is Mise,
Have you ever watched water breaching a dam/levee ? If you did you'd know that there's no stopping it !
Of course levees are good but they're not a permanent solution. Once levees are constructed they should be constantly built up until they actually become land wide enough to be built on !
Sort of land reclaiming on land !
It'd get rid of a hell of a lot of waste as well ! Plant trees & have drains leading back to the main stream. There's so much that could be done if only the experts were kept away from it all !

Indyvidual: "There's so much that could be done if only the experts were kept away from it all !"

Hmm, let me fix this for you:

"There's so much that could be done if only WE HAD A INFINITE AMOUNT OF MONEY !"

Like just about all your other crazy ideas, it not economically feasible to do what you suggest. It would cost more than you would gain to raise the land levels as you propose. Land reclamation makes sense in some parts of the world because the land they are creating is in areas where land is very expensive, for example, in Singapore, Netherlands, etc. Or places where the new land can be sold as an exclusive exotic are area to live even though the land was originally very cheap, such as canal estates created from swamps.

In the regional areas that IsMise is talking about, if you were to raise the level of the land by meters (for some of these flood areas we're talking over 10m) it would make the land too expensive to buy for the type socioeconomic locality that they are.

We could start funding town levees by using the money that’s being put aside for the upcoming next two referendums, and do much more good with it.

Indyvidual,
Levees are a permanent solution, you said so yourself where you suggest that they be wide enough to build on, surely you’re not suggesting that houses be built on non-permanent land.

This sounds like a project for my "Seniors National Service"! Lads, picks and shovels at the ready, we have now ditched the idea of lowering the rivers as proposed by Professor Nincompoop and will now build levees. How high you ask, good question, well I do believe the Murray River peaked at 95 meters, so 100 meters high should do the trick, just to be on the safe side. We shall build a string of new towns and burbs atop of our wondrous new levees including Indyville and Issyville, populated by overworked bureaucrats and public servants with free housing! With the savings we will be making by not paying out useless aged welfare, $25 billion in the first year alone, and billions more in the years after that! As the lads march from their newly established camp at Sunny Gulag to the tune of "Hi Ho Hi Ho It's Off To Work We Go" the lads will be reinvigorated in their twilight years, all at little cost to us poor suffering taxpayers.

Words of inspiration for my Seniors Army;

… We dig dig dig dig dig dig dig from early morn till night
We dig dig dig dig dig dig dig up everything in sight.

Without levees a huge part of the US Mississippi river basin would be uninhabitable, & a very large part of their agricultural production could not happen.

Levees developed naturally. Rivers built up their banks with silt, & man then extended the idea. The bottom of many large old rivers are actually above the surrounding flood plain, having built their own levees.

Some suggesting deepening the rivers by excavating the bottoms, which may help a little, but in a would be a bit like a pimple on a pumpkin as far as flood level is concerned. Then can you imagine the screams from the ratbag greens if you start removing all the debris & snags from rivers. Where will the poor fish find a home?

Of course levees must be maintained properly. Maryborough flooded earlier this year when the flood gates installed to allow rain water to drain from the town to the river failed to shut automatically, allowing part of the CBD to flood through them. Those levees have protected the city for years, pity the bureaucrats of the council did not do their job. Always a problem with government on any level.

Just read a learned paper on levees and they are described as a temporary solution, the authors completely ignore the Mississippi system as mentioned by Hasbeen above, they also ignore the Chinese levees on the Yellow River, some of which date back possibly 3,ooo years.
The authors of the paper argue.for climate change as part of the solution ??