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Crotty Dam and Lake Burbury, Lyell Hwy, Gormanston, TAS, Australia

Photographs None
List Register of the National Estate (Non-statutory archive)
Class Historic
Legal Status Indicative Place
Place ID 101584
Place File No 6/04/110/0014
Nominator's Statement of Significance
The claim of Crotty Dam and its impounded Lake Burbury for National Estate registration is primarily due to its relevance to the landmark events leading to its construction, the innovation adopted for its design and the scenery and tranquillity created by the lake. An assessment of these claims relevant to the Australian Heritage Commission criteria is given below.

CRITERION A3
Importance in exhibiting unusual richness or diversity of landscapes or cultural features

The new lake has transformed the mountainous landscape so characteristic of Tasmanias west coast. It provides an amenity of great worth and beauty of an area formerly extensively ravaged by mining, erosion, timber cutting and bushfires. Extra care was taken during dam construction to preserve the high scenic qualities of the area and to limit the final visual impact of roads. The Mt. Jukes Road, built both for tourist access to the south west wilderness area and for access between work sites, was a major engineering and environmental challenge. Although it crossed the rugged West Coast Ranges careful re-vegetation work and well researched route selection have virtually nullified its visual impact on the landscape.

Furthermore the new lake inundated 6km of the original Lyell Highway, and its King River crossing. To replace this loss a major new bridge 350m long (Bradshaw Bridge) was built to cross the lake as part of the new highway route.

New recreation benefits have also been provided by Lake Burbury. Boating and trout-fishing have been introduced with natural trout stocks built up by the release of wild brown trout fry and domestic rainbow fry. Special measures were taken prior to filling the storage to reduce the potential for pollution of the lake by heavy metals leached and drained from the old Mt. Lyell mine workings and tailings dumps. The level of pollution has been closely monitored and the readings show that the resulting level has little impact on fish life.

CRITERION A4
Importance for association with landmark events, developments or stages in Australian history or in the history of a State, region or community.

The construction of Crotty Dam was precipitated by the groundbreaking legal ruling of the Australian High Court in June, 1983, preventing further construction by the HEC of the Lower Gordon River Dam. This historic decision was seen by many as a major test of fundamental States rights on which Federation was based and as a highly popular reward for the environmental movement throughout Australia. In many ways it crowned a growing nationwide controversy, marked often by street marches, site conflicts, political tirades and major police efforts to control unruly public demonstrations. The eventual decision resulted in placing final authority for national environmental control in the domain of the Federal government and marked the official entry of environmental politics onto the national agenda.

The Tasmanian government, although monetarily compensated for the loss of the Gordon River power source by the Federal government, was forced to embark energetically on the King River Power Development, both to meet the predicted demand for power and to provide immediate continuing employment for the HEC construction work force. By good fortune the interim HEC camp and construction depots already created in the King River Valley for the Lower Gordon scheme were close to the Crotty Dam site, allowing a rapid re-focussing of the work force onto traditional dam building activities in the new location.

CRITERION C2Importance for information contributing to a wider understanding of the history of human occupation of Australia

The King River, on which Crotty Dam now stands, has a long history of sporadic human habitation. Traces of Aboriginal occupation have been found on its tributaries, for instance, the Nelson River, while the Sarah Island convict era of 1821-34 is evidenced by occasional rusty leg-irons discarded by escapees and found on the hills around the new lake.

While the former township of Crotty, named for James Crotty, and smelter sites are now inundated by Lake Burbury, archaeological investigations were carried out before the lake was filled and a number of artefacts were recovered. One heritage item unfortunately lost by the inundation was the 30m long North Mt. Lyell railway bridge over the King River. Built in 1900 and designed by the renowned British firm of Dorman Long Pty. Ltd, pre-fabrication in Melbourne and transportation and re-assembly on site was a feat of precision engineering remarkable for the time.

Thus Crotty Dam has drawn a peaceful shroud over the scene of a century of robust Australian history. In respectful recognition it now carries the name of a colourful and determined Australian entrepreneur and so recalls that historic era and its pioneering people.

CRITERION E1
Importance for a community for aesthetic characteristics held in high esteem or otherwise valued by the community

The lake is recognised for its mountain scenery and surface reflections and its magnificent backdrop of the West Coast Range. The numerous islands, the long shoreline, and the tranquillity created by the lake enhance the scenic value of the valley and bring out the contrast between the wilderness of the S.W. World Heritage Area and the beauty inherent in a large inland lake.

The Lyell Highway and Mt. Jukes Road offer many spectacular views of Lake Burbury within the King River valley, as well as prominent vistas of the more distant mountain ranges. Crotty Dam itself offers a prime vantage point for viewing the rugged grandeur of the King River Gorge. As already noted (2.1, p3) the mountains to the East and West offer unsurpassed views of the lake for bushwalking and mountaineering enthusiasts.

CRITERION F1
Importance for its technical, creative, design or artistic excellence, innovation or achievement

Contrary to traditional practice for rockfill dam design, the Crotty Dam spillway is incorporated in the dam. There is little precedent around the world for a service spillway on a fill dam of Crotty's magnitude. A fill embankment deforms when subjected to water load. A spillway chute on a fill embankment is subject to the movements of the downstream face when the embankment deforms and, as a consequence, there is a high risk of fast flowing water escaping from any fracture of the spillway chute.

Alternative spillways considered for Crotty Dam included a glory hole spillway and a side channel spillway on the right abutment. Both were discarded either because of their relative expense (a right bank side channel required extensive stabilisation works because of adverse geological conditions) or because their construction would conflict with the construction programme of the dam.

There were good reasons for considering a spillway on the crest of the dam and over the downstream face. Firstly, because the design flood rise for a 12.2m wide spillway crest and chute could be limited to 5m, the spillway crest slab could be constructed on top of the first stage rockfill at the same level as the dam crest wall. This greatly simplified the construction programme.

Secondly, for more than 20 years, the HEC has been measuring the deformation of rockfill dams during construction, reservoir filling and in service. The HEC had designed and built, at the time of the feasibility design for Crotty, eleven concrete-faced rockfill dams. This experience formed a sound basis for its understanding of rockfill behaviour.

The deformation measurements indicated that the envelope of downstream face movements measured on these dams was small. Thus a concrete slab on the downstream face, if properly articulated, would not be required to withstand a very great differential movement. Also, since the dam was to be made of gravel fill, which would be stiffer than rockfill, the movements would be proportionally smaller than those measured on past dams.

For all the above reasons, a downstream face spillway was adopted with complete confidence.

The dam embankment fill consists of river gravels with thin shells of rockfill upstream and downstream of the gravels. Rockfill is also used for drains in the riverbed and at the abutments. The dam has an upstream face slope of 1 on 1.3 and a downstream face slope of 1 on 1.5.

The gravels were obtained from extensive deposits located approximately 3km upstream of the dam and the rockfill came from spoil excavated from the headrace tunnel. The gravels offered a significant cost saving compared with quarried rock.

The gravels placed in the dam were 20 per cent washed and 80 per cent unwashed. They were well graded. The average dry density of test samples was high, at 2.45 tons per cubic metre. Construction modulus was also high, at 500MPa.

The spillway is a frontal approach, broad crested spillway with 12.2m wide crest and chute. The flow is aerated at four locations by means of four slots across the chute invert, and the side walls are 3m high. The spillway is required to pass 245 (cubic metres squared) only as the discharge required for the design flood of 435 (cubic metres squared) can be shared with a bottom outlet (a 2.8m dia. jet-flow gate located in the river diversion tunnel. At maximum discharge, the chute walls have an estimated minimum freeboard of 0.4m, including the effect of bulking of the flow due to aeration and the build-up of standing waves at the walls.

Outside the wall, on each side of the chute, a splash drain of 3m wide shotcrete is provided to prevent spray entering the dam fill during spillway discharge. A flip bucket at the end of the chute directs the jet of water clear of the dam and the valley walls downstream of the dam.

The spillway chute consists of five separate units. They are linked to each other by articulated joints at the aerator slots. The aerators provide air to the underside of the spillway flow, reducing the potential for cavitation. They also provide suitable locations for the articulation of the invert slabs. Each aerator consists of a vertical step with a small ski jump at the top of the step.

There have been a number of spills since the dam was completed in July 1991. The spills were relatively small, the maximum surcharge being 0.7m (spillway flow 16 (cubic metres squared) or 6.5 per cent of capacity). Two of the spills were of approximately one month duration each. The behaviour of the dam and spillway under more severe discharge conditions has yet to be seen; however the behaviour under normal full water load to date is as predicated.

CRITERION H1
Importance for close associations with individuals whose activities has been significant within the history of the nation, State or region

The dam takes its name from the former nearby township of Crotty which was named for James Crotty who founded the North Mt Lyell Copper Mining Company in 1897. Lake Burbury is named for Sir Stanley Burbury, a distinguished Tasmanian and a former Chief Justice and Governor of Tasmania.

The new bridge across Lake Burbury, the Bradshaw Bridge, is named after a well-known identity on the west coast of Tasmania, the late Cliff Bradshaw, who was an accomplished bushman and for many years operated a sawmill at the Princess River, a tributary of the King River. The mill was still in full production when it had to be moved out of the storage area, so that the new lake could be filled.
Official Values Not Available
Description
The Place

Crotty Dam is built in a narrow gorge of the King River, at the western extremity of an extensive gravel covered plain on the west coast of Tasmania. The King River valley has long been recognised as a natural landform suited to the containment of a major water storage for hydro-power generation. Efforts to dam the valley at the present site were made as early as 1917. Today Lake Burbury, (created by Crotty Dam), has transformed the mountainous landscape so characteristic of Tasmania's west coast.

The new lake is surrounded by a backdrop of mountains and well forested hills and valleys, and forms a tranquil setting for viewing from both the Lyell Highway to the east and from the Mt. Jukes Road to the west. From the east the whole King River valley is overlooked by the prominent west coast mountaineering peak, the Frenchman's Cap (1443m).

Historical summary

The discovery of gold in the 1880s first drew prospectors to Mt. Lyell and one - James Crotty- bought out a share in a local syndicate for 20 in 1895. His share was to be worth 1,500,000 thirteen years later.

Crotty had ambitious plans and his company spent a fortune developing a mine at Mt Lyell, a port on Macquarie Harbour, a railway from the port to the mine via the township of Crotty, and a smelter at Crotty. The smelter was a failure and, in May 1903, North Mt Lyell amalgamated with the Mt Lyell Mining and Railway Company at Queenstown. The township of Crotty, which had a population of 800 in 1901, virtually died overnight, but the railway continued to transport firewood and timber props to the Mt Lyell mine until 1926.

A hydro-electric power scheme was proposed for the Crotty Dam site in 1917; the layout was similar to the present scheme except that it was to be a concrete arch dam and the water was to be conveyed to the power station by aqueduct rather than by tunnel. The excavation of a rock cut to divert the river at the dam site was completed and is still visible. The electricity was required for the refining of zinc/lead ore at Rosebery. However a decision was made to establish the smelter at Hobart, using electric power from the Waddamana Power Station fed by water from the Great Lake and Miena Dam. For this reason the King River power scheme was abandoned.

Apart from Bradshaw's sawmill further habitation did not return to the King River Valley until 1982 when HEC road construction to the Lower Gordon Dam site required the setting up of a construction camp near the remains of the old Crotty township (Ref. Criterion A4). This single-men's camp also became submerged by Lake Burbury in 1992.

After James Crotty founded the North Mt Lyell Copper Mining Company in 1897, settlement at both Queenstown and Crotty followed rapidly and with it the titanic struggle between Crottys company and the Mt. Lyell Mining and Railway Co. Ltd. for control of the huge copper lode at Mt. Lyell. This struggle makes a well known and colourful page in Australia's mining history.

Historical biographies

James Crotty

The dam takes its name from the former nearby township of Crotty which was named for James Crotty who founded the North Mt Lyell Copper Mining Company in 1897 and died only one year later. Further detail is given in 2.2.

Sir Stanley Burbury

Lake Burbury is named for Sir Stanley Burbury, a former Chief Justice and Governor of Tasmania. The HEC has a tradition of naming its lakes after State governors, but Sir Stanley was significant in that he was a Tasmanian.

Cliff Bradshaw

The Bradshaw Bridge is named after a well-known West Coast identity, the late Cliff Bradshaw, who for many years operated a sawmill at the Princess River, a tributary of the King River. He was an accomplished bushman and he and his sons had extensively explored the environs of the King River valley and its tributaries. His sawmill was well known for its recovery of Huon Pine, particularly valued for boat building in Tasmania. The mill was still in full production when it had to be moved out of the storage area to Lynchford, near Queenstown, so that the new lake could be filled. The mill remains in the family and the bridge was officially opened by Cliff's wife Gertie in 1991.

Technical description

Crotty Dam, 83m high and 245m long, is located 10km SE of Queenstown. Together with Darwin Dam (a 10m high saddle dam), it harnesses the King River catchment to form Lake Burbury, the 5300ha storage for power generation. A 7km long tunnel conveys water from the storage to a single Francis turbine of 143MW capacity in the John Butters power station located on the lower reach of the King River above its junction with the Queen River.

The dam embankment fill consists of river gravels with thin shells of rockfill upstream and downstream of the gravels. The total volume of embankment fill is 800 x 1000 cubic metres.

Contrary to traditional practice for rockfill dam design, the Crotty Dam spillway is incorporated in the dam. It is a frontal approach, broad crested, chute spillway founded on the crest and over the downstream face of the dam. The spillway is required to pass 245 (cubic metres squared) of the 435 (cubic metres squared) design flood. The remaining 190 (cubic metres squared) is discharged via a bottom outlet.
History Not Available
Condition and Integrity
There have been a number of spills since the dam was completed in July 1991. The spills were relatively small, the maximum surcharge being 0.7m (spillway flow 16 (cubic metres squared) or 6.5 per cent of capacity). Two of the spills were of approximately one month duration each. The behaviour of the dam and spillway under more severe discharge conditions has yet to be seen; however the behaviour under normal full water load to date is as predicated.
Location
The dam is located on the King River 10km south-east of Queenstown.The boundary of the area (for National Estate listing) of the dam and its impounded Lake Burbury should be that area encompassed by the flood level of the lake plus the area of the dam including appurtenant structures.
Bibliography
ANCOLD - Register of Large Dams in Australia, 1990.

Fitzpatrick, M D - Crotty Dam Spillway Over Dam and Bottom Outlet, Trans16th ICOLD Congress, San Francisco, 1988, Session on Q63 Speaker 20 in Vol 5 p.582-585.

ICOLD - World Register of Dams, Paris 1988.

Li, S.Y. et al - Design of Crotty Dam and Spillway, Proc International Symposium on High Earth-Rockfill Dams, October, 1993, Beijing, China, Vol.1, pp 263-271.

Li, S.Y. et al - Design and Monitoring of Crotty Dam Spillway, ANCOLD Bulletin Issue No 98, December 1994.

Li, S.Y. et al - Five Years Monitoring of Crotty Dam Spillway, Trans 19th ICOLD Congress, Florence, 1997, Vol 1, C.21, p.789-806.

Geoffrey Blainey - The Peaks of Lyell, 5th Edition, St. David's Park Publishing, Hobart, 1993.

Hydro Development in Tasmania, Water Power & Dam Construction, December 1987.

Report Produced  Wed Aug 20 19:30:55 2014