Scaling of River Meander Skewing and Fattening Modulated by Environmental Conditions

Finite-amplitude meander growth is accompanied by higher-order planform distortion, including fore–aft asymmetry (skewing) and internal curvature redistribution (fattening and sharpening). Although these traits are widely observed in natural rivers, their systematic scaling and environmental modulation remain poorly constrained. Here, we analyze 1,697 individual bends from 12 freely meandering rivers spanning arid, highland, arctic, and tropical environments. Meander centerlines are fitted with a modified Kinoshita-type function to extract non-dimensional skewing and fattening coefficients, enabling consistent comparison across river sizes and environmental settings. Results reveal robust scaling relationships linking higher-order distortions to fundamental, first-order meander morphometrics, including inflection angle, sinuosity, and wavelength. Upstream skewing strengthens progressively with increasing bend amplitude and sinuosity, reflecting an autogenic outcome of nonlinear, curvature-driven meander growth. In contrast, fattening and sharpening are strongly controlled by normalized wavelength, indicating partially independent evolution of bend amplitude and wavelength. Allogenic forcings, including hydrological variability and riparian vegetation density, primarily modulate first-order morphometrics and the variability of skewing and fattening around scaling trends, producing systematic differences in meander geometry across river types. Together, our results define a continuous spectrum of natural meander planforms and provide a quantitative framework for synthesizing representative meander geometries and interpreting river evolution under contrasting environmental conditions.