1. McKnight's Physical Geography
Lectures
Chapter 16
Fluvial Processes
Modified by AJ Allred for Geography 1000
Salt Lake Community College
Original by Andrew Mercer
Mississippi State University
© 2014 Pearson Education, Inc.

2. 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.

3. 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.

4. 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

5. Streams and Stream Systems
Stream order
1 = small streams
2 = larger streams
3 = small rivers
4 = major rivers
[Insert Fig p. 376]

6. 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

7. Transportation - bed load, dissolved, and suspended
Stream competence – particle size a stream can transport
Stream capacity – amount of solid material a stream can transport

8. 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

9. Streams and Stream Systems
Hard-surfacing in dry country and urban areas greatly concentrates flood water.
What is the “100-year” flood program?

10. Straight channels – steeper terrain – water finds an easy slope
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.

11. 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

12. 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)

13. Structural Relationships
Antecedent streams – those that existed before new uplift occurs

14. Antecedent stream persisted in cutting its same path even as mountains grew up underneath.

15. 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

16. 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

17. 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.

18. Living near water can be hazardous
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