Sustainability Report 2006/07Managing our current supplies
Dealing with drought
The chronically dry conditions led to further reductions in environmental flows in the Yarra River and Thomson River to ensure continuing supplies of drinking water.
An additional 10,000 million litres of water a year from each river was made available to augment water supplies as part of emergency drought contingency planning.
Heading into summer, this meant environmental flows in the Yarra River downstream of the Yering Gorge pumping station were reduced to 200 million litres a day. Stringent environmental safeguards are in place to monitor the health of the Yarra and Thomson rivers.
Swingler Weir, normally under water in the Thomson Reservoir, has been rehabilitated and is diverting water flows in the Thomson River to help manage drought conditions. The weir is upstream of the Thomson Reservoir dam wall and was submerged in 1998 before being exposed by dropping water levels.
The weir diverts water flow from the Thomson River directly to the Upper Yarra Reservoir. This gives greater flexibility to balance Thomson and Upper Yarra storage levels and manage transfer flow rates during continued drought conditions.
As part of emergency drought contingency planning, we have prepared and tested two major portable pumps for extracting water from the Thomson Reservoir below the intake point, and prepared aerators for use in the Upper Yarra Reservoir to maintain water quality under low-level conditions.
In December, the Government agreed to a temporary qualification of the Southern Rural Water (SRW) Thomson/Macalister Bulk Entitlement, allowing SRW’s Thomson drought reserve to be transferred via the Melbourne water supply system to supply drought-affected irrigators in the Werribee and Bacchus Marsh irrigation districts.
We are also working with the Department of Sustainability and Environment and the retail water businesses to oversee two new Smart Water Fund studies into the socio-economic costs of water restrictions, and alternative forms of restrictions.
Maintaining high quality water supply
Melbourne Water consistently meets stringent requirements in the distribution of safe, high quality drinking water.
The water supply system is managed according to the Hazard Analysis and Critical Control Point system, which uses audits and accreditation to ensure quality management from collection, treatment and distribution to customers.
This year we supplied 381,097 million litres of drinking water to the retail water businesses. This compares with 411,747 million litres in 2006/07, and 444,365 million litres in 2005/06.
For 2007/08, Melbourne Water met requirements for water pressure, microbiological standards, and disinfection by-products. Targets were not met for turbidity and aluminium.
The turbidity issues were caused by heavy storms in late June 2007 across the Upper Yarra catchment, which was very dry after record low rains during 2006. In July 2007, water entering the reservoir contained high levels of suspended matter washed off hard dry ground and scoured from exposed silt beds in shallow streams.
Turbidity levels in the reservoir increased and boil water notices were issued to Upper Yarra communities, as water from the Upper Yarra Reservoir is unfiltered and the turbidity had the potential to affect disinfection processes.
We worked closely with Yarra Valley Water and the Department of Human Services to manage community concerns and impacts, and boil water notices were lifted in August when turbidity levels dropped.
To prepare for any future incidents we have constructed five small filtration plants to ensure safe water supply to Upper Yarra communities.
To protect the wider Melbourne water supply, we restricted distribution of water through the Upper Yarra conduit, which caused sediment to settle in the pipe. This was later cleared through maintenance cleaning operations.
In November, two drinking water samples taken from the Whittlesea Main exceeded Bulk Water Supply Agreement levels of 0.1 milligrams per litre for aluminium. The samples recorded aluminium levels of 0.14 and 0.21 milligrams per litre. The second sample was slightly above the Australian Drinking Water Guidelines limit for aesthetic water quality of 0.2 milligrams per litre. Aluminium at these levels can cause aesthetic issues, such as cloudiness in water. No customer complaints were attributable to these results.
It has not been possible to identify the cause of these higher than normal results. No elevated aluminium was recorded in the source water from the Winneke water treatment plant, and all other relevant operational conditions were normal at the time.
Melbourne Water also worked with City West Water to develop an improvement plan following several taste and odour complaints from City West Water customers.
Algal bloom in Tarago Reservoir
A blue-green algal bloom in Tarago Reservoir was detected in late January as a result of routine algal monitoring of water samples.
Increased reservoir inspections identified surface scum caused by the algae and a small number of dead fish, and an incident was declared on 6 February 2008.
Melbourne Water supplies Gippsland Water with water from the reservoir for the nearby township of Neerim South, and also releases water from the reservoir into the Tarago River for Southern Rural Water customers.
Further monitoring was undertaken to identify the extent of the bloom and the presence of the toxin, microcystin. Algal numbers at six of the seven monitoring sites exceeded the 5000 cells/mL level for a notifiable incident, and the highest reading was 68,000 cells/mL.
Extensive sampling of the reservoir and downstream in the Tarago River found that the algae seemed to be confined to the reservoir. Melbourne Water worked closely with the Department of Sustainability and Environment, the Department of Human Services, Southern Rural Water and Gippsland Water, and determined that it was not appropriate to dose the reservoir, nor was it necessary to interrupt supply to Neerim South.
Analysis of water samples continued, with algae levels dropping towards the end of March. The incident was closed on 15 april.
Protecting the catchments
With low rainfall and extended hot weather, Melbourne Water was on full alert again this year to protect our water supply catchments from bushfire.
A total of 112 firefighters were in place for the 2007/08 fire season, with 50 casuals and 30 volunteers supplementing 32 permanent staff based at Healesville, Warburton, Wallaby Creek and Thomson Reservoir.
The Melbourne Water-funded helicopter began operation in November, along with fire prevention programs such as road clearing, road grading and fuel break slashing.
Melbourne Water attended pre-season fire meetings organised by the Country Fire Authority, the Department of Sustainability and Environment and local municipalities, and about 300 kilometres of fire breaks protecting Melbourne Water catchments were completed along the Thomson and Upper Yarra catchment boundaries.
At the end of the prescribed burning season, Melbourne Water firefighters took part in a training program with the Department of Sustainability and Environment, Country Fire Authority and Parks Victoria to improve their skills and expertise in operational firefighting and fire planning.
We began a $1 million, five-year research program with Melbourne University to examine the potential impacts of bushfire in our water supply catchments and the best ways to protect them. Scientists will test how bushfires within the catchment might move under different conditions, and how various mitigation strategies would work.
Melbourne Water and Parks Victoria began a culling program to reduce numbers of sambar deer in Melbourne’s water supply catchments. The results of more than five years’ research into the environmental and potential health impact of deer were used to support an application for a permit to cull up to 400 deer over 12 months.
Catering for growth
Melbourne Water has identified actions to increase efficiency and effectiveness in supplying Melbourne’s water. Planning continues to ensure the water supply infrastructure needs are met for growing areas, particularly west of Melbourne. This includes planning for significant upgrades to transfer systems.
We began construction work on a new 2.6-kilometre water main in St Albans in January, and are on schedule to complete the project in the latter half of 2008. The work is one of several improvements to the St Albans-Werribee water supply system, which will increase the capacity of Melbourne Water’s supply system and service Wyndham, the fastest growing municipality in Victoria. These works followed the development of a strategy with City West Water.
Major renewal projects included replacement of a 100-year-old cast iron water main from Preston to North Essendon, and upgrade of steel water storage tanks at St Albans, Sydenham, Yuroke and Somerton to address corrosion of the floor plates.
We are also investing considerable effort into identifying leakage points in the water supply network, including reviewing 40 steel water tanks and using new technology to detect leaks on large diameter trunk water mains.
