1. Drainage Basin
Figure 11.3
Christopherson, Elemental Geosystems, Sixth Edition
Copyright © 2010 Pearson Education, Inc. 1

2. Drainage Basins Figure 11.5
Christopherson, Elemental Geosystems, Sixth Edition
Copyright © 2010 Pearson Education, Inc. 2

5. Drainage Basin System Figure 11.4
Christopherson, Elemental Geosystems, Sixth Edition
Copyright © 2010 Pearson Education, Inc. 5

6. Drainage Patterns topographic dome no structural control
folded structures
jointing
continental glaciation
structural dome
concentric rock
closely spaced
faults/monoclines
Figure 11.9
Christopherson, Elemental Geosystems, Sixth Edition
Copyright © 2010 Pearson Education, Inc. 6

7. Drainage Patterns
Random
Dendritic
f(topography)
Parallel
Radial

8. Drainage Patterns Random f(topography) f(lithology) Dendritic Parallel
Radial
f(lithology)
Trellis
Joint trellis

9. Highly Dissected Drainage
how frequently streams occur
on the land surface
Figure 11.8
Christopherson, Elemental Geosystems, Sixth Edition
Copyright © 2010 Pearson Education, Inc. 9

10. Drainage Density Low High Variables Climate Substrate Slope Vegetation
(<5km/km2)
low slope
low rainfall
permeable
dense vegetation
High
(> 500 km/km2)
steep slope
high rainfall
impermeable rock
Variables
Climate
Substrate
Slope
Vegetation

11. Badlands
Very high drainage density!
Why?

12. Drainage Basins Stream order (Strahler)
Means of classifying basin size
1st order = no tributaries
2nd = two 1st
3rd = two 2nd

13. 14 m across
3200 m across
Landscapes consist of ridge and valley topography at all scales, but only finest scale reveals the actual valley network and defines the transition between hillslopes and valley
fractals exhibit self-similarity; that is similar structure is observed at many scales. With self-similarity, the value of a property depends on the resolution of observation
Montgomery and Dietrich, 1992, Science

14. Channel networks are of finite extent. b b d
Channel networks are of finite extent.
The spacing of the finest-scale valleys depends on the competition of valley cutting and hillslope eroding processes.
Fractal analysis breaks down at the channel-hillslope transition.
River basin comprised of network and hillslopes. Hillslopes control production of runoff, sediment, and wood. Network routes these through basin.
Spacing or drainage density is another way of saying how well dissected is the landscape? Dissection limited by threshold of channelization.

15. Limitations of Horton-Strahler ordering
Order does not express the intuitive ‘size’ of a catchment very well
These look very similar in size, but the left hand net is of order 2, and the right hand net or order 3
Both of these are of order 2, but one looks much ‘bigger’ than the other!

16. Magnitude: an alternative approach (Shreve)
The left hand net has a magnitude of 9, and the right hand has a magnitude of 2
Both of these very similar networks have the same magnitude of 4
Magnitude may give a better idea of the size of the network
Shreve explored all the possible network topologies for a given magnitude

17. Magnitude and stream order
Magnitude of a basin is the number of first order or “exterior links” in a catchment. Magnitude correctly emphasizes identifying where the channel begins. Stream order is commonly done on nearly arbitrary network scales, and therefore means little. “Horton’s laws”, which are derived from analysis of stream orders, have no physical meaning.
M = 9
N= 2M-1
N= number of links (exterior + interior)
For channel head theory, see:
Istanbulluoglu et al. JGR 2005 for gully head theory
Tucker and Bras, 1998, WRR for theory to landscape evolution

19. Watershed Networks ­ Watershed network comprised of
7,100
14,200
21,300
28,400
3,550
Meters
Legend
nednet
<all other values>
Order 1 2 3 4
Logan River Network and Watersheds
delineated by TauDEM
Watershed network comprised of
headwater and network systems
First and second order streams often comprise 70% of the stream network (Benda et al, 1992)
High ecological value
Stream networks defined by:
Nat’l Hydrography Dataset (1:100,00)
Terrain analysis
(area, area-slope; area-length thresholds)

20. Effects of low order channels on downstream reaches in the network
Synchronous (or asynchronous) inflows of water, sediment, nutrients, and organic matter create a variety of channel conditions and biological assemblages
Connectivity of headwater systems to downstream reaches affects the cumulative and dispersed nature of material transport processes
Gomi, et al, Understanding processes and downstream linkages of headwater systems, BioScience, Oct. 2002, vol. 52, no. 10

21. Watershed Delineation by Hand Digitizing
Watershed divide
Drainage direction
Outlet
ArcHydro Page 57

22. River networks and channel morphology
Where do channels begin?
Channel network structure

23. Channel Initiation
Channel head: the upstream limit of concentrated water flow between banks (Dietrich and Dunne, 1993)
a major boundary between hillslopes and channels
“pivot point” in sediment transport between diffusive process and incisive process
Channel initiation requires runoff
Channel initiation occurs by:
saturated overland flow
seepage erosion
shallow landsliding

24. Channel Head Location and Topography
Montgomery and Dietrich, 1989

25. Channel head: threshold transition between hillslope and channel processes
Interplay of channel and hillslope evolution. Channel initiation = f( exposed lithology, vegetation cover, prevailing erosional mechanism) Whatever that might be: SOF, OF
channel head location influenced by area and slope

28. Channel Initiation and Basin Morphometry
Process model for channel initiation by shallow landsliding
convergent topography causes colluvium eroded from adjacent hillslopes to accumulate
at critical threshold, landsliding occurs exposing underlying material
erosion of underlying material by saturation overland flow initiates channel
Channel heads controlled by hillslope process rather than network extension
Inverse of source basin length ~ drainage density

29. Valleys Hillslopes Dietrich et al., 2003, PIG
channel heads assoc. with a change in sediment transport processes at a critical contributing area. Hillslope sed trans: slope-dependent. Ch. sed trans: slope and discharge-dependent
Hillslopes
Dietrich et al., 2003, PIG

30. Stock and Dietrich, 2003, WRR

31. Coos Bay, OR Dietrich & Perron, in press,Nature
inflection point is the handoff between landscape disturbances, typically thought of as mass wasting dominated regime to fluvial dominated regime
Location of inflection point reflects general environmental controls on ch. initiation (cli, veg)
Dietrich & Perron, in press,Nature

32. Montgomery and Dietrich, 1992, Science
N. California
Oregon Coast Range
channeled
channel head
unchanneled
S. California
Summary
channel heads are defined through a topographically defined ( CA and S) threshold between channeled and unchanneled regions of the landscape
threshold behavior
Montgomery and Dietrich, 1992, Science

33. a= roughness and transport parameters
T= transmissivity
q= effective rainfall
M=slope
F = friction angle
q= slope angle
a= roughness and transport parameters
prevailing erosional mechanism alluded to earlier
Example for humid, soil mantled landscape
Dietrich et al Geology

34. unchanneled = hillslope
Application of slope- area channel threshold to a digital terrain model
channeled
unchanneled = hillslope
a/b a proxy for contributing area. Mapped channel versus applying slope-area threshold to a DEM For the threshold, no channels observed below this range
network topology affects debris flow frequency and slope-area relation
transition
Observed channel in the field
Montgomery and Dietrich, 1992, Science

35. Summary
Channel heads typically occur at threshold changes in dominant transport process, and depend both on drainage area and local slope.
Channel network structure imparts a transport distance structure (width function) that influences sediment routing.