XII. Streams
A. The Hydrologic Cycle (components and
pathways)
B. Stream Velocity (controls and results)
C. Drainage Patterns and Landscape
Features (results of erosion and deposition)
D. Stream Valley Development (tectonic
uplift and downcutting)
The
Hydrologic Cycle
See Fig. 12.3
Drainage Basins

Systems of streams
and their tributaries
that collect runoff


Divide
Ground Water
Great Lakes
Drainage Basin
Steam Profiles
(Streams Shaping
the Land)
V-Shaped
Valley
Flood
Plain
What is this Drainage Pattern?
(What does is tell of the geology?)
Valley and Ridge Province of PA
(Trellis Stream Patters)
Stream Gradient


Slope of the land
Sinuosity of stream
10 m
10 m
1 km
10 m/km
1 km
10 m per 1¼ km =
8 m/km
Meander Velocity

Higher velocities on
outside of meanders
causes erosion
(cut bank)

Lower velocities on
inside of meanders
causes deposition
(point bar)

Fig. 10.6
Channel Shape and Roughness
A. Narrow and Deep


Less resistance
Faster flow
B. Wide and Shallow


More resistance
Slower flow
C. Rough Streambed


More resistance
Slower flow
Stream Velocity Controls:

How much and
what grainsize
of sediment is



Eroded and
Transported
Where and
what grainsize
size will be
sediment
First, Weathering
Stream Erosion


Then, Erosion
 Solution (chemical weathering)
 Hydraulic Action (lifting)
 Abrasion (crushing and grinding)

Pg. 276 .
Fracturing
(mechanical)
Loosening
(mechanical and
chemical)
Solution (chemical)
Stream
Transport



Dissolved Load
Suspended Load
Bed Load


Saltation
Rolling, sliding
Pg. 276
(ions)
Stream
Deposition

Erosion
Dominated

e.g., Alluvial Fans



Braided
Streams
Deposition
Dominated


Alluvial Fan
Fig. 12.14a
Fig. 12.14b
High gradients
Less resistance
Fast velocities

Lower gradients
More resistance
Lower velocities
Stream
Deposition

Midchannel bars

Fig. 12.7b
Point bars
Fig 12.9

Braided streams
Fig. 12.7a
Deltas

Reduction of
velocity due to
extreme
widening

Deposition of
silt and clay
Fig. 12.13
Erosion and
Deposition 
Transport
E.g., Meandering streams
 As meanders are
migrating



Cutbanks eroding
Point bars building
Sediment is moving
downstream
Meander Cutoff
How does the gradient change with meandering
and meander cutoff?
Meandering Streams
D
Identify
 Cutbanks
 Point bars
 Meander neck
 Oxbow lakes


Areas of Erosion
Areas of
Deposition
A
C
B
E
Natural Levees




Flooding
Overbank deposits
Widening of stream
into flood plain
Deposition of
sediment


Coarse near stream
Fine farther away
Fig. 12.11
Graded Streams
Increased velocity and
accelerated erosion.
Base level:
Lake or Sea
Erosion acts to grade the
Longitudinal stream profile to
concave-upward curve
Same
Base level
Drainage Patterns
Geology controls stream
patterns
A. Dendritic
A. Uniformly Erodible
(e.g., flat-lying sedimentary rocks
of the Midwest)
B. Conical Mountains
B. Radial
(e.g., Volcanoes)
C. Fractured bedrock
(shallow bedrock)
C. Rectangular
D. Resistant ridges of tilted
sedimentary rocks
(e.g., Valley and Ridge Province
of Pennsylvania)
D. Trellis