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1. Evaluating the Relationship Between Meander‐Bend Curvature, Sediment Supply, and Migration Rates

   https://doi.org/10.1029/2020JF006058  

   Donovan, Mitchell ; Belmont, Patrick ; Sylvester, Zoltán ( March 2021 , Journal of Geophysical Research: Earth Surface)

   River meander migration plays a key role in the unsteady “conveyor belt” of sediment redistribution from source to sink areas. The ubiquity of river meandering is evident from remotely sensed imagery, which has allowed for long‐term, high‐resolution studies of river channel change and form‐process relationships. Empirical, experimental, and theoretical research approaches have described two distinct relationships between channel curvature and river channel migration rates. In this study, we employ a novel application of time‐series algorithms to calculate migration rates and channel curvature at sub‐meander bend length scales using 6 decades of aerial imagery spanning 205 km of the Minnesota River and Root River, Minnesota, USA. Results from the Minnesota River provide the first empirical evidence demonstrating how migration‐curvature relations break down for rivers with low sediment supply, which is supported by the Root River data set. This not only highlights the importance of sediment supply as a driver of river migration, but also supports a simple means to detect river reaches lacking sediment supply. Furthermore, results from both rivers demonstrate that sub‐meander bend measurement scales are most appropriate for studying channel migration rates and further indicate that a quasi‐linear relationship—rather than the more commonly inferred peaked relationship—exists between channel curvature andmore »migration rates. The highest migration rates are associated with the highest measured channel curvatures in our data set, after accounting for a spatial lag ofchannel widths. These findings are consistent with flume experiments and empirical data across diverse geologic and climatic environments.

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2. Quantitative relationships between river and channel-belt planform patterns

   https://doi.org/10.1130/G49935.1  

   Dong, Tian Y. ; Goudge, Timothy A. ( June 2022 , Geology)

   Abstract Channel planform patterns arise from internal dynamics of sediment transport and fluid flow in rivers and are affected by external controls such as valley confinement. Understanding whether these channel patterns are preserved in the rock record has critical implications for our ability to constrain past environmental conditions. Rivers are preserved as channel belts, which are one of the most ubiquitous and accessible parts of the sedimentary record, yet the relationship between river and channel-belt planform patterns remains unquantified. We analyzed planform patterns of rivers and channel belts from 30 systems globally. Channel patterns were classified using a graph theory-based metric, the Entropic Braided Index (eBI), which quantifies the number of river channels by considering the partitioning of water and sediment discharge. We find that, after normalizing by river size, channel-belt width and wavelength, amplitude, and curvature of the belt edges decrease with increasing river channel number (eBI). Active flow in single-channel rivers occupies as little as 1% of the channel belt, while in multichannel rivers it can occupy >50% of the channel belt. Moreover, we find that channel patterns lie along a continuum of channel numbers. Our findings have implications for studies on river and floodplain interaction, storage timescalesmore »of floodplain sediment, and paleoenvironmental reconstruction.« less
3. Floodplain Sediment Storage Timescales of the Laterally Confined Meandering Powder River, USA

   https://doi.org/10.1029/2021JF006313  

   Huffman, Max E. ; Pizzuto, James E. ; Trampush, Sheila M. ; Moody, John A. ; Schook, Derek M. ; Gray, Harrison J. ; Mahan, Shannon A. ( January 2022 , Journal of Geophysical Research: Earth Surface)

   As sediment is transported through river corridors, it typically spends more time in storage than transport, and as a result, sediment delivery timescales are controlled by the duration of storage. Present understanding of storage timescales is largely derived from models or from field studies covering relatively short (≤10² year) time spans. Here we quantify the storage time distribution for a 17 km length of Powder River in Montana, USA by determining the age distribution of eroded sediment. Our approach integrates surveyed cross‐sections, analysis of historical aerial imagery, aerial LiDAR, geomorphic mapping, and age control provided by optically stimulated luminescence (OSL) and dendrochronology. Sediment eroded by Powder River from 1998 to 2013 ranges from a few years to ∼5,000 years in age; ages are exponentially distributed (r² = 0.78; Anderson‐Darlingpvalue 0.003). Eroded sediment is derived from Powder River's meander belt (∼900 m wide), which is only 1.25 times its meander wavelength, a value reflecting valley confinement rather than free meandering. The mean storage time, 824 years (95% C.I. 610–1030 years), is similar to the time required to rework deposits of Powder River's meander belt based on an average meander migration rate of ∼1 m/yr, implying that storage time distributions of confined meandering rivers can be quantified from remotely sensedmore »estimates of meander belt width and channel migration rates. Heavy‐tailed storage time distributions, frequently cited from physical and numerical modeling studies, may be restricted to unconfined meandering rivers.

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4. Flume Investigation Into Mechanisms Responsible for Particle Sorting in Gravel‐Bed Meandering Channels

   https://doi.org/10.1029/2022JF006821  

   White, Daniel C. ; Nelson, Peter A. ( January 2023 , Journal of Geophysical Research: Earth Surface)

   Meandering gravel‐bed rivers tend to exhibit bed surface sorting patterns with coarse particles located in pools and fine particles on bar tops. The mechanism by which these patterns emerge has been explored in sand‐bed reaches; however, for gravel‐bed meandering channels it remains poorly understood. Here we present results from a flume experiment in which bed morphology, velocity, sediment sorting patterns, and bed load transport were intensively documented. The experimental channel is 1.35 m wide, 15.2 m long, and its centerline follows a sine‐generated curve with a crossing angle of 20°. Water and sediment input were held constant throughout the experiment and measurements were collected under quasi‐equilibrium conditions. Boundary shear stress calculated from near‐bed velocity measurements indicates that in a channel with mild sinuosity, deposition of fine particles on bars is a result of divergent shear stress at the inside bend of the channel, downstream of the apex. Boundary shear stress in the upstream half of the pool was below critical for coarse particles (>8 mm), leading to an armored pool. Inward directed selective transport was responsible for winnowing of fine particles in the pool. Fine and coarse sediment followed similar trajectories through the meander bend, which contrasts earlier studies of sand‐bedded meandersmore »where the loci of fine and coarse particles cross paths. This suggests a different sorting mechanism for gravel bends. This experiment shows that a complex interaction of quasi‐equilibrium bed topography, selective sediment transport, and secondary currents are responsible for the sorting patterns seen in gravel‐bed, meandering channels.

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5. Remote Sensing of Riverbank Migration Using Particle Image Velocimetry

   https://doi.org/10.1029/2023JF007177  

   Chadwick, Austin J. ; Greenberg, Evan ; Ganti, Vamsi ( July 2023 , Journal of Geophysical Research: Earth Surface)

   Mobile river channels endanger human life and property and over centuries shape ecosystems, landscapes, and stratigraphy. Quantifying channel movements from remote sensing is difficult, in part due to the diversity of river mobility processes (e.g., channel migration, cutoffs, avulsion) and planform morphologies (e.g., meandering, braided). Here, we present a framework for quantifying riverbank migration from remote sensing that upscales recent methodological advances from laboratory flume studies utilizing particle image velocimetry (PIV). We apply PIV to image time series of 21 rivers worldwide, showing PIV ignores cutoff and avulsion processes by design and is well suited for tracking riverbank migration regardless of planform morphology. We show that PIV‐derived results for riverbank migration are consistent with published results from centerline‐ and bank‐based Lagrangian methods. Unlike existing methods, PIV offers a grid‐based Eulerian framework where defining channel centerlines is unnecessary and quantified uncertainty in riverbank positions is propagated into uncertainty in migration rates. PIV offers means to efficiently extract global patterns in riverbank migration from decades of satellite data, as well as investigate river response to climate change and human activities in our rapidly changing world.