Accurately measuring river meander migration over time is critical for sediment budgets and understanding how rivers respond to changes in hydrology or sediment supply. However, estimates of meander migration rates or streambank contributions to sediment budgets using repeat aerial imagery, maps, or topographic data will be underestimated without proper accounting for channel reversal. Furthermore, comparing channel planform adjustment measured over dissimilar timescales are biased because short‐ and long‐term measurements are disproportionately affected by temporary rate variability, long‐term hiatuses, and channel reversals. We evaluate the role of timescale dependence for the Root River, a single threaded meandering sand‐ and gravel‐bedded river in southeastern Minnesota, USA, with 76 years of aerial photographs spanning an era of landscape changes that have drastically altered flows. Empirical data and results from a statistical river migration model both confirm a temporal measurement‐scale dependence, illustrated by systematic underestimations (2–15% at 50 years) and convergence of migration rates measured over sufficiently long timescales (> 40 years). Frequency of channel reversals exerts primary control on measurement bias for longer time intervals by erasing the record of observable migration. We conclude that using long‐term measurements of channel migration for sediment remobilization projections, streambank contributions to sediment budgets, sediment flux estimates, and perceptions of fluvial change will necessarily underestimate such calculations. © 2019 John Wiley & Sons, Ltd.
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 and migration rates. The highest migration rates are associated with the highest measured channel curvatures in our data set, after accounting for a spatial lag of
- NSF-PAR ID:
- 10368649
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- Volume:
- 126
- Issue:
- 3
- ISSN:
- 2169-9003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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