Thursday, 4 June 2009

To dam or not to dam - that will be the question

This post is long - but important.  It is the section on dams from the report of the Inquiry into Melbourne's Future Water Supply.  For more information and the link to access the report in full, please go here.  In the extract below, footnotes and figures have been deleted.  Highlighting and Links are Miss Eagle's.  

I think that most of us agree that we are in a new epoch: the 21st century; economic reassessment; environmental resassessment. It is the time for new thinking and a return to an earlier tradition that connected us to the basics of life - fresh air, clean water, the land, the plants and species around us.  So please, dear Reader, as you read this post have on your Thinking Cap of New Thoughts so that together we will make the right decisions for the future of the planet and for humanity.

You will also notice, dear Reader, that the current government uses the phrase "rainfall dependent".  It uses this phrase in a way that indicates that we can be "rainfall independent".  What stupid stuff is this?  Our planet has a hyrdological cycle.  We are dependent upon it, we are permanently linked to it.  Rainfall is a part of that cycle.  There is no possible way - outside death - for humanity to ever be other than rainfall dependent.


8.1 Given the current climate change predictions and that over 80 percent of Melbourne’s water supply is rainfall dependent, the Committee believes that there is an urgent need to diversify the city’s water supply rather than invest in the construction of new dams. On this basis alone the Committee does not support the option of supplementing Melbourne’s water supply with new dams.

The 2004 Securing Our Water Future Together white paper notes that the traditional approach to managing Melbourne’s water supply has been to utilise “…rivers and aquifers, create dams to supply towns, industry and irrigation, and then dispose of the wastewater back into rivers or the ocean.”  A number of stakeholders suggested that the construction of one or more major new dams – or an increase in the capacity of existing dams – could address Melbourne’s future water supply needs.

Melbourne's piped water supply commenced operation in 1857, with the completion of Yan Yean Reservoir, adjacent to the Plenty River, with a capacity of 30 gigalitres.  Over the years, the traditional approach to managing drought has been to build new reservoirs to meet increasing demand for water, spurred by population growth, dry spells and occasional drought.

The late 1920s and early 1930s saw the completion of the Maroondah (1927), O’Shannassy (1928) and Silvan (1932) Reservoirs. Upon completion of the Upper Yarra Reservoir in 1957, Melbourne’s water storage capacity tripled to nearly 300 gigalitres. Severe drought and the introduction of water restrictions in the late 1960s, spurred another round of dam building with the construction of the Cardinia and Greenvale reservoirs in the late 1960s-early 1970s.  Stage 6 water restrictions were introduced in Melbourne during the 1982-83 drought.  The last and largest of Melbourne's water storages, the Thomson Reservoir, was completed in 1983.   The Thomson Reservoir was expected by government to drought-proof the city.

Today, the Victorian Government and Melbourne Water believe the ongoing reliance on reservoirs is no longer sustainable. Securing Our Water Future Together notes the government’s policy of no new dams for Melbourne in the next 50 years. The white paper states that:

If a new dam were built for Melbourne, it would need to be filled with water that is currently used by rural and regional communities and the environment: a new dam for Melbourne would take water from Gippsland or Goulburn Valley farmers who depend upon irrigation for their livelihoods; it would also take water from our rivers that are already stressed. This would not only harm the habitat of our native plants, fish and animals, but also threaten our waterways, tourism and recreation industry. Taking more water for Melbourne from Gippsland is also likely to harm the Gippsland Lakes, which are vital for Gippsland’s economy; a new dam for Melbourne would be expensive, costing Victorians up to one billion dollars. These costs are not justified when there are great opportunities to use the water already available to Melbourne more wisely. The cost of saving water through sensible water conservation is far less than the cost of building a new dam; and there is existing water supply infrastructure that can be used to harness increased supplies for Melbourne.

The Central Region Sustainable Water Strategy (CRSWS), 2006 notes that:

New dams do not create new water. They take water from rivers and downstream irrigators.   They would also seriously impact on the health of rivers, to which the community wants more water returned to protect their sustainability.

The CRSWS also notes that during the past ten years of drought, the levels of Melbourne’s reservoirs have fallen revealing that there is a significant risk in relying almost solely on water supplied from rivers and reservoirs. It is also expected that climate change will significantly reduce the volume of runoff available to store in reservoirs.  New dams are not part of the strategy. In response to declining storage levels, a number of stakeholders who provided evidence to the inquiry have argued that the government should revisit its policy on “no new dams”.  The submissions called for the construction of new dams to the east of Melbourne, notably a dam on the Mitchell River or a diversion weir on the Aberfeldy River.

In 2005, Sinclair Knight Merz (SKM) undertook a study for the Department of Sustainability and Environment into the financial, social and environmental impacts of new dams to augment Melbourne’s water supply. The diversion of the Aberfeldy River was not included in SKM’s analysis.

The Mitchell River is often identified as the river most suitable for damming to supplement Melbourne’s water needs. The proposed dam, according to the SKM report, would involve the construction of an 80 metre high dam wall with a 500 gigalitre storage capacity. The estimated annual yield would be 86 gigalitres. The dam would flood approximately 30 kilometres of river and over 2,700 hectares of private land.   While the Mitchell River proposal provides the greatest estimated yield of all the dam options considered (86 gigalitres), the analysis of the environmental impacts of this option were nearly all rated moderate to severe by SKM.

The SKM report found that:

The biggest question mark over the dam is the impact on the Gippsland Lakes, a Ramsar Wetland site. The Mitchell River is the highest freshwater flow contributor to the Gippsland Lakes. They already suffer water quality problems and a further reduction of freshwater inflow to the Gippsland Lakes would only aggravate these water quality problems – this has the potential to affect the environment as well as recreation and commercial use of the lake;

The Mitchell River is Victoria’s last largely untouched major river and has Heritage River status. Areas of inundation would include part of the northern extent of the Mitchell River National Park; and

A new dam would flood productive farmland and displace people living in the valley including the townships of Dargo and Tabberabbera.

The only other option considered in the report which is capable of providing a similar level of water yield to the Mitchell River proposal, is the Hume Corridor Scheme – 80 gigalitres.  The Hume Corridor Scheme involves the diversion of water from the Goulburn River near Seymour, downstream from Lake Eildon, and then treating and pumping the water to the Greenvale Reservoir.   The principle social impact of the scheme is the purchase of water rights. Water for the scheme would need to be purchased from current water users in compliance with the Murray Darling Basin Cap on water extraction.  This would reduce the availability of water for agricultural production and would be politically and socially sensitive to divert water north of the divide to Melbourne.  The report stated that:

Although minor economic impacts are predicted on a regional scale, there may be particular localities within these regions that are affected more severely than others. Where this occurs, the reduction in agricultural output may result in localised reduction in expenditure, leading to localised loss in employment, and other flow-on economic and social effects. Localised rural communities already considered under pressure may be more susceptible to such impacts.

It is anticipated that the scheme would have two primary environmental impacts, construction impacts resulting from the construction of the pipeline and pump and the alteration of river flow. However, of all the options considered, the Hume Corridor Scheme had the lowest overall environmental impact as it did not involve the construction of a new dam or diversion of water from a pristine waterway.

The SKM report concluded that, based on the cost and considerations of environmental and social impacts, the Hume Corridor Scheme was the preferred option. This scheme would have social consequences associated with the diversion of water resources from regional Victoria to Melbourne, and the likely reduction of agricultural production in the Goulburn River valley and associated economic activity.contingency ($M)

Benefits and impacts of new dams

Proponents of the construction of new dams highlighted the potential benefitsincluding:

the potential to augment Melbourne’s water supply by capturing water from rivers;

the potential to source water at a price cheaper than alternative watersources; and

the potential to provide a level of flood mitigation.

Evidence supporting the construction of new dams also noted a number of site specific benefits such as improved reliability of water for irrigators and minimal water treatment requirements.

The construction and operation of new dams is also likely to have a range of potential direct and indirect environmental and social impacts. These include:

loss of productive land;

negative impacts on downstream water quality;

loss of aquatic species;r

loss of habitat;

downstream transportation of construction sedimentation and pollution;

loss of trigger flows and changes in water temperature may impact upon flora and fauna;

threat to tourism and amenity values; and

threat to downstream agriculture and commercial fisheries.

Stakeholder evidence

The Victorian Government submission to the inquiry stated that:

Building a new dam does not create new water, it just takes water from existing users, including downstream irrigators and the environment. Dams are a significant investment and the most cost effective and reliable storages have already been built. New dams also involve flooding valuable farmland and forests. Flooded forests are themselves a major source of greenhouse gases as the vegetation breaks down.

For example, Mr Peter Harris, Secretary of the Department of Sustainability and Environment also noted that the certainty and reliability of water produced by a desalination plant is greater than that of dams, stating that:

By comparison with the Mitchell River, a significant heritage river, we will have environmental impacts and therefore we will have significant mitigators required to meet those environmental impacts, plus the amount of water that is available. In the end, desalination by comparison with a river-based solution, the river-based solution relies upon it raining and raining reliably, and our problem is we are here now because it has not been raining reliably; therefore a dam is inherently a more risky solution. As I said, it has more environmental impacts by comparison with a desalination plant in terms of the local environment and the pipeline effect from the Mitchell River. The pipeline would have had to have been longer.

Ms Kelly O’Shanassy informed the Committee that Environment Victoria does not support dams highlighting that water flowing down rivers provides an important ecosystem function:

We do not believe that all that water going to the sea is a waste or is wastewater. I think a lot of scientists and scientific evidence back that up. Even if you did not want to believe the scientists, you could just look at the Coorong or the Gippsland Lakes and see that water flowing out into estuarine ecosystems is an incredibly important component of the health of any way; there is only a very small number, and some of them are in Gippsland. There are one or two in northern Victoria, and those rivers are really important, particularly in the north, because they provide most of the environmental flows that go into the Murray at the moment because they are unregulated. So if you regulate those, you have real problems in the Murray River as well.

The National Council of Women’s submission to the inquiry highlighted the cost and environmental disruption of new dams noting that while dams may have a place in flood mitigation management, they are generally not appropriate for south east Victoria.

Professor John Langford, Director of Uniwater, noted that if a dam was to be considered, the only viable option would be to dam the Mitchell. Professor Langford stated:

It does have a significant amount of water in it. Pre the step-down in rainfall it was about 750 000 megalitres a year, so now probably 500 000. But if you were going to get any of that, you would need a very substantial dam. It is one of the few free-flowing rivers in Victoria, and it flows into the Gippsland Lakes, so the environmental consequences of doing anything to that — and in our current circumstance, building a dam takes a while, a long pipeline, it is energy intensive to get it here, plus we have got to wait till the dam fills. So it really is not an alternative to the desalination plant, because if we are trying to fill a dam in a dry sequence, it is not going to work. So it is definitely not an alternative to the desalination plant, and personally I do not think it is worth considering.

Dr Ian McPhail, Commissioner for Environmental Sustainability also informed the Committee of his lack of support for new dams noting that: the best sites for dams are already used; that dams do not create new water; and that the increasing interconnection of supplies is beginning to reduce the need for new dams. Dr McPhail also informed the Committee that:

The argument against the Mitchell is fairly straightforward. It will have a direct effect upon the Gippsland Lakes and would, I think, create a series of reactive situations that would be just as complex as what might have been solved by damming it.

In contrast to the views highlighted above, several stakeholders expressed strong support for the investigation into, or construction of, new dams or diversion weirs.  The Institute of Public Affairs’ (IPA) submission to the inquiry submission outlined the options of damming the Thomson/Macalister, Latrobe or Mitchell Rivers and highlighted the costs associated with each option. The submission concluded that the construction of a new dam to collect water from these rivers would likely be the most cost effective approach (compared to other alternatives such as desalination, recycling, rainwater harvesting and stormwater) and would act as a flood mitigation measure and provide improved water security for Gippsland farmers.

The Victorian Farmers Federation (VFF) expressed their support for a policy review regarding the construction of new dams noting that climate change is predicted to deliver more extreme weather events such as floods, and that a new dam has the potential to mitigate the impact of floods such as those experienced in Gippsland in 2007. The VFF went on to state that:

The VFF requests that the Government takes all the necessary steps to investigate the options for extending existing dams including the Big Buffalo dam and William Hovel dam, as well as building new dams including a dam on Mitchell River and capturing more of the rain that falls over the Otway Ranges. These options should be seriously considered on their relative merit of supplementing additional water.

A number of stakeholders informed the Committee that the construction of a diversion weir on the Aberfeldy River (east of the Thomson Dam) should be considered as an option to supplement Melbourne’s water supplies. It was argued that the construction of 30-40 metre high diversion weir on the Aberfeldy River accompanied by a diversion tunnel to the Thomson Dam would provide 25 gigalitres of water annually for Melbourne. Stakeholders noted that this option would provide low cost water ($0.37 per kilolitre), and reduce the amount of flooding and nutrient loss (which occurred during the Gippsland floods in 2007).

Plug the Pipe’s submission notes that any diversion placed on the Aberfeldy River may impact on flows available to the Maffra/Macalister Irrigation District.  The submission suggested that instead, a diversion of the Big or Black Rivers should be considered. Plug the Pipe argued that water sourced from these rivers would require minimal treatment and have minimal environmental impact.  The submission reported the volume of water available from these two schemes to be between 80-100 gigalitres annually. The Sinclair Knight Merz report noted that the Big River and Black River diversion schemes could provide between 31 and 43 gigalitres per year respectively, but that both schemes would pose a significant barrier to fish passage, sediment transport and reduce the availability of water for agricultural production.  Plug the Pipe’s submission also suggested that the construction of a storage reservoir on the Macalister River upstream of the Glenmaggie Reservoir should be considered. Plug the Pipe believe that the reservoir would provide irrigators with an increased security of supply, and reduce the volume of water released from Thomson Dam for irrigation purposes making it available for metropolitan use.

Dams in other jurisdictions

Advice provided to the Committee whilst overseas indicated that some jurisdictions are not constructing new dams due to their environmental impacts. The Committee notes that the future role of dams in providing urban water supplies is not a management issue unique to Victoria.

The United States of America

As part of its investigations the Committee was briefed by representatives of the Bureau of Reclamation, United States Department of the Interior, on the role of dams in the United States of America. Mr Michael Hood, Senior International Affairs Specialist informed the Committee that, beginning in the early 1900s, the Bureau had been responsible for the construction of most of the major water infrastructure in the United States, including the Hoover and Grand Coulee dams, and is now responsible for the operation of more than 350 dams.   However Mr Hood also noted, that the Bureau had not constructed a new dam since the 1970s and that it was now considered unlikely that another major dam would be built in the United States due to the environmental impacts and costs associated with dam construction combined with a lack of political will.   Mr Hood informed the Committee that some dams in the USA, which were built in the 1930s and 1940s, are now being demolished in an attempt to address the environmental and other impacts caused by their construction.

The Committee was also advised that the viability of some dams in the USA is subject to a number of additional recent pressures. Perhaps most notable among these is a predicted decline in future storage levels for some major dams. This point was reinforced by Mr Michael Hood who referred to work by the National Sciences Academy of the United States which suggests that the last half of the 20th century may have been a relatively wet period in historical terms for the Colorado River.   Mr Hood went on to note that the combined effects of drought, climate change, population growth and increased security challenges, posed serious water policy challenges for the future.

The effect of these pressures is illustrated at Lake Mead, on the Colorado River behind the Hoover dam, where the storage level has been falling since October 1998. Lake Mead is one of the most important water resources in the western United States and is one of the world’s largest water reservoirs which, since the 1930s, has supplied water to farms, homes and businesses in Arizona, Nevada, California, and northern Mexico.  As at 25 October 2007, the level of the lake had fallen to 46 per cent capacity.  While the level of Lake Mead has fallen to similar or lower levels on occasions during preceding decades,  a 2008 report on the status of Lake Mead by scientists at the Scripps Institution of Oceanography has predicted that there is now a 50 per cent probability of the lake becoming completely dry by 2021, due to climate change and overuse of water from the Colorado River.


The Committee inspected a new reservoir which has been constructed in the centre of Singapore city – the Marina Barrage. The Marina Barrage extends 350 metres across the mouth of the Marina Channel and is now the largest of Singapore’s 15 reservoirs with a catchment area of around 10,000 hectares – approximately one-sixth of the country’s total landmass. Located in the centre of the city, construction of the Marina Barrage began in early 2005 and the Barrage was officially opened on 31 October 2008.

The Marina Barrage incorporates a system of nine hydraulically operated steel gates, spaced along the length of the dam wall, which, combined with natural flushing and tides, will create a freshwater reservoir over a period of one to two years.  The freshwater will then be treated using reverse osmosis membrane technology prior to consumption. When operational, the Marina Reservoir will meet more than 10 per cent of Singapore’s current water demand.

The Marina Barrage will also form part of a flood control system for the city’s low-lying areas, including Chinatown, Boat Quay, Jalan Besar and Geylang. During periods of heavy rain, the dam’s series of nine crest gates will be opened to release excess stormwater into the sea at low tide. During high tides, excess stormwater will be expelled into the sea by large pumps which have the capacity of pumping an Olympic-sized swimming pool each minute.


The Committee was particularly interested in the advice it received from US water experts on the trend away from building dams in the US on the basis of environmental effects and costs, and the move towards decommissioning old dams for various reasons. The Committee also acknowledges the compelling evidence it received from experts such as Professor Tony Wong from Monash University who cautioned that under a worst-case scenario in terms of peak flow into our current dams, Melbourne’s dams will never fill again.

Furthermore the Committee understands that Melbourne may experience a second significant drop in the level of its inflows to water storages, as has been the case in Perth. In Perth, as a consequence of a climatic shift, planners are examining water supply scenarios where they do not source water from dams.

Given the current climate change predictions and that over 80 per cent of Melbourne’s water supply is rainfall dependent, the Committee believes that there is an urgent need to diversify the city’s water supply rather than invest in the construction of new dams. On this basis alone the Committee does not support the option of supplementing Melbourne’s water supply with new dams. Furthermore the Committee understands from the SKM report that there are environmental impacts of constructing a dam that cannot be managed, including connectivity, sediment transport, nutrient/carbon transport, scouring downstream of the dam, loss of productive land and loss of habitat (including native vegetation and threatened species habitat).  The two likeliest options, by volume - Mitchell River and Hume Corridor – have significant drawbacks. As noted above the environmental impacts of the Mitchell River option were nearly all rated moderate to severe. The Hume Corridor option has social consequences and would impact on agricultural production.

Accordingly the Committee recommends that:

Recommendation 8.1

No additional dams be constructed to supplement Melbourne’s watersupply.nt cost


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