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The Living Edens
How Much Water Will The Desert Hold?

Instructional Objectives
Background Material
Procedure
Evaluation / Alternative Assessment
Web Resources


Instructional Objectives:

Students will:
  1. Build a container, fill with sand to measure the amount of water that can be absorbed
  2. Determine how much water will be retained by sand in the activity and identify similar conditions in the Namib Desert
  3. Draw conclusions as to why there is so little water in Namib
  4. Identify characteristics of the desert environment

Background material:

The desert is a very dry place. Water is scarce and what little water is present is not easily obtained by the animals that live in the desert. Sand retains water very well. This activity will show the amount of water retained by the sand used in our sample. The intense heat of the Namib Desert is responsible for the small amounts of rain and also for the creation of fog as shown in the Namib program. The Benguela current which is offshore in Namib also plays a role in the weather in this part of the world. (Spectrum Guide to Namibia, Compiled and Edited by CAMERAPIX, Hunter Publishing, Edison, New Jersey, 1994 and PBS' The Living Edens "Namib" program, which aired July 16, 1997)

Target Grade Level:

Middle Level Students, grades 5-9.

Materials Needed:

For each group of 3-4 students:
  • One 1.5 litre plastic soda bottle with cap
  • Sufficient dry sand to fill one third of the soda bottle
  • One large plastic cup (or a graduate for more accurate measurement)
  • Science journals/pencils
  • One plastic shoebox to catch draining water
  • One 4 x 4 inch piece of nylon hosiery
  • Scissors
  • One rubber band
  • Centimeter ruler
  • Colored marker
  • Water for each group/approximately 1/4 gallon (This will vary depending on how dry the sand sample is when used in the activity and what kind of sand is used)

Procedure:

(See the diagram provided for this activity) For each group of 3-4 students:
  1. Have students cut the bottom off of the soda bottle.
  2. Have students measure 10 centimeters from the cap opening up the side of the soda bottle and make a 10 centimeter mark on the bottle side.
  3. Have students cut the 4 x 4 inch section of nylon hosiery, cover the cap opening and use a rubber band to secure the nylon hosiery screen. Place the cap over the nylon and screw tightly.
  4. Have students fill the 1.5 litre plastic bottle which must be held upside down with dry sand to the ten centimeter mark.
  5. Have students use the plastic cup and measure full or partial cupfuls (or milliliters if using a graduate) of water to be poured into the bottom end, now standing upright, of the plastic soda bottle. Bring the water level in the bottle to that of the sand. Record the amount of water used in student science journals.
  6. Remove the cap from the nozzle of the plastic soda bottle. Collect and measure the amount of water that drains from the bottle through the nylon hosiery filter. Measure and record the amount of water drained in student science journals.
  7. Have students discuss how well water will absorb in the sand in the plastic soda bottle and offer suggestions as to why the desert is so dry.

Evaluation/Alternative Assessment:

Observe students as they complete the activity and lead a group discussion as to the absorbency of the sand and why if sand absorbs the water so well, why is there so little water in the desert. Have students present the data they collected to the class in groups. Record the amount of water used in student science journals. Refer to The Living Edens "Namib" program regarding the fact that it almost never rains and that fog from the sea brings moisture in to the creatures of the Namib. You might also want to graph the amount of water in and water out to have a visual representation of the results.

Elementary Extension:

This activity might be better as a demonstration for lower elementary students in that manipulation of the materials might present a problem.

You might want to try different kinds of sand in this activity. Sand collected from warm tropical areas and sand from local lakes might show differences in results.

High School Extension:

High school students should use graduates and make all measurements more precise.

Additionally they may want to create an activity where they can measure how long it will take to have the water evaporate from the plastic soda bottle container.

Additionally, different kinds of sand at different temperatures might be some good variables to examine.

Investigate the Benguela current and determine its effect on the climate of Namib.

Web Resources:

Benguela Current:
http://www.ldeo.columbia.edu/physocean/BEST/text3.html

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