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					Meandering (High Sinuosity) Channels




            Brazos River, Texas
Features of Meandering Systems

Outer (Cut)                L
  Bank




                           A


                                     Point of
          Inner Bank                Inflection
             with                       Or
           Point Bar                Crossover


                  L: Meander Length
                  A: Meander Amplitude
 Point Bar
Development
Channel Width-Length Relationship
Plan and Cross Section of
ideal meander bend




Velocity distribution across
a meander bend.
Willow Cut-Off, Marshall
Point Reach, Mississippi
Abandonment of meander
loops by neck cut-off and
chute cut-off




Channel avulsion: abandonment
of whole channel segments
Brazos River, Texas: Neck Cut-Off
Brazos River, Texas: Point Bar
Brazos River, Texas: Point Bar with
  Almost Complete Neck Cut-Off
Ox-Bow Lake (Neck Cut-Off)
Ox-Bow Lake
Old Ox-Bow Lake,
 Partly Sedimented
            Point Bar Chutes




Wood River, Fairbanks, Alaska: near bank-full river stage
                                                       Photo by A. Miall
Chute Cut-Off, Louisiana
Sand Waves and Ripples on Point Bar




                       Amite River, Louisiana
       Mud Drape on Point Bar Surface




                                    Wind-blown
                                       sand

Amite
River,
Louisiana            Current Flow



                         Mud
     Surface Expression of Bioturbation
            on Point Bar Surface




Amite River,
Louisiana
Shale Clasts
Upper Point Bar
Surface


           Amite River,
           Louisiana
        Sand Waves, Deposited at Flood
        Stage, Cover the Levee Surface




Amite River,
Louisiana
The next series of photographs are exposures of recent
point bar/levee sediments of the Brazos River (Texas)
          and the Amite River (Louisiana).

  The photographs show a vertical profile through a
        complete point bar sequence from the
       basal channel sands and conglomerates
               to levee sands and silts
 Basal Point Bar: Cross-Bedded
Channel Sands and Conglomerates
Cross-Bedded Channel Sands
Vertical Sequence: Cross-Bedded Channel Sands
 Grade Up into Ripple Bedded Point Bar Sands
Ripple Drift Cross Lamination:
       Upper Point Bar
Ripple Drift and Ripple Cross Lamination with
      Partial Distortion, Upper Point Bar
Levee Sediments:
Very fine sands and
mud-rich silts, ripple
drift cross-laminated,
partially vegetated --
characteristic of the
lower portions of the
natural levee
        Basal Levee Sediments:
Very fine sands, and mud-rich silts, ripple drift
        cross-laminated and contorted
Levee Sediments:
Very fine sands, and
mud-rich silts, ripple
drift cross laminated,
alternating with thin
beds of rooted mud
(top). Lower levee
grading up into main
portion of the levee.
Note contorted bedding
in some of the muddy
sediments
Point Bar Model

				
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posted:1/28/2012
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Description: About education about study geology, geophysic, sedimentation of rock, earth, facies, diagenesis, river and meandering