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
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?)
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
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
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
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)
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
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
