Raising the height of the Warragamba dam wall to protect one of Australia's most flood-prone regions from inundation is not the best approach, a leading water researcher says.
Responding to reports the Federal Government wants to raise the wall by 23 metres, Stuart Khan, a senior lecturer at UNSW's Water Research Centre, said that while the flood risk in the area is "very real”, the issue would be better dealt with water management.
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“It doesn't matter how big that dam is – it's not that it's not big enough – it just that the management needs to change,” he said.
“We need to reserve some storage capacity in the reservoir for when those big inflows come along.”
A larger dam would face the same overflow issues unless operating procedures changed to allow early release of water, he said.
Raising the dam wall would also have significant environmental issues with forested areas and indigenous rock paintings inundated, Dr Khan said.
The Federal Government plans to spend $50 million in flood mitigation efforts, as part of its pitch to win back support in western Sydney in the run-up to this year's election.
As Prime Minister Julia Gillard prepares for a week-long blitz of marginal seats in the city's west, the government hopes the project will drive down insurance premiums for residents in the Hawkesbury-Nepean valley.
But it is unclear who will bear the rest of the expense of the project, which has been costed at $500 million.
The funding for the Warragamba dam project is part of a $100 million redirection of money from terrorism reinsurance premiumsto flood mitigation.
Ms Gillard, Financial Services Minister Bill Shorten and Emergency Management Minister Mark Dreyfus will announce the policy in Ipswich.
The Commonwealth will set up a National Insurance Affordability Council, which will manage the national co-ordination of flood-risk management and make recommendations on flood and other natural disaster mitigation projects.
Part of the $100 million over two years will be allocated to flood mitigation projects in the Queensland towns of Ipswich and Roma.
Debate over Warragamba Dam and its operations has been revived in recent weeks after two major low pressure weather systems caused major flooding from areas to the north of Sydney all the way to the mid-Queensland coast.
Warragamba also began spilling this week for the third time since 1999, contributing to minor flooding in the Nepean Hawkesbury valley. The spill may continue for some days yet with more rain landing in the full catchment today and the weather bureau predicting minor to moderate flooding downstream from Thursday onwards.
While the region hasn't had a major flood since 1991, it remains a focus of insurers and emergency service planners alike. The area has recorded 120 floods in the last two centuries but the influx of many more residents from Sydney's sprawl has raised the economic and human risks of future floods with the damage bill from a major flooding estimated to reach as high as $8 billion.
Dr Khan said Sydney's abundant water resources – which now include a moth-balled desalination plant – mean that Warragamba “doesn't need to be filled to the brim to reserve some capacity to mitigate floods".
Instead of spending some $500 million to raise the dam wall, government would be better served encouraging water savings and recycling efforts. “It's not like we have a water supply crisis.”
He called on the state government to change legislation to allow the dam to serve as flood mitigation as well as water supply purposes. It's a change the O'Farrell government “could make tonight.”
The state government repeated this week its intention to continue its review of the Nepean Hawkesbury flood risks and to release the findings before the end of the year.
Ms Gillard will next week leave Kirribilli House and check into a hotel in Rooty Hill where she will be based for her five-day swing through a number of marginal seats.
Opposition Leader Tony Abbott, who last month held a mini-campaign launch in Western Sydney, is also believed to be planning to visit western Sydney next week.
'Basically a sewer'
Opened in 1960, the dam wall has a height of 142 metres and a thickness of 104 metres at its base.
“It’s a pretty spectacular and protected part of the Sydney basin,” he said.
In contrast, increased environmental flows to the river systems – which would result from managing the dam for flood mitigation – would be of great benefit downstream.
“The Nepean is in an appalling state, as is the Hawkesbury,” Dr Khan said, a view echoed by Leigh Williams, a Greens councillor on the Hawkesbury City Council.
The existing dam is “the greatest curse for the Hawkesbury Nepean valley,” Mr Williams said, with just 5 per cent of the natural flows remaining. “It’s basically a sewer at the moment.”
The decision of the federal government to intervene on Warragamba, meanwhile, has been welcomed by the Western Sydney Regional Organisations of Councils, which groups 10 councils in the valley including Penrith, Blacktown and Parramatta.
“It’s very reassuring,” said Tiffany Tree, the senior vice president of the grouping and also deputy mayor of Hawkesbury City Council, noting the state government is also reviewing flood mitigation efforts for the region. “We may get somewhere.”
Infrastructure NSW had already identified raising the dam wall as the single most important project in the state, Ms Tree said.
Dredging of the river should also be considered, she said.
With Dan Harrison and AAP