The Brisbane River through Brisbane is tidal, and with a huge inflow from up stream and urban run-off, coupled with high tides, flooding is inevitable. What were once rare events, but now with the impact of climate change will occur far more frequently.

The new suburbs, ie. those that you are claiming
thinkabit,
So, all these rooftops barely sticking out of the water on the news are 100+ year old homes ?

In the case of Brisbane, some are yes! But the others are buildings that have replaced older buildings.
Much of inner Brisbane has been rebuilt many times. Sometimes this is due to buildings having been destroyed by fire/flood/old age. But most times it is an economics thing- the land keeps raising in value so people replace them with taller and taller buildings. Even though they know they are building in flood prone areas. Note that this is *not* new green field development, but people rebuilding on existing sites. These days it takes literally just minutes to consult a flood map, which are freely and widely available, eg: http://floodinformation.brisbane.qld.gov.au/fio/ . So you can't blame the council if people are stupid enough to build on existing parcels of land where it is a *known* flood zone.

By-the-way: I use to live in a NewMarket in not far north of Brisbane City and in the 5 years I lived there I saw many buildings knocked down to make way for higher density dwellings. Some of those demolished were beautiful old Queenslanders (although sometimes they relocate Queenslanders instead of destroy them), some post war fibro-shacks (which themselves replaced Queenslanders), some were 1970/80's monstrosities (monstrosities in my opinion anyway) which made way for nicer buildings, etc. These buildings were replaced in the main for economic reasons.

individual: "I have previously suggested parallel water course developments which can double as high end canal development real estate to fund the bulk of the work."

So let me get this right. You've been complaining about people being allowed to create new suburbs by green field development of land near the river in the Brisbane City area recently (which is factually wrong as I've explained). But now you've come up with the "solution" for flooding by building canals for people to live by?

Hmm, do you know the meaning of the word "hypocrisy"?

thinkabit,
you should thinkabit more. You remind me of that woman who was against dredging our harbour because making the channel deeper would lower the water level in other areas of the harbour & boats would get stranded.
Canal developments offer & accommodate spread for increased volume without raising the level dramatically.
Once you comprehend this you won't resort to use words like hypocrisy !

Diversion channels need to be deep, wide and straight, so around Brisbane, unless tunnelling is resorted to, there would need to be much removal of existing housing that is not a problem re flooding.

You really don't get it do you individual! Your canal will have to deal with *all* the flood water. This is means that it is going to have to be *BIGGER* than the Brisbane river itself. Look at a map to see how big the Brisbane river is- at Kangaroo Point in the middle of Brisbane it's about 200m wide.
So to build your brain-fart canal are going to have to forcefully resume land from orders of magnitude more people than what the floods affect.

Can you not see the hypocrisy in this?

But not only that, the floods we've just had in Southern Queensland and Northern New South Wales in monetary terms haven't done much damage: it's just low billions (http://www.afr.com/politics/floods-damage-bill-set-to-top-2b-20220302-p5a0z5). And these floods are very infrequent, they occur on decadal timescales. To put this cost figure in perspective, the cost is projected to be about ballpark comparable with the amount that Australian's spend on coffee EVERY YEAR.

Your canal would be the largest civil works project ever undertaken in Australia. It would cost orders of magnitude more than the damage caused by the flooding. It would bankrupt the state of Queensland before it was ever finished. We simply couldn't build your canal realistically.