Raising Warragamba Dam probably can’t stop floods. There’s a simpler solution closer to home
Warragamba Dam was built in 1960 to hold water from the Dyarubbin (NepeanHawkesbury River) as a water supply for Sydney. It also had some flood-mitigation potential, to hold back water when it wasn’t full.
During droughts when the dam had “too little water”, a desalination plant was built at Botany Bay. Now, when it has “too much water” in floods, there is a push to raise the dam wall to increase its volume. The New South Wales premier has declared he will build it, with or without federal funding.
There are several downsides to this proposal.
First, it’s hideously expensive. The current cost estimate is $1.6bn. That could pay for a lot of social housing in western Sydney.
Second, it will drown a vast area of ecological and Indigenous importance along the river, adding to the damage the dam has already done.
Third, and worst of all, it’s highly doubtful that it could have a significant effect on flood mitigation – this needs to be managed very differently.
Which raises the question: why don’t we use the dam for flood mitigation as it is, by lowering its water level now? We could use the dam in the same way that the “wall-raisers” suggest, only with better management and at far less cost.
That would require making do with far less water storage for Sydney. Can we take away a substantial part of the dam’s role as a water supply and lower its regular height, so that it can perform the flood mitigation role?
The answer is yes – but it requires a different way of thinking about water supply.
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Water is a widely distributed resource. Rain is everywhere, like sunshine on solar panels. It falls, often heavily, all over Sydney, and can be trapped locally on a house-by-house basis in tanks. Collecting it from a wide area, aggregating it into a single dam to store it and then distributing back out to the city is a nonsense in terms of physics and economics.
Using rainwater to substitute for the loss of dam water requires two things: encouraging the greater use of tank water, and pricing water to encourage everyone to minimise the use of dam water.
More than half (55%) of the water in a house goes to non-potable uses – toilets, laundry and external (for example, gardens and car washing). Rainwater from a tank could be used instead.
How to incentivise residents to swap? Well, water’s too cheap. We need a pricing policy that increases the cost with the amount used.
A house could have 50% of its current average usage at low cost. More than that would be charged at a much higher rate, encouraging the use of alternative sources of water. A pricing policy is a far better way to encourage sensible use than the latest approach in Los Angeles, which is fitting flow restrictors to celebrity mansions.
Most Sydney houses are freestanding homes but there would need to be carve-outs for how we define a single dwelling, and exemptions for apartments – which are already substantially more sustainable. Profligate users would pay their way, with the excess money set aside for times when the desalination plant (using high-energy reverse osmosis) is needed. It is, after all, “bottled electricity”, to cite the former premier Bob Carr’s memorable phrase.
We know that 18 years of NSW Building Sustainability Index requirements have led to rainwater storage tanks being installed in almost every new individual dwelling, with a consequent reduction in mains water consumption. We also know that many tanks are permanently full and lying idle, with the water becoming a liability, not an asset.
We need to ensure that all households that can have, or want to have, a tank have one; and we need an education campaign to ensure their optimal use. This is where we should direct a small portion of the “dam-raising moneys” – so every suburban house has an appropriate-sized tank, say 2,000 to 10,000 litres, which is used safely for all the purposes that do not need drinking water: toilets, washing machines and hoses.
The NSW government could then turn the remaining savings into relocating residents hit hardest by the floods and urgently building evacuation roads in western Sydney for those remaining.
Damn dam. Win win.
This article was originally published in Architecture and Design magazine. Tone Wheeler is the principal architect at Environa Studio, an adjunct professor at UNSW and is the president of the Australian Architecture Association