![]() ![]() Much of the water in rivers comes directly from rainfall runoff from the landscape.Īs with all aspects of the water cycle, the interaction between precipitation and surface runoff varies according to time and geography. The runoff entering this creek is beginning its journey back to the ocean. The runoff in this case is flowing over bare soil and is depositing sediment into the river (not good for water quality). This picture gives a graphic example of how surface runoff (here flowing off a road) enters a small creek. Water will flow along channels as it moves into larger creeks, streams, and rivers. During a heavy rain you might notice small rivulets of water flowing downhill. It is easy to see if it flows down your driveway to the curb and into a storm sewer, but it is harder to notice it flowing overland in a natural setting. ![]() When rain hits saturated or impervious ground it begins to flow overland downhill. Still, it is true that much of the water in rivers comes directly from runoff from the land surface, which is defined as surface runoff. That is "overly simplified" because rivers also gain and lose water to the ground. Many people probably have an overly-simplified idea that precipitation falls on the land, flows overland ( runoff), and runs into rivers, which then empty into the oceans. The oceans are kept full by precipitation and also by runoff and discharge from rivers and the ground. In our section about water storage in the oceans we describe how the oceans act as a large storehouse of water that evaporates to become atmospheric moisture. ![]()
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