Purpose: |
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To demonstrate how
watersheds are formed. |
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Background: |
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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.
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Materials: |
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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) |
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Procedure: |
- Place diatomaceous earth in the large plastic box.
- Puncture the bottom of the plastic jug with a pencil and insert
the tubing. If leaks occur, caulk around the tubing.
- Fill plastic jug with water and add blue food coloring dropwise
until desired color is obtained. (optional)
- 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.
- 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).
- 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.
- 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.
- 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."
- 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.
- 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.
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Extension: |
You can use mister bottles to allow for rain conditions while the rivers
are forming. Observe how rain effects the formation of rivers.
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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
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