They need to analyse where the water came and build johads or check dams. These slow the water downstream and allow it time to soak into the ground restoring groundwater. If they had these in place they could have eliminated much of the flood damage. They are remarkably cheap to build. In India they are built by hand with rubble. Australia could build them with mechanical diggers and using hardcore as a foundation. They are very small but if they do it over time then the risks will be eliminated.

No they wouldnt. The ground was allready saturated because of high rainfall in the preceding months. The water was just running off the surface as the ground could not absorb anymore.

Slowing the water down when extremes of rainfall have occured could also make drainage and therefore recovery more lengthy. Of course the plus side is that groundwater levels increase providing better protection for drought, and vegetation may increase to help prevent soil erosion in future floods.

Yes but there can also be additional boreholes to help the water get down deeper. If the surface ground is saturated it does not mean that the aquifers have been restored. Were the aquifers full as well? Australia had been through a long drought.

Boreholes to insert water? With the energy required you may just as well pump water over the ranges to the red centre. Why hasn't that been done yet, cost. As long as repair is cheaper than prevention it will never be done. Basic economics at the end of the day, and if you then want to consider lives lost then recent snow in europe should be considered first.

They can be relatively shallow boreholes only ten feet or so. Many diggers have an attachment that can do it. The boreholes only have to be deep enough to get past the initial blockage. Many rocks can be sedimentary and slow drainage. It only has to be enough in the johads to allow faster drainage.