Global Accounting of River Cutoffs Indicate Chute Channels are Associated with Non-forested Land Cover
Abstract
Freely meandering and highly sinuous rivers are often viewed as the quintessential river form found in nature. Meandering inexorably results in river cutoff, which occurs when sinuosity is reduced as the river takes a more direct path down its valley. Cutoffs are thus essential for the process of meandering, but their stochastic nature has prevented detailed understanding of connections between cutoff processes and meandering processes. While cutoffs have been classified based on whether the new channel connects bends less than one channel-width apart (neck) or connects more distant bends by carving a new distinct channel through the floodplain (chute), there is a fundamental lack of information on the distribution of each type and the conditions that cause them. Here we present a global accounting of river cutoffs, identifying 1255 cutoffs which have occurred on lowland, freely meandering rivers greater than 50 m in width since 1985. We use satellite imagery hosted on Google Earth Engine Timelapse to find the location, year of occurrence, and cutoff type, and find that 395 (31.5%) are chute cutoffs. Strikingly, about 30% of chute cutoffs occur in non-forested reaches, whereas about 5% of neck cutoffs occur in non-forested reaches. Our results indicate that chute cutoffs are dependent on erodibility of floodplain and river hydrology, because unlike neck cutoffs, chute cutoffs require overbank flow to carve a new channel into the floodplain. This observation suggests that human-induced changes to floodplain characteristics and river flows could shift the distribution of chute and neck cutoffs over time. Analysis of temporal trends in cutoff support this hypothesis by showing that the global ratio of chute to neck cutoffs increased linearly between 1985 and 2018 (R2 = 0.26). This research suggests that human-caused land cover changes could be driving fundamental shifts in the cutoff behavior of meandering rivers.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMEP005..05L
- Keywords:
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- 1820 Floodplain dynamics;
- HYDROLOGY;
- 1860 Streamflow;
- HYDROLOGY;
- 1862 Sediment transport;
- HYDROLOGY;
- 5419 Hydrology and fluvial processes;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS