Fluvial Geomorphology

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Fluvial Geomorphology
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Significance of fluvial processes

• water is ubiquitous landscape shaping agent
• rivers constitute important natural habitats
• river processes create significant natural
  hazards

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mountain river, western Cascades, Oregon
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meander bends, Itkillik River, Alaska
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braided channels, Chitina River, Alaska
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Outline

• River mechanics
• How do rivers respond to change?
• Example from Vermont

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River mechanics
Discharge amount of water carried by a river per
unit time
Discharge area x velocity area f(width,
depth) velocity f(slope, roughness)
Cross-section view
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River mechanics (continued)
Velocity varies across the channel cross-section
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River mechanics (continued)
Longitudinal view
Systematic changes in downstream direction -
slope, width, depth, velocity
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mountain river, western Cascades, Oregon
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meander bends, Itkillik River, Alaska
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River mechanics (continued)
Roughness changes systematically in the
downstream direction
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River mechanics (continued)
Form of the river changes characteristically
along the longitudinal profile hydraulic
geometry
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River mechanics (continued)
Sinuosity channel lengh (Lc) valley
length (Lv)
Lc
Lv
Plan view
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River mechanics (continued)
As slope decreases, river will tend to meander
laterally, creating a floodplain.
Floodplain
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How do rivers respond to change?
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Equilibrium concept
Rivers seek to attain a form that allows them to
balance force provided by the flow with
resistance provided by sediment
Adapted from Lane, 1965
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Channel adjustment
Excess water river degrades (deeper, narrower)
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Channel adjustment
Excess sediment river agrades (shallower, wider)
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Rivers attempt to reach some equilibrium between
erosive power of running water and resistance
offered by bed, banks (sediment)

• How? By altering their geometry...
• width
• depth
• roughness
• slope
• sinuosity

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Channel change in Vermont
From Kathleen Donna, Assessing Channel Change on
the Upper White River, Vermont University of
Vermont, M.A. Thesis, Dept of Geography, 2002
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Upper White River
White River watershed
Study area - Upper White River drainage basin
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Table 1 Sources and characteristics of black
and white aerial photography
Characteristics of black and white aerial
photography
1975
 
1990
 
1 Refers to mean daily discharge recorded at USGS
Station 01144000 on the date that air photos
were taken.

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Mapped land cover
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Mapped channel features
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Assessing channel change
Reach 1
Reach 3
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Assessing channel change
Reach 4
Reach 6
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Land cover change over time
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1939
120,000
1956
1975
1982
1990
2-gt5yr. 2-gt2yr.
1- gt10yr.
1- 10yr.
1-gt50yr.
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Channel change and restoration planning