TY - JOUR
T1 - Steady-State Parallel Retreat Migration in River Bends With Noncohesive (Composite) Banks
AU - Waterman, David M.
AU - García, Marcelo H.
N1 - This work was funded by the Illinois Water Resources Center (Grant: Streambank Erosion in the Mackinaw River, Illinois) when the first author was a graduate student at University of Illinois at Urbana-Champaign. Thanks are extended to the following: Gary Parker and Davide Motta for many helpful discussions during the analysis; Zhenduo Zhu and Dimitrios Fytanidis for assistance with field work; Don Rollo, the property owner, for cooperation with field work and allowing access to the site. Finally, thanks are extended to three anonymous reviewers whose constructive criticism helped improve the quality of the manuscript.
This work was funded by the Illinois Water Resources Center (Grant: Streambank Erosion in the Mackinaw River, Illinois) when the first author was a graduate student at University of Illinois at Urbana‐Champaign. Thanks are extended to the following: Gary Parker and Davide Motta for many helpful discussions during the analysis; Zhenduo Zhu and Dimitrios Fytanidis for assistance with field work; Don Rollo, the property owner, for cooperation with field work and allowing access to the site. Finally, thanks are extended to three anonymous reviewers whose constructive criticism helped improve the quality of the manuscript.
PY - 2022/3
Y1 - 2022/3
N2 - A substantial body of research has addressed the equilibrium cross-sectional geometry of straight noncohesive channels, along with bends having fixed outer banks. However, development of a characteristic cross-section during active migration has been confounded by inaccurate treatment of noncohesive bank erosion processes. This analysis characterizes a steady-state migrating cross-section and the associated migration rate for the highly conceptualized case of an infinite bend of constant centerline radius with noncohesive lower banks consisting of uniform-sized grains mobilized as bedload. Analytical, numerical, and field analyses are presented to rationally constrain the geometry and obtain a physically based migration rate equation dependent on the following dimensionless groupings: excess Shields stress, flow depth to radius of curvature ratio, and noncohesive bank thickness to grain size ratio. Migration rate is shown to be dictated by transverse sediment flux at the thalweg due to secondary flow, not bank slope as in previous formulations developed from similar principles. Simple outward translation of the noncohesive portion of the cross section is achieved with concurrent mass failure in the upper cohesive layer. Such translation cannot be achieved using a linear excess shear formulation applied to noncohesive fluvial erosion. A numerical model of cross-sectional evolution to steady-state migration is developed; when applied to the lower Mackinaw River in Illinois, it reveals that the river behaves as if the critical shear stress is considerably larger than that indicated by the grain size distribution. This conceptualized treatment is intended to provide a canonical basis of comparison for actual meander bend geometries.
AB - A substantial body of research has addressed the equilibrium cross-sectional geometry of straight noncohesive channels, along with bends having fixed outer banks. However, development of a characteristic cross-section during active migration has been confounded by inaccurate treatment of noncohesive bank erosion processes. This analysis characterizes a steady-state migrating cross-section and the associated migration rate for the highly conceptualized case of an infinite bend of constant centerline radius with noncohesive lower banks consisting of uniform-sized grains mobilized as bedload. Analytical, numerical, and field analyses are presented to rationally constrain the geometry and obtain a physically based migration rate equation dependent on the following dimensionless groupings: excess Shields stress, flow depth to radius of curvature ratio, and noncohesive bank thickness to grain size ratio. Migration rate is shown to be dictated by transverse sediment flux at the thalweg due to secondary flow, not bank slope as in previous formulations developed from similar principles. Simple outward translation of the noncohesive portion of the cross section is achieved with concurrent mass failure in the upper cohesive layer. Such translation cannot be achieved using a linear excess shear formulation applied to noncohesive fluvial erosion. A numerical model of cross-sectional evolution to steady-state migration is developed; when applied to the lower Mackinaw River in Illinois, it reveals that the river behaves as if the critical shear stress is considerably larger than that indicated by the grain size distribution. This conceptualized treatment is intended to provide a canonical basis of comparison for actual meander bend geometries.
KW - meandering rivers
KW - migration rate equation
KW - noncohesive bank erosion
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U2 - 10.1029/2021WR030762
DO - 10.1029/2021WR030762
M3 - Article
AN - SCOPUS:85127241367
SN - 0043-1397
VL - 58
JO - Water Resources Research
JF - Water Resources Research
IS - 3
M1 - e2021WR030762
ER -