Meandering Stream

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Meandering Stream
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Floodplain Definitions

• Topographic first flat surface found along the
  river above the bankfull channel
• Geomorphic landform composed of unconsolidated
  sediments transported and deposited by the
  related stream (created by the river and composed
  of alluvial materials)
• Hydrologic surface subject to periodic flooding
  by the stream and exerts a role in the hydrologic
  characteristics of the drainage basin (example
  100-year floodplain).

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Topographic Features

• Levees Ridge that runs parallel to the river
  due to enhanced deposition of sediment along the
  channel margins and a decrease in sediment size
  away from the channel
• Splays fan-shaped deposits associated with a
  breach in a levee Splays are generally composed
  of coarser sediments than the levees
• Oxbows and oxbow lakes created by meander
  cutoffs Slowly fill in with sediment commonly
  fine-grained (clay plugs), but not always.

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From reineck and Singh, 1980
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Overbank Flood Deposits (1997) Deposits are
Contaminated with Hg
112,000
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Overbank Flood Deposits
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Primary Processes Involved In Floodplain
Formation

• Lateral Migration lateral movement of the
  channel across the floodplain consists of
  erosion of outer bank and deposition on the point
  bar. Produces fining upward deposits of
  semi-uniform thickness.

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Lateral Accretion of Floodplain Deposits by a
Meandering Channel
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Primary Processes Involved In Floodplain
Formation

• Lateral Migration lateral movement of the
  channel across the floodplain consists of
  erosion of outer bank and deposition on the point
  bar. Produces fining upward deposits of
  semi-uniform thickness.
• Vertical Accretion deposition of sediment over
  the top of the floodplain during flood events
  Produces horizontally bedded layers with varying
  degrees of lateral continuity.

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Vertical Accretion
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Common Stratigraphic Facies

• Lateral accretion deposits produced by lateral
  accretion.
• Vertical accretion deposits produced by vertical
  accretion.
• Channel Fill Deposits sediments deposited during
  aggradation of an active channel or a
  paleochannel (e.g., an oxbow) variety of types.
• Channel lag deposits found at base of the
  channel formed by extensive reworking of the
  materials (and winnowing of the fines) during
  floods associated with the thalweg
• Colluvium material shed from the surrounding
  hillslopes under the influence of gravity with
  may be interbedded with alluvial sediments
  commonly more angular and coarser grained than
  floodplain materials.

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From reineck and Singh, 1980
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From Leeder, 1982
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Qa3
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From Miller et al., 1998
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From Miller et al., 1998
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From Macklin, 1996
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From Macklin, 1996
22
Overbank Flood Deposits (1997) Deposits are
Contaminated with Hg
112,000
23
From Miller et al., 1999
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SIERRA NEVADA
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California
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