Melbourne
Water overview

Significant water events

Even though below-average rainfall conditions were recorded across the state of Victoria, there was continued recovery of storage volumes in the Thomson Reservoir (which is outside the region) following a prolonged period of drought. During the 2012–13 year rainfall across the Melbourne region was generally below-average (see Climate overview). Below-average rainfall translated into a reduction of runoff into Melbourne's surface water storages, and the storage volume was 68% of total storage capacity at the end of 2012–13 year (refer to the 'Water resources and systems', Surface water note for more information). 

In addition to the slight decrease observed in Melbourne's storage volumes, the prevailing dry conditions resulted in slightly lower allocations of surface water resources in the Melbourne region (see line item 21.1 Surface water allocation announcements).

Streamflow

During the 2012–13 year, annual flow in the recorded at the most downstream gauging stations in the Bunyip and Yarra rivers were above the mean annual flow (Table W1). In contrast, annual flow in the Werribee and Maribyrnong rivers was below the mean annual flow.  

Table W1 Annual and Mean annual river flow

River

Period of record

Years of record

Number of years of complete record

Mean annual flow (ML) *

2012–13 total flow (ML)

2012–13 as % of mean annual flow *

Bunyip

1962–2013

51

42

115,725

128,851

111%

Yarra

1975–2013

38

10

445,608

611,388

137%

Maribyrnong

1985–2013

28

27

68,659

62,652

91%

Werribee

1911–2013

102

61

52,814

38,707

73%

* The calculated mean flow volume is based on complete yearly data records

Figure W1 shows the location of the streamflow gauging stations and catchment boundary used to prepare hydrographs for the four main rivers in the Melbourne region.

Figure W1 Map of key gauging stations along the main rivers and catchments within the Melbourne region
Figure W1 Map of key gauging stations along the main rivers and catchments within the Melbourne region


Figures W2, W3, W4 and W5 compare the total monthly flow for the Bunyip, Yarra, Maribyrnong, and Werribee rivers respectively with long–term average and percentile flows.


Figure W2 Graph of total monthly flow for the Bunyip River compared to long-term average and percentiles at gauging station 228213A
Figure W2 Graph of total monthly flow for the Bunyip River compared to long-term average and percentiles at gauging station 228213A


Figure W3 Graph of total monthly flow for the Yarra River compared to long-term average and percentiles at gauging station 229143A
Figure W3 Graph of total monthly flow for the Yarra River compared to long-term average and percentiles at gauging station 229143A

During the period of July to August rainfall was above average across the region (see Climate overview) which is reflected in total monthly flows observed for the Yarra River greater than both the mean annual flow and the 90th percentile for those months. Monthly flows in the Bunyip, Maribyrnong and Werribee rivers were also above average in the months of July, August and September, which were due to a wetter winter and early spring seasons recorded in 2012. Across the region, below average monthly stream flows were recorded for all four major rivers during late spring, summer and autumn seasons which are consistent with below average rainfall except for the month of February.


Figure W4 Graph of total monthly flow for the Maribyrnong River compared to long-term average and percentiles at gauging station 230200D
Figure W4 Graph of total monthly flow for the Maribyrnong River compared to long-term average and percentiles at gauging station 230200D

The daily stream flow data quality code for three days on August 18,19 and 20 has been recorded as 150 and 149 which mean "Poor data/historical rating or rating not verified/use with caution at clients discretion" and "Raw data as received from contractor/ only quality codes changed". This extremely poor data quality is reflected in the total monthly flow volume for the month of August, 2012. The flow volumes recorded do not correlate with the total of 19mm rainfall observed during the three day period at the nearby rainfall gauging station (RAAF Laverton). The August monthly total flow volume is approximately 12,065 ML if the three days of recorded poor data quality are excluded. However it can be safely assumed that the August total monthly flow was above average.



Figure W5 Graph of total monthly flow for the Werribee River compared to long-term average and percentiles at gauging station 231204B
Figure W5 Graph of total monthly flow for the Werribee River compared to long-term average and percentiles at gauging station 231204B

Major water initiatives

Completed major projects relating to water supply augmentation in the region included Melbourne to Geelong pipeline and the Victorian desalination plant at Wonthaggi.

The 59-km underground Melbourne-Geelong pipeline was completed in early 2013, and enables the transfer of water from the Melbourne system, including surface water from theThomson Reservoir and water from the desalination plant, to Geelong. Barwon Water is entitled to take 16,000 ML/year of water available through the transfer process. The Melbourne to Geelong Pipeline provided no drinking water to Geelong during the reporting period. It is an important back-up supply that may need to be called upon in times of drought.

The Victorian desalination plant (Figure P9) at Wonthaggi was completed and declared operational in December 2012. The plant is able to augment Melbourne's urban water supply with the capacity to provide up to 150,000 ML/year of desalinated water. For further information on the Victorian desalination plant refer to the Aquasure website.

The Office of Living Victoria is a new agency within the Department of Environment and Primary Industry established during the 2012–13 year. Reporting to the Minister for Water, it is charged with implementing the Victorian Government's Living Victoria and Living Melbourne policies. On 23 April 2012, a new vision for Melbourne's water future final report was released by the Victorian Government to support the development of Integrated Water Cycle Management projects across Melbourne region and Victoria.