Grotzinger • Jordan
Understanding Earth
Sixth Edition
Chapter 18:
STREAM TRANSPORT
From Mountains to Oceans
© 2011 by W. H. Freeman and Company
Chapter 18
Stream
Transport:
From Mountains
to Oceans
About Stream Transport
• Streams and rivers are major geological
agents of change in landscapes.
• Streams are any flowing body of water,
but rivers are major branches of a
stream system.
• Stream flow is related to the interaction
of plate tectonic and climate systems.
Lecture Outline
1. The form of streams
2. Where do streams begin? How running
water erodes solid rock
3. How currents flow and transport
sediment
4. Deltas: the mouths of rivers
5. Streams as geosystems
1. The Form of Streams
● The three basic parts of a stream
● valley (sloping area around
the stream)
● channel (bottom of valley)
● floodplain (flat area in valley
level with top of channel)
Stream
Valleys,
Channels,
and
Floodplains
Stream
Valleys,
Channels,
and
Floodplains:
Incised
Meanders
of the
San Juan
River, Utah
1. The Form of Streams
● Channel patterns
● meanders (low sediment load,
low velocity)
● oxbow lakes
● point bars and cut banks
● braided streams (high sediment
load, high velocity)
Stream
Valleys,
Channels,
and
Floodplains:
Meandering
Streams
Low-velocity, low-sediment
streams form meanders.
Meanders shift from side to
side in a snaking motion.
The current is faster at outside
banks, which are eroded.
Stream
Valleys,
Channels,
and
Floodplains:
Meandering
Streams
Low-velocity, low-sediment
streams form meanders.
Meanders shift from side to
side in a snaking motion.
The current is faster at outside
banks, which are eroded.
Sediments get deposited in
inside banks forming point
bars.
The bends grow closer and
the point bars bigger.
Point bar
During a major flood, the
river cuts across the loop.
The abandoned loop remains
as an oxbow lake.
Stream Valleys, Channels, and Floodplains:
A Meandering River in Alaska
Stream Valleys, Channels, and Floodplains:
An Oxbow Lake in Montana
Stream Valleys, Channels, and Floodplains:
Braided Stream in Alaska
1. The Form of Streams
● The stream floodplain
● fine-grained sediment layers
● agricultural resource
● natural levees
Stream
Floodplains
Stream
Floodplains
Stream
Floodplains
Stream
Valleys,
Channels,
and
Floodplains:
Natural
Levees
of the
Mississippi
Delta
Drainage Networks
● Drainage divides and basins
● drainage networks
● dendritic
● rectangular
● trellis
● radial
Drainage
Networks:
The
Drainage
Divide
Drainage
Networks:
Example
of the
Drainage
Basin
Drainage Networks: Stream Patterns
Drainage Networks
● Drainage patterns and geologic
history
● antecedent streams
● superposed streams
Drainage Networks:
Drainage Patterns and Geologic History
Drainage
Patterns
and Geologic
History:
Example of an
Antecedent
Stream –
the Delaware
Water Gap,
Pennsylvania – New Jersey
1. The Form of Streams
Thought questions for this chapter
You live in a town on a meander bend of a river. An
engineer proposes that your town invest in new, higher
artificial levees to prevent the meander bend from being
cut off. Give the arguments, pro and con, for and against
this investment.
What kind of drainage network do you think has been
established on Mt. St. Helens since the 1980 eruption?
Define the drainage basin where you live in terms of the
divides and drainage networks.
Thought questions for this chapter
The Delaware Water Gap is a steep, narrow valley cut
through a structurally deformed high ridge in the
Appalachian Mountains. How could it have formed?
2. How Running Water
Erodes Solid Rock
● Gullies and headward erosion
● Abrasion and wearing away
● potholes
● Chemical and physical weathering
● Undercutting action of currents
How
Running
Water
Erodes
Solid Rock:
Gullies
and
Headward
Erosion
How
Running
Water
Erodes
Solid
Rock:
Potholes
3. How Currents Flow and
Transport Sediment
● Two kinds of fluid flow
● laminar
● turbulent
● Factors affecting laminar/turbulent
● velocity, depth, and viscosity
3. How Currents Flow and
Transport Sediment
3. How Currents Flow and
Transport Sediment
3. How Currents Flow and
Transport Sediment
● Erosion and sediment transport
● suspended load
● bed load
● Competence and capacity
● velocity and volume of flow
3. How Currents Flow and
Transport Sediment
3. How Currents Flow and
Transport Sediment
● Settling of suspended sediment
● saltation
● settling velocity
3. How Currents Flow and
Transport Sediment
3. How Currents Flow and
Transport Sediment
● Sediment bed forms
● dunes
● ripples
3. How Currents Flow and
Transport Sediment
Thought questions for this chapter
Why might the flow of a very small, shallow stream be
laminar in winter and turbulent in summer?
Describe and compare the river floodplain and valley
above and below the waterfall shown in Figure 18.13.
In some places, engineers have artificially straightened a
meandering stream. If such a straightened stream were
then left free to adjust its course naturally, what changes
would you expect?
4. Deltas: The Mouths of Rivers
● Delta sedimentation
● distributaries
● bays and marshes
● bars
4. Deltas: The Mouths of Rivers
● Delta bedding structure
● topset
● foreset
● bottomset
4. Deltas: The Mouths of Rivers –
Delta Sedimentation and Bedding
4. Deltas: The Mouths of Rivers
● The growth of deltas
● addition of sediment
● The effect of tides, waves, and
tectonics
● shape and size
The
Growth
of Deltas:
The
Mississippi
River
Delta
sedimentation
The
Growth
of Deltas:
The
Mississippi
River
Delta
Thought questions for this chapter
A major river, which carries a heavy sediment load, has no
delta where it enters the ocean. What conditions might be
responsible for the lack of a delta?
5. Streams as Geosystems
● Stream behavior: discharge
●Q=AxV
● Effect of tributaries on streams
● Q increases downstream
5. Streams as Geosystems
Glaciers
Dendritic
drainage
Lake
Waterfall
Rapids
Braided
channel
Midstream
sandbar
Point bar
Cut bank
Terraced
floodplain
Oxbow
lake
Meandering
channel
Swamp
and marsh
Subsidence occurs
in deltas.
Distributary
channel
5. Streams as Geosystems
Rainfall and snowmelt gather
to create streams and rivers.
Glaciers
Dendritic
drainage
Lake
Waterfall
Rapids
Braided
channel
Midstream
sandbar
Point bar
Cut bank
Terraced
floodplain
Oxbow
lake
Meandering
channel
Swamp
and marsh
Subsidence occurs
in deltas.
Distributary
channel
5. Streams as Geosystems
Rainfall and snowmelt gather
to create streams and rivers.
Glaciers
Dendritic
drainage
Coarsegrained
sediments
Incised
bedrock
Lake
Waterfall
Rapids
Braided
channel
Midstream
sandbar
Point bar
Cut bank
Terraced
floodplain
Oxbow
lake
Meandering
channel
Swamp
and marsh
Subsidence occurs
in deltas.
Distributary
channel
5. Streams as Geosystems
Rainfall and snowmelt gather
to create streams and rivers.
Glaciers
Dendritic
drainage
Coarsegrained
sediments
Incised
bedrock
Lake
Waterfall
Rapids
Slopes are steep and
only the coarsest sediments
are deposited.
Braided
channel
Midstream
sandbar
Point bar
Cut bank
Terraced
floodplain
Oxbow
lake
Meandering
channel
Swamp
and marsh
Subsidence occurs
in deltas.
Distributary
channel
5. Streams as Geosystems
Rainfall and snowmelt gather
to create streams and rivers.
Glaciers
Lake
Waterfalls
develop where
rocks resist
erosion or where
faulting offsets
the streambed.
Dendritic
drainage
Coarsegrained
sediments
Incised
bedrock
Waterfall
Rapids
Slopes are steep and
only the coarsest sediments
are deposited.
Braided
channel
Midstream
sandbar
Point bar
Cut bank
Terraced
floodplain
Oxbow
lake
Meandering
channel
Swamp
and marsh
Subsidence occurs
in deltas.
Distributary
channel
5. Streams as Geosystems
Rainfall and snowmelt gather
to create streams and rivers.
Glaciers
Lake
Waterfalls
develop where
rocks resist
erosion or where
faulting offsets
the streambed.
As the slope
decreases,
rivers form
braided channels.
Dendritic
drainage
Coarsegrained
sediments
Incised
bedrock
Waterfall
Rapids
Slopes are steep and
only the coarsest sediments
are deposited.
Braided
channel
Midstream
sandbar
Point bar
Cut bank
Terraced
floodplain
Oxbow
lake
Meandering
channel
Swamp
and marsh
Subsidence occurs
in deltas.
Distributary
channel
5. Streams as Geosystems
Rainfall and snowmelt gather
to create streams and rivers.
Dendritic
drainage
Glaciers
Lake
Waterfalls
develop where
rocks resist
erosion or where
faulting offsets
the streambed.
Coarsegrained
sediments
Incised
bedrock
Waterfall
Rapids
As the slope
decreases,
rivers form
braided channels. Natural
levee
Slopes are steep and
only the coarsest sediments
are deposited.
Braided
channel
Midstream
sandbar
Point bar
Cut bank
Terraced
floodplain
Oxbow
lake
Meandering
channel
Swamp
and marsh
Older sediments
Fine-grained
sediments
of silt and clay
Subsidence occurs
in deltas.
Distributary
channel
5. Streams as Geosystems
Rainfall and snowmelt gather
to create streams and rivers.
Dendritic
drainage
Glaciers
Lake
Waterfalls
develop where
rocks resist
erosion or where
faulting offsets
the streambed.
Coarsegrained
sediments
Incised
bedrock
Waterfall
Rapids
As the slope
decreases,
rivers form
braided channels. Natural
levee
Slopes are steep and
only the coarsest sediments
are deposited.
Braided
channel
Midstream
sandbar
Point bar
Cut bank
Terraced
floodplain
Oxbow
lake
Meandering
channel
Swamp
and marsh
Sediments may be eroded
to produce terraces.
Older sediments
Fine-grained
sediments
of silt and clay
Subsidence occurs
in deltas.
Distributary
channel
5. Streams as Geosystems
Rainfall and snowmelt gather
to create streams and rivers.
Dendritic
drainage
Glaciers
Lake
Waterfalls
develop where
rocks resist
erosion or where
faulting offsets
the streambed.
Coarsegrained
sediments
Incised
bedrock
Waterfall
Rapids
As the slope
decreases,
rivers form
braided channels. Natural
levee
Slopes are steep and
only the coarsest sediments
are deposited.
Braided
channel
Midstream
sandbar
Point bar
Coarse
sediments
Fine-grained
sediments
Coarse deposits
from older rivers
Cut bank
Terraced
floodplain
Oxbow
lake
Meandering
channel
Swamp
and marsh
Sediments may be eroded
to produce terraces.
Older sediments
Fine-grained
sediments
of silt and clay
Subsidence occurs
in deltas.
Distributary
channel
5. Streams as Geosystems
Rainfall and snowmelt gather
to create streams and rivers.
Dendritic
drainage
Glaciers
Lake
Waterfalls
develop where
rocks resist
erosion or where
faulting offsets
the streambed.
Meandering channels form.
Coarse-grained sediments
are deposited.
Coarsegrained
sediments
Incised
bedrock
Waterfall
Rapids
As the slope
decreases,
rivers form
braided channels. Natural
levee
Slopes are steep and
only the coarsest sediments
are deposited.
Braided
channel
Midstream
sandbar
Point bar
Coarse
sediments
Fine-grained
sediments
Coarse deposits
from older rivers
Cut bank
Terraced
floodplain
Oxbow
lake
Meandering
channel
Swamp
and marsh
Sediments may be eroded
to produce terraces.
Older sediments
Fine-grained
sediments
of silt and clay
Subsidence occurs
in deltas.
Distributary
channel
5. Streams as Geosystems
Rainfall and snowmelt gather
to create streams and rivers.
Dendritic
drainage
Glaciers
Lake
Waterfalls
develop where
rocks resist
erosion or where
faulting offsets
the streambed.
Meandering channels form.
Coarse-grained sediments
are deposited.
Coarsegrained
sediments
Incised
bedrock
Waterfall
Rapids
As the slope
decreases,
rivers form
braided channels. Natural
levee
Slopes are steep and
only the coarsest sediments
are deposited.
Braided
channel
Midstream
sandbar
Point bar
Coarse
sediments
Fine-grained
sediments
Coarse deposits
from older rivers
Cut bank
Terraced
floodplain
Meandering
channel
Oxbow
lake
Natural levees maintain
the flow of water. When
rivers flood, sediments
are able to fill
surrounding areas.
Swamp
and marsh
Sediments may be eroded
to produce terraces.
Older sediments
Fine-grained
sediments
of silt and clay
Subsidence occurs
in deltas.
Distributary
channel
5. Streams as Geosystems
Rainfall and snowmelt gather
to create streams and rivers.
Dendritic
drainage
Glaciers
Lake
Waterfalls
develop where
rocks resist
erosion or where
faulting offsets
the streambed.
Meandering channels form.
Coarse-grained sediments
are deposited.
Coarsegrained
sediments
Incised
bedrock
Waterfall
Rapids
As the slope
decreases,
rivers form
braided channels. Natural
levee
Slopes are steep and
only the coarsest sediments
are deposited.
Braided
channel
Midstream
sandbar
Point bar
Coarse
sediments
Fine-grained
sediments
Coarse deposits
from older rivers
Cut bank
Terraced
floodplain
Meandering
channel
Oxbow
lake
Natural levees maintain
the flow of water. When
rivers flood, sediments
are able to fill
surrounding areas.
Swamp
and marsh
Sediments may be eroded
to produce terraces.
Older sediments
Fine-grained
sediments
of silt and clay
Subsidence occurs
in deltas.
Distributary
channel
The current slows and deposits
its fine sediments as a delta.
5. Streams as Geosystems:
Q=AxV
5. Streams as Geosystems:
Q=AxV
1 m/s
3m
10 m
A river with lower cross-sectional area
and velocity has a lower discharge…
1 m/s
3m
10 m
5. Streams as Geosystems:
Q=AxV
2 m/s
10 m
9m
…than a river with higher cross-sectional
area and velocity.
2 m/s
10 m
9m
5. Streams as Geosystems
● Floods
● recurrence interval
● climate
● width of floodplain
● size of channel
Annual maximum discharge(m3/s)
Probability of occurrence (in any given year)
A large flood of 1800 m3/s
has a probability of 10
percent and a recurrence
interval of about 12 years.
Recurrence interval (years)
5. Streams as Geosystems
● Longitudinal profile and the concept
of grade
● equilibrium of stream flow
● topography (slope)
● climate
● streamflow (Q and V)
● resistance of rock
● sediment load
Altitude above
sea level (m)
Stream
Profile
Distance from headwaters of river (km)
Source
Mouth
Stream
Profile
Altitude above
sea level (m)
Rivers are steep
near the head…
Distance from headwaters of river (km)
Source
Mouth
Stream
Profile
Altitude above
sea level (m)
Rivers are steep
near the head…
…and almost flat
at the mouth.
Distance from headwaters of river (km)
Source
Mouth
5. Streams as Geosystems
● Longitudinal profile and the concept
of grade
● changes in base level
(the quest for equilibrium)
● graded stream profiles
(the quest for a variable balance)
5. Streams as Geosystems
TIME 1
A mature stream has developed
a classic stream profile.
base level
5. Streams as Geosystems
TIME 2
A change in base levels
changes the profile.
new
base level
old
base level
5. Streams as Geosystems
TIME 3
Sediment is now deposited
in the lake.
5. Streams as Geosystems
TIME 4
Eventually, the original stream
profile is restored.
5. Streams as Geosystems
● Places where streams adjust
to changing conditions
rapidly
● alluvial fans
● terraces
5. Streams as Geosystems:
The Alluvial Fan
5. Streams as Geosystems:
Terraces
5. Streams as Geosystems
● The effect of climate
● temperatures
● rainfall
5. Streams as Geosystems
● Lakes
● “accidents” of the longitudinal
profile
● ephemeral
The
Lake in this
Instance,
man-made,
and its
effect
Thought questions for this chapter
If global warming produces a significant rise in sea level,
how will the longitudinal profiles of the world’s rivers be
affected?
In the first few years after a dam was built on it, a stream
severely eroded its channel downstream of the dam.
Could this erosion have been predicted?
Your hometown, built on a river floodplain, experienced a
50-year flood last year. What are the chances that another
flood of that magnitude will occur next year?
Key terms and concepts
Abrasion
Alluvial fan
Antecedent stream
Base level
Bed load
Bottomset bed
Braided stream
Capacity
Channel
Competence
Delta
Dendritic drainage
Discharge
Distributary
Divide
Key terms and concepts
Drainage basin
Drainage network
Dune
Flood
Floodplain
Foreset bed
Graded stream
Laminar flow
Longitudinal profile
Meander
Natural levee
Oxbow lake
Point bar
Pothole
Ripple
Key terms and concepts
Ripple
River
Saltation
Settling velocity
Stream
Superposed stream
Suspended load
Terrace
Topset bed
Tributary
Turbulent flow
Valley