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Activity S-1: What is a Watershed?
This youth activity is one in a series of two activities that can be used to introduce watershed concepts.  This activity can be adapted for any age group.  Younger audiences will be interested in manipulating the flow rate of the incoming water to see how rivers are formed, how they can meander, and the effects of a flood event.  Older audiences will be interested in seeing how changes in the soil surface and stream manipulation affect the downstream characteristics of the river such as gully formations, channelization, streambank erosion, and impoundments.
To demonstrate how watersheds are formed.
The term watershed refers to a geographic area in which water sediments and dissolved materials drain to a common outlet such as a larger stream, lake, underlying aquifer, estuary, or ocean.  This area is also called the drainage basin of the receiving water body.  A watershed can be large, like the Mississippi River drainage basin, or very small, such as the 40 acres that drain to a farm pond.  Large watersheds are often called basins and contain many smaller watersheds.

No matter where you live, you're in a watershed.  Your watershed may be made up of farmland, surburban development, industry, and/or urban areas.  Changes in land management may affect the quality and quantity of water in a watershed.  For instance, when more homes and roads are built, woodland is cleared, or parking lots are created, water runoff is intensified.  Without natural protective barriers, greater quantities of water enter ditches, streams, and ponded areas faster.  The result is often a higher and more rapid flow, during or after storm events, which can trigger flooding and the erosion of streambanks.  The rapid flow carries more water away, leaving less for dry weather periods.  The water may also carry pollutants, both dissolved and suspended, which will be deposited down stream.

* large plastic "blanket box" w/ lid, ~18"x24" (avail. at Walmart for ~$5.00)
* 10 lbs diatomaceous earth (coarse kind from pool supply store-50 lbs ~$16.00)
* blue food coloring
* 2 ft - 1/8" ID plastic tubing
* adjustable drip valve to fit end of 1/8" tubing (adjustable for slow drips)
* plastic jug to hold colored water (empty milk jug works well)
* miniature trees (clippings from evergreens works well)
* houses (monopoly pieces work well)
* rocks, pea gravel
* toothpicks
* tin foil and pieces of felt
* plastic spoon
* 3/8"-1/2" copper pipe fittings (angles, elbows, tees, straight pieces, etc.)
* sponge
* container for "props" (double sandwich box works well)
  1. Place diatomaceous earth in the large plastic box.

  2. Puncture the bottom of the plastic jug with a pencil and insert the tubing.  If leaks occur, caulk around the tubing.

  3. Fill plastic jug with water and add blue food coloring dropwise until desired color is obtained.  (optional)

  4. Connect the valve to one end of the tubing and secure it to one end of the plastic box containing the diatomaceous earth.  Clothes pins or paper clips work well.

  5. Mound the diatomaceous earth up towards the valve.  Allow the colored water to drip very slowly onto the diatomaceous earth to establish the meandering rivers; otherwise, gullies form and the river won't meander.  Allow 2-4 minutes of dripping to establish the river(s).

  6. Once the river(s) are established, you can increase the flow and manipulate the watershed using your "props."  Use the toothpicks for bridges, the tin foil for concrete, the pieces of felt for cropland and lawns, the plastic spoon as a back hoe, the pipe fittings as water diversions, and the sponge as the sun to evaporate ponded water.

  7. You can create flood events by allowing more flow through the valve, but I recommend that you don't do this until the rivers are established.

  8. Eventually, the diatomaceous earth will erode or "wash" away during the stream channel formation (forming an alluvial fan!).  You can scoop-up the diatomaceous earth with your hands and reform the "earth."

  9. Clean-up is easy.  Dip the props in fresh water (use a bucket) -- diatomaceous earth washes off easily.  If the diatomaceous earth gets on clothing, allow the clothing to dry and the diatomaceous earth will brush off like flour.

  10. You can store this project with the water in it.  Upon sitting, the diatomaceous earth will separate from the water.  You will need to mix the water and diatomaceous earth together before using again; allow some time to do the mixing -- it takes a while.


You can use mister bottles to allow for rain conditions while the rivers are forming.  Observe how rain effects the formation of rivers.

This activity was adapted by Dr. Kitt Farrell-Poe and Mike Allred (Utah State University Extension) from "Ridges to Rivers" by Judy Neuhauser found in the California 4-H environmental education program Science Experiences and Resources for Informal Education Settings (SERIES).

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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture, The University of Arizona. The University of Arizona College of Agriculture is an Equal Opportunity employer, authorized to provide research, educational information, and other services only to individuals and institutions that function without regard to sex, race, religion, color, national origin, age, Viet Nam Era Veteran's status, or disability.

For problems or questions regarding this web contact Dr. Kitt Farrell-Poe.
This document was last modified: 31-Aug-2005 .