The document provides an overview of fluvial geomorphology and stream processes. It discusses the three main processes streams perform: erosion, transportation, and deposition. It describes drainage systems and watersheds. Key factors that influence erosion rates are discussed, such as flow speed, turbulence, and the resistance of bedrock. The different forms that stream load is transported in are explained. Concepts around competence, capacity, and deposition of alluvium are introduced. Common stream flow patterns like meandering and braiding are covered. The document concludes by looking at how streams work towards establishing an equilibrium condition through processes like valley deepening, widening, and lengthening.

1. Chapter 11
Fluvial Geomorphology

2. Streams
The work that streams do:
• Erosion/Denudation
– Movement away of rock, rock
fragments and/or soil from its
original position
• Transportation
– Continuous movement of material
from one place to another
• Deposition
– Setting down (depositing) of eroded
and transported material

3. Drainage Systems
• Drainage system—A branched,
hierarchical network of
streams and tributaries
• Valley—Where a drainage
system is clearly established
• Interfluve—(“inter”=between,
“fluvia”= rivers) High ground
that separates valleys
• Drainage divide—The invisible
line separating two drainage
basins

4. Drainage basin
or Watershed
• A single network system; includes both the channeled
valley and any other land surface contributing overland
flow or groundwater to the stream
• Scale varies

5. Erosion
• Overland flow—
unchannelized flow of water
• Splash erosion—Raindrops
hitting exposed ground
surface, shifting individual
particles, which can then be
transported away

6. Overland Flow
• Sheet erosion—if there is very little ground
cover (vegetation), not much water may
infiltrate and sheet flow can occur, moving
particles downslope

7. Erosion
• Hydraulic action—The physical force of water
pounding on rocks and land materials, breaking
them apart
• Abrasion—Rock materials hitting the bed (bottom)
of the river and its banks (sides)
• Corrosion—The chemical action of water dissolving
minerals and rock material

8. How Quickly Erosion Occurs
Depends On…
• Flow Speed
• Turbulence
• Resistance of the bedrock

9. 1. Flow Speed

10. 1. Flow Speed
• Flow Speed
–The faster the water, the more force it has
–Faster water = more erosion

11. What makes the water go faster?

12. What makes the water go faster?
1. Steeper gradient

13. What makes the water go faster?
1. Steeper gradient
– Gradient—The rate of fall in elevation of the stream
surface in the downstream direction (as in 20 ft./mi.)

14. What makes the water go faster?
1. Steeper gradient
– Gradient—The rate of fall in elevation of the stream
surface in the downstream direction (as in 20 ft./mi.)
• Steeper gradient = faster flow = more erosion

15. What makes the water go faster?
1. Steeper gradient
– Gradient—The rate of fall in elevation of the stream
surface in the downstream direction (as in 20 ft./mi.)
• Steeper gradient = faster flow = more erosion
2. Volume of flow (discharge)

16. What makes the water go faster?
1. Steeper gradient
– Gradient—The rate of fall in elevation of the stream
surface in the downstream direction (as in 20 ft./mi.)
• Steeper gradient = faster flow = more erosion
2. Volume of flow (discharge)
– More water = higher speed = more erosion

17. What makes the water go faster?
1. Steeper gradient
– Gradient—The rate of fall in elevation of the stream
surface in the downstream direction (as in 20 ft./mi.)
• Steeper gradient = faster flow = more erosion
2. Volume of flow (discharge)
– More water = higher speed = more erosion
• Flood events move bigger material—and more of it!

18. What makes the water go faster?
1. Steeper gradient
– Gradient—The rate of fall in elevation of the stream
surface in the downstream direction (as in 20 ft./mi.)
• Steeper gradient = faster flow = more erosion
2. Volume of flow (discharge)
– More water = higher speed = more erosion
• Flood events move bigger material—and more of it!
3. Channel width—the narrower the channel, the
swifter the flow, for the same volume of water
(Remember the Venturi effect?)

19. How much erosive force?

20. How much erosive force?

21. How much erosive force?

22. How much erosive force?

23. 2. Turbulence

24. 2. Turbulence
• Water swirling and tossing, not smooth flow

25. 2. Turbulence
• Water swirling and tossing, not smooth flow
• Turbulence is determined by:
–Flow speed

26. 2. Turbulence
• Water swirling and tossing, not smooth flow
• Turbulence is determined by:
–Flow speed
•Faster flow = increased turbulence

27. 2. Turbulence
• Water swirling and tossing, not smooth flow
• Turbulence is determined by:
–Flow speed
•Faster flow = increased turbulence
–Roughness of the stream channel

28. 2. Turbulence
• Water swirling and tossing, not smooth flow
• Turbulence is determined by:
–Flow speed
•Faster flow = increased turbulence
–Roughness of the stream channel
•A rough, irregular channel = more turbulence

29. 2. Turbulence
• Water swirling and tossing, not smooth flow
• Turbulence is determined by:
–Flow speed
•Faster flow = increased turbulence
–Roughness of the stream channel
•A rough, irregular channel = more turbulence

30. 3. Resistance of bedrock
• More resistance (harder rocks)
= less erosion

31. Transportation: Stream Load
• Stream load (rock material transported by streams) is
carried in three forms:

32. Transportation: Stream Load
• Stream load (rock material transported by streams) is
carried in three forms:

33. Transportation: Stream Load
• Stream load (rock material transported by streams) is
carried in three forms:
1. Dissolved load—dissolved minerals carried in solution

34. Transportation: Stream Load
• Stream load (rock material transported by streams) is
carried in three forms:
1. Dissolved load—dissolved minerals carried in solution
2. Suspended load—small particles that never touch the
stream bed

35. Transportation: Stream Load
• Stream load (rock material transported by streams) is
carried in three forms:
1. Dissolved load—dissolved minerals carried in solution
2. Suspended load—small particles that never touch the
stream bed
3. Bedload—larger rock fragments that drag, roll, skip or
bounce along the stream bed

36. Transportation: Stream Load
• Stream load (rock material transported by streams) is
carried in three forms:
1. Dissolved load—dissolved minerals carried in solution
2. Suspended load—small particles that never touch the
stream bed
3. Bedload—larger rock fragments that drag, roll, skip or
bounce along the stream bed
• Material is picked
up, dropped and
picked up again

37. Transportation: Stream Load
• Stream load (rock material transported by streams) is
carried in three forms:
1. Dissolved load—dissolved minerals carried in solution
2. Suspended load—small particles that never touch the
stream bed
3. Bedload—larger rock fragments that drag, roll, skip or
bounce along the stream bed
• Material is picked
up, dropped and
picked up again

38. Transportation: Stream Load
• Stream load (rock material transported by streams) is
carried in three forms:
1. Dissolved load—dissolved minerals carried in solution
2. Suspended load—small particles that never touch the
stream bed
3. Bedload—larger rock fragments that drag, roll, skip or
bounce along the stream bed
• Material is picked
up, dropped and
picked up again

39. Transportation: Competence

40. Transportation: Competence
• The faster the stream is flowing, the larger
the particles it can transport

41. Transportation: Competence
• The faster the stream is flowing, the larger
the particles it can transport
• This measurement is called competence

42. Transportation: Competence
• The faster the stream is flowing, the larger
the particles it can transport
• This measurement is called competence
– Competence varies to the sixth power of the
water’s speed

43. Transportation: Competence
• The faster the stream is flowing, the larger
the particles it can transport
• This measurement is called competence
– Competence varies to the sixth power of the
water’s speed
If flow speed doubles:

44. Transportation: Competence
• The faster the stream is flowing, the larger
the particles it can transport
• This measurement is called competence
– Competence varies to the sixth power of the
water’s speed
If flow speed doubles:
26 = 64 times the size!

45. Transportation: Competence
• The faster the stream is flowing, the larger
the particles it can transport
• This measurement is called competence
– Competence varies to the sixth power of the
water’s speed
If flow speed doubles:
26 = 64 times the size!
– This is why flood events are so significant in
stream transportation

46. Transportation: Capacity

47. Transportation: Capacity
• Capacity—A measure of the amount of solid
material potentially transported (volume/time
past a given point: gal/sec)
• The capacity of a given stream depends on:

48. Transportation: Capacity
• Capacity—A measure of the amount of solid
material potentially transported (volume/time
past a given point: gal/sec)
• The capacity of a given stream depends on:
1. Water volume
(volume↑, capacity↑)

49. Transportation: Capacity
• Capacity—A measure of the amount of solid
material potentially transported (volume/time
past a given point: gal/sec)
• The capacity of a given stream depends on:
1. Water volume
(volume↑, capacity↑)
2. Flow speed
(flow speed↑, capacity↑)

50. Transportation: Capacity
• Capacity—A measure of the amount of solid
material potentially transported (volume/time
past a given point: gal/sec)
• The capacity of a given stream depends on:
1. Water volume
(volume↑, capacity↑)
2. Flow speed
(flow speed↑, capacity↑)
3. The type of load material

51. Transportation: Capacity
• Capacity—A measure of the amount of solid
material potentially transported (volume/time
past a given point: gal/sec)
• The capacity of a given stream depends on:
1. Water volume
(volume↑, capacity↑)
2. Flow speed
(flow speed↑, capacity↑)
3. The type of load material
(lighter material, capacity↑)

52. Deposition
• Deposition occurs when either flow speed or
volume decrease
• Conditions that cause deposition:
–Change in gradient
–Channel widening
–Change of direction
–Flowing into less active water

53. Deposition: Alluvium
• Alluvium—Any stream-deposited debris
–Sorting—Based on size (smaller particles carried
farther than large ones; as stream flow decreases,
larger particles will drop out of suspension first)

54. Sorting after a flood event
erosion

55. Sorting after a flood event

56. Sorting after a flood event
deposition

57. Sorting after a flood event
deposition
(particles settle biggest first, smallest last)

58. Deposition: Alluvium
• Alluvium
–Particle shape—Alluvial material is generally
smooth and round due to rocks hitting each other
and the stream bed; the longer it’s transported in
the stream, the more rounded and smooth a rock
will become

59. (some well-rounded alluvial deposits)

60. Stream Flow
• How does friction from the channel sides and
bottom affect stream flow?

61. Stream Flow
• Patterns
– Straight
– Sinuous
– Meandering
– Braided

62. Stream Flow
• Patterns
– Straight
– Sinuous
– Meandering
– Braided

63. Stream Flow
• Patterns
– Straight
– Sinuous
– Meandering
– Braided

64. Stream Flow
• Patterns
– Straight
– Sinuous
– Meandering
– Braided

65. Just like a lake, water balance must
be maintained, or the stream will
become an ephemeral stream

66. Equilibrium: A Graded Stream
• All factors are balanced (gravity, stream
load, deposition, down-cutting)
• A graded condition is more theoretical than
actual, because equilibrium is so difficult to
achieve—and maintain

67. Which processes happen as a stream
tries to attain a graded condition?
• Valley deepening
• Valley widening and flattening
• Valley lengthening

68. Valley Deepening:
Knickpoint Migration
• Downcutting progresses
upstream, until the
valley is all at one level

69. Valley Deepening:
Knickpoint Migration
• The Case of Niagara
Falls

70. Valley Widening and Flattening

72. Valley Widening and Flattening
The Role of Meanders

73. Meanders and Oxbow Lakes

74. Meanders and Oxbow Lakes

75. Can you find the oxbow lake?
Where is a cutoff about to form?

76. 34

77. Structures of a Floodplain

78. Structures of a Floodplain

79. Valley Lengthening:
Headward Erosion

80. Valley Lengthening:
Delta Formation and Distributaries

81. Valley Lengthening:
Delta Formation and Distributaries

82. Valley Lengthening:
Delta Formation and Distributaries

83. Valley Lengthening:
Delta Formation and Distributaries

84. Stream Rejuvination
and Entrenched Meanders

85. Stream Rejuvination
and Entrenched Meanders

86. Stream Rejuvination
and Entrenched Meanders

87. Next: Oceans