What are the methods you use for preventing a river from flooding?

Question

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Answer 1

dams that restrict / control flow of water.  building embankments on the sides of the river.  trenching so that the river flows downards etc are some steps that can be taken.  that being said, all of these have a number of limitations and that is the reason for the high number of flooding all over the world

AM

Answer 2

Set up a barrier on the banks, be it sand bags, walls, dams, or FEMA documents, and hope these work, even until the river goes down, if ever.

Answer 3

It's very hard to prevent a river from flooding as the amounts of water involved in even quite modest rivers are enormous. Many major cities with a flood risk have overflow trenches to divert flood waters - in effect creating numerous small, man-made rivers to relieve the pressure on the main river course. Some cities use underground sewers to the same effect. The river banks themselves can also be raised by building earthworks or concrete structures to contain the river while giving it room to rise in level rather than flood out sideways. Many cities have banned developers from building on flood plains (the natural area that a river would take over when it flooded) and that minimises damage to property - with it's associated cost. By limiting the amount of building in what the British term 'Green Belt' land - semi-rural or countryside areas around the major towns - the rainfall on these areas can be soaked up by the local water table and prevent surges of flood water in extremely wet weather (which is all the time in Britain!). Hope this helps.