I have tried to inject some practical facts into this debate a few times.

Like the fact that it takes 26,000 gallons of water to put just one inch on one acre. That is more than we use in our household in a year. Of course being on our own tank water means we use less than town water users. I use 145000 gallons of irrigation water year on my one acre house paddocks shrubs & trees, with not a single drop used on grass areas ever. That is just enough to keep them alive in a dry period.

No my sandy loam in a dryish time, not full drought, half an inch a week will keep the place mildly productive. An inch a fortnight is basically useless, as the vegetation is severely stressed by losses from evaporation after about 10 days.

On my better black soil country, it won't even notice an inch. It takes at least 3 inches for it to even start to green up, & about 5 inches to start to become productive.

A local lucerne farmer told me he doesn't irrigate at all until there has been the first good spring/summer rain. He found it took ridiculously large amounts of irrigation to get anything happening, before a good natural downpour. It was just not economically viable to pump enough water to get stuff growing. This is with a high value crop, pumping from a river adjacent to his crop.

Don't forget western grazing rates are one beast to a minimum of 20 acres. That would require half a million gallons of water per beast, for just one inch of irrigation, which in a major drought would do very little.

I would like to be able to do it, as much as anyone, but the facts are it is just not economic, or even possible.

The Sydney Morning Herald had this interesting
article on solutions to Australia's drought
problems. I'm no expert, but I think the article
is worth a read:

http://www.smh.com.au/opinion/underground-dams-the-solutions-to-australias-drought-problems-20140316-34v8m.html

Bradfield had a plan to turn the Northern rivers around.
One factor many forget is that water is heavy. If it has to be pumped
then it is expensive water.
If dams can be built on the ranges somewhere then maybe it could be diverted into south west flowing rivers.
Certainly worth a study.

Bradfield and his plan figured in a thread I started along much the same lines
Parts of the USA saw water transported great distances in man made ground systems
Israel can show us a lot
Costs? if we wish to continue to grow we will be faced with them one day why not now
The Snowy River while a power source is also an irrigation system
IF we stopped dumping sewage in to the sea, pumped it less than 100 klm,s inland, costs in doing so would be returned ten fold over time

Flooding Lake Eyre could be done with sea water from the south. Then, with that large a body of water evaporation will do the rest. Cost ? The cost of a canal is less than daily wasting by bureaucracy.
The Bradfield scheme is a viable proposition as long as it remains a Govt project without the involvement of overseas companies. Hundreds of young people could cut their teeth on such a project. Imagine the value of lakeside real estate & the leisure industry. I can see nothing but economic & environmental windfall.

individual,
Flooding Lake Eyre with sea water would cost orders of magnitude more than you think - it's a very long way from the sea (were you perhaps conflating it with Lake Torrens?). Plus all that extra salt would destroy the Lake Eyre ecosystem. But most importantly, it wouldn't affect the climate in the way you think. Consider: the Indian Ocean is an even larger volume of water, yet the Pilbara's still arid!

It's technically possible to divert rivers, albeit at enormous cost. But environmental issues must take priority (however much the dinosaurs on this board disagree). There are some rivers that, for environmental reasons, should not be dammed. And there are also some that, to stop the spread of pest species, should not be connected.

But assuming the environmental issues can be overcome, why do you think inland agriculture deserves such a huge subsidy to get it going? Won't the money it makes be at the expense of currently viable farms elsewhere?