Deposition

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Deposition

• By Tom,
• Joe and
• Ryan

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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.

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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

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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.

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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.
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Change in the Mississippi Delta
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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.

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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.

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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.
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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.

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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.

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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