A flood can occur, obviously, when too much rain falls and the ground can't absorb it quickly enough. If it happens very quickly with little warning, it's called a 'flash flood.'
But flooding also happens if a dam or levee breaks, or after heavy snowfall melts.
The area where flooding has happened or is expected to happen is called the "floodplain."
We have seen flooding in Minnesota, and North and South Dakota. These have usually been associated with a river overflowing its banks. Sandbags are assembled and piled up as people try to prevent the flood from reaching their homes.
Here is the progress of flooding in Louisiana and southern states earlier this month:
Moving water has a lot of power. As it moves through whatever outlets it can find, it will erode dirt underneath buildings and trees and drag all of it along as it goes. The water may contain sewage and always contains bacteria, and can also be carrying pieces of buildings or harmful trash that can injure people trying to slog through it. Frequently, this results in contaminated drinking water.
When a home is damaged by water, the greatest damage is probably mold that will grow on surfaces that never dry out. Replacing the whole building is the only way to start over; there is nothing to rid that house and its contents of all the water and resulting mold and bacteria from forming.
Building any kind of structure on unstable ground is never a good idea. This would include roads, homes, and bridges. People continue to re-build too close to the shore of the ocean after their homes are destroyed, most often by hurricanes and the huge amounts of water that flood beyond the shores. This also holds true for building too close to a river or a lake.
Built with bricks but probably on shifting ground.
Even in areas where you might not expect flooding, there has been a trend in home building where the builders attempt to fill in an area that is naturally wetlands with dirt in order to build on top of it. This is unwise as the wetland will always be unstable.
Here is National Geographic's information about flooding: http://environment.nationalgeographic.com/environment/natural-disasters/floods-safety-tips/
What careers are involved in studying floods and making structures safer?
- Building trades