During the millennial drought (2006 -2010) there was great concern that Melbourne might run out of water. The Labor government in Victoria pushed for the construction of a desalination plant.
Graphs and statistics were presented showing historical records of Melbourne’s water supply and usage, as well as projections for the future. All emphasized the gravity of the problem not only in the short term but also in the context of future population growth. The Climate Change (Global Warming) movement had just begun to peak as a broad moral crusade.
Many of us have forgotten the daily messages about water restrictions and the doom and gloom scenarios run in the media. There was even a countdown clock to Armageddon showing when we would run of water, that appeared daily in The Age.
In 2007, Prof Flannery, Australia’s Chief Scientist declared:
Even the rain that falls isn’t actually going to fill our dams and river systems.
Any consideration of building another dam was out of the question for a government tied to the vocal Greens party. Flannery’s prognostication added weight to the government’s case.
In this context the desalination plant was approved in 2009 at a construction cost of A$3.5 billion and a contractual arrangement (involving several parties signing up to a public private partnership (PPP)) for an operational cost of A $5.7 billion until 2039. It commenced operation in 2012.
What still intrigues me is that one of the main graphs used to show the state of Melbourne’s water supply and to promote the case to the public for the desalination plant was unusual, to say the least. I will explain.
The Thomson Dam was built in the 1970’s and was first filled in 1981. It more than doubled the combined capacity of all the other dams supplying Melbourne, so its impact on Melbourne’s water supply was enormous. This should have been depicted by a gigantic peak in the graph commencing 1981 but there wasn’t even a blip. How could this be so?
I wrote to the CEO of Melbourne Water and was advised that it had performed an unusual technique I’ll refer to as “extrapolating backwards’; that is, they recreated historical data using a model to project backwards, and in this case to fill a not-yet-constructed dam with estimated rainfall back to 1901. According to the graph the Thomson Dam was filled before it was built! Yes, believe it or not, Melbourne had more water in its dams ten, twenty or fifty years before the Thomson was built. The graph remained on the Melbourne Water website until very recently (30/09/2021) and is now replaced with an equally deceptive graph.
The current graph is located in a section called Historical Water Storage Levels. The graph itself is untitled. The vertical axis is labelled percent full and the horizontal axis is labelled with years running from 1940 to the present. Looking at the graph one could easily be deceived into believing we now have less water in our dams than we had in 1940 and that yet again the Thomson had absolutely no impact on supply. Quite a feat given the Thomson came on stream in 1981 and more than doubled Melbourne’s total dam capacity!
You can view this graph here, so judge for yourself. Drop down to historic water levels and click on all years to see graph.
N.B. As at (4/10/2021) Melbourne’s dams contained 1,812,175 ML and were 84.4% full. The Thomson Dam contained 1,068,000 ML and was 84% full and made up 58.9% of the total water stored.
For the 2021-22 financial year an amount of 125 gigalitres of water has been ordered to supplement supplies as required. Usage to date is provided here.
All data for this post was sourced from the Melbourne Water website.