Sustainability Report 2006/07Overview
Melbourne’s drinking water is highly regarded by the community. Most of it comes from more than 156,000 hectares of protected catchments high up in the Yarra Ranges east of Melbourne.
Water flows from the catchments to nine major reservoirs that have a capacity of 1,773,000 million litres.
This water is of excellent quality and requires only minimal treatment at water treatment (disinfection) plants. Bulk water is transferred through about 1030 kilometres of water mains and 200 kilometres of aqueducts and tunnels to about 60 service reservoirs in the metropolitan area and delivered to the retail water businesses, which distribute it to individual customers.
Changing rainfall patterns
Autumn inflows to our four major harvesting reservoirs in 2008 were the lowest on record, revealing the additional pressures we face through changing rainfall patterns.
The lack of traditional autumn rain to wet the catchments, accompanied by shorter, more intense rainfall, reflects predicted climate change impacts.
Without autumn rain, dry soils impacted by heavy rain later in the year created increased levels of turbidity due to erosion and more exposed banks in reservoirs that were already at low levels, causing potential water quality issues.
Dry soils also soaked up the rain leading to reduced run-off, so that even when we received good falls, dam levels declined.
Storage levels continue to drop
Our storages continued to fall throughout the year, with Stage 3a water restrictions remaining in force until at least 30 November 2008.
By 30 June 2008, the storage level had dropped to 29.5% (523,526 million litres). This compared with 30.7% (544,415 million litres) at the same time the previous year.
With the drought entering its 11th year, the extent of the drought has raised questions about the impact climate change is having on our water resources. The prolonged dry conditions during 2007/08 highlighted the need to continue efforts to conserve supplies and find new water sources.
Winter and spring rain boosted the storage level to more than 40% by November 2007, but the record low 2008 autumn inflows reflected the extent of the ongoing drought.
This year, streamflows into the four major harvesting storages (Maroondah, O’Shannassy, Upper Yarra and Thomson) were 89% above the previous year but only one-third of the average for 1998-2007.