The Upper Nepean Scheme is a series of dams in the catchments of the Cataract, Cordeaux, Avon and Nepean rivers of New South Wales, Australia. The scheme includes four dams and supplies the Macarthur and Illawarra regions, the Wollondilly Shire, and metropolitan Sydney.
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The Upper Nepean Scheme was completed in 1888. The Scheme was a significant feat of engineering at the time of construction, it worked by diverting water from weirs on the Cataract, Cordeaux, Avon and Nepean rivers to Prospect Reservoir via 64 kilometres (40 mi) of tunnels, canals and aqueducts collectively known as the Upper Canal. Between 1907 and 1935 a dam was built on each of the rivers to increase the water supply for Sydney. The Scheme is managed by the Sydney Catchment Authority. Each dam includes a public picnic area.
In total, the four dams hold 510,660 megalitres and can safely provide 353 megalitres/day.
Cataract Dam is a straight dam with an unlined side spillway extending from the left abutment. It is 56 meters tall; 247 m long; and it holds 94,300 megalitres of water. Cataract Dam was the first dam built in the Upper Nepean Scheme, it was also first dam in Australia to use pre-cast moulded concrete blocks for the upstream face of the dam. The downsteam face is of mass poured basalt concrete, with a basalt facing. A readily accessible source of suitable rock was located some distance away at Sherbrooke, also known as Ferndale, situated near the top of Bulli Pass. To transport the basalt from the quarry to the dam construction site, a 2 ft (610mm) gauge steam tramway, 8.8 km long, was constructed [1]. Dam construction began in 1902 and was completed in 1907, and the spillway was widened in 1915. Ernest Macartney de Burgh was the supervising engineer for the project from 1904[2]. Poet Banjo Paterson wrote a satirical ballad "The Dam that Keele Built" about the politics behind the construction of Cataract Dam.
Cordeaux Dam is a curved dam with an unlined side spillway on the left abutment. It is 57 m height; 405 m long; and holds 93,640 megalitres. Construction began in 1918 and was completed in 1926.
The blue metal used in the construction of the dam was supplied from the Government Quarries at Kiama and brought by rail to Douglas Park. From here it was conveyed by aerial ropeway across the Nepean Gorge to an interchange on the eastern side where the material was transferred to a 2 ft (610mm) gauge steam tramway to a point adjacent to the dam site[3].
Avon Dam is a curved dam, it is 72 m tall; 223 m long; and it holds 214,360 megalitres. It has the largest capacity of all the dams in the Scheme. Construction began in 1921 and was completed in 1927. All materials for construction were transported from Bargo railway station on a specially built road, all the other dams in the scheme used rail transport. There were some light tramways constructed at the dam site, however it would appear that no locomotives were employed; skips, etc., being moved by winch, horse or manpower[4].
Nepean Dam is a curved dam, it is 82 m tall; 216 m long; and holds 81,360 megalitres. Construction on the Dam began in 1926, construction was delayed for two years during the Depression, it was finally completed in 1935.
Railway sidings were established on the Main Southern Line at a point between Bargo and Yerrinbool. Transport to the dam site was again by light railway, on this occasion of standard gauge. This avoided transhipment from the Government vehicles bringing materials from large commercial quarries, effectively making the line an extended privately owned siding. The line was 4 km long through gentle countryside. Trains were worked by a variety of locomotives, including a former Sydney Steam Tram Motor. Additionally, there was a system of narrow (610mm) gauge lines in use at the dam construction site[5].
Additional work was carried out on the spillway between 1943 and 1947 to prevent scouring of the dam foundations.