What is a catchment?
A catchment is an area that catches rainfall and directs it to a creek, river, reservoir or (in built-up areas) a gutter. Our water catchments feed the reservoirs that provide our drinking water.
Forested (closed) catchments
Around 80% of our drinking water comes from closed water catchments in the Yarra Ranges. 157,000 hectares of forest has been closed to the public for over 100 years. These native forests filter rainwater as it flows across land into creeks, rivers and our reservoir storages.
Melbourne is one of five cities in the world with protected water catchments. We believe it is better to start with as much high quality water as possible, rather than treat it to reach the required standards.
Some of the catchments are now National Parks managed by Melbourne Water and Parks Victoria.
Inside the forested catchments
The foresight of our city founders in putting aside land for catching and storing water has given us a fantastic legacy. These catchments have remained largely undisturbed for more than 100 years, preserving the biodiversity of the ecosystem.
Mountain ash forests have an understorey of tree ferns with gullies of cool, temperate rainforest. The trees are among the world's tallest, sometimes towering to more than 100 metres. Large pristine areas of these trees and other vegetation are of national and state significance, including the Slender Tree-fern.
Indigenous eucalypts and smaller flora
The catchments also have a large range of indigenous eucalypts, as well as many smaller understorey flora including Cinnamon and Myrtle Wattle, Prickly Currant Bush, Common Ground-Fern and Rough Tree-Fern.
Ideal habitat for animals
Mountain ash forests support a unique ecology. They are crucial for the conservation of hollow-dwelling species including bats, forest owls and parrots. Among the most significant of these is the endangered Leadbeater's Possum, one of Victoria's faunal emblems.
The catchments also support extensive tracts of old-growth mountain ash forest, conditions that are critical for animals such as the Yellow-Bellied Glider - a native, gliding possum.
Large fallen logs provide habitat for small mammals, reptiles and invertebrates, providing basking sites for reptiles like the Highland Copperhead and Tiger Snake, and subterranean nesting sites for the Native Bush Rat. Other animals (like brightly coloured velvet worms) use large fallen logs to hunt prey such as slugs.
Birds in the catchments
An amazing diversity of species and populations of birds can be found:
- Pink Robin
- Yellow-tailed Black Cockatoo
- Australian King-Parrot
- Pied Currawong
- Grey Goshawk
- Crimson Rosellas
Most cities source their water from open catchments. Unlike closed catchments, these areas have mixed land uses (like farming) instead of being used exclusively to harvest water.
About 20% of Melbourne's water comes from open catchments.
Water from open catchments is put through sophisticated filtration and treatment to make sure it meets the same requirements as water from closed catchments.
Protecting the catchments
Safeguarding Melbourne's water supply catchments is a priority for us. Bushfires, unauthorised public entry and erosion are the main risks that we manage to ensure our water is protected.
Bushfires leave soot and ash, which can be washed from the catchments into the reservoirs. Fires can also destroy the mountain ash trees that cover about half the catchment areas. We invest about $2.4 million a year on fire prevention to protect against bushfire.
Major bushfires in February 2009 damaged about 30% of Melbourne's water supply catchments. Our 2 biggest catchments, Thomson and Upper Yarra, were successfully protected. There was no impact on drinking water provided to Melbourne. Recovery work in the damaged catchments is continuing.
Access to the water supply catchments is restricted to minimise the risk of human-borne disease entering our water supply system. The system of uninhabited catchments provides a significant barrier against contamination of the water supply by Cryptosporidium, Giardia and other pathogenic micro-organisms. There is also strict monitoring of water quality.
In recent years, we have increased security for the catchments and our assets by upgrading signage and security systems. Security teams patrol the catchments regularly, and people are prosecuted and fined for unauthorised entry.
We pay particular attention to the roads in the catchments to ensure appropriate drainage is constructed and maintained to minimise erosion and sediment flowing into the water.
Location of our catchments
To see where our catchments are located and how they supply water to Melbourne view our interactive Water Supply Network Map (opens in a new window):