QLD wanted to drain over a year’s worth of water from Wivenhoe dam
Releasing up to 413 days’ worth of water supply from a key south-east Queensland dam last summer was actively considered by the state following devastating floods, internal documents reveal.
Follow-up advice from Wivenhoe Dam’s operator on the ultimate call to only forgo about 139 days’ supply, reducing levels from 90 to 80 per cent of full drinking supply capacity, was only sought three days before that decision.
The previously unreported detail of lower 75 and 60 per cent proposals was contained in documents from Seqwater, the government-owned body responsible for the regional water grid, obtained by Brisbane Times under right to information laws.
While noting a drain-down could offer benefits dealing with any potential flooding during a third wet La Nina summer, later forecast to be short-lived, Seqwater warned the decision would probably only harm ongoing water security.
With what’s expected to be a dry summer ahead, and the water grid falling towards triggers to boot up its largely unused recycled water scheme, public and political focus has shifted from flood to drought mitigation and new water sources.
In a September 29 response to the Water Department for advice to inform Water Minister Glenn Butcher’s decision, Seqwater said it had never previously advised on a proposal to lower Wivenhoe to 60 per cent.
Chief executive Neil Brennan wrote that such a temporary lowering almost doubled the probability within five years of the water grid dropping below 50 per cent, triggering a drought declaration and medium-level water restrictions, to 22.64 per cent.
Across this period, the probability of dropping below 40 per cent – when Seqwater would ask approval to top up Wivenhoe with recycled water – would be more than doubled to 6.73 per cent.
“Modelling shows that the likelihood that the [water grid storage] level will reach key drought response levels within the next five and 10 years materially increases for lower Wivenhoe Dam TFSL [temporary full supply level] scenarios,” he said.
“The magnitude of the benefit [of flood mitigation] will vary depending on the size and nature of the flood event.”
Wivenhoe’s flood storage capacity is more than double its 100 per cent drinking supply level.
Emails among the documents show initial August 2022 Seqwater and departmental planning for the annual discussions had resulted in a proposal of lowering Wivenhoe to 75 per cent, before a “more aggressive option” was sought for Butcher on September 2.
Internal Seqwater discussion followed about the relevance of guidance from forecasts of a wet summer, “which in a typical year our infrastructure can handle”.
The minister and others were more worried about harder-to-predict outlier rain events.
“That’s why the ministers gets paid the big bucks – it’s a hard call to make,” one staff member recalled another saying.
Less than a fortnight after the formal Seqwater response from Brennan, and three days before Butcher’s October 13 decision, the department wrote back seeking “high level” advice on the ultimate 80 per cent Wivenhoe level.
Butcher told Brisbane Times a 60 per cent supply level at Wivenhoe was considered because this was about its position immediately before the February 2022 floods.
The 80 per cent scenario was added, though Butcher was not drawn on why, “to provide a further option that considered the additional water security benefits”.
“I won’t apologise for taking advice from experts and making decisions to protect Queenslanders,” he said.
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