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131 Cards in this Set

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fluvial
(Latin)river
Fluvial processes
associated with running water dominate 3/4 of the lands area
water is the most
prevalent shaper of the land surface
water generally moves
slower than wind but moves much more material
water moving as
sheet flow on the landscape can also remove and transport sediment.
most fluvial geomorphologists are interested in
the ability of water to effect changes on the landscape
Erosion, Transportation, and Deposition...
-(3 phases of a single activity)
-that these are natural processes
-people can alter their rates with changes in land use
Erosion
a process where large rocks and loose materials are dissolved from a part of the earth’s surface.
(Erosion)Hydraulic action
water easily sweeps away loose materials
(Erosion)Abrasion
material carried in running water is capable of scraping rocks in the bed and bank of a stream.
(Erosion)Solution/carbonation
the dissolving of rocks
The greater the sedement load in a stream,
the more that stream is able to erode.
The greater the velocity of the water in a stream—
the greater its ability to erode
The greater the friction caused by surface roughness in a stream,
the greater the amount of turbulance in the water
The greater the resistance of rocks,
the harder it is to break them down.
The steeper the slope,
the easier it is for a given amount of water to erode material.
The less the amount of land surface cover,
the greater the rate of erosion
Variation in these factors
can occur over short distances leading to substantial differences in the rate of erosion along different parts of the same stream.
streams simultaneously erode
both vertically and horizontally
Steeper gradients
across space lead to more vertical erosion or down cutting
relatively gentle gradients
cause more horizontal erosion.
rivers and streams have
steep gradients near their headwaters, moderate gradients along their middle reaches, and gentle gradients further down stream.
most streams attempt to
cut down to base level—a concept intended to describe the depth a stream will ultimately cut down to. Theoretically, base level for many streams is sea level (their ultimate destination), but this is seldom the case in reality.
(Many geomorphologists say:) rivers and streams are in dynamic equilibrium with their...
environment.(they appear not to change at all)
-until environmental change occurs
-(such as climate change or tectonic uplift)
-the river processes change in reaction to environmental changes
Floods are
-periodic and natural events.
Floods occur...
-the river reaches flood stage
-happens 2 out of 3 years in natural streams.
People chose to live in
-flood plains
flood plains--
-the portion of the stream that usually does not contain water
-but can contain water when the stram nears the flood stage or surpasses it.
Floods are important because they have the
large amounts of energy needed to cause rapid erosional changes.
Floods occur at varying
magnitudes and frequency
Lower magnitude floods
have less discharge BUT higher frequency
High magnitude floods
have larger discharge, BUT lower frequency
recurrence interval (aka the return period)
the # of years between floods of equal or greater magnitude.
RI=N+1/Rank
Transportation refers to
the actual movement of sediment, rocks, or dissolved materials.
Once a particle has been eroded, it takes much
less energy to continue moving it.
a substantial portion of any stream’s
load consists of dissolved material.
Coarse materials are called
bed load because they are too heavy to remain suspended.
bed load
(coarse materials), bounce or slide along the stream load and usually only when there is relatively sediment discharge and velocity.
stream’s load is
suspended sediment , relatively fine textured material mixed in with the water.
Deposition occurs
when a stream’s carrying capacity decreases (usually due to reduced volume or velocity). Carrying capacity always changes, and when it declines, some of the stream’s load stops moving.
The first materials deposited are the
heaviest; then progressively smaller materials are deposited until the stream’s load is reduced to its capacity
Very fine textured materials may
remain suspended indefinitely.
Accumulations of stream laid deposits are called
alluvium. Thick deposits are frequently (but not always) found near stream banks and along valley floors and they can be quite fertile
Discharge
-is the amount of water in a stream passing a particular point in a given amount of time.
-a way of accounting for volume
Discharge usually measured
either as cfs or cms.
the greater the amount of turbulance in the water
the greater the water’s ability to erode solid material.
In streams and rivers steep gradients near
their headwaters
In streams and rivers moderate gradients along
their middle reaches
In streams and rivers gentle gradients further
down stream
The greater the sediment load in a stream
the more that stream is able to erode.
The greater the velocity of the water in a stream...
the greater its ability to erode...
The greater the resistance of rocks,
the harder it is to break them down.
The steeper the slope
the easier it is for a given amount of water to erode material.
The less the amount of land surface cover
the greater the rate of erosion
Variation in:
discharge
sediment
velocity
friction
turbulence
resistance of rocks
slope
land surface cover
-can occur over short distances
-leading to substantial differences in the rate of erosion
-along different parts of the same stream.
Most streams simultaneously erode both
vertically and horizontally
Steeper gradients across space lead to
more vertical erosion or down cutting in any given stream.
relatively gentle gradients
cause more horizontal erosion.
most streams attempt to cut down to
base level (a concept intended to describe the depth a stream will ultimately cut down to.)
base level for many streams
is sea level
-not usually the case
rivers and streams are in dynamic
equilibrium with their environment.
-they reach an apparent “steady state”(a condition where they appear not to change)
-until environmental change occurs (such as climate change or tectonic uplift and so forth).
-THEN the river processes change in reaction to environmental changes.
Floods are
periodic and natural events.
Floods occur when
a river or stream reaches flood stage
a river or stream reaches flood stage
2 out of every 3 years in natural streams.
Floods are important because they
have the large amounts of energy needed to cause rapid erosional changes.
Floods occur at varying
magnitudes and frequency
High magnitude
floods have larger discharge, BUT lower frequency
Lower magnitude
floods have less discharge BUT higher frequency
The recurrence interval
(also called the return period) is the number of years between floods of equal or greater magnitude.
Transportation
refers to the actual movement of sediment, rocks, or dissolved materials.
Once a particle has been eroded,
it takes much less energy to continue moving it.
a portion of any stream’s load consists of
dissolved material.
is suspended sediment ,
relatively fine textured material mixed in with the water.
Coarse materials are called
bed load
bed load
-are too heavy to remain suspended.
-They bounce or slide along the stream bottom
-usually only when there is relatively high discharge and velocity.
Deposition occurs
when a stream’s carrying capacity decreases
-(usually due to reduced volume or velocity).
-Carrying capacity always changes, and when it declines, some of the stream’s load stops moving.
The first materials deposited are the
heaviest
smaller materials
are deposited until the stream’s load is reduced to its capacity
Very fine textured materials may
remain suspended indefinitely.
the stream’s carrying capacity is more likely to
be exceeded at some places than at others
carrying capacity is more likely in:
-Inside bends of a stream.
-Places where the stream channel widens.
-Along the lower reaches of a stream, especially where a stream empties into a standing body of water
-Behind dams in reservoirs.
River systems are separated
into watersheds or drainage basins.
Small creeks join to form
larger streams which join to form still larger streams
network of creeks, streams and rivers that drain all
runoff from watersheds.
As tributaries meet a master stream
the discharge, width, and depth of the master stream increase
drainage divides
The boundaries of watersheds
drainage divides are “topographic...
highs” that mark places where water flows down slope in one direction or the other.
the most significant drainage divide in North America
is the Continental Divide.
eroded materials
can be washed away in such quantities as to leave badlands.
These are large areas of
rugged topography created by erosion
-These can also be called erosional hills or mountains because they are formed when large areas are dissected by running water
Rivers & their Valleys are Environmental systems that are instabile in
climatic, hydrologic, and riparian [river bank] vegetation systems is strongly connected to instability in river channels
rivers are
dynamic environments.
Physical processes make meandering
streams the most common form of river channel
The “loops” in meandering streams may eventually become
so large that they are cutoff from the main channel leaving oxbow lakes (which eventually become filled with sediment.)
The inside bends of meandering streams are usually
shallower and slower flowing (hence they are sites of deposition ) while the outside bends are usually deeper and faster flowing (hence the site of more erosion)
The inside bends of meandering streams are
usually shallower and slower flowing (hence they are sites of deposition ) while the outside bends are usually deeper and faster flowing (hence the site of more erosion)
When rivers appear to have ______ channels, they are called
many/braided channels; and they are caused by excessive deposition and are extremely unstable environments.
River channels do not always have
water in them.
Arid environments frequently
have ephemeral rivers or streams.
Rivers constantly changes
position and this action over time creates (carves) flood plains and valley floors
Flood plains are
relatively flat areas adjacent to the channel that occasionally hold water
The flood plain is formed
by the material deposited on the inside of channel bends and the material [alluvium] deposited when the river overflows
its banks.
relatively resistant rocks
line one or both sides of a flood plain producing bluffs
natural levees are
the elevated areas of land on either side of a channel's banks
When streams overtop their banks, water leaving the channel is quickly exposed to much more
friction than in the stream.
This overflow slows the water down and forces
the heaviest sediments (like sand and course silt) to be deposited on and near the banks creating a natural levee.
Levees can be as high as
15 feet above the adjacent flood plain along the lower end of the Mississippi River, but in most other (smaller) streams they are usually are much lower.
Back swamps are
low lying portions of the flood plain lying between the natural levee and edge of flood plain (bluffs).
Yet the concept of flood plains comes primarily from the
eastern half of the United States where such features are relatively well defined.
In many parts of the western U.S., flood plains
are not present. Deeply cut (incised) streams may have no flood plain at all and some braided streams may cover a wide area that might otherwise be called a flood plain
there is little or no flood plain in relatively young mountain streams
presumably because down cutting is too rapid to allow much if any lateral movement. Outside mountainous regions, down cutting is slow enough that lateral shifting (eroding) makes the valley and flood plain wider than the channel itself.
river terrace
is an abandoned flood plain located above the present stream (including present flood plain)
Changing climate or tectonic uplift may cause
-cause down cutting below the existing flood plain, and if enough time passes
-a new flood plain is created below the original one.
“If incision and aggradation [deposition] occur repeatedly,
it is possible to develop any number of terraces.”
Waterfalls and rapids are portions of channels
with steep gradients. Erosion is most intense here and these features are eventually worn “back.”
Deltas
-are deposits of alluvium formed when streams enter standing water (either lakes or oceans)
-The word comes from the Greek letter delta, which is the shape of the classic Nile River Delta in Egypt.
As with natural levees,
the sudden reduction of capacity causes the river to deposit its sediment.
Deltas take on a variety of shapes depending on the
coastline, sediment load, water depth, and off shore currents.
These seaward extensions of (Deltas) the flood plain can be
fertile if drained.
Alluvial fans are usually found in relatively
dry and mountainous environments.
Alluvial fans are much like Deltas
in that when the swift moving mountain streams reach the valley, they slow down and deposit much material.
because Alluvial fans form in dry environments, they usually
do not have water
in them.
Plateaus are
extensive areas of relatively flat land in places of higher elevation.
Mesas have
steep sides and appear to be somewhat smaller plateaus surrounded by lower lying plains.
Buttes are
even smaller, flat-topped elevated places with steep sides.
Glaciers
are masses of freshwater ice, formed on land, and which are in or have been in motion.
The chief source of glacial ice
is snow Accumulations producing glaciers occur only when snowfall is greater than melting & sublimation in the zone of accumulation.
Glaciers currently cover a relatively
small portion of the earth’s land area (11%).
Alpine glaciers
are more like frozen rivers that exist at very high elevations, sometimes near the equator.
can reach up to a
mile in width and maybe as much as 60 miles long.
Alpine glaciers exist
on all continents except Austalia
Continental glaciers
(frequently called ice sheets) currently cover huge land areas in very high latitudes.