Lecture 25 running water

Today:

Chapter 15: Running Water


Announcements:
Please do not call Aurora on her
cell phone number. If you need
to make contact, do so
by email. Thanks!
Homework assignment: Review
Interlude E: The hydrological cycle
and complete assignment. Will be
handed out on Monday at the beginning
of class and will be due on Wednesday.
Quiz next Wednesday covering:
- Interlude D: Fossils and Evolution
- Chapter 12: Deep Time
(Historical Geology)
- Chapter 16: Mass wasting
- Chapter 17: Running water


oceans

dams

plants

s
r

e
ir v
evaporation

lakes
rain

sediments
& soil

mountains

snow

To think about for Monday’s
homework: The hydrological cycle

Describe how these 10 elements are
interrelated in the hydrological cycle.


Chapter 15: Running Water
Topics for today:

Hydrological cycle
Surface run-off
Sheet wash
Channel flow
Discharge = Velocity x Channel Area
Turbulent and laminar flow

Stream transport processes
Drainage basins and divides
Base level and stream profiles
Processes of stream erosion
How streams carve their channels
Processes of stream deposition
Downstream changes in channel
form and bahavior
Effects of changing base level


Running Water: Why Care?


Running Water:
Why care?


Running Water:
Why care?


Hydrological Cycle & Running Water
Hydrological cycle (see video):
Continuous cycling of water between the atmosphere, oceans
and land, driven by gravity and energy from the Sun.
Running water is the most effective agent of erosion
and the dominant external factor in shaping the
Earth’s surface.

Important factors that affect the ability
of running water to alter the landscape:
 Rainfall
 Surface runoff
 Rate of evaporation


Earth’s Water Inventory


Sources of water that sustain stream flow….

Fig. 17.02
W. W. Norton


RUNNING
WATER

Process Begins with Surface Runoff

“Sheet flow”: Thin sheets of water accumulate
and flow over surface.
Controlled by:  Intensity/duration of rainfall.
 Soil texture.
 Soil saturation.
 Slope angle.
 Vegetation
Initiation of stream erosion: Sheet flow
then accumulates and self-organizes into

rivulets and small channels that eventually
feed into streams.


Major River Systems of the Earth


RUNNING
WATER

Stream Valleys

Most common surface landform on Earth!
V-shaped near headwaters,
with many water falls and
rapids. Slotted canyons may
form where bedrock is
easily eroded.
Widen downstream due to
erosion of by slope wash
and gravity.


Fig. 17.19
Stephen Marshak


Major River systems consist of a hierarchy
of tributaries that range from small rivulets
to streams to major rivers…

Fig. 17.05 b
W. W. Norton



Drainage patterns are strongly controlled
by the structure of the underlying rock units…

Fig. 17.04abcd
W. W. Norton


Drainage basins are areas that are drained
by the same stream system…

Fig. 17.06
W. W. Norton

Drainage basins
are separated by
drainage divides,
where streams
on either side flow
opposite directions.


Drainage basins are areas that are drained
by the same stream system…

Fig. 17.06
W. W. Norton

Drainage basins
are separated by
drainage divides,
where streams
on either side flow
opposite directions.


Major Drainage Basins of North America

Fig. 17.07


RUNNING
WATER

Stream Profiles

Longitudinal Stream Profile: A cross sectional
view that shows how the slope of a stream channel
changes along its course.


Longitudinal stream profile

Fig. 17.05 a
W. W. Norton

Cross sectional profiles at
different points along
stream course.


RUNNING
WATER

Base Level

Base level:
The downward limit to which a stream
will erode its channel.
Temporary base level:
Along a stream gradient, this is a
temporary level to which a stream will
erode its channel. Example: Lake
Ultimate base level:
Sea level.


Fig. 17.21 a
W. W. Norton


Fig. 17.18 a
W. W. Norton