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The Evolution of a Tie Channel. Joel C. Rowland & William E. Dietrich University California - Berkeley. Source: Google Earth. Goal of Study. Develop a conceptual model for the development of a self-formed leveed channel created by a sediment-laden current entering still water. Tie channel.

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The evolution of a tie channel
The Evolution of a Tie Channel

Joel C. Rowland & William E. Dietrich

University California - Berkeley

Source: Google Earth


Goal of study
Goal of Study

  • Develop a conceptual model for the development of a self-formed leveed channel created by a sediment-laden current entering still water


What is a tie channel

Tie channel

250 m

Fly River , Papua New Guinea

What is a Tie Channel?

  • Self-formed leveed channel

  • Connect rivers to lakes

  • Jet entering still water

  • Bi-directional flow

  • Stable



2 km


Why Raccourci Old River ?

  • Largest known tie channel

  • Largely unaltered channel in naturally functioning floodplain

  • Unprecedented documentation of channel development

  • Data sources:

  • Historical records

  • Hydrographic surveys (> 1880s)

  • Aerial photographs (> 1940s)

  • Satellite imagery

  • ALSM data (Lidar)

  • Long-term records for Miss River

  • Field data


Talk Outline

  • Channel Characteristics

    • Morphology

    • Sedimentology

  • Conceptual Model

    • Levee growth

    • Channel widening



Mississippi River

Oxbow lake margin

1 km

Long profile of channel levees and width



Channel and levee growth

  • Vertically accretes

  • Channel widens

  • Levee flanks broaden


Levees composed of sub-horizontal alternating layers

  • Sand deposition: U* > Ws in channel, U* < Ws over levees

  • Mud and organic deposition: U* < Ws everywhere


TC Levee Coarse

TC Levee Fine

TC Bed

Miss Susp Sed

Miss Bed

Incoming load sorted by tie channel processes

clay

silt

sand



150 m

Jet Sedimentation

  • Large “quasi-2D” turbulent structures

  • Scale with jet width

  • Sweep across newly forming channel advecting sediment to margins


150 m

Localized shear along inundated levee crests

?


Lake level > levee crest

  • Unpaired levee crests heights

  • Super-elevated bends

  • Asymmetric levee x-sections

Large-scale advective transfer of sediments

Lake level < levee crest


Local advective transfer of sediments: Splays

  • Locally erode crests

  • Deposit on flanks

Concepts Watershed, 2005



Conclusions

  • Channel selectively sorts and deposits incoming sediment

  • Majority of levee sedimentation occurs during submerged/inundated conditions

  • Splays redistributes sediments and broaden levees

  • Channel width controlled by mass failures which are linked to levee height



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