There are a few elephants in the room that are worth raising.

The big positive is that increasing the storage capacity of Warragamba Dam or building new dams is the most economic way of assuring Sydney's water supply. Unlike desalination plants, dam water comes at little variable cost and generally feeds by gravity to user cities. Desalination plants by contrast use vast amounts of electricity and are generally more expensive to construct.

Raising the dam wall at Warragamba does entail some increased risk. The bigger the dam, the greater the damage potential in the (unlikely) event of the dam wall failing. Also, with 80 per cent of Sydney's water already coming from this one source, raising the dam wall places even more "chickens in the one basket".

Overall, Australia's major cities (especially the fast growing ones) all urgently need more investment in water storage to reflect variable rainfall and rising demand.

Clarification needed here:
How much of this dam raising would be for additional storage (where areas would be flooded for months at a time)? And how much for flood control (where the inundation would last less than a week)?

Concrete reaches its maximum strength in the eighty years following pouring! And given that is so, any concrete wall holding back billions of tons of water, will one day not too long after that date with destiny, crack and become a catastrophe in the making.

Adding to that already considerable pressure by increasing the height of the wall is the height of mindless irresponsibility and possible mass murder in the making?

Aside from all the other considerations and cultural consequences? A damned dam isn't worth a damned dam if there's not enough damn rain to ever fill the dam thing.

The mighty Aswan project, the biggest damned dam in creation, evaporates more dam water than it dam well stores!

And we are the driest inhabited continent on the damned planet.

All this insanity? Done to avoid facing the one inescapable reality? We need to guarantee our domestic water supplies, whether it rains or not, or enough, with desalination and the only way we can do that, is with deionisation dialysis desalination. And that needs power so cheap that we can push this new water anywhere, be it to the snowy mountains or any domestic reservoir!

That could be truly massive scale, solar voltaic, with proven prices as low as an unsubsidised 5 cents PKWH!

Or MSR thorium, which, if also used to very very safely burn other nations nuclear waste? The subsequent power prices could be as low as 1 cent or less PKWH!

It's that last scenario frightens the living bejesus out of our corrupt and conflicted self-serving (coal-fired) pollies!?

For them, the light at the of the tunnel is the headlight of steaming express train of climate change, thundering in their direction!

And it the cap fits?
Alan B.

Unlike Bren who clearly only understands desalination as membrane reliant reverse osmosis. which as he correctly identifies, requires, nay demands monstrous electricity usage, given the quite massive pressure requirements of the task!

Further complicated by absolutely insane outsourcing to some private entities who demonstrably price gouge and fail, it would seem, to provide adequate maintenance schedules? Which it seems, are considerable?

New space-age desalination requires no such pressure nor maintenance schedules, but delivers an electric shock wave to the flowing water, sending the salt and numerous other ions in one direction and desalinated potable water, around 95% in the other direction for a quarter of the electricity usage of traditional desalination!

In fact in Texas, some years ago now, [where their power prices (around 6 cents PKWH) were one-third of ours], deionization dialysis desalination was field trial on broad scale agriculture and at a healthy profit!

We are an island continent surrounded by endless eternally enduring water! And given power prices as low as 1 cent PKWH and space-age dialysis, we could not only drought-proof the joint but turn huge swathes of arid desert wasteland into ultra-productive gardens of Eden and take the maximum advantage of the next boom, the food boom!

The only question we need ask, who and what prevents just that!?
Alan B.

Alan B.,
Maximum strength is irrelevant - it does not equate to required strength!
There are indeed my competing desalination technologies, all with advantages and disadvantages, so I'm puzzled as to why you're so convinced electrodialysis is the best. Is it anything more than what a system manufacturer says on its website? AIUI that method's best suited to water from brackish aquifers rather than seawater.

Alan B is concerned at the possibility of the wall's failing when he says that any concrete wall holding back billions of tons of water, will crack and become a catastrophe in the making.

What he may not appreciate is that Warragamba's wall was built using interlocking blocks which were later grouted together to form a continuous, monolithic wall.

It is so large that engineers had to prevent the temperature from becoming too hot as the concrete set. They embedded cooling pipes into the concrete and circulate chilled water through the pipes. As a result, the dam wall was cooled in a few months instead of the estimated 100 years it would have taken to cool naturally.

This means that the entire wall is also bonded by this myriad of piping which adds to its strength.