Cotter Dam

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The Cotter Dam is a concrete gravity and rockfill embankment dam across the Cotter River, located in the Australian Capital Territory, Australia. Both the dam and river are named after early settler in the area Garrett Cotter. The impounded Cotter Reservoir is a supply source of potable water for the city of Canberra and its environs.

Original dam completed in 1915

Waterfall surrounded by stone walls in brown wooded hills; many of the standing trees are barren, gray, and dead.
The Cotter Dam in December 2005, surrounding country still showing the effects of the 2003 bushfires.

The original concrete gravity Cotter Dam was designed by Harry Gustav Connell (The Department of Home Affairs supervising engineer in Canberra from 1912 to 1916). The construction was started in 1912 and finished by 1915 when the city of Canberra was being established. The height of the dam wall was raised to a height of Script error: No such module "convert". in 1951 in order to increase capacity of the reservoir. The Script error: No such module "convert". dam wall was Script error: No such module "convert". long and created a reservoir with a surface area of Script error: No such module "convert".. The uncontrolled spillway was capable of discharging Script error: No such module "convert".. At that time, the top water level of the dam was Script error: No such module "convert". above sea level and the reservoir had a capacity of Script error: No such module "convert"..[1] A subsequent review in October 2006, using more accurate mapping methods, resulted in capacity being re-estimated downwards from the previous estimate of Script error: No such module "convert".. Additional galleries and drains were constructed between 1984 and 1986.[1] In order to supply the city with potable water, water from the reservoir was pumped to Mount Stromlo, and from there the water flowed by gravity to fill the city's reservoirs.

From the 1960s onwards, better quality water could be supplied without pumping using the newly completed Bendora and Corin dams, and Cotter Dam was only used when water was in short supply. However, in December 2004, ACTEW Corporation brought the dam back on line in response to the ongoing drought.[2]

Enlarged dam completed in 2013

Completed in 2013, the enlarged Cotter Dam comprises a new Script error: No such module "convert". high roller compacted concrete dam wall built downstream from the old Script error: No such module "convert". high dam wall, along with two auxiliary embankment dam walls along low-lying adjoining valleys. Constructed on rock foundations by an Abigroup / John Holland joint venture, with engineering design by GHD, the main dam wall is Script error: No such module "convert". long, with the two rockfill embankments Script error: No such module "convert". and Script error: No such module "convert". long and Script error: No such module "convert". and Script error: No such module "convert". high respectively, both with internal earthen cores.[1] The enlarged dam walls increased the storage capacity of the Cotter Reservoir from the previous Script error: No such module "convert". to Script error: No such module "convert"..[3]

The old dam wall remains, inundated by the water held behind the new dam wall and acting as a sediment trap for the new dam's intake tower. The old dam may only be visible in exceptional circumstances of drought. Completion was originally scheduled for the end of June 2011,[4] however construction was delayed until August 2013[5] due to heavy rainfalls in the summer of 2010/2011,[6] the discovery of an unexpectedly large rock seam at the site of the foundations in 2011,[7] and severe flooding in March 2012.[8] The uncontrolled spillway is capable of discharging Script error: No such module "convert". with a high water level approximately Script error: No such module "convert". above sea level.[2]

File:CSIRO ScienceImage 11545 Cotter Dam.jpg
Aerial view (June 2011)

Engineering heritage

The dam precinct received a Historic Engineering Marker from Engineers Australia as part of its Engineering Heritage Recognition Program.[9]

See also

References

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External links

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Template:Rivers of the Australian Capital Territory

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