Fluvial Processes
(Chapter 16)
The Fluvial Processes
Fundamental Concepts
Stream Systems
Stream Channels
Valleys
Stream Rejuvenation
Theories of Landform Development
Fundamental Concepts
Valleys and Interfluves
Drainage Basins
Drainage Patterns
1
Valleys and Interfluves (divides)
Figure 16-2
Drainage Basins
“nested”
Figure 16-3
Stream Systems
Stream Order
Erosion and Deposition
Overland Flow and Streamflow Erosion
Transportation and Stream Load
Deposition
Time and the River
Discharge
Perennial and Ephemeral Streams
2
Stream Order
Figure 16-4
Drainage Patterns
Dendritic Pattern
Trellis Pattern
Figures 16-A and 16-B
Fluvial erosion and deposition
Overland flow
• Splash erosion
• Sheet erosion
• Rills, rill erosion
• Gullies
3
Streamflow Erosion
Figure 16-7
Stream flow erosion – sediment load
!! Abrasion !!
Figure 16-8
Stream flow - discharge
Total volume of water that passes a given point in a
stream per unit time
Discharge (m3/s)
= width (m) × depth (m) × average velocity (m/s)
Q=wxdxv
4
Stream flow erosion – sediment load
Competence - measure of largest
particle size that can be transported
(proportional to v2)
Capacity – total volume of sediment
that can be carried at a given point in
the stream channel (proportional to V
and Q)
Stream flow - deposition
Erosion, v high
Stream profile
Deposition, v low
“Alluvium”
Time dependent behavior of streams
Seasonal variations of discharge
perennial
ephemeral
intermittent
Figure 16-9
5
Stream Channels
Channel Flow
Channel Patterns
Straight
Meandering
Braided
Channel Flow – laminar flow
Low velocity
Parallel streamlines
Figure 16-11
Channel Flow – turbulent
6
Channel Pattern:
Straight and Meandering
Figure 16-13
Channel Pattern: Braided
Figure 16-14
Shaping and Reshaping Valleys
Valley Deepening
Valley Widening
Valley Lengthening
Valley Deposition
Floodplains
7
Valley deepening
Vertical erosion, v high
Stream profile
Lateral erosion
and deposition, v low
Base level
Headward Erosion
Figures 16-20
Stream
Capture
Figure 16-G
8
Base Level
Figure 16-15
Knickpoints
Figure 16-16
Niagra Falls
9
Lateral Erosion
Figure 16-17
Lateral erosion
Figure 16-18
Floodplain
LandformsFloodplain
Landforms
Figure 16-27
10
Formation of Oxbow Lakes
Levees
Stream
profile
Base level = sea level
11
Stream
profile
Stream rejuvenation
Base level =
new sea level
Figure 16-28
Stream Rejuvenation:
Stream Terraces
Stream rejuvenation: entrenched meanders
Figure 16-29
12
Deltas
Location of significant sedimentation -where a river meet the sea.
Typical Large Marine Delta
Mississippi Delta
Fig. 13.26
13
Shifting Mississippi
River Delta Over the
Past 6000 Years
Largest Deltas & Delta-less Rivers
Figure 16-23
Theories of Landform
Development
The Geomorphic Cycle
Crustal Change and Slope Development
Equilibrium Theory
14
The Geomorphic Cycle (Morris Davis)
Initial surface uplifted
Youth
Maturity
Old Age
Peneplain
. . . new uplift
Crustal Change and Slope Development
- No peneplains
- Some erosion has to occur in initial uplift
- Evidence of stages weak at best
- Slopes not convex (not downcutting)
- Slope retreat parallel (Penck)
Equilibrium Theory
- Resistance of underlying materials varies significantly
- Harder rocks give steeper slopes, softer rocks gentler slopes
(Davis and Penck questioned)
- Erosion and uplift often in equilibrium
- Potential problems in tectonically stable areas
and limited streamflow (deserts)
Figure 16-32
15
End
16