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Earth Science. - presents-. Groundwater. What You’ll Learn. How large amounts of water are stored underground. How groundwater dissolves limestone and forms caves and other natural features.

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slide1

EarthScience

-presents-

Groundwater

slide2

What You’ll Learn

  • How large amounts of water are stored underground.
  • How groundwater dissolves limestone and forms caves and other natural features.
  • How groundwater is removed from the ground by humans and what problems endanger our groundwater supply.
slide3

Vocabulary Terms

  • Infiltration
  • Porosity
  • Zone of saturation
  • Water table
  • Permeability
  • Impermeable
  • Aquifer
  • Topography
  • Cave
  • Stalactite
  • Stalagmite
  • Travertine
  • Spring
  • Geyser
  • Drawdown
  • Artesian Well
slide4

Movement and storage of groundwater

3%

freshwater

The Hydrosphere

  • The hydrosphere is
  • water on or in
  • Earth’s crust.
  • “hydros” is the Greek word for water.

97%

Ocean Water

slide5

Movement and storage of groundwater

10%

50%

90%

From the 3% of

freshwater, how much do you think is trapped in the polar ice caps and glaciers?

97%

Ocean Water

slide6

?

?

?

?

Polar caps

Glaciers

Both a and b

What is the greatest source

of freshwater on Earth?

slide7

Movement and storage of groundwater

Precipitation and Groundwater

slide8

Movement and storage of groundwater

Precipitation and Groundwater

  • Much of the precipitation
  • that falls on land enters the ground through a process called infiltration and becomes groundwater.
  • Only a small portion of runoff is directly returned to the oceans through streams and rivers.

Precipitation

slide9

Movement and storage of groundwater

Precipitation and Groundwater

  • Solid precipitation such as snow takes a long while before it becomes runoff or infiltrates to become groundwater.
  • Eventually, the groundwater returns to the surface through springs and then flows back to the ocean.

Precipitation

slide10

Movement and storage of groundwater

Groundwater

Storage

The amount of space between rock particles in underlying sediment is referred to as

porosity.

Well sorted High

sediments Porosity

slide11

Movement and storage of groundwater

Groundwater

Storage

The amount of space between rock particles in underlying sediment is referred to as

porosity.

Poorly sorted Low

sediments Porosity

slide12

Movement and storage of groundwater

Groundwater

Storage

a.

b.

Q: Which of these two do you think will absorb groundwater faster after rainfall?

slide13

Movement and storage of groundwater

Groundwater

Storage

The porosity of sand can range from 2% to 50% ! The greater the porosity…the faster water is absorbed.

slide14

Movement and storage of groundwater

The Zone of

Saturation

The depth below the Earth’s surface at which groundwater completely fills the pores of material is called the zone of saturation.

slide15

Movement and storage of groundwater

The Zone of

Saturation

The upper boundary of the zone of saturation is called the water table.

slide16

Movement and storage of groundwater

The Zone of

Saturation

Only the water that exists in the

Zone of saturation is called groundwater.

slide17

Movement and storage of groundwater

The Zone of

Saturation

Zone of aeration– materials are moist

but contain mostly air.

slide18

Movement and storage of groundwater

The Water

Table

The depth of the water table varies with the slope of the land.

slide19

Movement and storage of groundwater

The Water

Table

The topography of the water table follows the contours of the land.

slide20

Movement and storage of groundwater

The Water

Table

The water table rises and falls depending on the season and the amount of precipitation.

slide21

?

?

?

?

Floodplain

A Swamp

A Hilltop

Where is the water table closest to Earth’s surface?

slide22

Movement and storage of groundwater

Groundwater

Movement

In saturated sediment all materials are coated with a thin film of motionless water.

In coarse grained materials like sand, this film occupies a relatively

small portion of the “pore space”.

1 mm

slide23

Movement and storage of groundwater

Groundwater

Movement

Because of this

moving water can flow freely past the open pore spaces.

Groundwater flows downhill due to gravity and in the direction of the landscape slope.

1 mm

slide24

Movement and storage of groundwater

Groundwater

Movement

Because water has to squeeze through the small pores in the subsurface material, it usually travels very slow.

1 mm

slide25

Movement and storage of groundwater

Groundwater

Movement

vs.

0.1 mm

1 mm

Sometimes the pores are so small not even a single water molecule can get through.

slide26

Movement and storage of groundwater

Groundwater

Movement

vs.

0.1 mm

1 mm

The ability of a material to let water pass through it is called permeability.

slide27

Movement and storage of groundwater

Groundwater

Movement

vs.

0.1 mm

1 mm

Q: Which of the two examples of sediment above have the highest permeability.

Highly permeable materials include sandstone, limestone, and fractured bedrock.

Flow rates for these materials can be as fast as 1 m/h (one meter per hour).

slide28

Movement and storage of groundwater

Groundwater

Movement

0.1 mm

0.1 mm

With such tiny pores, some fine grained material is considered impermeable.

Examples of impermeable materials are silt, clay, and shale.

Flow velocities in impermeable materials are often measured in m/yr (meters per year).

slide29

?

?

?

?

Answer:

The flow velocity depends on the slope of the water table and the permeability of subsurface materials.

What two factors determine the flow velocity of groundwater?

slide30

Movement and storage of groundwater

Groundwater

Movement

Most groundwater flow takes place through permeable layers called aquifers.

slide31

Movement and storage of groundwater

Groundwater

Movement

Impermeable layers called aquacludesare barriers to groundwater flow.

slide32

?

?

?

?

What is an aquifer?

Answer:

An aquifer is a permeable layer that allows groundwater to flow through it.

slide33

Groundwater

Systems

Springs

Aquifers are commonly composed of sand, gravel, sandstone and limestone.

Remember: Limestone is easily dissolved by groundwater…..that’s how cavities in aquifers appear. (A cavity is an open space…like a cave).

slide34

Groundwater Erosion and Deposition

Caves

Caves form near or below the water table.

slide35

Groundwater Erosion and Deposition

Caves

Stream valleys are lowered and streams become empty as they infiltrate cave openings.

slide36

Groundwater Erosion and Deposition

Caves

Collapsing caves (or dissolved bedrock) near the surface of the Earth produce sink holeson the Earth’s surface.

slide37

?

?

?

?

Answer:

Since there are a lot of open spaces due to dissolved limestone, the ground water can flow FASTER in this area of an aquifer.

Since the Limestone area of an aquifer is filled with “cavities”, how would this affect the rate of groundwater flow?

slide38

Groundwater Erosion and Deposition

Caves

Caves are usually located just beneath the water table.

As water drips from the ceiling of a cave, it leaves behind small trace amounts of minerals found within the water itself.

After a long period of time, these minerals collect to form cone shaped structures called “stalactites”.

slide39

Groundwater Erosion and Deposition

Caves

As the water drips to the floor, minerals left begin to build up mound shaped, dripstone deposits.

This type of deposit is called a “stalagmite”.

Eventually, stalactites and stalagmites will join together to form dripstone columns within the cave!

slide40

?

?

?

?

Answer:

The aquaclude stops water flow…so when aquifers and aqucludes meet, water is forced out of the Earth….see photo on page 249.

So what happens when an aquifer meets an aquaclude?

slide41

Groundwater

Systems

Springs

When aquifers meet aquacludesat or near the surface of the Earth, water is forced out of the Earth….thus producing a SPRING.

slide42

Groundwater

Systems

Springs

The volume of water produced by a spring can be a mere trickle or a raging river!

In a “Karst Region”, springs yield extremely fast moving waters….. they’re called Super Springs.

slide43

Groundwater

Systems

Springs

In areas where there is horizontal sedimentary rock, Springs emerge in valleys very close to aquifers.

slide44

Groundwater

Systems

Springs

Springs can occur at the edges of perched water tables.

slide45

Groundwater

Systems

Springs

Sometimes Springs emerge along fault lines!

Springs can also emerge at fault lines.

slide46

Groundwater

Systems

Springs

Sometimes Springs emerge along fault lines!

In Limestone regions, springs discharge water from underground pathways.

slide47

Temperature

Of Springs

Groundwater

Systems

Spring water can be hot, warm, or cold….depending upon where the spring is located.

Groundwater vs. Air

Water

Air

Temperature

Air

Water

Winter Summer

slide48

Temperature

Of Springs

Groundwater

Systems

slide49

Temperature

Of Springs

Groundwater

Systems

Hot Springs are defined as groundwater with temperatures higher than that of the human body.

slide50

?

?

?

?

Answer:

Hot Springs get their “heat” from aquifers deep within the Earth.

So where do hot springs get their “heat” from?

slide51

Temperature

Of Springs

Groundwater

Systems

Sometimes the groundwater from these aquifers absorb so much heat…..they erupt!

Hot Springs that erupt are called

geysers!

slide52

Groundwater

Systems

Wells

The red dashed line represents where the water table used to be before most of the water was pumped out!

slide53

Groundwater

Systems

Wells

The distance between the deepest part of

the cone of depression and the “old”

Water table line is called drawdown.

slide54

Groundwater

Systems

Wells

Eventually, water from runoff and precipitation is added back to the zone of saturation.

This process is called

recharge.

slide55

Groundwater

Systems

Confined

Aquifers

Water-table aquifers are often polluted when chemicals spill on surface sediment.

slide56

Groundwater

Systems

Confined

Aquifers

If an aquifer is located between two aquacludes, it can be protected from pollution.

slide57

Groundwater

Systems

Confined

Aquifers

In essence, the aquacludes become “body guards” to the aquifer.

slide58

Groundwater

Systems

Confined

Aquifers

An aquifer “sandwiched” between two aquacludes is referred to as a

Confined Aquifer.

slide59

Groundwater

Systems

Confined

Aquifers

Confined aquifers usually contain water under pressure since the area of “recharge” is at a higher elevation.

slide60

Groundwater

Systems

Confined

Aquifers

Confined aquifers usually contain water under pressure since the area of “recharge” is at a higher elevation.

slide61

Groundwater

Systems

Confined

Aquifers

This type of aquifer is called an Artesian aquifer and water that spurts from it is called an Artesian Well.

protecting our water supply
Protecting Our Water Supply
  • There are a number of ways in which groundwater resources can be protected and restored.

All major pollution sources need to be identified and eliminated.