Significant water events
During the 2010–11 year the Melbourne region experienced very much above-average rainfall and, in parts of the western area of the Melbourne region, rainfall was the highest on record (see Climate overview). As a result, streamflows in Melbourne's four major rivers exceeded the long-term mean annual flow by an order of magnitude (see below). Above-average rainfall also translated into significant runoff into Melbourne's surface water storages, with storage volumes increasing substantially from 47% to 85%, as a percentage of total storage capacity (refer to the Resources and systems Surface water note for more information). Similar wet conditions were recorded across the state of Victoria, allowing storage volumes in the Thomson Reservoir to recover following a prolonged period of drought.
In addition to the great improvement observed in Melbourne's storage volumes, the prevailing wet conditions influenced the allocation of surface water resources in the Melbourne region (see line item 21.1 Surface water allocation announcements) and the qualification of rights to water (see discussion below).
Rights may be suspended, reduced, increased or otherwise altered after a water shortage has been declared under section 33AAA(2) of the Water Act 1989 (Vic).
Although above-average rainfall was experienced throughout Melbourne, three qualifications of rights in the Yarra and Thomson basins continued during the 2010–11 year to secure Melbourne's water supplies if dry conditions continued.
In July 2010, the Victorian Minister for Water restored environmental flows of 22,000 ML to the Yarra and Thomson rivers that were being retained in storage to supplement Melbourne's water supplies.
Under the qualifications of rights, the environmental flows were not due to be returned until Melbourne's water restrictions eased; however, increased rainfall, water projects and conservation measures allowed environmental flows to be restored earlier than scheduled.
The temporary qualification of rights in the Thomson River of September 2009 expired in September 2010 and the remaining temporary qualifications in the Thomson and Yarra rivers were revoked in October 2010.
More information on qualification of rights is available on the water.vic.gov.au website.
During the 2010–11 year, annual flow in each of the four major rivers was well above the mean annual flow (Table W1). The higher flows in these rivers reflect above average rainfall across the region during the 2010–11 year.
|River||Period of record||Mean annual flow (ML)||2010–11 flow (ML)||2010–11 as % of mean annual flow|
Figures W1, W2, W3 and W4 show the total monthly flows for the Yarra, Bunyip, Maribyrnong and Werribee rivers respectively.
Figure W1. Chart of monthly flow for the Yarra River compared to long-term values for the region
Figure W2. Chart of monthly flow for the Bunyip River compared to long-term values for the region
Figure W3. Chart of monthly flow for the Maribyrnong River compared to long-term values for the region
Figure W4. Chart of monthly flow for the Werribee River compared to long-term values for the region
Major water initiatives
Major projects relating to water supply augmentation in the region include the Wonthaggi desalination plant and the Melbourne to Geelong pipeline.
Construction of the Wonthaggi desalination plant continued. It will be operated by a private consortium and will supply water to the Melbourne region. Commissioning of the plant is underway and reliability testing is expected to be finalised in February 2013. The plant is scheduled to produce up to 150 GL/year. The project will be delivered through a public-private partnership with the AquaSure consortium. Degrémont Thiess Services will be responsible for the operation and maintenance of the plant and pipeline to July 2039.
The Melbourne-Geelong pipeline is being built to enable the transfer of water from the Melbourne system, including Thomson and desalination sources, to Geelong. The pipeline is scheduled to begin operation in 2012, with Barwon Water entitled to take 16,000 ML/year.