Thomson Reservoir
Area of catchment
48,700 hectares
Type of dam
Earth and rockfill embankment
Maximum height of main dam from river to crest
165 metres
Length measured along top of dam
590 metres (main bank only, saddle dam has additional length of 580 metres)
Surface area (top water level)
2,230 hectares
Total available capacity
1,068,000 megalitres
Volume as at 9/9/2010 : 311,307 megalitres (29.1% full)
Rainfall to 8am 9/9/2010 : 4.4 mm
These results are preliminary and are validated at the end of the month.
Access rainfall data for your area here.
Where the water goes
Supplies Silvan via Upper Yarra for distribution throughout the metropolitan area.
Date of completion
1984
The Thomson Reservoir is the largest of all of Melbourne’s reservoirs, with a capacity of 1,068,000 ML, and it contributes approximately 60% of Melbourne's total reservoir storage capacity.
The Thomson Reservoir was completed in 1984 and was designed to build up water reserves in wet years for use in dry years. Never has it been more valuable than over the past 12 years of drought.
The historical storage levels show the effect of reduced inflows since 1997, in which time the amount of water in Thomson has continued to decline as inflows have continued to be well below average. The Thomson and Melbourne's nine other dams will still play a vital role in our water supply, but we need to diversify our supply sources to include those that don't rely on rainfall.
The Thomson Reservoir also provides environmental flows to the Thomson River, irrigation releases for agriculture and hydro-power generation.
Drought Reserve
Thomson Reservoir more than doubled Melbourne's total storage capacity when it was included in Melbourne’s total water supply capacity for the first time in 1984. It has been full three times, in 1992, 1993, and 1996. The capacity of the Thomson Reservoir has provided multi-year drought reserve for Melburnians. Typically, transfers from Thomson Reservoir to the Melbourne system are lower during wet or average years and higher during dry years.
Environmental Flows
Continuous releases are made from Thomson Reservoir to satisfy minimum environmental flow requirements in the Thomson River. The minimum environmental flows are specified in the Environmental Bulk Entitlement for the Thomson River.
Irrigation Releases
Southern Rural Water is responsible for managing the Macalister Irrigation District, including irrigators downstream of Thomson Reservoir. Southern Rural Water has a Bulk Entitlement providing a 45,000 ML share of Thomson Reservoir storage capacity and a 6% share of its inflows.
Hydro Power Generation
Downstream releases from Thomson Reservoir are made via a small hydro power plant which contributes to the State power grid. Due to the state-wide drought, only minimum releases for the environment and irrigation have been passed through the hydro since October 1997.
Fast Facts
- When full, holds enough water to fill Sydney harbour twice, or the MCG 628 times, or an Olympic swimming pool 427,200 times.
- Thomson is the third largest reservoir connected to a major city in Australia (behind Warrangamba Dam and Brisbane's Wivenhoe Dam).
- With a capacity of 1,068 billion litres, could fit all of the dams servicing Canberra, Adelaide and Perth.
- When first proposed in 1968, Thomson and Melbourne's other dams were designed to serve a city of 5 million people, based on rainfall and consumption patterns of the time.
- Still virtually empty when factored into Melbourne's total water system storages, Thomson's size dragged down the city's storage levels from 65% to 26% overnight on 31 July, 1984.
- Was awarded the Engineering Excellence Award (1985) by the Australian Institution of Engineers.
- The nearby town of Rawson was built to house more than a thousand Thomson Dam construction workers and their families, and remains to this day.
See also:
| Thomson Key Rainfall Facts (in mm) | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Tot | |
| Wettest | 151.4 (1991) |
216.8 (1994) |
159.0 (1979) |
337.8 (1990) |
179.8 (2000) |
325.0 (2007) |
198.6 (1987) |
227.6 (1990) |
236.6 (1993) |
296.5 (1976) |
200.0 (2007) |
178.6 (1986) |
1467.2 (1990) |
| Driest | 11.6 (1976) |
3.0 (1976) |
10.2 (2004) |
17.9 (1981) |
15.4 (2009) |
7.9 (1979) |
20.8 (1976) |
13.4 (1982) |
41.2 (2001) |
28.1 (1977) |
32.0 (1979) |
25.4 (1977) |
623.5 (1982) |
| Average | 59 | 47.8 | 65.3 | 76.7 | 68.2 | 100.2 | 98.6 | 100.1 | 110.3 | 100.3 | 93.9 | 81.8 | 1002.2 |
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