1. Chapter 16: The Fluvial
Processes
McKnight’s Physical Geography:
A Landscape Appreciation,
Tenth Edition, Hess

2. The Fluvial Processes
• The Impact of Fluvial Processes on the
Landscape
• Streams and Stream Systems
• Stream Channels
• Structural Relationships
• The Shaping and Reshaping of Valleys
• Floodplains
• Theories of Landform Development
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3. The Impact of Fluvial Processes
on the Landscape
• Moving water is
widespread
• Effective as an agent of
erosion and deposition
• Influence on landscape
dominant
• Smoothes irregularities
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Figure 16-1

4. Streams and Stream Systems
• Any channeled flow of water is a stream
• Fluvial processes are those which involve running
water
• Unchanneled downslope movement of water—
overland flow
• Channeled movement of water—streamflow
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5. Streams and Stream Systems
• Valleys and interfluves
– Valley—portion of terrain in
which a drainage system is
established
– Interfluve—higher land
above valley walls that
separates adjacent valleys
• Drainage basins
– Watersheds
– Areas that drain to the
valley
– Drainage divide
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Figure 16-2

6. Streams and Stream Systems
• Stream orders
– Small streams join larger
ones
– Relationship called stream
orders
– First order versus second
and third order
– Smaller numbers in stream
order are more frequent
– Larger numbers are longer
in length and watershed
order
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Figure 16-4

7. Streams and Stream Systems
• Fluvial erosion and deposition
– Splash erosion
– Sheet erosion
– Rill erosion
– Gully erosion
• Erosion by streamflow
– Once channeled, erosion
is greatly enhanced
– Erosion increased by debris
the streamflow picks up
– Chemical weathering—corrosion
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Figure 16-6

8. Streams and Stream Systems
• Perennial and intermittent streams
– Perennial streams—permanent, in humid regions
– Intermittent streams—seasonal
– Ephemeral streams
• The role of floods
– Amount of water in a stream, discharge
– Most excavating of valleys accomplished during
floods
– Stream gages used to measure flow characteristics
– Flood recurrence intervals (i.e., the “100-year flood”)
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9. Stream Channels
• Streamflow normally
confined to channels, giving
it a three-dimensional
complexity
• Friction effect of flow along
bottom and sides of
channel
• Highly turbulent flow
irregularities produce local
currents which modify
streamflow
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Figure 16-11

10. Stream Channels
• Stream channel patterns, four
categories
– Straight channels: short and
indicative of strong geologic
structure control
– Sinuous channels: irregular and
gentle curvature that is sinuous
in appearance
– Meandering channels: highly
variable curvature
– Braided streams: multiple
interwoven channels separated
by loose bars or islands
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Figure 16-14

11. Structural Relationships
• Stream development
affected by many factors
• Most important factor is
geologic-topographic
structure
• Consequent versus
subsequent streams
• Antecedent streams—those
which existed before new
uplift occurs
• Superimposed streams
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Figure 16-16

12. Structural Relationships
• Stream drainage patterns
– Dendritic pattern: treelike
pattern with random merging
of streams
– Trellis pattern: forms in areas
of hard and soft bedrock in
close contact, shape modified
by structure of bedrock
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Figure 16-19

13. Structural Relationships
• Stream drainage patterns
(cont.)
– Radial pattern: streams
descend a concentric uplift
– Centripetal pattern: streams
converge into a uniform basin
– Annular pattern: forms in
areas of hard and soft domes
or basins, flow follows soft
bedrock and is confined by
hard bedrock
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Figure 16-23

14. The Shaping and Reshaping
of Valleys
• Valley deepening
– Downcutting—hydraulic power of
the moving water to lower the
streambed
– Base level—lower limit to the
amount of downcutting that can
occur—ultimate base level is sea
level
– Knickpoints—channel irregularities
such as rapids and waterfalls
– Knickpoint migration
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Figure 16-25

15. The Shaping and Reshaping
of Valleys
• Valley widening
– Widening slows when
above the base level
– As gradient decreases,
stream flow meanders and
lateral erosion occurs
– Water moves fastest on
outside of curves (cut bank)
– Slowest water on inside of
curves accumulates
alluvium (point bar)
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Figure 16-28

16. The Shaping and Reshaping
of Valleys
• Valley lengthening
– Headward erosion: fast
moving water from slope
break between interfluve
and valley wall causes
material collapse
– Results in decrease of
interfluve area and increase
in valley area
– Causes a headward
extension of the valley into
the interfluve area
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Figure 16-29

17. The Shaping and Reshaping
of Valleys
• Stream capture
– Headward erosion causes
one stream to be diverted to
the basin of another stream
naturally
– Captor versus captured
stream
– Beheaded stream
– Elbow of capture
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Figure 16-32

18. The Shaping and Reshaping
of Valleys
• Delta formation
– Slowed flow when it
reaches an ocean or lake
results in deposited
sediment
– Debris builds up and
forms a delta
– Distributaries
• Deposition in valleys
– Aggradation
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Figure 16-34

19. Floodplains
• Low-lying near flat alluvial
valley floor that is
periodically inundated with
floodwaters
• Floodplain landforms
– Bluffs
– Cutoff meander
– Oxbow lake
– Meander scars
– Natural levees
– Backswamps
– Yazoo streams
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Figure 16-38

20. Floodplains
• Modifying rivers to control
flooding
– Humans live on floodplains
due to flat land, abundant
water, and productive soils
– Manmade levees, dams,
and overflow floodways
created to avert disaster
– Example of the Mississippi
River
– Human-induced changes to
the deltas and floodplains
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Figure 16-42

21. Stream Rejuvenation
• Lowering of sea level during
ice ages or increase of
elevation from tectonic uplift
increases gradients
• Gradient increases restart or
rejuvenate vertical incision
by streams
• Stream terraces
• Entrenched meanders
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Figure 16-43

22. Theories of Landform
Development
• Davis’s geomorphic cycle
– Continuous sequence of uplift,
fluvial erosion, and denudation
– Youth stage, streams become
established and drainage
pattern develops
– Mature stage, streams approach
equilibrium
– Old age stage, erosion reduces
landscape to near base level
– Rejuvenation, new uplift restarts
the cycle
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Figure 16-45

23. Theories of Landform
Development
• Penck’s Theory of Crustal
Change and Slope
Development
– Criticisms of Davis’
geomorphic cycle
– Stated the land slope has a
parallel retreat, same slope
angle over time
– Many ideas have been
substantiated by
subsequent works
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Figure 16-46

24. Theories of Landform
Development
• Equilibrium theory
– Variations in influence of crustal movement and resistance
of underlying rock
– Slope forms adjust to geomorphic processes to achieve
energy balance
– Shortcomings in areas that are tectonically stable
– Prime theory used today
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Figure 16-47

25. Summary
• Fluvial processes are those which involve moving water
• Fluvial processes impact the landscape through erosion
and deposition
• Valleys, interfluves, and drainage basins describe the
impacts of fluvial processes on landscape
• Stream orders help describe the structure of stream
systems
• Streams affect the landscape through numerous types
of erosion and deposition
• Friction along stream channels and turbulence within the
channels affects their patterns
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26. Summary
• There are four primary types of stream channels
• Consequent and subsequent streams develop along
areas of new land formation
• Antecedent and superimposed streams result from slow
uplift of land affecting the pattern
• There are five patterns of stream drainage
• Streams affect valleys by both widening them and
deepening them through downcutting
• The base level is the lowest level at which a stream will
downcut
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27. Summary
• Knickpoints are irregularities in the channel flow, such as
waterfalls or rapids
• Valleys can be lengthened by headward erosion, stream
capture, and delta formation
• Floodplains are flat land areas that have fertile soil but
are prone to occasional flooding from nearby streams
• Numerous landforms related to floodplains exist
• Stream rejuvenation occurs when uplift increases the
slope gradient of a stream
• There are numerous theories of landform development
and their relationship to fluvial processes
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