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. What is a Tie Channel? Self-formed leveed channel Connect rivers to lakes Jet entering still water Bi-directional flow Stable 250 m Fly River, Papua New Guinea Tie channel

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

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 silt sand clay

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 Large-scale advective transfer of sediments Lake level > levee crest Unpaired levee crests heights Super-elevated bends Asymmetric levee x-sections

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

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