river meanders
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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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
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Red River, near Aubigny, southern Manitoba
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Turkey River, Clayton County, IA
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Pecatonica River near Mineral Point, WI
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(Bridge, 2003)
Plan
Cross section
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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
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(Hey and Rainbard, 1996)
Point bar (inner bank) Outer bank
Secondary flow pattern in a meander bed
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Balance between centrifugal force and pressure gradient
rmuFc
2
force lCentrifuga nhg
ru
2
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(Bridge, 2003)
Observed for River South Esk
Simulated
Mean Flow Velocity
Predicted
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(Bridge, 2003)
Outside Outside InsideInside
Simulated
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(Bridge, 2003)
Observed for River South Esk
Simulated
Water Surface Topography
Predicted
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(Bridge, 2003)
Observed for River South Esk
Simulated
Flow Depth
Predicted
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(Bridge, 2003)
Observed for River South Esk
Simulated
Relative BedloadTransport Rate
Predicted
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(Bridge, 2003)
Observed for River South Esk
Simulated
Bedload Grain Size
Predicted
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(Knighton, 1998)
Maximum shear stress Flow field
Secondary flowFlow structure
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(Julien, 2002)
Controls on Meander Wavelength
L WL ~ 12.34W
L rc
L ~ 4.59rc0.98
Combining: rc~2 to 3W
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(Julien, 2002)
Controls on Meander Wavelength
L Qbb; b~0.5
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(Knighton, 1998)
Meander Movement
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(Knighton, 1998)
Types of Meander Growth and Shift
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(Julien, 2002)
Shear Stress and Meanders
tt0 hU2/rc
tt0t0
tt max qmW-1.61
tt high when rc~2.5W
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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
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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