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Hume Dam, Vic & NSW.

The Hume Dam is on the Murray River 16 kilometres upstream from Albury-Wodonga. The primary purpose of the Hume Dam is to conserve water in periods of high river flow for later release in periods of low river flow; in other words, the Hume Dam evens out the flow of the Murray River. Water from the dam is mainly used for irrigation in Victoria, New South Wales and South Australia but water is also diverted from the Murray River for domestic use, for industrial use and for urban water supplies in South Australia. While the primary purpose of the Hume Dam is for water conservation, mainly for irrigation, the dam also has a flood-mitigation function if water storage space is available. The Hume Dam also incorporates a hydro-electric power station and the water storage is available for recreational pursuits and water sports. Landholders in the Murray Valley discussed ways of managing the waters of the River Murray for navigation, irrigation and flood control from about 1860. In 1915 the River Murray Waters Agreement, ratified by the Comonwealth Goverment and the governments of Victoria, New South Wales and South Australia, provided for a water storage on the upper Murray and the site of the Hume Dam was subsequently selected from 25 alternatives. Construction began in 1919 with planned capacity of 1,360 gigalitres. In 1924 planned capacity was increased to 2,470 gigalitres but this was reduced to 1,540 gigalitres due to the Depression. Construction was completed in 1936. The Snowy Mountains Scheme provided increased water flows in the Murray River and the Hume Dam was enlarged as part of the Snowy scheme to its current capacity of 3,038 gigalitres. This work, including the addition of 29 spillway gates, was completed in 1961. In 1957 a 50 megawatt hydro-electric station was incorporated into the Hume Dam to generate power from released water. Description The dam itself is made up of four embankments and a concrete spillway section. Total length is 1,616 metres. Capacity is 3,038 gigalitres. The spillway hoist bridge is 51 metres above the bed of the storage. Total surface area is 201.9 square kilometres. The two longest earthen embankments (numbers 1 and 4), on either side of the concrete spillway section have a central concrete core 1.8 metres thick at the base, tapering to 0.6 metres at the top. On both sides of the core wall there is a narrow zone of selected clay as well a vertical drainage zone on the downstream side. The remainder of the embankments are earth. The core concrete wall is an impervious waterproof wall while the surrounding earth and clay provides the strength for the wall. Operation The Hume dam is the primary regulating storage in the Murray system and receives water from its own catchment, from the Dartmouth Dam (on the Mitta Mitta River) and from the Snowy scheme. The volume of water in the Hume storage usually increases during winter and spring, although inflow in a drought year may be only about ten per cent of inflow in a flood year. Water is released into the Murray River from November to May, primarily to supply irrigation water. The storage is full enough to spill water on average one year in two; although there can be several drier years in succession when it does not spill.

Hume Dam - page 2

While the storage is being filled a minimum of 600 megalitres per day is released to provide sufficient water flow for downstream environmental needs and to ensure the health of river bank vegetation. Filling typically lasts from the end of the irrigation season in mid-May to late winter or spring and may overlap with flood control. If space is available in the storage, flooding flows from upstream will be absorbed and downstream regions will be fully protected from flood. But if the storage is full then flood inflows are passed downstream via the spillway gates and power station without endangering the dam itself. If storage levels and inflow are high in winter or spring, before the irrigation season, then water may be released to provide space in the storage to mitigate floods; this "pre-release" water is in excess of downstream needs but does not exceed river channel carrying capacity. Hume Reservoir provides significant flood protection for downstream areas but once the storage is full its flood mitigation potential is very limited until water is released. As the irrigation season begins, water is released into the Murray River. Water takes 25 days to reach the South Australian border so releases must be made well in advance of requirement. During the peak of the growing season the daily demand in South Australia and in the irrigation areas along the Murray can exceed 30,000 megalitres a day but the river channel can handle only 25,000 megalitres a day between the Hume and Yarrawonga. Further downstream, narrowing in the river at the Barmah Choke near the Barmah Millewa forest can handle only 8,500 megalitres a day before flooding occurs; a further 2,000 megalitres a day can be sent via the Edward River. As far as possible, releases are lower than channel full capacity to minimise disruption for people living and working along the river. To minimise the need for high flows, efforts are made to release water to lower storages, such as Lake Victoria near the South Australian, border early in the season.

Information: ¶  Murray Darling Basin Commission at http://www/mdbc/gov/au.htm

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