Catchment - Melbourne's Water Supply

Maroondah Dam and Catchment Source - Museum Victoria Photographer - Rodney Start

All of Melbourne's water comes from a series of weirs and dams in the forest-clad mountains east of the city. Melbourne enjoys a town water supply of excellent quality. The main reasons for this involve the geology and the management of the forested catchments.

The mountains cause moisture-laden air to rise, cool and release the moisture as rain and snow. Thus the rainfall is far higher in the mountains than in flatter areas around Melbourne. A certain amount runs off immediately into the rivers but much will be 'captured' by the dense forest vegetation, percolate through the soil and reach the water table. The water table contains the ground-water, which is confined within porous aquifers, and which emerges from the ground at springs to form creeks. Such ground-water enables creeks to keep running even if dry weather prevails. The levels of dissolved material in these streams is naturally very low because they flow through an ancient landscape; most of what could be dissolved was washed away long before Europeans decided to use these streams as sources of water. The water is therefore very pure.

Artists' impression of Melbourne water system Source - Melbourne Water

From the 1870s, authorities began to set aside water catchment areas and prohibit farming and logging in these large areas of the forest. The initial impetus for this was to improve public health in the city by ensuring that fertilisers, silt or human settlement did not pollute Melbourne's water. Later, the argument moved to water quantity once it was understood that 'untouched' mature forests produce more stream-water flow than forests which have been logged and have more vigorous thirsty regrowth trees.

The policy of catchment protection has ensured that Melbourne's water is of an excellent quality, but the argument about the effects of timber-getting on water quality and quantity continues. Water authorities claim that logging will reduce stream flows, silt up the reservoirs, and pollute the water, and that the water would need to be further treated before it is suitable for domestic uses. Timber authorities argue that scientific logging need not undermine the water yield and purity from the catchments, and present social and economic reasons in favour of harvesting the catchment areas.

About 300 hectares (out of the 157,000 hectares) of water catchments is logged each year by the Department of Natural Resources and Environment. Measures in place to minimise the impact on water quality and yield include leaving buffer zones along streams and installing drainage on logging tracks. Melbourne Water makes sure that the roads are well-maintained, so that access is easy for fire control.

The forest has been viewed by the water authorities as a source of pure water, an abundant resource which could allow the expansion of suburban Melbourne. Country interests argue that this growth of Melbourne is at the expense of country areas, and that some of the forest water should be used in irrigation schemes north of the range.

Unlike Melbourne's catchment, this dam at Targo has farming in the catchment area. Source - Melbourne Water

The building of reservoirs, dams and water channels to transport water from the hills to the houses of Melbourne was an impressive surveying and engineering feat. Engineers met the challenge of damming valleys and diverting streams. The areas around the dams were landscaped, becoming picnic areas planted with introduced trees; these are now favourite parts of the visitor's experience of the Mountain Ash range.

Access to many catchment areas is limited - they are closed to public entry and open only to bushwalkers (on specified tracks), university researchers and fire fighters. The majority of the catchment area now forms part of the Yarra Ranges National Park or the Kinglake National Park.

Because of this, large parts of the Mountain Ash forest have been protected, and are nearly in a 'wilderness' state. These developments indicate how the economic value of the forest (in this case its role in producing water for the city) has led to a preservation and fostering of wilderness areas.

For further information, visit the Melbourne Water website.