Download Drainage patterns and landforms

An Introduction to Fluvial
Geomorphology
Streams and Rivers Lab: An Introduction to Fluvial
Geomorphology
Geomorphology is the study of the Earth's landscapes and landforms, the
processes by which the landforms originated, their age, and the nature of the
materials underlying them. Fluvial geomorphology is the study of landforms
and processes associated with rivers.
The Fluvial System Model
A model is a simplified idealized representation of reality. The basic fluvial
system can be represented as a model in order to help us understand its
structure and processes. The basic fluvial system is often considered to be a
drainage basin. Drainage basins differ in size and complexity, and are often
subject to scale considerations. Often, a small watershed is part of a tributary to
a much larger drainage basin. The following diagram of a fluvial system is an
idealized representation to help you conceptualize its structure. The diagram is
presented as three nested basins of small, medium, and large scale.
Courtesy of Dr. Zbigniew Zwolinski
Institute of Quaternary Research and Geoecology
Adam Mickiewicz University
Fredry 10, 61-701 Poznan, Poland
voice: +48-61 8294676 or 8294569, fax: +48-61 8530234 Original Image online at = http://main.amu.edu.pl/~sgp/gw/sf/sf.html
Zone 1: Drainage Basin or Watershed
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principal area from which runoff flows
principal area from which dissolved solids and sediments are derived
Zone 2: Area of Transfer
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inflow of water roughly equals outflow
assuming stability, influxes of dissolved solids roughly equals fluxes out
Zone 3: Area of Deposition
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discharge of water into larger streams or bodies
influxes of dissolved solids roughly equals fluxes out
alluvial-fan and alluvial-plain environments
estuarine and deltaic environments
costal environments
Exercise I: Stream Drainage Patterns
PRE-LAB ACTIVITY:
Below are descriptions and illustrations of a number of classic drainage
patterns. In lab you will be asked to identify some of these features (and
others) on topographic maps, aerial photographs and remotely sensed
imagery. You should review your knowledge about drainage systems by
studying these illustrations as well as those shown in your textbook. You
will be asked to answer some questions in writing on a lab sheet that will
be provided. Try also to answer the questions included here - how many
of these places can you identify?
Dendritic -- a tree-like arrangement of
small streams that join to form a larger
river. It is the type of stream one
expects to find in a region that has
adequate rainfall and no unusual
geologic features. The tiny creeks form
a dendritic pattern and the modifying
effects of any underlying geologic
structure are not apparent until the
stream gets quite large.
Where do you think this might be?
Trellis -- a squared off drainage pattern
in which streams often flow directly
toward each other from opposite
directions and then make right angle
turns when they meet. Trellis patterns
are common in places where layered
sedimentary rocks are tilted up from
the horizontal. The rivers usually follow
the layers of less-resistant rock until
they get big enough to break through the
resistant layers. Those gaps have
enormous strategic value for
transportation.
What is the name of one of the US's
most famous "gaps"? Where in the US
would expect to find this drainage
pattern?
Parallel -- an elongated variant of the
dendritic pattern, in which the tributary
streams flow in the same general
direction and usually join at small
angles. Parallel drainage occurs in areas
with a regional slope, prevailing wind,
or some other factor that causes streams
to flow unusually far in one direction
before merging with another.
What type of structural geological
processes do you think produced this
landscape and the pattern of rock
structure and drainage systems
observed? Where do you think this
place is located?
Parallel -- Another view of drainage
patterns produced by
structural geological processes. Here
one can see the short
parallel drainage patterns down the
"back-tilted" side of
a cuesta landform in the "Green River
Formation" area
of Wyoming.
Radial -- a circular arrangement of
streams that flow outward in all
directions. , away from a central high
area. Radial drainage patterns are
common in the vicinity of volcanic
cones, salt domes, granite intrusions,
and other localized uplifts.
A type of feature that usually has a radial
drainage pattern - where do you think this
place is located?
One of the most famous
stratovolcanoes in North
America - what is its name and where is
it located?
It also would have a radial drainage.
Centripetal -- a circular arrangement of
streams, where water flows inward from
all directions toward the center of the
area. Centripetal drainage is likely in
karst topography and in deserts where
intermittent streams flow toward a
temporary salt lake or basin. The map
also show clearly some large alluvial
fans (agriculture is shown in green) another typical fluvial landform feature
of regions such as this.
Where do you think this place is
located? Hint - it is one of the largest
basins of interior drainage in the
world?
Meanders -- a pattern of sweeping
curves and loops. Meanders are
common where terrain is flat enough to
allow a river to move sideways,
undercutting its bank on the inside of
the curve. This lateral stream
movement is responsible for a
distinctive cycle of loop formation and
enlargement, followed by abandonment
of old channels when the river takes a
shortcut across the neck between two
large meanders.
In what type of climatic region do you
think this fluvial system is found?
Would this be in the "up-stream"
watershed area or in the lower reaches-the floodplain--where deposition is
the more dominant process?
Braided -- a rope-like pattern of
twisting channels that separate and then
join again all along the stream. Stream
braiding is common in semi-arid
regions, where floods bring more
sediment into the channel than the
normal flow of the stream is capable of
carrying. A maze of sandbars and low
islands may form during periods of low
water and then be destroyed when
floodwaters carry the material farther
downstream.
This stream is chocked with alluvium
it can't transport downstream. What type
of climatic or geologic situation
might produce this situation? Where do
you think this river
is located?
Another braided stream: the river
flows from a series of glaciers
in a very humid "marine west coast
climate" region.
Where do you think this river is
located? What causes the heavy
milky-white sediment in much of the
stream--what is it called?