1. Channel Pattern Outline Description of channel pattern Alternate bars Channel pattern continua and evolution Controls of channel pattern

2. Description of Channel Pattern Defined by the nature of channel splitting around braid bars or islands, and the sinuosity of channel segments Since patterns can be flow dependent, should be described at some intermediate flow stage Single channels of varying sinuosity Straight Meandering Multiple channels of varying sinuosity Braided Anastomosed

3. (Thorne et al., 1997) Channel Types

4. Bridge (2003) 1.Bed evolves towards a statistically constant geometry composed of alternate bars 2.Channel responds to alternate bars by inducing bank erosion and channel widening 3.Bed adjusts to sediment fluxes and thalweg wanders

5. Alternate Bars (Ikeda, 1984)

6. Alternate bars in the Naka River, an artificially straightened river in Japan. Image courtesy S. Ikeda. Alternate Bars

7. Alternate bars in a flume in Tsukuba University, Japan: flow turned low. Image courtesy H. Ikeda. Alternate bars in the Rhine River between Switzerland and Lichtenstein. Image courtesy M. Jaeggi. Alternate Bars

8. Tokachi River, Japan Alternate Bars

9. Channel Response to Alternate Bars As water level drops, highest parts of the bars become emergent Bar tail, riffle, and head become recognizable Cause localized flow diversions, and localized erosion and deposition Deposition on convex banks inside of river bend  point bars Deposition in mid-channel  braid bars

10. (Bridge, 2003) (Schumm and Khan, 1972) (Point bar, Madison River, MT) (Bar tail, River Feshie, Scotland) Single-row alternate bars

11. (Bridge, 2003) (Braid bars, Saksatchewan River, CAN) (Unit bars, P. Ashmore) Double-row alternate bars

12. (Bridge, 2003) (Braid bars, P. Ashmore) (Braid bars, Sunwapta River, CAN) (Braid bar, Sagavanirktok River, AK) Double-row alternate bars

13. Channel Pattern Defined by the nature of channel splitting around braid bars or islands and the sinuosity of channel segments Single channels Straight Meandering Multiple channels Braided Anastomosed

14. Channel Description Sinuosity Braiding index

15. (Knighton, 1998) Controls on Channel Pattern Conceptual

16. Controls on Channel Pattern Braudrick & Dietrich (2009) hypothesize that meandering rivers also require: 1)bank strength from either cohesive material or vegetation, 2)overbank flows to attach bars to their floodplains, 3)fine sediment to fill the downstream end of bars and chutes. Ingredients: (1) vegetation to reinforce banks and prevent erosion, and (2) sand to build point bars and block off cut-off channels and chutes http://www.berkeley.edu/news/media/releases/2009/10/05_meanders.shtml

17. (Bridge, 2003) Controls on Channel Pattern S  Q -b Meandering Braided

18. (Bridge, 2003) Controls on Channel Pattern S  Q -b D c Braided

19. (Bridge, 2003)   D 50 b Meandering Braided Controls on Channel Pattern

20. (Bridge, 2003) Parker (1976) using channel stability theory Meandering Braided Controls on Channel Pattern

21. Channel Pattern and Stream Restoration Bed topography and flow redirection are the primary controls on channel pattern, as conditioned by boundary composition Indices can be used to facilitate design of stable stream patterns, though these must be combined with sediment transport relationships

22. Channel Pattern Conclusions Alternate bars play an important role in the evolution of straight channels Channel pattern defined by channel splitting around bars and the sinuosity of channel segments Discharge, slope, sediment load, etc., all interact with river flow to modify channel pattern