How does increasing the speed of flow of river help to prevent flooding??

Question

For my geography assignment.

Answers will be very much appreciated.

10 points for best answer. :)

Answer 1

This should be attributable to simple mass-flow of the system-  the river being the system in this case, and its banks/levees being its means of "containment".  If you can get the water out of the area faster than it is entering the area, you will have a net loss of water.  This will present itself as a lowering water level.

Think of it another way - if a dam breaks, what happens?  The area downstream gets MILLIONS of gallons of "input" water, right?  The area naturally floods.  Mass flow in > mass flow out.  Eventually the downstream area drains out, but the surge will have done its damage by then.  

Flood Control Projects are aimed at providing sufficient means for surges like that to safely exit without overflowing (flooding) - and they're remarkably simple in design - just make a very large, deep, wide exit channel for your river!