My sympathies to Australians who have been hit by flooding.
For all DIY enthusiasts, garden shed engineers and entrepreneurs out there, if you click here you can find out how to build a pump using an outboard motor, a few stout bits of wood, and a few carpentry skills.
I made one myself and tested it in the local river. It worked very well. It does high volume, low head water shifting - ideal for moving the last couple of feet of floodwater out of defined areas.
It would prove ideal for use in Australia where many households near the coast will have outboard motors. Make a frame up, get it going, take it to where it is needed.