Hawkesbury flood mitigation forum hears Warragamba Dam levels need to be lowered now | VIDEO

Approximately 300 people turned up to the meeting at Hawkesbury Race Club to hear University of NSW's Professor Stuart Khan, a leading expert in water management, talk on the aspects of lowering the Full Supply Level (FSL) of Warragamba Dam as a method of flood mitigation.

He said any reduction in reliance on Warragamba Dam "must be accompanied by the introduction of new rainfall-independent water sources, such as new seawater desalination or water recycling".

Hawkesbury MP Robyn Preston - who attended the meeting - said she was "100 per cent committed" to lowering the dam's FSL and had taken the issue to Parliament.

However, the forum heard the dam level needed to be lowered straight away, ahead of the third consecutive La Nina event forecast for spring, which would coincide with an Indian Ocean Dipole weather system.

This could potentially cause more flooding in the Hawkesbury as early as next month.

The forum was organised by Hawkesbury Community Alliance, a new community action group designed to act as a voice for change in the Hawkesbury.

The forum heard the community could not wait until the Warragamba Dam wall was raised - an option which was likely years away.

Lowering the dam's FSL by 12 metres could have a flood peak reduction of up to 2.6 metres at Windsor, according to Dr Khan. This would save many houses and properties.

Numerous people took to the microphone at the event, proving there was a growing fear among residents affected by floods in the region over the past three years.

The highest flood on record at Windsor was in 1867 when the water reached 19.7 metres, and the probable maximum flood for the region is 26.4 metres, according to Hawkesbury Council.

Windsor resident and former Hawkesbury Councillor, Christine Paine - who acted as chair for the event - said she had lived in Windsor for 44 years and considered herself as flood-resistant, however "the last 15 months has been horrendous".

"I have never seen in my 44 years here the velocity of the floodwaters that was here in July, and I know it's wrecked many, many houses. If you've got time, go down to Cornwallis and see gouges out of the river bigger than football fields," Ms Paine said.

Samantha Magnusson, Hawkesbury Community Alliance spokesperson, said "the reason we're all here is an absolute tragedy".

"We know another flood is coming, we don't know exactly when, and we don't know how big it will be - 10 metres, 14, 17, even bigger."

She said the dual climate drivers meant the Hawkesbury was "in pretty rare territory".

"For us in the Hawkesbury, the ramifications of this could not be worse."

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Ms Magnusson said the NSW Government plan to raise the Warragamba Dam was "10 years too late".

"It is too late for those of us here today who will again face the terror of another flood in the coming weeks and months," she said.

"Be under no illusion, we are facing a catastrophe of proportions never seen in the valley before."