Transcript Chapter 13

Chapter 13 Water and Erosion
Chapter Outline
• 13.1 The Water Cycle
– Water Budget
– Water Conservation
• 13.2 River Systems
– Stream Erosion
– Channel Erosion
– Stages of a River System
• 13.3 Stream Deposition
– Deltas and Alluvial Fans
– Flood Deposits
– Flood Control
13.1 The Water Cycle
• Outline the stages of the water cycle.
• Explain the components of a water
budget.
• List two approaches to water
conservation.
Ahead to 13.2
Stages of the Water Cycle
• Evaporation – process by which liquid water changes into
water vapor
• Transpiration – process by which plants give off water vapor
into the air
• Condensation – process by which water vapor in the
atmosphere expands and cools forming water droplets which
then collect and form clouds
• Precipition – process by which water falls from clouds to the
earth’s surface
• Runoff – water that flows over the land
• Ground water – water that soaks deep into soil and rock
1. Stages of the Water Cycle
Water Cycle: the continuous movement of water from the atmosphere to
the earth’s surface and back to the atmosphere again
• 6 ways water
moves in the water
cycle:
1. evaporation
2. transpiration
3. condensation
4. precipitation
5. runoff
6. groundwater
3
4
2
5
1
6
Back to 13.1
The Water Cycle
Evapotranspiration
Together the processes of evaporation and
transpiration are called evapotranspiration
2. Water Budget
Definition: gains and losses of water in a region
Negative budget
Factors that affect local water budget:
•
Temperature
•
Presence of vegetation
•
Wind
•
Amount and duration of rainfall
Positive budget
Back to 13.1
Earth’s Water Budget
• Precipitation = Income
• Evapotranspiration and runoff = expenses
The earth as a whole is balanced because the
amount of precipitation is equal to the
amount of evapotranspiration and runoff
• The local water budget usually is not
balanced
3. Water Conservation
3. New Supplies of Fresh Water
• Desalination
Back to 13.1
Life Without Water
The Water Cycle
13.2 River Systems
• Describe the way in which a river
develops.
• Explain how a stream causes
erosion.
• Describe youthful, mature, and old
river valleys.
Ahead to 13.3
River Systems
• A river system consists of
a main (trunk) stream and its
tributaries
• The land drained by these
streams is called the drainage
basin or watershed
• Ridges or areas of high
ground that separate
watersheds are called divides.
Watersheds of Virginia
Back to 13.2
1. Stream Development
• Headward Erosion: lengthening and branching of a
stream
1. Stream Development
Stream Piracy: the capture of a stream in one
watershed by a stream in another watershed
2. Channel Erosion—Stream Load
• Stream Load: the materials carried by a stream
– Suspended load (fine sand and silt carried by the water)
– Bed load (coarse sand and gravel that moves by sliding, rolling or saltation)
– Dissolved load (dissolved mineral matter)
2. Channel Erosion—
Discharge and Gradient
– Discharge: volume of water moved by a stream within a given
time at a given place
– Gradient: steepness of the slope
greater discharge=more erosion
less discharge=less erosion
2. Channel Erosion—
Discharge and Gradient
higher gradient =
higher velocity =
more erosion
lower gradient = lower velocity =
less erosion
2. Channel Erosion--Quiz
A
B
Which stream probably has greater discharge?
Which stream has a higher gradient?
B
A
Which stream has greater velocity?
A
Which stream is probably eroding its channel more quickly?
A
2. Channel Erosion—
Water and Wind Gaps
Water Gap
Water Gap
Water Gap:
deep notch left
where a stream
erodes through a
mountain as it is
uplifted
Wind Gap: a
water gap
through which
water no longer
flows
Back to 13.2
3. Stages of a River System
3. Stages of a River System
• Youthful River
►V-shaped valley, steep sides
►waterfalls and rapids common
3. Youthful Stage
Yellowstone River
3. Stages of a River System
Mature River
► Floodplain developed
► Few waterfalls and rapids
► Has meanders and oxbow lakes
► Lower gradient
3. Floodplain
Mature Stage
3. Meanders and Oxbow Lakes
Sevier River, TN
Sweetwater River, Wyoming
3. Oxbow Lake
• Definition: an abandoned meander loop
3. Stages of a River System
Old Stage
– Deposits more than erodes
– Forms a broad, flat plain
– Fewer tributaries than “Mature”
3. Stages of a River System
Sevier River, TN
3. Stages of a River System
Rejuvenated Stage
► Cuts deeper into the valley floor
► Slope of the land increased by movement of the earth’s crust
► Often has characteristics of youthful and mature stages combined
3. Stages of a River System
• Rejuvenated
Stage
3. Stages of a River System
• Rejuvenated Stage
abandoned meander
San Juan River, Utah
Back to 13.2
13.3 Stream Deposition
• List two types of stream deposition
and explain the differences between
them.
• Describe the change in a stream that
causes flooding.
• Identify direct and indirect methods
of flood control
1. Two Types of Stream Deposition
Delta—a fan-shaped deposit at the mouth of a stream
Mississippi River
Nile River
1. Two Types of Stream Deposition
Alluvial fan—a fan-shaped deposit at the base of a slope on land
Death Valley, California
1. Two Types of Stream Deposition
Differences between deltas and alluvial fans:
Deltas:
Deposited in water
Made up of mostly mud
Surface is relatively flat
Ganges River
Alluvial Fans:
Deposited on land
Made up of mostly sand
and gravel
Surface is sloping
Back to 13.3
2. Flood Deposits
Floodplain—part
of the valley floor
that may be covered
with water during a
flood
Natural Levees—
raised riverbank that
results when a river
deposits its load at the
river’s edges
Back to 13.3
3. Flood Control
Direct control:
– Dams
– Artificial levees
Devil’s Gate Dam, CA
Artificial levee on the Mississippi River
Back to 13.3