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River Meanders

River Meanders. Outline Primary flow characteristics within a meander bend Flow and sediment transport within meander bend Controls on meander wavelength Meander migration and shift. Red River, near Aubigny, southern Manitoba. Turkey River, Clayton County, IA.

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River Meanders

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  1. River Meanders Outline • Primary flow characteristics within a meander bend • Flow and sediment transport within meander bend • Controls on meander wavelength • Meander migration and shift

  2. Red River, near Aubigny, southern Manitoba

  3. Turkey River, Clayton County, IA

  4. Pecatonica River near Mineral Point, WI

  5. Plan Cross section (Bridge, 2003)

  6. Primary Flow Characteristics • Flow-transverse component of water surface slope towards the inner bank • Secondary flow pattern (spiral or helical flow) due to • (a) curvature-induced centrifugal forces and • (b) pressure gradient of the transverse sloping water surface • Effects proportional to velocity and inversely proportional to radius of curvature • Flow field is stage-dependent

  7. Secondary flow pattern in a meander bed Point bar (inner bank) Outer bank (Hey and Rainbard, 1996)

  8. Balance between centrifugal force and pressure gradient

  9. Observed for River South Esk Mean Flow Velocity Predicted Simulated (Bridge, 2003)

  10. Outside Inside Outside Inside Simulated (Bridge, 2003)

  11. Observed for River South Esk Water Surface Topography Predicted Simulated (Bridge, 2003)

  12. Observed for River South Esk Flow Depth Predicted Simulated (Bridge, 2003)

  13. Observed for River South Esk Relative Bedload Transport Rate Predicted Simulated (Bridge, 2003)

  14. Observed for River South Esk Bedload Grain Size Predicted Simulated (Bridge, 2003)

  15. Maximum shear stress Flow field Secondary flow Flow structure (Knighton, 1998)

  16. Controls on Meander Wavelength L  W L ~ 12.34W L rc L ~ 4.59rc0.98 Combining:rc~2 to 3W (Julien, 2002)

  17. Controls on Meander Wavelength L Qbb; b~0.5 (Julien, 2002)

  18. Meander Movement (Knighton, 1998)

  19. Types of Meander Growth and Shift (Knighton, 1998)

  20. Shear Stress and Meanders t0 tt0 tt0 hU2/rc tt max qmW-1.61 tt highwhenrc~2.5W (Julien, 2002)

  21. Meanders and River Restoration • Links channel process with form • Designing or creating meandering rivers appears to be optimal channel form used in river restoration • Provides the boundary conditions for the hydraulic stability of a meandering planform

  22. River Meanders Conclusions • Spiral or helical flow in meander bend is a balance of centrifugal and pressure gradient forces • All flow, bed, and sediment parameters then are modified by this flow pattern • Meander wavelength can be determined from width and discharge relations

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