What happens in your neighborhood when it rains? A little rain can interfere with our plans, but it can also be refreshing. If you have ever experienced a drought, you can appreciate that rain is necessary for plants, animals, and human life. As it is raining, several things are happening at once. Some water re-evaporates before it hits the ground! Plants and their leaves are slowing down the raindrops. Some water is soaking into the tiny spaces between soil and rock particles. Some water runs on the surface before evaporating or soaking in. This water is called runoff .
Runoff will flow until something changes. Some runoff finds a level area and makes a puddle. Some eventually soaks in or evaporates. Other times, runoff joins a river that flows all the time. (Geologists call all permanent flowing water a stream, whether it is a brook or a big river.) Runoff is an important contributor to the water in many streams, but it is not the only one.
