Thomson Reservoir
The Thomson Reservoir is owned and operated by Melbourne Water. Its useable capacity is 1,068,000 ML and it contributes approximately 60% of Melbourne's total reservoir storage capacity.
The Thomson Reservoir was completed in 1983 and serves to provide drought security for Melbourne, environmental flows, irrigation releases and hydro-power generation.
Volume as at 6/1/2009 : 214,242 megalitres (20.1% full)
Rainfall to 8am 6/1/2009 : 0.0 mm
These results are preliminary and are validated at the end of the month.
Access rainfall data for your area here.
Drought Security
Thomson Reservoir has more than doubled Melbourne's total storage capacity. This has provided multi-year drought security 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 simultaneously satisfy minimum environmental flow requirements in the Thomson River at three locations downstream of the dam:
- immediately downstream of the dam;
- 11 km downstream of the dam at the Narrows and;
- 23 km downstream of the dam at Coopers Creek.
The minimum environmental flows shown in the table below are specified in the Environmental Bulk Entitlement for the Thomson River.
The bulk entitlement for the Thomson River Environment also allocates to the environment 10,000 ML of inflow to be held in the Thomson Reservoir for release to the waterway at a time that would achieve optimal river health.
The Thomson River Environmental Bulk Entitlement is managed by the West Gippsland Catchment Management Authority on behalf of the Minister for Environment.
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.
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
Minimum daily flow requirements downstream of Thomson Reservoir
| Month | Below Dam | Narrows | Coopers Ck |
|---|---|---|---|
| Jan | 75 ML/d | 120 ML/d | 200 ML/d |
| Feb | 75 ML/d | 120 ML/d | 180 ML/d |
| Mar | 75 ML/d | 80 ML/d | 155 ML/d |
| Apr | 25 ML/d | 80 ML/d | 155 ML/d |
| May | 25 ML/d | 80 ML/d | 150 ML/d |
| Jun | 25 ML/d | 80 ML/d | 150 ML/d |
| Jul | 25 ML/d | 80 ML/d | 216 ML/d |
| Aug | 25 ML/d | 80 ML/d | 238 ML/d |
| Sep | 25 ML/d | 80 ML/d | 245 ML/d |
| Oct | 25 ML/d | 80 ML/d | 225 ML/d |
| Nov | 75 ML/d | 120 ML/d | 205 ML/d |
| Dec | 75 ML/d | 120 ML/d | 200 ML/d |
| Total | 15,100 ML/a | 34,000 ML/a | 70,600 ML/a |
Thomson Reservoir flows and releases since filling began
| Calendar Year | Inflows to Thomson Reservoir (ML) |
Transfers from Thomson to Upper Yarra Reservoir (ML) |
Irrigation Releases from Thomson Reservoir Under Entitlements (ML) |
Total Downstream Releases from Thomson Reservoir¹ (ML) |
|---|---|---|---|---|
| 1984 | 219,000 | 16,500 | 0 | 44,500 |
| 1985 | 240,500 | 500 | 0 | 32,000 |
| 1986 | 236,500 | 0 | 0 | 32,500 |
| 1987 | 187,500 | 37,000 | 0 | 34,000 |
| 1988 | 205,000 | 90,500 | 8,000 | 42,500 |
| 1989 | 245,500 | 0 | 2,500 | 43,500 |
| 1990 | 310,000 | 71,000 | 6,500 | 143,000 |
| 1991 | 273,500 | 85,500 | 0 | 176,000 |
| 1992 | 319,000 | 45,000 | 0 | 238,500 |
| 1993 | 275,000 | 70,500 | 0 | 231,500 |
| 1994 | 206,000 | 211,000 | 2,500 | 144,000 |
| 1995 | 278,500 | 81,000 | 3,500 | 143,500 |
| 1996 | 309,500 | 13,500 | 0 | 195,000 |
| 1997 | 93,500 | 254,500 | 22,500 | 172,500 |
| 1998 | 182,000 | 181,500 | 25,500 | 75,000 |
| 1999 | 125,500 | 194,500 | 1,000 | 56,000 |
| 2000 | 228,000 | 96,000 | 23,500 | 74,000 |
| 2001 | 175,500 | 135,000 | 7,500 | 51,000 |
| 2002 | 139,500 | 198,500 | 4,500 | 46,500 |
| 2003 | 210,500 | 161,000 | 3,500 | 46,000 |
| 2004 | 179,500 | 67,000 | 4,000 | 50,000 |
| 2005 | 152,000 | 138,000 | 3,000 | 53,000 |
| 2006 | 73,500 | 214,000 | 12,000 | 84,000 |
| 2007 | 179,000 | 96,000 | 12,000 | 52,000 |
¹ Including spills plus environmental, SRW and hydro releases
** All figures rounded to nearest 500 ML
Note the impact of the current drought as flows from the Thomson decrease after it received approximately half its average rainfall in December 1996 and continued to receive minimal rainfall during subsequent years.
| 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) |
216.2 (1991) |
198.6 (1987) |
227.6 (1990) |
236.6 (1993) |
296.5 (1976) |
171.2 (1985) |
178.6 (1986) |
1467.2 (1990) |
| Driest | 11.6 (1976) |
3.0 (1976) |
10.2 (2004) |
17.9 (1981) |
18.4 (1976) |
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 | 62.3 | 47.9 | 68.1 | 77.7 | 70.4 | 98.1 | 95.8 | 102.3 | 111.1 | 106.7 | 89.5 | 82.4 | 1012.3 |
