Rivers and other meandering systems: Natural examples and laboratory results
Abstract
Rivers meander due to an instability that is a fundamental property of fluid flow resulting from a spatial imbalance between a driving body force and resistive force. Although river meandering has been attributed to the erosion and deposition of sediments along river banks, the fundamental cause of the instability has not been identified. Rivers are only one of many fluid systems that exhibit meandering behavior, and no other involves sediments at all. Meandering is observed in derailed trains, jackknifed tractor trailer trucks, glacial meltwater, the Gulf Stream, free-falling streams, and other systems. We address the conditions that lead to the meander instability, suggesting that meandering in all systems is driven by an adverse pressure gradient, such that the resulting downstream deceleration imposed upon the fluid causes it to be energetically favorable to divert the flow to either side of its original direction. This universal framework enables determination of the conditions the meandering instability will manifest in altered flow and channel morphology. We tested the hypothesis that an adverse pressure gradient can trigger meandering under laboratory conditions in 2- and 3-D, and analyzed natural river systems that exhibit both straight and meandering behavior. Examples from natural rivers show meandering in cases of a decrease in slope, and straightening in cases of an increase. Our laboratory experiments demonstrate the onset of meandering in initially straight channels through implementation of a downstream blockage or slope decrease. Overall, this supports a fundamental instability for the onset of meandering, applicable across all meandering systems. Better understanding of meandering and its causes has implications for infrastructure near rivers, including bridges, levees, and other engineered structures, and understanding other meandering systems, such as derailed trains and, more commonly, jackknifed tractor-trailer trucks.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP42B..01S
- Keywords:
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- 1824 Geomorphology: general;
- HYDROLOGY;
- 1825 Geomorphology: fluvial;
- HYDROLOGY;
- 1830 Groundwater/surface water interaction;
- HYDROLOGY;
- 1856 River channels;
- HYDROLOGY