1. Chapter 6: Fluvial Landforms
Drainage systems
Origin of stream courses
Drainage patterns
Stream capture

2. Hypsometric curves and the stabilization of drainage basin form

3. Hortons’s hierarchy of
Drainage systems
stream ordering
Hortons’s hierarchy of
streams
lower order streams are:
shorter,
steeper,
drain smaller areas
Drainage density
D = L/A
measure of how well or poorly
a basin is drained by streams
4th order
drainage
basin

4. Drainage systems stream ordering Drainage density D = L/A
measure of how well or poorly
a basin is drained by streams
higher for steeply sloping,
low-permeability landscapes,
which promote runoff, gullying,
channeling.
lower for low-relief, high
permeabilty landscapes.
-what about karst?
drainage texture
-Note crenulated
contours
4th order
drainage
basin

5. Drainage systems
stream
ordering
what’s
outlined in
red?
yellow?

6. Origin of stream courses
Virgin land surface (new landscapes)
fresh volcanics
newly glaciated
emergent marine areas
recently uplifted terranes

7. Origin of stream courses
What determines the path taken by a stream on a
virgin land surface (new landscapes)?
slope of ground
consequent streams
random headward erosion
homogeneous materials
insequent streams
selective headward erosion
materials of varying resistance
subsequent streams

8. Drainage patterns Pattern Origin Characteristics Geology dendritic
insequent
random,
acute-angle junctions
homogeneous,
horizontal beds
trellis
subsequent
parallel streams,
high-angle junctions
heterogeneous,
tilted beds
rectangular / angular
high-angle junctions,
high-angle bends in
tributaries
jointed rocks
annular
circular patterns
breached domes
radial
consequent
streams flowing in all directions from
central high area
volcanic or intrusive domes

9. Drainage patterns Yangtze River, China NASA photo
Yemen (very dry climate)
Fluvial/drainage_patterns1a.htm
New Zealand, Wikepedia
Yangtze River, China
NASA photo

10. Drainage patterns

11. Drainage patterns

12. Stream capture Diversion of a stream’s flow from its
original channel to the channel of
a neighboring stream.

13. Stream capture Two types:
abstraction– faster rate of headward erosion on one side of drainage
divide because of steeper gradient or less resistant rocks.
intercession – lateral movement of meander bend intersects meander
bend of another stream.

14. Stream capture this is example of what type of stream capture?
where might we see
this in Appalachians?

15. The Hadhramawt Plateau of South Yemen exhibits a complex dendritic drainage pattern and excellent examples of "stream piracy." Wadi Hadhramawt opens into the sand-filled Ramlat Sabatayn in the southwest corner of the Rub-al-Khali (The Empty Quarter), yet drainage is toward the sea. The southern coast of the Arabian Peninsula is at the upper portion of the photograph. (S ; Gemini IV.)

16. Stream capture

18. Fluvial landforms Landform Origin Processes/ Materials floodplains
constructional
lateral and vertical accretion,
channel and overbank deposits
pediments
destructional
lateral planation,
sheet and rill wash,
weathering,
formation of graded surface
alluvial fans
deposition of coarse-grained sediments on land,
fanhead trenching,
mudflows
deltas
deposition in standing water,
turbidity currents,
birdfoot deltas

21. The Cycle of Erosion
introduced by Davis (1909), a foundational concept in geomorphology for many years, formed basis for interpreting landforms.
idealized sequence of landscape/landform evolution.
begins with uplifted, virgin landscape.
culminates with featureless plane eroded to base level.
in between passes through stages, each with a set of recognizable landforms.

22. The Cycle of Erosion

23. The Cycle of Erosion
sequence of forms: 1) youth 2) maturity 3) old age

24. The Cycle of Erosion Youthful stage initial drainage poorly developed
consequent drainage initiated
low drainage density
swamps and lakes
insequent drainage begins to develop
headward erosion and vertical downcutting dominant
steep stream gradients promote valley deepening
narrow, V-shaped valleys

25. The Cycle of Erosion Mature stage reduction in basin relief
streams become graded (adjust to load and discharge)
stream gradients reduced, valley widening accelerates
V-shaped valleys transition to flatter profiles
flood plains develop
valley sides and divides are smoothed and rounded

26. The Cycle of Erosion Old age – “penelplane”
gently sloping plane, just above
base level
very gradual transition between floodplain and valley walls
real examples hard to find—why?
uplifted peneplains?—erosional surfaces
complicated by existence of broad, flat surfaces not result of fluvial processes.

27. The Cycle of Erosion Stage Landscape Processes youthful
steep hillsides,
drainage divides predominant
V-shaped valleys
headward erosion,
stream downcutting
mature
rounded hills,
valley walls predominant
graded streams
broad floodplains
lateral erosion,
streams adjust to discharge/load
old age
“peneplane,”
close to base level
very low relief,
sluggish stream flow,
poor drainage

29. Cyclic stream terraces
former valley floors that lie above active stream channels.
result from:
uplift
change in base level
change in load/discharge
interrupts cycle of erosion

30. Types of cyclic stream terraces
cut-in-bedrock terraces
bedrock terraces
covered by thin veneer of alluvium
interpreted events:
erosion by graded stream
uplift/change of base level
downcutting
fill terraces
composed of alluvium, depositional in nature
filling of valley by aggradation of graded stream

31. Types of cyclic stream terraces (cont.)
cut-in-fill terraces
composed of alluvium, erosional in nature
interpreted events:
valley cut into alluvium
uplift/change in base level
downcutting
nested fill terraces
composed of alluvium,
multiple terraces, all depositional in nature
successive cycles of aggradation and downcutting

34. Non-cyclic surfaces erosional surfaces on resistant materials
do not represent periods of sustained erosion but rather a resistant surface.
slope of surface conforms to bedding, not to slope
of stream that formed it.
may slope up-valley
will not have concave-upward profile as a valley
floor would.