What are the dangers of building a town next to a river flowing within levees?

Question

And also what precautions should people take in order to avoid those dangers?

Answer 1

When the levee breaks (according to Led Zeppelin) the land generally is very low-lying, so the water floods into the floodplain through the break, but also has a hard time draining out of the break.  So we end up with a flooded area that can't drain easily.  Farmlands and towns are left with weeks of standing water (like North Dakota in the big flood of 2000 (or so)).

Precautions include building better levees, but that just passes the flood water to the next town down the line that didn't invest.  The best precaution is to not build on floodplains.  It'll end in tears.

Answer 2

Building a town next to a river puts that town at risk of flooding from that river. If you build levees to limit the river flow, then most of the time the town will be safer, but in times of extreme flow, such as a spring melt, or after a massive rainfall upstream, then the danger is that the levees might break, and the flood be all the more catastrophic. Think of New Orleans, a coastal city built below sea level.

Also, in its natural state, the river changes its course over time through erosion and sedimentation, so these natural processes might undermine a levee system, leading to a breach.

Isn't it much safer to build on higher ground?