ycled water seemed (at least to some, myself included) to be a great idea. But the plan to drink the recycled water has not yet gone ahead because of one word: “yuck!”
That powerful psychological response to the idea of drinking treated effluent is one of the main reasons why you don’t hear any politicians advocating DPR. They don’t believe that they can successfully sell the idea. And of course, the yuck factor is normal, so politicians, engineers and scientists all experience it too.
But the disastrous flooding of Wivenhoe Dam may change all that. Now, finding some additional spare capacity in the reservoir to hold back such enormous flood surges seems an even more important priority. Fortunately, DPR offers a solution that can achieve both outcomes at once.
Like many reservoirs, Lake Wivenhoe has two conflicting roles. On one hand, it must provide security of drinking water supply by storing as much water as possible. One the other, it must protect Brisbane from otherwise inevitable regular flooding by maintaining as much empty space as possible. To achieve this somewhat schizophrenic expectation, the reservoir is divided into two distinct components. The bottom 1,165 billion litres is kept as full as possible for drinking water supply and the top 1,450 billion litres is maintained empty for flood control.
When operating at full capacity, the WCRWP can produce around 35 per cent of the total water consumption of Brisbane and surrounding areas.
If this water was used directly as part of Brisbane’s water supply, Lake Wivenhoe could be relied upon for 35 per cent less water supply. This means that the same security of water supply could be maintained while dropping the full supply capacity of Wivenhoe by 35 per cent and thereby freeing additional space for flood mitigation. The flood mitigation capacity would be increased by around 425 billion litres, which is an increase of around 30 per cent.
In terms of water storage capacity, this new-found 425 billion litres of flood mitigation space is the same as immediately constructing a new equivalent sized reservoir, without the cost of construction and without having to relocate a single home or farm. In addition to completely avoiding the environmental impacts of new dams, it would enable less water to be captured by the dam enhancing natural flow regimes in the Brisbane River.
To put this extra storage capacity into some context, a new 425 billion litre reservoir would be the fourth largest reservoir to supply drinking water to a major city in Australia (after Warragamba in Sydney, Wivenhoe in Brisbane and Thompson in Melbourne). It would be more than 70 per cent of the total water storage capacity of Perth and twice the total storage capacity of Adelaide.
Using the existing infrastructure of the WCRWP, water would be available immediately and there would be negligible construction costs. But most importantly, the freed-up storage space will also be immediately available to help capture and control major flooding events when they occur.
With careful management, this additional storage capacity would have been sufficient to capture and contain the entire peak flow into Wivenhoe Dam that occurred between 9th and 13th January 2011. There would have been no flood in Brisbane.
With all of this in perspective, the yuck factor is starting to seem like an emotional response that we would do well to live without.
Dr Stuart Khan is a Senior Lecturer at the School of Civil and Environmental Engineering at the University of New South Wales.