1. Fluvial Geomorphology
Ecological Perspective
(1) Sediment size distribution
(2) Channel Form
X-sec
Planform
Basin
Downstream changes
Drainage pattern
Channel size
(3) Sediment movement
Distance
Elevation

2. Fluvial Geomorphology
Definition:
Fluvial --> “Of or found near a river”
Geomorpholgy --> study of Earth’s physical features
There is a dynamic balance between Flow regime (Q) Sediment regime (Qs)
Maintains the shape of the channel
What happens if Q >> Qs??
Depends on ‘transport capacity’ of channel (function of how steep channel slope is)

3. Fluvial Geomorphology
Water moves sediment during higher flows
Sediment gets stored during lower flows
Movement and Storage
From Ecological Perspective
(1) Sediment size distribution
(2) Channel Form
(3) Sediment movement
Habitat Structure
Habitat Dynamics

4. (1) SEDIMENT SIZE Wentworth Scale (Table 3.1) Particle size names:
Boulder, Cobble, Pebble, Gravel, Sand, Silt, Clay
Phi (f) value is -log2 scale for particle size
from Boulder (< -8) to silt > 5

5. (2) CHANNEL FORM or MORPHOLOGY
3 ways to view Channel Form
Cross-section of stream (local or transect scale)
Planform (reach scale)
Longitudinal (whole basin)
Controls on channel geometry
Discharge
Bed mobility
Bank stability
Can you think of factors that influence these?

6. (2) CHANNEL FORM or MORPHOLOGY
A) View#1: Cross-section
Channel geometry
Width, average depth, wetted perimeter
Channel occurs in valley
Floodplain
Terrace
Hillslope

7. B) View #2: Planform Channel geometry:
At “Reach Scale”: ~20 x channel width
Channel geometry:
average Width
average Depth
Gradient or Slope (S)
S = Dy/ Dx = drop in elevation with distance
Sinuosity = channel (thalweg) length / downvalley length [draw on board]
number of channels, etc.

8. 4 channel types defined at reach scale, based on 3 features
Number of channels
Channel stability
Sinuosity
photo: S. Hillebrand. U.S. Fish & Wildlife Service Digital Library System
single channel types
Straight (Sinuosity << 1.5)
Meandering (Sinuosity > 1.5)

9. multiple channel types
Braided
Qs >> Q
… channels unstable, move during floods
Anastomosing / Anabranching Cohesive banks.
… channels stable, don’t move
photo: © Michael Collier. Image source: Earth Science World Image Bank photo ixvt9i

10. How do meanders form? Differential erosion Cut off At a point in time
Movement through time
Cut off

11. Meander scaling laws

12. Sine curves (meanders) represent the most uniform distribution of change of energy dissipation along a curve.
From Leopold (1994, A View of the River)

13. C) View#3: Whole Basin scale
Perspective of Downstream Changes in …
Discharge
Stream gradient
Sediment grain-size
Influence of riparian
Distance
Elevation
outlet
max
source
High gradient
Width
Depth
Velocity (why?)
Low gradient

14. More scaling relations (Fig.3.3 text)
Low order
High order W
What changes fastest downstream? D
Is average velocity greater in large river than in small stream? U

15. Perspective of Drainage Pattern
Reflect geology mostly

16. Channel Classification at whole basin scale
2 Classifications (Fig. 2.1 Knighton):
Horton/Strahler (1945, 1952) - Stream Order
Shreve (1967) - Link Order
For point X, what is:
stream order?
link order? X

17. Scaling Relations (Fig. 2.1 Knighton)