Much Water Will The Desert Hold?
Evaluation / Alternative Assessment
- Build a container, fill with sand
to measure the amount of water that can be
- Determine how much water will be
retained by sand in the activity and identify
similar conditions in the Namib Desert
- Draw conclusions as to why there
is so little water in Namib
- Identify characteristics of the
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.
For each group of 3-4 students:
- One 1.5 litre plastic soda bottle
- 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
- One 4 x 4 inch piece of nylon
- 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)
(See the diagram provided for this activity)
For each group of 3-4 students:
- Have students cut the bottom off
of the soda bottle.
- 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.
- 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
- Have students fill the 1.5 litre
plastic bottle which must be held upside down
with dry sand to the ten centimeter mark.
- 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.
- 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
- 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.
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.
This activity might be better as a
demonstration for lower elementary students in that
manipulation of the materials might present a
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.