Runoff consists of precipitation that neither evaporates , transpires nor penetrates the surface to become groundwater . Even the smallest streams are connected to larger rivers that carry billions of gallons of water into oceans worldwide.
Excess runoff can lead to flooding, which occurs when there is too much precipitation .
Two recent events in the United States have caused major flooding. In early spring of 1997, the Northern Plains endured devastating floods. Towns along the Red River like Grand Forks, North Dakota were shut down due to flooding that completely paralyzed the city, leaving entire downtown areas underwater. Floodwater is shown here in white while unmelted snow is shaded red. During the Fall of 1996, towns along the Red River received record amounts of rain.