Transcript Unit 6: Rivers

Delta Types
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River Delta Quiz
River Delta’s
Homework assignment will be emailed to you
on Sunday
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Delta is a low lying area at mouth of river
formed by deposition of silt deposition
occurs because river slows as it enters ocean
or lake.
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As a river is moving, it carries eroded material
with it. The eroded material continues to
flow downstream until it reaches still water of
an ocean, sea, lake, or bay.
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When the river reaches the still water, the
heavy particles are first to settle out.
The lighter particles are carried further from
shore. This process is then repeated farther
out and a delta forms.
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Deltas are often popular areas for farming
due to the presence of fertile alluvial soils
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Bird's Foot or Digitate Delta
Arcuate Delta
Estuarine delta
Cuspate Delta
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A bird's foot delta
forms where
sediment is
deposited in
relatively calm
offshore waters. An
example of a bird's
foot delta is the
Mississippi river delta
Large amounts of
sediment
Jetties have
been built
and
dredging
occurs to
allow large
vessels to
navigate the
delta
channel
Note the
large
amounts of
sediment
that
surrounds
the delta
A bird’s foot delta located in Louisiana adjacent to the Gulf of Mexico
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when a river meets
the sea in a place
where the waves,
currents, and tides
are strong. It is
often bow shaped
and has a number
of distributaries
flowing across it.
An example is the
Nile delta of Egypt.
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When the mouth of a river enters the sea and
is inundated by the sea in a mix with
freshwater and very little delta, it is called an
estuary. An example of a estuarine delta is
the Seine river delta in France or the
Mackenzie river delta in Canada.
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is formed when a river
drops sediment onto a
straight shoreline with
strong waves. Waves
force the sediment to
spread outwards in
both directions from
the river's mouth
making a pointed tooth
shape with curved
sides. An example is
the Tiber delta in Italy.
Usually has one
distributary
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Rivers change over time and seem to go
through three stages:
◦ Youth
◦ Maturity
◦ Old Age
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Youth:
◦ Are usually found in highland or
mountain regions.
◦ Tend to have a steep slope (high
gradient)
◦ Usually have a small volume of water
◦ Have a rapid flow of water
◦ Usually very rapid erosion especially
vertically
◦ A narrow ‘V’ shaped valley is
characteristic
◦ Water falls and rapids are common
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Maturity/Late Maturity:
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Most high relief is eroded
Gentler slope
Many well developed tributaries
Broad flat river valley
Well developed flood plain
More lateral erosion than vertical
 Meandering results
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Old Age:
◦ Almost no slope
◦ Very little relief
◦ Elaborate meandering
◦ Oxbow lakes develop
◦ Often swampy areas around river
◦ Very muddy due to slow speed
 Most susceptible to flooding because of a large flood plain
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Evaluating Evidence to Determine the Age of
Rivers
◦ There are six common pieces of evidence you can
look for to determine the stage of a river.
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Slope of the river (steeper = younger)
Relief of the banks (steeper = younger)
Width of the valley (wider = older)
Meandering (more = older)
Size of flood plain (wider = older)
 Rapids or water falls (more = younger)