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
rmuFc
2
force lCentrifuga nhg
ru
2
(Bridge, 2003)
Observed for River South Esk
Simulated
Mean Flow Velocity
Predicted
(Bridge, 2003)
Outside Outside InsideInside
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 BedloadTransport Rate
Predicted
(Bridge, 2003)
Observed for River South Esk
Simulated
Bedload Grain Size
Predicted
(Knighton, 1998)
Maximum shear stress Flow field
Secondary flowFlow structure
(Julien, 2002)
Controls on Meander Wavelength
L WL ~ 12.34W
L rc
L ~ 4.59rc0.98
Combining: rc~2 to 3W
(Julien, 2002)
Controls on Meander Wavelength
L Qbb; b~0.5
(Knighton, 1998)
Meander Movement
(Knighton, 1998)
Types of Meander Growth and Shift
(Julien, 2002)
Shear Stress and Meanders
tt0 hU2/rc
tt0t0
tt max qmW-1.61
tt high when rc~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