Download River morphology and process class

River morphology and
process class
1.
consider physics of flow and erosion
2.
review river taxonomy
3.
examine the germane processes that control the shape
of river channels
4.
consider the graded profile
5.
consider the impact of floods and tectonic setting on
river channels
Gravity = driving force
Solar = energy source
• Gravity responsible for movement of water down
gradient, PE = mgh ~  h
• Precipitation maintains supply of fluid, driven by solar
forcing
• Tectonics maintains gradient, driven by erosion and
endogenic forces
• Consider fluid forces acting on sediment, critical
shear stress (crit, need to detach grains
• Balance of erosion, sediment supply shapes
channels
1
Hujlstom Diagram
1
1
MODES OF SEDIMENT
TRANSPORT
• Sliding
• Rolling
• Saltation
• SHOW FLASH MOVIE
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Taxomony
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2
Downstream
Organization
2
Channel Mobility
Watts Branch, MD
2/3
Flow is not uniform in plan view
3
Water velocity is not uniform
with depth
Consider friction and laminar flow;
mean velocity at 0.6 d
Idealized
flow
patterns
Dye tracing
Alluvial,
meandering
river
3
Graded profile, idealized form
• rivers will try and adjust to minimize energy gradient
• tectonics and climate change get in the way
Can the river
keep up?
•Gorges reflect cutting
•Knick zones reflect inability to cut
quickly enough
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Taiwan
What does climate change do?
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Glacial hanging valleys,
bedrock channel erosion
Gaysville before the flood
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1927 flood - Gaysville, VT - after