Canem,
Fresh water flows from the Great Dividing Range to the Gulf of Carpentaria.

There is a limit to how much water we can extract, as if too much water were extracted, salt water from the Gulf of Carpentaria would enter the GAB. But we're nowhere near that limit at the moment.

Tunnels could be negated to a great extent by deepening natural gorges & existing water courses to get a fall towards the western side of the GDR.
Where pumping is unavoidable, water wheels or wind mills can do the job. We must not forget that the aim is to gradually, not instantly refill the GAB. Most objectors to the scheme for some reason appear to envisage massive streams being diverted in a short period. That is not so. It has to be a gradual saturation of the ground so as to finally start having an effect on the weather pattern. Once permanent vegetation takes hold, wildlife remains in the area then & only then should larger human settlements be considered.
It's not something investors & australian investors in particular would not be all that interested in due to it being a long-term, generational project that'd enable long-term outback employment to start with. It'd be a National project in the interest & for the guaranteed benefit of this nation.
The argument that "it'd cost too much" is opportunism-based on selfishness.
We could introduce a "Greening the interior" Levy of $1/month from wages, $2/month from salaries & $2/month from companies. That'd fund earth moving gangs to start immedeately. As there have already been surveys from A-Z no more hyper-expensive "studies" are required, only dumpy level crews.

Canem Malum.
Thanks for that. some very interesting graphs.

When somebody mentions world population I think it is worthwhile pointing to the work done in Iran and Thailand in relation to government sponsored family planning. It has shown that all is not lost and that realistic birth reductions can be made if governments have the will.

The sooner some countries start birth reductions the better off we will be

HenryL - Thanks for your feedback.

Aidan- Thanks for the clarification.

Wouldn't, according to illogical bureaucratic thinking, a greater population provide more taxpayers i.e. increase funding availability for projects ?
Just kidding !