Watersheds

    The land area that drains all the surface water runoff into a stream or river is called a watershed. Precipitation in the form of rain and snow have four options: it can evaporate back into the atmosphere; it can flow as runoff into a stream; it can soak into the ground where it is used by plants and returns to the atmosphere in the process of transpiration;or it can seep deep into Earth as groundwater.     

    Water sheds aren't located just in mountains, forests, or plains, but can also be in parking lots, school yards, meadows, farm fields, and even your own back yard!

Copyright 2002 by TASA Graphics Arts, Inc.




   


 As snow melts and flows over rocks, the runoff dissolves minerals in the rocks and contributes to the weathering process.




          Photo Courtesy of the USDA
          Natural Resources Conservation Service

Watershed Effects

    As a river flows through flatter land, it loses energy and moves at a slower speed. This allowes dirt and silt mixed in the water to settle out onto the river's bottom.



    As a river slows, meanders form. Meandering means then river starts to form "S" shaped curves.

    Deltas are the lowest part of a watershed that flows to the ocean.

Copyright 2002 by TASA Graphics Arts, Inc.
    




    In the delta (a triangular
piece of land) the water
is divided into smaller channels.

    
    When these channels flood
low lying land, they form
wetlands, marshes, and swamps.
Many of the wetland plants
filter pollution out of the water.




Images Copyright 2002 by TASA Graphics Arts, Inc.





    When the delta divides the river, these smaller channels are called bayous and sloughs.












Desert Water Sheds

    Desert watersheds are often located underground in aquifers. The water held in a desert water shed rarely makes it to the ocean. The water held in the aquifer under the Snake River Plain is an example. However, some of the water flowing through the Snake River Plain aquifer eventually flows into the Snake River at Thousand Springs and will flow into the Pacific Ocean.

Learn More

For more information about desert watersheds go to:

             http://imnh.isu.edu/digitalatlas/hydr/main/srbfr.htm