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This report primarily focuses on two main reservoirs in Melbourne – Sugarloaf and Cardinia Reservoir. It also describes the general problem of distribution of potable water to Melbourne and the measures proposed to overcome this problem.
There are ten main reservoirs which distributes water to the Melbourne city and other surrounding areas. These ten reservoirs have a combined capacity of 1,812,175 million litres of water. The sediments in the catchment water stored in the storage reservoirs settle down to the bottom of the reservoir. The impact of natural sunlight will help to disinfect the settled water. Melbourne’s largest reservoir is the Thomson Reservoir. It contributes to 60% of Melbourne’s total reservoir storage capacity. Cardinia, Sugarloaf, Yan Yean and Greenvale are the only reservoirs with no catchment. They get water from other sources. Whereas the other reservoirs like Thomson, Upper Yarra, Silvan, Tarago, Maroondah and O’Shannassy receives water from the catchment areas. All these reservoirs are interconnected like a web link network. In case of any emergencies like bush fire, water from one reservoir can be transferred to another. Thus, protecting and saving the water from debris and other contaminants.
Table 1: Water Storage level
Figure 1: Water storage graph
The above graph shows the water level of the reservoirs from 2009 to 2012. Compared to the previous years, it can be clearly seen that the water level in 2012 has increased to 70%. During the first half of the year, the water storage level has decreased drastically. On the other hand, the water level storage for the second half of the year has increased as compared to the first half.
1.1 Cardinia Reservoir
Cardinia is the second largest reservoir in Melbourne with a total water storage capacity of 286,911 mega litres and is situated in the south-eastern suburbs of Melbourne, Australia. The construction of the reservoir commenced in May 1970 and completed in 1973 with a cost of more than AUD11.4 million dollars. Cardinia receives water through the pipeline from Silvan Reservoir, which is the fifth largest. It was constructed as rolled earth fill and rock fill embankment. Maximum height of the main dam from the river to crest is 85 metres. Length measured along the top of the dam is 1,542 metres. This includes main bank only. The saddle dams have an additional crest length of 2,841 metres. The Surface area of top water level is 1,295 hectares. The current water holding of this reservoir as of 3rd July 2012 is 219,724 mega litres, which is 76.6% full. Cardinia supplies water to Melbourne’s southern and south-eastern suburbs, and the Mornington Peninsula.
1.2 Sugarloaf Reservoir
Sugarloaf Reservoir is the fourth largest of all among the ten, located in northeast of Melbourne. It was completed in 1981 and constructed as rolled rock fill embankment with upstream concrete face. Its total capacity is 96,253 mega litres. Area of the catchment is 915 hectares off stream storage. Maximum height of the main dam from the river to crest is 89 metres. The length measured along the top of the dam is 1,050 metres. This includes main bank only. The saddle dams have an extra length of 690 metres. The Surface area of top water level is 440 hectares. The current water holding of this reservoir is 94,514 mega litres as of 3rd July 2012, which is 98.2% full. The water feeds the northern, western and central suburbs. In February 2010, the North South Pipeline from the Goulburn River was connected to the main reservoir.
2.0 SOURCE OF WATER
Cardinia and Sugarloaf reservoir, both has no catchment, but the water is transferred to it by other sources. A catchment is an area that catches the rainfall water and directs to a river, creek, reservoir or gutter. The water catchments are sent to the reservoirs that provide drinking water. There are two types of catchments – closed or forested catchment and open catchment. Around 80% of the drinking water comes from the closed water catchments in the Yarra Ranges. About 20% of Melbourne’s water comes from open catchments. The water from open catchment is pumped to the water treatment system, and the filtered water is distributed to the household. Melbourne has protected water catchments i.e. public are not allowed to enter inside the protected area.
The Sugarloaf reservoir receives water from Yering Gorge pumping station which can extract water from the Yarra River, including water released from Maroondah and O’Shannassy. It also receives water from Goulburn River via North- South pipeline. This is operated only in critical times. Water leaving from Sugarloaf Reservoir is treated and purified at Winneke Treatment Plant. The water will leave from this plant only if it meets the required standard for drinking.
The Cardinia Reservoir receives water from the Silvan Reservoir and nearby Wonthaggi Desalination Plant. It is used to stockpile water for Melbourne. The recent bush fire contaminated over 30% of water in Melbourne. At this time, most of the water was transferred to Cardinia Reservoir. The water from Cardinia flows out to other service reservoirs for household distribution.
3.0 WINNEKE TREATMENT PLANT
The Winneke treatment plant plays a prominent role in Melbourne’s water supply system. It was commissioned in November 1980, and it was the first time that fully treated water was introduced into the water supply system. More than 50% of Melbourne’s water is treated and purified at Winneke Treatment Plant. The plant is located 32 kilometres northeast of Melbourne at Sugarloaf Reservoir in Christmas Hills. The Sugarloaf Reservoir is one in ten reservoirs in Melbourne and is the fourth largest. The water requires full treatment process as it is not received from the protected catchment areas. The water comes into the plant from three main different sources- the Maroondah Reservoir by the Maroondah aqueduct and Yering Gorge pumping station, Yarra River by Yering Gorge pumping station and Goulburn River by the North-South pipeline.
3.1 Water Treatment Process overview
Water treatment process involves coagulation, clarification, filtration, disinfection and pH correction (chlorination) and fluoridation. The water is passed through 14 sand filters before being added with chlorine, lime and fluoride. The filtered water is distributed only if it meets the Australian standard for drinking.
Figure 2: Winneke Process Flow Diagram
Untreated water is pumped from the Sugarloaf Reservoir to the Winneke inlet control structure. At this stage, lime and aluminium sulphate (alum) is added. The alum acts as a coagulant, which will suspend solids and other microorganisms to form larger particles.
The water then flows through an underground channel to a water distribution chamber. The water is sent to one of five sludge blanket clarifiers and polyelectrolyte injected to promote flocculation and sedimentation processes. Water is circulated in the clarifiers for 3 to 4 hours. The clarifiers improve the coherence and entrapment of the suspended solids and thus eliminate the colour from the water. Solid particles are separated from the raw water as settled water and sludge.
The settled water is delivered through concrete channels to 14 gravity filters (Sand filters). This will remove most of the remaining suspended solids. Each filter is a rectangular concrete structure with a bed of sand supported on a layer of pebbles.
The water comes out of the filter is disinfected by the process called chlorination. A small amount of chlorine is added to disinfect the filtered water which will eliminate the residual microorganisms. This will help to kill bacteria and other micro organisms which spread waterborne diseases. Drinking water typically contains 0.2 milligram per litre (mg/l) – 1.6 mg/l of chlorine. Lime is added to maintain the alkalinity and acidity (pH) level. The treated water flows into a large enclosed storage reservoir which is located adjacent to the treatment plant. This reservoir act as buffer storage and the water is released according to the needs.
Fluoride is added in small quantities to prevent tooth decay. Natural water contains concentrations up to 1MG/L (milligram per litre) of fluoride. Fluoride is a naturally occurring substance in rocks, soils and plants. Fluoride is added to drinking water at a concentration of approximately 0.7MG/L or less than 1 part per million. The left over debris from the plant is recycled for bike paths and building roads.
4.0 MELBOURNE WATER
Melbourne Water is owned by Victoria Company. It maintains all aspects from water collection to distribution. A complex interconnected pipeline system distributes water from Melbourne’s main water storage reservoirs to the three retail business water companies and to their customers. Melbourne Water operates and maintains around 157,000 hectares of protected catchments in the Yarra Ranges. It has main ten water storage reservoirs and distributes to around 1,062 kilometres. It has 214 kilometres of aqueducts with 65 service reservoirs and 42 water treatment plants.
4.1 Water collection and distribution
Majority of Melbourne’s water catchment is located in the forest areas of Yarra ranges. These forests capture and filter rainwater as it flows across the land into streams and then to the reservoirs.
From the main reservoir storages, through large pipes the water flow to the service reservoirs by gravity. There are about 55 service reservoirs, which is stored only for one or two days. These reservoirs will ensure that a constant supply of water during the peak demanding periods. From the service reservoirs, water flows down again by the gravity through smaller underground pipelines to households and businesses by the water retail network of pipes. Water pressure is adjusted so that all households receive water at all times.
5.0 Yarra River
The Yarra River upstream of Warrandyte is the main source of Melbourne’s water supply. The progressive development of water supply infrastructure in Melbourne is driven primarily by population growth. The growth in consumption is been made possible by ever increasing abstractions from the Yarra catchment upstream. Water harvesting has caused flows in the Yarra River to be much less than they would otherwise be. Larger dams restrict the sediment flow down of the rivers. Another major issue with the removal of water from the Yarra River is the change in the echo system and diversion in river path.
6.0 Methods of providing Potable water
A number of possible alternative water supply options have been put forward to extend the water supply to Melbourne and its surrounding areas into the future.
Desalination (Wonthaggi Desalination)
Rain/ storm water catchment
Dual pipe recycling
Upgrade of Sewage treatment plant
Sugarloaf Pipeline Project
Management of current water supplies (restrictions and public awareness )
Raising the height of the dam
Re-opening past water sources for the sole purpose of water supply
Construction of new dams
Melbourne’s water resource is large enough to feed the entire population in the city. Water is available for urban use from the north east catchments of Melbourne. Building a new dam to collect water from the Thomson/Macalister, Latrobe or Mitchell basins is the most cost-effective approach. This can be a blessing for the Gippsland farmers. This should be the preferred approach. Water can also be brought from north of the Great Divide with the Sugarloaf scheme, but this would be a costly approach. The stormwater collection in Greenfield urban area is another option. Rainwater tanks have a higher capacity than urban stormwater collection but are inefficient and enforce unnecessary costs on the new house developments where they are mandatory and on the taxpayer where the tanks are subsidized. Regulations requiring their installation should be removed and subsidies to their installation should be discontinued. Similarly, the proposals for recycling of water from the Eastern Treatment Plant and for desalination should be rejected. The proposed Wonthaggi desalination plant, according to the estimates provided by the government, would result in excessive capital costs of $2 billion and significantly higher operating costs compared with making use of water from the catchment area. Various options for the Eastern Treatment Plant, including exchanging treated water for more harvesting from the Yarra, seem to be high cost approaches but could be further investigated.
Modifying or increasing the release of flows from the reservoir and other points of regulation would prefer fewer benefits for in stream, riparian and wetland ecosystems than would measures to restore native vegetation, natural floodplain drainage patters or incentives or controls to improve the quality of discharge from agricultural and especially urban areas. Public awareness and cooperation are essential, as many of the actions which need to be taken to maintain or restore the ecosystem of the Yarra upstream of Warrandyte involve private land.
The above methods of providing water for the future are all available but at a high cost to the taxpayer. The best option is to ensure that the all the measures implemented are well in place to organize and maintain its current resources. Climate change also has to be considered as this will have a negative impact on the ground water resource. Though ground water is replenished every year by the annual rain fall, figures are decreasing and evaporation rates rising as predicted under the CSIRO Climate Science. Public awareness is needed to ensure less wastage of water and maintain supply for the future.
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