| Burrinjuck Dam | |
|---|---|
Burrinjuck Dam under construction in 1911 |
|
| Construction began | 1907 |
| Opening date | 1928 |
| Dam and spillways | |
| Type of dam | Concrete gravity |
| Height | 93 m (305 ft)[1] |
| Length | 233 m (764 ft)[1] |
| Impounds | Murrumbidgee River |
| Type of spillway | Three sector gates with two side channel spillways |
| Reservoir | |
| Creates | Lake Burrinjuck |
| Capacity | 1,026 GL[1] |
| Catchment area | 12,953 km2 (5,001 sq mi)[1] |
| Surface area | 5,500 ha (14,000 acres)[1] |
| Max. water depth | 72 m (236 ft) |
| Power station | |
| Owner(s) | Snowy Hydro |
| Installed capacity | 28 MW |
Burrinjuck Dam is a 93-metre (305 ft) high,[1] concrete gravity dam on the Murrumbidgee River approximately 60 km from Yass, New South Wales, Australia.[1] The Yass and Goodradigbee Rivers flow into the dam. The dam divides the upper and lower catchment of the Murrumbidgee[2] and is the headwater storage for the Murrumbidgee Irrigation Area (MIA). The dam wall is 233 m long at the crest.[1]
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The pastoralist Samuel McCaughey accumulated hundreds of thousands of hectares in the Riverina after owning his first property in 1864.[3] He had an interest in water conservation that led him to construct a series of irrigation channels and steam pumps that were critical to the rice-growing activities in the area at the turn of the century. The New South Wales government liked his ideas so much they agreed to build a larger dam.[3]
Construction commenced in 1907. Prior to about February 1911, the dam was known as Barren Jack, a corruption of the Aboriginal name of the locality.[4][5] A narrow gauge (610 millimetres (2.00 ft)) railway was constructed from the New South Wales Government Railways' Main Southern Line at Goondah to bring materials to the site.[6][7] The railway was about 45 kilometres (28 mi) long, had a grade of 1 in 30 and some 90 foot-radius curves and took about 2 hours and 20 minutes to traverse.[8]
Delays were experienced throughout the construction period. Problems were found in part of the foundations of the dam wall in 1911, which led to a 12-month delay in completion of the first stage of the construction works[9][10]. Delays were caused by World War I, construction of extensions to the spillways, and the fact that deep foundations were necessary.[11]
Flooding in July 1922 filled the reservoir to the record height of 1,178 feet (359 m) above sea level, or 198 feet (60 m) above the bed of the Murrumbidgee River at the dam wall.[12] The flood waters tore through the unfinished southern spillway and fell 200 feet (61 m) to the river below, resulting in a massive fog which one journalist compared to that of Niagara Falls.[12] The flood water came within 2 feet (0.61 m) of spilling into the finished northern spillway,[12][13] which was being used as a storage site for sand and granite used in the dam's construction. Had the water entered the northern spillway, the construction materials, worth £25,000, would have been swept away.[12]
Another major flood in May 1925 far exceeded all previously recorded floods and resulted in the dam wall being overtopped to a depth of 1 metre (3 ft 3 in).
Due to World War I, the dam was not completed until 1928. At the end of 1927, £1,712,730 had been spent on construction work, excluding the cost of the hydroelectric facilities.[11][13]
In 1937, it was discovered that the dam had developed a structural weakness that required remedial action. The weakness was not due to a design flaw per se; rather it was due to strains and stresses that were not scientifically understood at the time the dam was designed.[14] The State Government brought in dam engineering expert Professor P.G. Hornell from Sweden to report on the defects that had developed in the dam.[15]
Apparently there were real fears of the dam wall bursting, so detailed plans were prepared for the evacuation of 20,000 people in the Murrumbidgee basin downstream of the dam in the event that the dam wall failed.[16][17] The State Government played down these fears and felt that the evacuation plans would never have to be used.[17] In the event of a catastrophic failure of the dam wall, it was anticipated that flood waters would reach Jugiong with in an hour, Gundagai within 90 minutes, Wagga Wagga in six hours and Narrandera in 22 hours. Arrangements were made with police, the New South Wales Government Railways, the postal service, military and air force officials, radio stations, boat operators and local committees to be put into effect at a moments' notice.
Remediation work was carried out between 1937 and 1957. The remediation work was authorised by the NSW Cabinet around January 1939, and at the time was anticipated to cost more than £1,000,000.[18] The first stage of remediation works involved lowering the dam wall by 10–15 feet (3.0–4.6 m) and was estimated in 1937 to cost approximately £100,000.[19]
In 1941, the State Government appointed a committee to estimate the probability of the dam flooding. This flood probability was used by consulting engineers to estimate the cost of the remediation work. The engineers estimated the remedial work would cost £1,800,000 but according to Government experts this figure was likely to be substantially exceeded.[20]
In February 1951 a fire destroyed some of the workshops at the construction site. The compressing room, machine shop and first-aid surgery were the worst affected, and much of their contents were destroyed. The damage was estimated to cost between £50,000 and £100,000.[21]
Eventually, the remediation work strengthened and enlarged the dam wall, increased the discharge capacity of the spillways (to about twice the peak discharge of the 1925 flood), and increased the storage capacity of the dam from about 652,000 acre feet (804,000,000 m3) to 837,000 acre feet (1.032×109 m3).[22]
A major flood in 1974 eroded unweathered granite from an unlined spillway discharge channel which then resulted in the destruction of a penstock to the Burrinjuck Power Station. The outlet valves of the dam were also destroyed during the same flood. These events prompted a review of the safety of the dam which recommended a new remedial works program.
In response to the 1974 floods, the Burrinjuck Dam Flood Security Upgrading project was undertaken to raise the existing dam wall by 12 metres (39 ft) to its present height of 92 metres (302 ft) metres and to install post-tensioned ground anchor cables to improve the security of the dam during major floods. At the time, the project was unprecedented in two respects[23] :
The upgrading works were completed in 1999 at a cost of A$79.5 million.
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