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O'Shannassy Reservoir facts for kids

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O'Shannassy Dam
Country Australia
Location McMahons Creek, Victoria
Coordinates 37°40′30″S 145°48′20″E / 37.67500°S 145.80556°E / -37.67500; 145.80556Coordinates: 37°40′30″S 145°48′20″E / 37.67500°S 145.80556°E / -37.67500; 145.80556
Purpose Water supply
Status Operational
Construction began 1922
Opening date 1928
Operator(s) Melbourne Water
Dam and spillways
Type of dam Embankment with an internal reinforced concrete wall
Impounds O'Shannassy River
Height 34 m (112 ft)
Length 226 m (741 ft)
Dam volume 245×10^3 m3 (8.7×10^6 cu ft)
Spillways 1
Spillway type Uncontrolled
Spillway capacity 500 cubic metres per second (18,000 cu ft/s)
Reservoir
Creates O'Shannassy Reservoir
Total capacity 3.123 GL (687,000,000 imp gal; 825,000,000 US gal)
Catchment area 11.9 ha (29 acres)
Surface area 27 ha (67 acres)

The O'Shannassy Reservoir is an Australian man-made water supply dammed reservoir. The 3.1-gigalitre (680,000,000 imp gal; 820,000,000 US gal) water store across the O'Shannassy River is located near the locality of McMahons Creek, approximately 80 kilometres (50 mi) east of Melbourne, Victoria. The dam that creates the impoundment is called the O'Shannassy Dam.

Location and features

The reservoir is part of Melbourne's water supply system. Water flows under gravity to Silvan Reservoir, then to storage and distribution reservoirs around Melbourne. It is the smallest of the water storage reservoirs managed by Melbourne Water, with a capacity of approximately 3.1 gigalitres (680,000,000 imp gal; 820,000,000 US gal), but it is on a very productive catchment, with stream flow averaging 80 gigalitres (1.8×1010 imp gal; 2.1×1010 US gal) per annum.

The location was selected as it is at sufficient altitude for gravity supply to the elevated eastern suburbs of Melbourne. A diversion weir on the O'Shannassy River and aqueduct to the Surrey Hills Reservoir in Melbourne were completed in 1914. The weir was complemented by the construction of the dam and its reservoir in 1928, but the weir was still used to divert river flows into the aqueduct. The construction of the Yarra-Silvan conduits in the 1950s resulted in reduced requirements for the aqueduct which was decommissioned in 1997.

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