Journal Article

How Is Time Distributed in a River Meander Belt?

Viero, D. P., Finotello, A., Lapôtre, M. G. A., Graham, A., Ielpi, A., Ghinassi, M.

2023

Overview

River meandering controls the age of floodplains through its characteristic paces of growth and eventual cutoff of channel bends, forming oxbows. Hence, floodplain‐age distributions should reflect a river's characteristic size and migration rate. This hypothesis has been previously tested in numerical simulations, yet without systematic comparisons with natural systems. Here we analyze oxbow spacing and timescales of bend evolution and abandonment in natural and numerically simulated meander belts. In both cases, a saturated state is achieved whereby oxbows are spaced ∼1 meander radius apart. At saturation, the distribution of floodplain ages and probability of sediment‐storage time can be constrained from characteristic timescales of bend evolution and abandonment. Owing to the similar relationships between floodplain width and characteristic timescales in natural and simulated rivers, we postulate that this approach should apply to unconfined meandering rivers elsewhere—a hypothesis to be tested with independent geo‐ or dendrochronological data. Plain Language Summary Meandering rivers have curvy channels characterized by erosion and deposition along their inner and outer banks, respectively. Over time, continued erosion and deposition shuffle sediment along the river plain, and lead to channel bends joining each other, through a process—called neck cutoff—that isolates a channel segment in between. These processes control the age of sediment and soil in a river plain over timespans much longer than human life, such that evolution models of meandering rivers often rely on numerical simulations. Here, data from both natural and simulated rivers show that, over time, neck cutoffs find themselves in closely spaced arrangements, and that their position can inform typical sediment ages once the river's characteristic pace of erosion and deposition are accounted for. These results may be tested in the future with direct age determination and, if corroborated, could further inform future studies on river organic‐carbon budgets. Key Points Natural and simulated river meander belts reach a saturated state whereby oxbows are arranged ∼1 meander radius away from each other Distribution of floodplain sediment age is controlled by meander location, sizes, and channel migration rate Natural and numerically simulated floodplains display similar relationships between their width and sediment‐age distribution

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Abandonment / Age / Age determination / Bank erosion / Belts / Carbon budget / Channel bends / Chronology / Current meandering / Dendrochronology / Deposition / dynamic time warping / Evolution / floodplain / Floodplains / fluvial / Fluvial sediments / Hypotheses / Mathematical models / Meander belt / Meandering / modeling / numerical simulation / Numerical simulations / Probability theory / River channels / River meandering / River meanders / Rivers / Saturation / Sediment / Sediments / Simulation / Soil erosion / Storage