Abstract
AbstractRiver channels are among the most common landscape features on Earth. An essential characteristic of channels is sinuosity: their tendency to take a circuitous path, which is quantified as along-stream length divided by straight-line length. River sinuosity is interpreted as a characteristic that either forms randomly at channel inception or develops over time as meander bends migrate. Studies tend to assume the latter and thus have used river sinuosity as a proxy for both modern and ancient environmental factors including climate, tectonics, vegetation, and geologic structure. But no quantitative criterion for planform expression has distinguished between random, initial sinuosity and that developed by ordered growth through channel migration. This ambiguity calls into question the utility of river sinuosity for understanding Earth's history. We propose a quantitative framework to reconcile these competing explanations for river sinuosity. Using a coupled analysis of modeled and natural channels, we show that while a majority of observed sinuosity is consistent with randomness and limited channel migration, rivers with sinuosity ≥1.5 likely formed their geometry through sustained, ordered growth due to channel migration. This criterion frames a null hypothesis for river sinuosity that can be applied to evaluate the significance of environmental interpretations in landscapes shaped by rivers. The quantitative link between sinuosity and channel migration further informs strategies for preservation and restoration of riparian habitat and guides predictions of fluvial deposits in the rock record and in remotely sensed environments from the seafloor to planetary surfaces.
Highlights
Single-thread channels abound on planetary surfaces with varied fluids and substrates (Komatsu and Baker, 1996; Karlstrom et al, 2013; Allen and Pavelsky, 2018; Fig. 1)
For natural channels that lack indicators of channel migration, we propose that spatially correlated randomness as expressed by the AR-2 model represents the null hypothesis for river sinuosity and can be used to test the significance of environmental interpretations
The low probability of exceeding this critical value (Sc = 1.5; Fig. 2C) indicates that for channels with S > Sc, the null hypothesis can be rejected, and that non-random, ordered channel migration is a necessary condition for the sinuosity observed
Summary
Single-thread channels abound on planetary surfaces with varied fluids and substrates (Komatsu and Baker, 1996; Karlstrom et al, 2013; Allen and Pavelsky, 2018; Fig. 1). For natural channels that lack indicators of channel migration, we propose that spatially correlated randomness as expressed by the AR-2 model represents the null hypothesis for river sinuosity and can be used to test the significance of environmental interpretations. We systematically characterized the AR-2 model and quantitatively compared its outputs to natural channels to predict the natural range of river sinuosity due to initial randomness in the channel path.
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