Tensions over the management of Sydney's Warragamba Dam are rising as quickly as the dam itself with major disagreements between senior state government cabinet ministers.
The dam began to spill on Saturday causing major flooding issues for western Sydney suburbs like Penrith, as well as impacts downstream for Windsor, Richmond and surrounding areas where evacuations are taking place.
It's been a long-running issue for Emergency Services Minister David Elliott, who has been in disagreement with Water Minister Melinda Pavey over the dam's management.
He said more should have been done to prepare for such an event.
"It's probably another full and frank conversation we'll have when this is over," he said on Sunday.
"Mitigation is going to be part of the operation review and we will have that discussion."
A statement from Ms Pavey's office said that "in recent months 130 gigalitres has been released to keep it at its operational safety level of one meter below full supply."
"Up until Saturday afternoon when Warragamba's gates opened, Warragamba Dam had not contributed to the flooding in the Sydney Basin, where roads and bridges were already being closed and inundated due to local tributary flooding."
Water NSW said the dam was releasing water at a rate of 450 gigalitres per day and that rate could increase as inflows to the storage continued to rise.
Premier Gladys Berejiklian said more than three quarters of the dam would have had to have been emptied to make way for the extra water.
"Given the rainfall that we're experiencing in the next few days, you would have had to reduce the capacity of the dam to around 20 or 25 percent which just wouldn't have been feasible," she said.
"That puts into context just how much rain we're expecting to get over the next few days."
Proposal to raise dam wall criticised
The NSW government has also proposed to raise the dam wall, but it's a plan that has a number of critics.
Jamie Pittock from the Australian National University said it was a bad idea based on international experience.
"The Hawkesbury Nepean valley is very dangerous, very flood prone because there are some geographical choke points that cause large floods to back up over some of the inhabited areas," he said.
"When you build this kind of flood control infrastructure, it only encourages more development in harm's way, and indeed that is what's been proposed in Western Sydney."
There has been rapid urbanisation in the area, with about 70,000 residents currently living on the flood plain.
The state government plans to move 130,000 more people into the area by 2050.
"That's a really silly idea," Professor Pittock said.
"I would argue that the best approach is to prevent development on the flood plains ... use that land for agriculture, and recreation and nature conservation. But don't put more houses there."
There have also been concerns about the impact of raising the wall on Indigenous heritage and cultural sites in the area.
Minister for Western Sydney Stuart Ayres said it should be full steam ahead on raising the wall and that the government had been restricting where people could build in the valley.
"There isn't a single silver bullet to mitigate floods in Western Sydney," he said.
"But having a higher Warragamba Dam wall with 14 metres of airspace to hold water back will have a profound impact on the amount of people who would have to be evacuated and the amount of properties that would be inundated."
“There’s no doubt there’s a trade off here. We’re saying that the small impacts that will happen behind the dam wall are worth the benefit of protecting people downstream.”
“As we’re evacuating people from places like Penrith, Richmond, Windsor, Wilberforce, Pitt Town, I think we’re getting a very practical example of what that trade-off looks like.”
He said the government had considered a number of options for flood mitigation, including buying back properties, expanding the Sackville Gorge and dredging the Nepean River.
Senior SES figure among those opposed to plan
State Emergency Service planner and former deputy commissioner Chas Keys is also opposed to raising the wall, saying the government should instead focus on evacuation routes and slowing down population growth in the area.
"There is a capacity in places like Windsor to kill heroic numbers of people because they won't be able to be got out in time," he said.
"That means that you should be focusing in my view on evacuation routes, building up roads so that they are above all of the very worst floods and they buy time to get people out."
He said this event should be a major wake up call to authorities.
"I mean we are putting thousands and thousands of people on flood plains between Penrith and downstream of Windsor in the Valley of south creek and the valley of the Hawkesbury proper," he said.
"Now flood plains are bound to flood, they are designed by nature to flood and we are aiming to double the population of the Hawkesbury-Nepean over certain years, to me there is a certain insanity in that."
An environmental impact statement into the raising of the wall will be released later this year.
By Antonette Collins