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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. 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

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  1. The Evolution of a Tie Channel Joel C. Rowland & William E. Dietrich University California - Berkeley Source: Google Earth

  2. 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

  3. 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

  4. Global distribution of known tie channels

  5. Raccourci Old River Tie Channel • 65 km upstream Baton Rouge, LA • Formed in 1851 2 km

  6. 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

  7. Talk Outline • Channel Characteristics • Morphology • Sedimentology • Conceptual Model • Levee growth • Channel widening

  8. Channel Characteristics

  9. Mississippi River Oxbow lake margin 1 km Long profile of channel levees and width

  10. Channel bed from dam into lake mouth bar

  11. Channel and levee growth • Vertically accretes • Channel widens • Levee flanks broaden

  12. Levees composed of sub-horizontal alternating layers • Sand deposition: U* > Ws in channel, U* < Ws over levees • Mud and organic deposition: U* < Ws everywhere

  13. TC Levee Coarse TC Levee Fine TC Bed Miss Susp Sed Miss Bed Incoming load sorted by tie channel processes clay silt sand

  14. Model of Channel Formation

  15. 150 m Jet Sedimentation • Large “quasi-2D” turbulent structures • Scale with jet width • Sweep across newly forming channel advecting sediment to margins

  16. 150 m Localized shear along inundated levee crests ?

  17. 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

  18. Local advective transfer of sediments: Splays • Locally erode crests • Deposit on flanks Concepts Watershed, 2005

  19. Widening by mass failure and narrowing by sediment drapes

  20. 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

  21. Acknowledgements

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