mcknight's physical geography lectures chapter 16 fluvial processes © 2014 pearson education,...
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McKnight's Physical Geography
Lectures
Chapter 16
Fluvial Processes
© 2014 Pearson Education, Inc.
Original by Andrew MercerMississippi State University
Modified by AJ Allred for Geography 1000
Salt Lake Community College
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Learning Goals of This Chapter• Differentiate between stream flow and overland flow.• Define valley, interfluve, drainage basin, watershed,
drainage divide, and tributary.• Determine the stream orders in a drainage network.• Explain erosion by stream flow and the three fractions of
stream loads.• Explain recurrence interval and 100-year flood, and
identify and explain the common misunderstanding about the latter.
• Describe the flow velocity in a cross section of a straight stream channel.
• Explain the circumstances that cause steams to develop sinuous, meandering, and braided channel patterns.
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Learning Goals of This Chapter
• Differentiate between competence and capacity of a stream.
• Differentiate between perennial, intermittent, and ephemeral streams.
• Define discharge and stream gage, and explain the differences in lag time and crest height on a hydrograph for an urban versus a rural area.
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Streams and Stream Systems
• Channeled flow of water – a stream
• Fluvial processes – those that involve running water
• Some water flows overland as a sheet, not in a stream channel
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Streams and Stream Systems
Stream order
•1 = small streams •2 = larger streams
•3 = small rivers•4 = major rivers
[Insert Fig. 16-4 p. 376]
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Streams and Stream Systems• Fluvial erosion and
deposition– Splash erosion is powerful
– Sheet erosion
• Erosion by stream flow– Once channeled, erosion is
greatly enhanced
– Chemical weathering – corrosion
These rocks in Asia are just like rocks in Utah
– heavily worn and eroded
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• Transportation - bed load, dissolved, and suspended
– Stream competence – particle size a stream can transport
– Stream capacity – amount of solid material a stream can transport
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Streams and Stream Systems• Deposition – streams eventually dump their loads
– Alluvium – stream deposited sediments
• Perennial and intermittent streams– Perennial streams – permanent, in humid regions
– Intermittent streams – seasonal
– Ephermal streams – flow only with occasional large storms
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Streams and Stream Systems
Hard-surfacing in dry country and
urban areas greatly concentrates flood
water.
What is the “100-year” flood program?
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Stream Channels
– Straight channels – steeper terrain –
water finds an easy slope
– Sinuous channels – winding meanders on shallow slopes. Water searching for a path to the ocean.
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Floodplains
• Low-lying near flat alluvial valley floor that is periodically inundated with flood waters
• Floodplain landforms– Bluffs
– Cutoff meander
– Oxbow lake
– Meander scars
– Natural levees
– Backswamps
– Yazoo streams
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The Shaping and Reshaping of Valleys
Valley widening
– Water moves fastest on outside of curves (cut bank)
– Slowest water on inside of curves accumulates alluvium (point bar)
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Structural Relationships
• Antecedent streams – those that existed before new uplift occurs
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Antecedent stream persisted in cutting its same path even as mountains grew up underneath.
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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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The Shaping and Reshaping of Valleys
“Knick Points”
Where under-cutting softer rock underneath eventually causes
surface failure.
The “knick point” gradually moves upstream by under-cutting erosion.
Example: Niagara Falls in New York
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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
• Alluvial fans – similar deposition at the bottom of the valley.
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Floodplains• Modifying rivers to control flooding
– Humans live on floodplains – flat land, abundant water, and productive soils
– Levees & dams for flood control
– Human changes to deltas and floodplains
Living near water can be hazardous