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

Pecatonica River near Mineral Point, WI

(Bridge, 2003) Plan Cross section

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

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

Balance between centrifugal force and pressure gradient

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

(Bridge, 2003) Outside Inside Simulated

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

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

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

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

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

(Julien, 2002) Controls on Meander Wavelength   W  12.34W  r c  4.59r c 0.98 Combining:  r c ~2 to 3W

(Julien, 2002) Controls on Meander Wavelength  Q b b ; b~0.5

(Knighton, 1998) Meander Movement

(Knighton, 1998) Types of Meander Growth and Shift

(Julien, 2002) Shear Stress and Meanders  t0  hU 2 /r c  t0 00  t max   m    t high  when r c ~2.5W

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

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