Thomson Reservoir

Thomson Reservoir is the largest of Melbourne’s reservoirs. It has a capacity of 1,068 billion litres, and makes up about 60% of Melbourne's total storage capacity.

Thomson supplies Silvan Reservoir (via Upper Yarra Reservoir), which distributes water throughout the Melbourne metropolitan area. The dam at the reservoir is an earth and rockfill embankment.

Thomson reserior aerial photograph

Thomson Reservoir was completed in 1984, and was designed to build up water reserves in wet years for use in dry years. It was critical to maintaining water supply to Melbourne in the most recent drought from 1997 to 2009, in which time it went from almost full to just 16% full.

Learn how Thomson Reservoir has been used over the years to supply Melbourne with water in times of drought:

Fast facts about Thomson Reservoir

Facts about Thomson reservoir

Thomson Reservoir:

  • can hold enough water to fill Sydney harbour twice, or the MCG 628 times, or an Olympic swimming pool 427,200 times
  • third-largest reservoir connected to a major city in Australia, behind Warrangamba Dam and Brisbane's Wivenhoe Dam – large enough to fit all of the dams servicing Canberra, Adelaide and Perth
  • designed to serve a city of 5 million people, based on rainfall and water use at the time it was proposed in 1968
  • dragged down Melbourne’s storage levels from 65% to 26% overnight when it was factored into the total water system storages – it was still virtually empty
  • awarded the Engineering Excellence Award in 1985 by the Australian Institution of Engineers
  • built by more than a thousand construction workers, who were housed with their families at the purpose-built town of Rawson nearby – which remains to this day

Other uses for Thomson Reservoir

As well as servicing Melbourne in times of drought, Thomson Reservoir also provides water for the Thomson River, agriculture and hydroelectricity generation.

Environmental flows at Thomson River

Water is continuously released from Thomson Reservoir to maintain healthy flows in the Thomson River. The Environmental Bulk Entitlement specifies what the minimum environmental flows are, and how much water is available for additional releases to imitate natural flows. Additional releases can be ordered by the West Gippsland Catchment Management Authority.

Irrigation releases

Southern Rural Water manages the Macalister Irrigation District, which includes irrigators downstream of Thomson Reservoir. Southern Rural Water has a bulk entitlement allowing them access to 45 billion litres of Thomson Reservoir’s storage capacity and 6% of its inflows.

Hydroelectricity generation

Downstream releases from Thomson Reservoir pass through a small hydro power plant, which generates electricity and feeds it into the state power grid. Find out more about how our reservoirs generate renewable energy:

Rainfall figures for Thomson Reservoir

Key rainfall facts (mm)

Month​ Wettest​ Driest​ Average​
January​ 160.8 (2016)​  8.0 (2013)​ 60.9
February​ 216.8 (1994)​ ​3.0 (1976) ​51.7
March​ 170.6 (2012)​ ​10.2 (2004) ​68.4
April​ ​337.8 (1990) ​17.9 (1981) 74.4
May​ ​179.8 (2000) ​14.8 (2009) ​72.4
Jun​e ​325.0 (2007) ​7.9 (1979) ​107.2
Jul​y ​198.6 (1987) ​20.8 (1976) ​100.1
Aug​ust ​227.6 (1990) ​13.4 (1982) ​102.2
September​ ​236.6 (1993) 36.6 (2015)​ 105.8
October​ 296.5 (1976)​ 16.0 (2015)​ 98.7
November​ 200.0 (2007)​ 32.0 (1979)​ 94.4
December​ 178.6 (1986)​ 25.4 (1977)​ 81.4
All time​ 1467.2 (1990)​ 623.5 (1982)​ 1017.5

Historical rainfall data (1975-2019)

graph of Thomson Reservoir rainfall data

Location of Thomson Reservoir

View map of Thomson Reservoir

Last updated:
19 November 2020