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Deposition

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By Tom, Joe and Ryan Deposition Deposition is the release of the particles that a river is carry due to a decrease in the velocity of the river. The Hj lstrom Curve ... – PowerPoint PPT presentation

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Title: Deposition


1
Deposition
  • By Tom,
  • Joe and
  • Ryan

2
Deposition
  • Deposition is the release of the particles that a
    river is carry due to a decrease in the velocity
    of the river.
  • The Hjülstrom Curve shows the relationship
    between the velocity of the river and the size of
    particles that the river will deposit, transport
    or erode. It shows that the river begins to
    deposit boulders first, then gradually deposits
    smaller particles as the rivers velocity
    decreases. Ending with the deposition of
    particles any less than 0.01mm at 0.1cm/s.

3
Deltas
  • A delta forms when the rivers velocity drops due
    to it entering a slower moving body of water. As
    the river begins to slow down it deposits the
    largest of the transported particles first, then
    as the velocity decreases ever more the size of
    the particles that the river deposits slowly gets
    smaller. Therefore the large sediment is found
    at the front of the delta with the sediment size
    decreasing as the delta nears the sea. Deltas
    are normally triangular in shape and there are
    two types Arcuate and Bird-foot.
  • Distributaries are also form part of delta
    formation. These occur when the river splits and
    becomes more than one individual river. A good
    example of this is the Mississippi delta, a
    picture of this is shown on the following slide

4
Deltas Flocculation
  • Flocculation refers to a process by which a
    solute comes out of a solution. As the sediment
    is dropped the charged particles, such as clays
    and polymers, clumps together to form flocs.

5
An arcuate delta that has formed on the
south-west coastline of Greenland, near
Narsarsuaq.
A close up image of the currently active
Mississippi delta, which is a bird-foot delta.
6
Change in the Mississippi Delta
7
Braided river
  • A braided river is a channel that consists of a
    network of smaller channels separated by small
    and often temporary islands called braid bars.
    However some braid bars become that stable that
    they become almost permanent, with some having
    settlements on them. Braided streams are common
    wherever a drastic reduction in velocity causes
    the rapid deposition of the stream's sediment
    load. Braided channels are also common in river
    deltas.
  • The channels and braid bars frequently move, with
    the river layout often changing significantly
    during flood events. Channels move sideways via
    differential velocity On the outside of a curve,
    deeper, swift water picks up sediment (usually
    gravel or larger stones), which is re-deposited
    in slow-moving water on the inside of a bend.

8
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9
Levees
  • The ability of a river to carry sediments is
    dependent on it velocity. When a river floods
    over its banks, the water spreads out, drops in
    velocity , and deposits its load of sediment.
    Over time, the river's banks are built up above
    the level of the rest of the floodplain. The
    resulting ridges are called natural levees. The
    sediment that is left on the floodplain is known
    as alluvium.
  • When the river is not in flood it may deposit
    material within its channel, raising its level.
    The combination can raise not just the surface,
    but even the bottom of the river above the
    surrounding country. Natural levees are
    especially noted on the Yellow River in China
    near the sea where ocean-going ships appear to
    sail high above the plain on the elevated river.
    Natural levees are a common feature of all
    meandering rivers in the world.

10
Levees
The largest sediment will be deposited closest to
the bank because the larger sediment requires the
greater velocity. As the velocity decreases as
the river floods, the sediment will decrease in
size as the distance from the river increases.
11
Flood Plains
  • A floodplain is flat or nearly flat land adjacent
    to a stream or river that experiences occasional
    flooding. Floodplains are formed by the
    deposition of sediment carried by river as it
    floods.

12
Flood Plains
  • As the river continuously floods, the sediment
    that is deposited accumulates in depth and
    therefore as the depth of the sediment increases,
    the age of the sediment at the base of sediment
    will increase.
  • Also the river will constantly change its course,
    this will cause lateral erosion of the banks of
    the valley. This means that the width of valley
    will increase over geological time.

13
Bibliography
  • http//www.web.umr.edu/rogersda/levees/Should20I
    20Tru...
  • http//www.wikipedia.org.
  • http//www.google.ca
  • http//www.internal.eawag.ch/uehlinge/Pictures.ht
    ml
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