The water cycle & Groundwater
HYDROLOGIC CYCLE
condensation
precipitation
transpiration
evaporation
infiltration
runoff
Water table
aquifer
I.
Groundwater flow
Stream,
spring,
lake, or
ocean
WATER CYCLE – Water circulates continually between the Earth and the
Atmosphere. Water from the oceans, rivers, soil and vegetation
EVAPORTATES into the air. Air rises, cools, and CONDENSES to form
clouds. As the cloud droplets grow in size, eventually they get heavy enough
and fall back to the ground as PRECIPITATION. Some of the water
becomes RUNOFF, and flows into streams and is carried to the sea. Some of
the water INFILTRATES into the ground to become part of the groundwater
or it is absorbed by plants. While some other water particles evaporate back
into the atmosphere.
a. Key vocabulary terms to know
i. EVAPORATION – liquid to gas – energy is absorbed
ii. PRECIPITATION – water falling to the ground due to gravity
iii. CONDENSATION – gas to liquid – energy is released
iv. RUNOFF – water flowing over the surface of the Earth
v. VEGETATION – plants
vi. INFILTRATION – process of water being absorbed into the soil
vii. TRANSPIRATION – process of water getting into the air from
plants
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II.
GROUNDWATER
A.
B.
Water enters the ground through the process known as infiltration
Water can only enter the ground if the ground is PERMEABLE.
a. If the ground is IMPERMEABLE the water will become RUNOFF.
As permability increases, runoff decreases.
b. The factors that control the Permeability of the soil are:
i. PARTICLE SIZE: The larger the particle size of the soil
the greater the permeability.
ii. The SATURATION level of the ground is also a factor.
1. If the ground is already soaked, then no more
water can soak into it. If the ground is dry and
there is space between the soil particles for water,
then water will infiltrate and become groundwater.
iii. The SLOPE or GRADIENT of the ground: If the ground is relatively
flat or has a gentle slope then water will likely infiltrate. If the
ground is steep then runoff will occur.
iv. Vegetation. Plant roots help create pathways for water to flow
through into the ground.
c. Other important descriptions of soil are POROSITY & CAPILLARITY
i. POROSITY is the amount of empty space between the soil particles.
Porosity depends on particle shape, not particle size. If the particles
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are rounded, the porosity will be approximately 38%. If the particles
are more flat the porosity decreases dramatically.
ii. CAPILLARITY does depend on particle size. Capillarity is the
ability of water to move upward through soil as it clings to the
particles. The greater the surface area, the greater the capillarity.
Capillarity is why some water is retained in the intermediate belt in the
diagram above.
A
B
C
Porosity
Capillarity
Permeability
iii. If the diagram above represents soils with different particle (grain)
sizes.
1. Water would pass (permeate) through C the easiest since has the
largest particle size. C also has the largest pore spaces.
2. Sample A would have the greatest capillarity and water retention
since it has the smallest particle size and therefore the most
surface area. Water will cling to the surfaces of the particles.
Also, water will have a difficult time traveling down through the
sample because the pore spaces are small
3. Sample A, B, & C all have the same porosity. Since each sample
is composed of all round particles, the porosity of each contairer
is the same. Sample A has many small pores, and C has fewer
large pores but the total amount of pore space is equal.
4.
A
B
C
A
B
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C
Practice Questions
1. Which container would have the greatest rate of infiltration?
2. Why would the container with the mixed particle sizes have the least porosity?
3. Which container would have the greatest capillarity?
More Practice:
1. Which column would the water climb up the highest?
2. If the columns are filled with uniform shape & size particles, compare the
porosity of each?
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