Drainage Basin

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

Drainage Basins

Figure 11.5

Copyright © 2010 Pearson Education, Inc.Christopherson, Elemental Geosystems, Sixth Edition

Drainage Basin System

Figure 11.4Copyright © 2010 Pearson Education, Inc.Christopherson, Elemental Geosystems, Sixth Edition

Drainage Patterns

Figure 11.9

Copyright © 2010 Pearson Education, Inc.Christopherson, Elemental Geosystems, Sixth Edition

no structural control

structural domeconcentric rock

continental glaciation

topographic dome

jointing

folded structures

closely spaced faults/monoclines

Drainage Patterns

• Random– Dendritic

• f(topography)– Parallel– Radial

Drainage Patterns

• Random– Dendritic

• f(topography)– Parallel– Radial

• f(lithology)– Trellis– Joint trellis

Highly Dissected Drainage

Figure 11.8Copyright © 2010 Pearson Education, Inc.Christopherson, Elemental Geosystems, Sixth Edition

how frequently streams occur on the land surface

Drainage Density

• Low– (<5km/km2)– low slope– low rainfall– permeable– dense vegetation

• High – (> 500 km/km2)– steep slope– high rainfall– impermeable rock

• Variables– Climate– Substrate– Slope– Vegetation

Badlands

• Very high drainage density!

• Why?

Drainage Basins

• Stream order (Strahler)

• Means of classifying basin size

• 1st order = no tributaries

• 2nd = two 1st

• 3rd = two 2nd

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

Montgomery and Dietrich, 1992, Science

c

b

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.

c

b

d

a

Limitations of Horton-Strahler ordering

• Order does not express the intuitive ‘size’ of a catchment very well

Both of these are of order 2, but one looks much ‘bigger’ than the other!

These look very similar in size, but the left hand net is of order 2, and the right hand net or order 3

Magnitude: an alternative approach (Shreve)

• Magnitude may give a better idea of the size of the network

• Shreve explored all the possible network topologies for a given magnitude

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 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.

Istanbulluoglu et al. JGR 2005 for gully head theory

Tucker and Bras, 1998, WRR for theory to landscape evolution

M = 9

N= 2M-1

N= number of links (exterior + interior)

For channel head theory, see:

Watershed Networks• 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)

0 7,100 14,200 21,300 28,4003,550

Meters

Legend

nednet

<all other values>

Order

1

2

3

4

Logan River Network and Watersheds

delineated by TauDEM

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

Watershed Delineation by Hand Digitizing

Watershed divide

Drainage direction Outlet

ArcHydro Page 57

River networks and channel morphology

1) Where do channels begin?

2) Channel network structure

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

Channel Head Location and Topography

Montgomery and Dietrich, 1989

Channel head: threshold transition between hillslope and channel processes

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

0 0.2 0.4 0.6 0.8 1 1.2 1.4

g ra d ie n t

1

10

100

1000

10000

dra

ina

ge

are

a p

er

con

tou

r le

ng

th, a

/b (

m)

C onvergent

D ivergent

Valleys

Hillslopes

Dietrich et al., 2003, PIG

Stock and Dietrich, 2003, WRR

Coos Bay, OR

Dietrich & Perron, in press,Nature

Montgomery and Dietrich, 1992, Science

channeled

channel head

unchanneled

Oregon Coast Range N. California

S. California Summary

Dietrich et al. 1992 Geology

T= transmissivity

q= effective rainfall

M=slope

= friction angle

= slope angle

= roughness and transport parameters

Example for humid, soil mantled landscape

Application of slope- area channel threshold to a digital terrain model

unchanneled = hillslope

transition

channeled

Observed channel in the field

Montgomery and Dietrich, 1992, Science

Summary

1) Channel heads typically occur at threshold changes in dominant transport process, and depend both on drainage area and local slope.

2) Channel network structure imparts a transport distance structure (width function) that influences sediment routing.