Interaction between meander dynamics and floodplain heterogeneity in a large tropical sand‐bed river: the Rio Beni, Bolivian Amazon

Abstract

The evolution of meandering river floodplains is predominantly controlled by the interplay between overbank sedimentation and channel migration. The resulting spatial heterogeneity in floodplain deposits leads to variability in bank erodibility, which in turn influences channel migration and planform development. Despite the potential significance of these feedbacks, few studies have quantified their impact upon channel evolution and floodplain construction in dynamic settings (e.g., locations characterized by rapid channel migration and high rates of overbank sedimentation). This study employs a combination of field observations, GIS analysis of satellite imagery and numerical modelling to investigate these issues along a 375 km reach of the Rio Beni in the Bolivian Amazon. Results demonstrate that the occurrence of clay-rich floodplain deposits promotes a significant reduction in channel migration rates and distinctive styles of channel evolution, including channel straightening and immobilisation of bend apices leading to channel narrowing. Clay bodies act as stable locations limiting the propagation of planform disturbances in both upstream and downstream directions, and operate as 'hinge' points, around which the channel migrates. Spatial variations in the erodibility of clay-rich floodplain material also promote large-scale (10-50 km) differences in channel sinuosity and migration, although these variables are also likely to be influenced by channel gradient and tectonic effects that are difficult to quantify. Numerical model results suggest that spatial heterogeneity in bank erodibility, driven by variable bank composition, may force a substantial (c. 30%) reduction in average channel sinuosity, compared to situations in which bank strength is spatially homogeneous.This article is protected by copyright. All rights reserved. KeywordsMeander migration; floodplain heterogeneity; bank erosion; numerical model; planform evolution This article is protected by copyright. All rights reserved.

High spatiotemporal resolution of river planform dynamics from Landsat: The RivMAP toolbox and results from the Ucayali River

“…Nevertheless, a growing number of studies have leveraged Landsat imagery to map and measure planform changes of major rivers [e.g., Yang et al ., ; Baki and Gan , ; Gupta et al ., ]. Rivers flowing through the tropical Amazon region have been of particular interest [ Kalliola et al ., ; Constantine et al ., ; Schwendel et al ., ] partly due to their rapidly changing planforms. For example, full lifecycles (i.e., inception to cutoff) [ Schwenk et al ., ] for a number of smaller meander bends in the Amazon were captured within the growing 32 year window of Landsat imagery.…”

Multi‐annual contemporary flood event overbank sedimentation within the vegetated lower Orinoco floodplain, Venezuela

“…As pointed out by Steiger, Tabacchi, Dufour, Corenblit, and Peiry (), overbank sedimentation processes, rates and patterns are controlled by many different factors from basin (e.g., sediment production, Latrubesse & Restrepo, ) to local scales (e.g., formation of a sediment tail, i.e., an obstacle mark, in the lee of a floodplain tree; Rodrigues et al, ; Corenblit et al, ). Therefore, the spatial variability of floodplain sedimentation tends to be inherently complex in terms of quantity and quality (e.g., texture, nutrient and contaminant content; Walling & Bradley, ; Asselman & Middelkoop, ; Steiger & Gurnell, ; Aalto, Wesley, & William, ; Schwendel, Nicholas, Aalto, Sambrook Smith, & Buckley, ; Omengo, Alleman, Geeraert, Bouillon, & Govers, ).…”

Meander cutoffs nonlocally accelerate upstream and downstream migration and channel widening

“…Oxbow lakes form "plugs" through the consolidation of silt, clay, and organic matter that increase local resistance to erosion and impede or confine meander migration [Fisk et al, 1949;Hudson and Kesel, 2000]. On the other hand, oxbow lakes may also promote meander migration if the migrating channel revisits the oxbow before plugs have formed [Schwendel et al, 2015]. A study of over 90 years of migration observations along the Sacramento River determined that cutoffs alone accounted for nearly 20% of the total channel migration [Micheli and Larsen, 2011].…”