9
Annual generation	576 gigawatt-hours (2,070 TJ)
Website hydro.com.au/energy/our-power-stations/king-yolande

The Crotty Dam, also known during construction as the King Dam,^[1] or the King River Dam on initial approval,^[2] is a rockfill embankment dam with a controlled and uncontrolled spillway across the King River, between Mount Jukes and Mount Huxley, located in Western Tasmania, Australia.

The impounded reservoir is called Lake Burbury.

The dam was constructed in 1991 as part of the King River Power Development Scheme, by the Hydro Electric Corporation (TAS) for the purpose of generating hydro-electric power via the John Butters Power Station located 8 kilometres (5.0 mi) below the dam wall.^[3]

Features and location

The Crotty Dam, together with the Darwin Dam, are two major dams that form the headwaters for the King River Hydroelectric Power Development. 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 downstream of the dam.

The Crotty Dam wall, constructed with 770 thousand cubic metres (27×10^⁶ cu ft) of concrete faced rock and gravel fill core, is 83 metres (272 ft) high and 245 metres (804 ft) long. At 100% capacity the dam wall holds back 1,081,420 megalitres (38,190×10^⁶ cu ft) (43,000×106 cu ft) of water. The surface area of Lake Burbury is 53,250 hectares (131,600 acres) and the catchment area is 559 square kilometres (216 sq mi). The single uncontrolled and controlled spillway is capable of discharging 435 cubic metres per second (15,400 cu ft/s).^[4]

Spillway

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 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, also 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".^[5]

Power station

The water from Lake Burbury is conveyed through a 7-kilometre (4.3 mi) long unlined tunnel that runs through Mount Jukes to the John Butters Power Station, which is located on the King River downstream of the dam and King River gorge, near the confluence with the Queen River.^[6]

History

The dam was constructed in the 1980s following the abandonment of the Gordon-below-Franklin power development scheme, part of the Franklin Dam. The Crotty Dam was commissioned in 1991, with the King River Power development being completed by 1992.^[7]

The dam is named in honour of 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 "Lake Dorothy" as a name for the reservoir.

In 2001, Engineers Australia selected Crotty Dam as one of the 25 dams with the greatest Australian heritage value.^[5] It was awarded a Historic Engineering Marker as part of the Engineering Heritage Recognition Program.^[8]