How do levees protect people from flood?

You know when you go Bowling, you can get bumpers put up in your lane to keep the ball from going in the gutter? A levee is basically the same thing, although on a much larger scale. Generally they're piles upon piles of dirt that are put along the side of a river to keep the water from going over the sides and flooding whatever is next to it. Hope this answered your question! (: