Water Holding Capacity and Permeability of different Grain Sizes
Cascades to Coast GK-12 Curriculum
Fellow: Ted Hart (PSU Environmental Science)
Teacher: Kirk Ordway (Mt Tabor Middle School)
Advisor: Dr. Alan Yeakley (PSU Environmental Science)
Learning goal:
Practice lab techniques commonly used by soil scientists and hydrologists, and make a physical
connection between grain (particle) size, porosity (% of open space), water holding capacity
(soil moisture) and permeability (infiltration rate).
Target Grade:
6th grade Integrated Science. Earth and Physical emphasis.
State Standards:
6.1P.1 Describe physical and chemical properties of matter and how they can be measured.
6.2E.1 - Explain the water cycle and the relationship to landforms and weather.
8.3S.2- Organize, display, and analyze relevant data, construct an evidence-based explanation
of the results of a scientific investigation, and communicate the conclusions including possible
sources of error. Suggest new investigations based on analysis of results.
Activity Summary:
Two 40-50 minute activities (1st day form hypotheses and collect data, 2nd day construct graphs
and form conclusions) using the scientific method to investigate the properties of grain size and
porosity in order to determine which soil type will have greater water holding capacity and
permeability during dry and wet conditions.
Activity Plan:
Groups of 3 students work well, but this can be done in pairs.
Set up: (5 minutes)
1) Number the wash bins to indicate the number of the group
2) Assemble the following for each group on the class room tables:
a. One plastic 1-L graduated cylinder
b. One plastic container with sand and another gravel (15-20 ¼ in holes in bottom)
c. Jug of tap water
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d. Wash bin
e. Ruler
f. Stop watch
g. Sponge and paper towels
3) Place all the smaller items (sponge) in the wash bin
Introduction (5-10 minutes):
1) Review the USGS grain (particle) size chart (last page)
2) Show students how to measure the diameter of a piece of gravel and the distance
between grains.
3) Discuss with students how porosity size might affect water holding capacity (soil
moisture) and permeability (infiltration rate).
4) Discuss with students their sand and gravel using terms in the USGS chart (i.e. poorly
sorted).
5) Brainstorm hypotheses with students that compare the porosity and permeability of
sand and gravel. Discuss how dry and wet sand and gravel may affect these properties
and processes.
Work time (30 minutes):
1) Demonstrate steps 7-17 filling out values in the table.
2) Double check all values are recorded in everyone’s table.
3) If desired pool class data and calculate averages at the front of the room on white
board/overhead for students to graph.
4) Provide examples for graphs and explain how they answer hypotheses
Related Concepts:
Structure (hydrogen bonds) and properties (cohesion, adhesion, etc.) of water. Structure
(shape) and chemistry (quartz) of rocks and soil. Sorted versus poorly sorted grain size.
Materials:
Each student group will need the following:
1) One plastic 1-L graduated cylinder
2) Two 1-L plastic containers (slightly smaller or larger is ok). Drill 15-20 ¼ in diameter
holes in bottom of each container. Holes should be approximately ½ in from each other
so the bottom of the container doesn’t develop cracks.
3) 4 L jug of tap water (class room sink is ideal)
4) One 12-L wash bin
5) 0.5 L of sand (preferably 0.5-2mm diameter of similar size/well sorted) and 0.5 L of
gravel (preferably 3-5mm diameter of similar size/well sorted). Home improvement
stores carry landscaping sand and gravel that often are of this size and work well.
6) Ruler with mm increments
7) Stop watch
8) Sponges and paper towels (cleaning up)
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Extensions: Grain size analysis, water properties, soil maps. Students will start to see why
different grain sizes are used for different applications such as using drain rock for irrigation
and sand in soccer or baseball fields.
Assessment Questions: On worksheet below.
Handouts and worksheets: Next page.
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Water
Grain diameter (mm)
Porosity (mm)
Why grain size (diameter) matters:
Gravel in your driveway and sand in your lawn
Inquiry: What is grain size and how do we use them to build areas like driveways
and lawns? ________________________________________________
__________________________________________________________________
Give an example at your house/near where you live: ________________________
Materials: Each group needs
1 graduated cylinder
1 plastic container filled with sand
1 plastic container filled with gravel
1 jug of tap water
1 wash bin
1 ruler
1 top watch
1 Sponge
Condition: Dry
1000
Water in (ml)
Water out (ml)
Water in soil (ml)
Time (min:sec)
Sand
Wet Difference
1000
Dry
1000
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Gravel
Wet Difference
1000
Procedure:
1)
2)
3)
4)
5)
6)
OBSERVATIONS AND FORMING HYPOTHESES
Measure the diameter of ten sand and ten gravel grains from the plastic
containers. Show work here:
a) Sand: ________________________________________ / 10 =
b) Gravel: ______________________________________ / 10 =
Are the averages within the sand and gravel dimensions listed on the
USGS chart? ________
On white notebook paper, clump approximately 15 grains of sand
together so as much of sand grains are touching but the sand grains are
not on top of one another and you can still see the white paper between
the sand grains (picture above).
Measure the diameter of the space (porosity) between the grains. Do this
10 times for each grain type. If it’s too difficult to do for sand just do
gravel. Show work here:
a) Sand: ________________________________________ / 10 =
b) Gravel: ______________________________________ / 10 =
How does the average porosity diameter compare with the average
diameter of the grains?
__________________________________________
Write 2-3 hypotheses that compare the porosity and permeability of sand
and gravel. You may include whether it’s dry or wet.
Hypothesis # 1:____________________________________________
_______________________________________________________
Hypothesis # 2:____________________________________________
________________________________________________________
Hypothesis # 3:____________________________________________
_______________________________________________________
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RUNNING TEST
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Empty bin.
Fill graduated cylinder with 1 L of water.
Hold container with 0.5 L of sand approximately six inches above the bin.
Start the stop watch right when you pour the water into the container
with sand.
Poor the 1 L of water from the graduated cylinder slowly (should take
about 30 seconds) into the container with sand. Don’t spill any water over
the edges of the container holding sand, as all water should be either in
the container with sand or in the bin.
Let the container with sand drain until constant flow ceases (only slow
dripping).
Stop the stop watch and record the time (dry sand column) in the table
(first page) it took for the water to pass through the container with sand.
Measure the volume of water (ml) that passed through the sand.
Record this value in the table (dry sand column).
Subtract this value from the amount poured in (1000ml or 1L) to find the
amount of water in the sand.
Record this value in the table (dry sand column).
Repeat steps 7-17 for the same container with sand (now wet sand
column).
Repeat steps 7-17 for gravel, first dry then wet.
Double check all data is recorded in your table.
Using your table, construct graphs for:
a. Water retained by sand and gravel during the dry and wet tests
b. Time to infiltrate for sand and gravel during the dry and wet tests.
Questions:
1) Explain how dry sand or gravel might increase water holding capacity:
___________________________________________________________
___________________________________________________________
2) What other properties of gravel make it suitable for driveways?
___________________________________________________________
___________________________________________________________
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3) What other properties of sand make it suitable for lawns?
___________________________________________________________
___________________________________________________________
4) Write your conclusion for each of your hypotheses:
Hypothesis # 1:____________________________________________
_______________________________________________________
Hypothesis # 2:____________________________________________
________________________________________________________
Hypothesis # 3:____________________________________________
_______________________________________________________
USGS grain size chart (http://core.ecu.edu/geology/rigsbyc/rigsby/Sedimentology/OrangeBible.html).
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