Effects of the Kurnell Desalination Plant

Sydney's Kurnell Desalination Plant began operating during the first week of February 2010. At full capacity it produces some 250 megalitres a day of potable water. As I flew from Sydney to Launceston yesterday, I managed to glimpse it through the window as we flew over Kurnell.

It has not been a great time for proponents of desalination plants, at least in Australia. Popular opposition to the plants focuses upon the greenhouse gases produced by the increased energy needed to operate the plant (a problem offset by the co-construction of a wind farm that produces more kW-h over a 12 month period than is consumed by the desalination plant), the added cost it places upon tap water (which is only a problem when water supplies are not low) and the pollution caused by pumping brine back into the sea (a process which causes increased salinity in the affected area but is also a natural part of the water cycle).

Another problem is that the plant has begun operating during a severe La-Nina event which is known to cause high rainfall levels in Australia. The plant was conceived and built during an El-Nino period when Australia was suffering prolonged drought and low rainfall.

Over the past year I have been collating data from the Sydney Catchment Authority which runs a weekly data series on Sydney water storage and supply - specifically the amount of water gained and pumped by Sydney's network of dams. When compared to the previous six years (2004-2009), 2010 stands out as the year the least amount of water was delivered from dams - a direct result of the increased supply of the Kurnell Desalination Plant.

According to the Data I have collated, the average amount of water delivered from the first week of February to the second last week of December is 466,438.91 megalitres. In 2010, the water delivered in this period was 387,674.83 megalitres, which means that the Desalination plant prevented up to 78,764.08 megalitres from being pumped from Sydney's dams.

At the time that this article was published, Sydney Dam levels have risen to 1,863,500 megalitres, mainly as a result of increased rainfall. This represents 72.2% of capacity, the highest since 2002. If we do the math, we prove that, since 78,764.08 megalitres was saved due to the desalination plant, then we can expect the current dam levels to be 3.1% less than what they currently are - 69.1% - if the desalination plant was not operating.

Moreover, simply by crunching the numbers already shown above, we can see that the desalination plant produces around 17% of Sydney's water - at least if we compare 2010's results with the averages of 2004-2009.

The Kurnell plant was built with the understanding that it would be "mothballed" during periods of high dam capacity. It was also decided that the plant would run continuously for two years to iron out any problems before any "mothballing" would occur, so the chances are that the plant will continue to operate throughout 2011 no matter how full the dams get.

The Kurnell plant has been designed to allow for a doubling of capacity if needed - land has been set aside at the site for more buildings and the piping to and from the plant has been designed to allow for a doubling of capacity. If rainfall levels in Australia and Sydney continue to decline (despite the recent wet weather) then increasing the capacity of the plant will be a cost effective solution to any declining dam levels.

Since it would be more efficient to operate the plant for long periods and mothball it for long periods (as opposed to short periods for both), I would suggest some sort of "trigger" mechanism to be put into place:

* 75% Capacity: The plant will be shut down and mothballed once stored water supplies reach 75% capacity.
* 50% Capacity: The plant will begin operating once stored water supplies dip below 50% capacity.
* 25% Capacity: The plant will be doubled in size once stored water supplies dip below 25% capacity, or else another desalination plant built if this has already happened. (This assumes that the plant has been operating continuously since supplies dropped below 50%)

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