Name ____________________________
Date _________
Porosity and Permeability
AIM: How does soil type affect the movement of groundwater?
Background Information: Groundwater is water that moves through soil and rocks
below Earth’s surface. When ground water moves through soil, the structure of the
soils affects its movement. Groundwater moves through the spaces between soil
particles. These spaces are called pores. Not all soils have the same amount of pore
space. Porosity depends on the number and size of pores in soil. The pores in soil are
all connected, allowing water to pass through them. This means that soil is permeable.
The ease with which water moves though the soil is call permeability.
A soil's porosity and
permeability are important to
many people. Farmers must be
aware of these soil conditions
so they can determine the best
way to grow crops. Builders
also consider these conditions
in the area they plan to build.
Environmentalists are concerned with
porosity and permeability when there is a
risk that a pollutant might be introduced
into the groundwater supply.
Explain porosity and permeability in your own words.
Porosity:
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Permeability: _________________________________
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Hypothesis: Using the soil types in the chart below, which soil type do you think will be
most permeable? Explain your reasoning. Use the terms porosity permeability, and
sediment size in your answer.
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Procedure:
1. Go to:
http://www.glencoe.com/sites/common_assets/science/virtual_labs/CT02/CT02.html
2. To select a type of soil, change the percentages of sand, silt, and clay by sliding the
two bars on the Soil Meter.
3. Click the Test This Soil button to move 100 mL of the soil mixture to the funnel.
Name ____________________________
Date _________
3. Click the Pour Water button to begin pouring water on the soil. The water will
automatically stop when the first drop of water begins to form at the bottom of the
funnel.
4. Observe the readout that displays how much water was poured. This is the volume of
water the soil held. Write the number in the chart.
5. Find the porosity of the soil place this percentage in the Table. In the formula below,
Vw stands for the volume of water and Vs stands for the volume of soil.
Vw
--------- x 100 = % Porosity
Vs
6. Click Reset and repeat steps 1 through 5 for each of the soil type below.
Soil Type
Volume of the water (Vw) Porosity % (show work)
Sand
(100% sand)
Silt
(100% silt)
Clay
(20% sand, 30% silt, 50% clay)
Sandy Loam
(50% sand, 50% silt)
Silt Clay
(50% silt, 50% clay)
Clay Loam
(30% sand, 40% silt, 30% clay)
Heavy Clay
(100% clay)
Sandy Clay
(50% sand, 50% clay)
Questions:
1. What determines the texture of soil?
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Name ____________________________
Date _________
2. What is meant by the permeability of a soil?
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3. What is porosity and how is it related to permeability?
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4. Based on this investigation, which type of soil is the most permeable? Which is the
least permeable? How do you know? Support your statement with evidence.
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Think about it:
a) Explain why surface runoff, or rain not absorbed by the soil, occurs much more often
in areas with soils with high clay content.
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b) On Tuesday a city receives 3 inches of heavy rain, but no flooding is observed. The
very next day the same city receives 2 inches of rain and widespread flooding is
reported. Explain why 2 inches of rain caused flooding on Wednesday, but 3 inches of
rain on Tuesday did not cause flooding?
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Name ____________________________
Date _________
c) Two adjacent cities, Pebbleville and Claytown, each receive 2 inches of rain on the
same day. The cities are named for the size of the particles that make up their soil.
Which city’s residents are more likely to experience flooding due to the heavy rain?
Explain your answer.
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d) Farmers often have problems with soil erosion when they clear their fields after the
growing season. Soil type is one factor that influences erosion. Some soil types are more
prone to erosion than others. Based on the data you gathered in this experiment, which
soil types do you think are the most easily eroded, soils with a high sand content or soils
with a high clay content? Explain your answer.
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