Modeling morphodynamic processes in meandering rivers with spatial width variations

Abstract

.[1] Most morphodynamic models of river meandering assume spatially constant width; depending on the intensity of spatial width variations, different meandering styles actually exist, often associated with midchannel bars and islands. When intense enough, width oscillations characterize transitional planforms between meandering and braiding. We investigate, on a modeling basis, morphodynamic feedbacks between spatial curvature and width oscillations in river meanders and related bedform patterns. Our review of existing mathematical models suggests that width-curvature interactions can be comprehensively analyzed by a hierarchy of models that descend from a two-parameter perturbation solution of the governing depth-averaged morphodynamic model. The focus is on in-stream, autogenic hydromorphodynamic processes, and not explicitly on bank processes. Curvature-width interactions are fundamentally nonlinear: the perturbation approach allows us to investigate the key effects at the first nonlinear interaction. In meanders with initially constant width, curvature nonlinearly forces midchannel bar growth, promoting symmetrical bank erosion further downstream, possibly triggering width oscillations. These in turn can significantly affect the process of bend stability and therefore condition the curvature dynamics. Wider-at-bends meanders develop shorter bends and are morphologically more active compared to equiwidth meanders, coherently with the few available field observations. River evolution models aiming to separately simulate bank erosion and accretion processes should incorporate these autogenic flow-bed nonlinearities. Because of its focus on meandering morphologies close to the transition with braiding, the proposed approach can be taken as a novel, physically based viewpoint to the long-debated subject of channel pattern selection.Citation: Zolezzi, G., R. Luchi, and M. Tubino (2012), Modeling morphodynamic processes in meandering rivers with spatial width variations, Rev. Geophys., 50, RG4005,

Bifurcation instability and chute cutoff development in meandering gravel-bed rivers

“…As the chute channel widened and the main channel closed, a stable bifurcation formed with k > 5/3. These findings show that the development of the two types of cutoffs are controlled by different mechanisms (in agreement with Zolezzi et al, 2012;Grenfell et al, In press). Gradient advantage affected the development of the bend cutoff more than the scroll slough cutoff (Table 4).…”

“…The process of chute cutoffs has been associated with the transition from a meandering to a braiding style (Ashmore, 1991;Kleinhans and van den Berg, 2011;Zolezzi et al, 2012) because the frequent occurrence of cutoffs render a river multichannel and weakly braided by definition and because chute cutoffs are also frequently observed in braided rivers contrary to neck cutoffs. Furthermore, chute cutoffs limit bend growth and channel sinuosity much more severely than neck cutoff, which only occurs in highly sinuous rivers (Howard, 1996).…”

“…Furthermore, chute cutoffs locally increase the sediment load causing deposition elsewhere, which affects navigation through the river (Zinger et al, 2011). Recently, significant progress was made in understanding the dynamics of chute cutoffs in field studies (Constantine et al, 2010b;Micheli and Larsen, 2011;Grenfell et al, 2012), while morphodynamic models have remained underemployed for this purpose (Howard, 1996;Zolezzi et al, 2012). Here we study the controlling factors for initiation and development of chute cutoffs based on field observations, a morphodynamic three-dimensional (3D) model, and a onedimensional (1D) model with a nodal-point relation for the partitioning of flow and sediment.…”

Numerical simulation of large‐scale bed load particle tracer advection‐dispersion in rivers with free bars

“…For instance, bed forms (ripples, dunes, and antidunes) [ Blom and Parker , ], multiple‐row bars [ Fujita , ; Schuurman et al ., ], braiding [ Kasprak et al ., ], and meandering [ Asahi et al ., ] are dynamic components that add complexity to the problem of tracer dispersal. Corresponding static components include curvature‐induced forced bars [ Blondeaux and Seminara , ], midchannel bars driven by channel width variation [ Zolezzi et al ., ], and floodplains occasionally accessed by the flow [ Lauer and Parker , ]. Interactions among components of dynamic bed evolution at different spatial and temporal scales can result in a complex pattern of bed surface elevation variability, and static components can serve to store large amounts of sediment.…”

Variable input parameter influence on river corridor prediction

“…Meander migration models further assume that the channel width remains constant in space and time, implying that the lateral channel shift is governed by bank erosion and that opposite bank accretion occurs at the same rate. Zolezzi et al (2012) analysed the effects of channel width variations in phase with the channel curvature and found that width variations enhance river bed dynamics.…”