A Heuristic Method for Measurement and Characterization of River Meander Wavelength

Historically, meander planform data have been analyzed by various statistical and geometrical techniques, but uncertainty persists about the wavelength, frequency, and reference geometry. Therefore meander wavelength was analyzed in the Fourier frequency domain by power spectral analysis in terms of hierarchical centerlines as a reference geometry, eliminating some of the subjective bias associated with wavelength measurements. Equally spaced sampling points were located along the talweg of meandering streams. Sample values were measured as the perpendicular distance to a reference line connecting meander belt midpoints. This line, itself meandering, constitutes a river's second‐order meander frequency, which is analyzed with respect to a still higher‐order reference line. Sampling along the talweg attenuates the spectral estimates of natural frequencies of meanders. Corrections are obtained by multiplying frequency peaks by the sinuosity of the study reach. Power spectra obtained from hierarchical reference lines of first‐ and second‐order meanders of the White River in southern Indiana indicate discrete frequencies in each order. First‐ and second‐order harmonics are observed at high and low frequencies. Complex meandering along the Dolores River in western Colorado is characterized by very low‐frequency energy in third‐order meanders and successively higher frequency energy in second‐ and first‐order meanders. A comparison of power spectra for hierarchical and arbitrary reference lines shows that arbitrary references condense spectral estimates of meander energy within artificially averaged frequency bands. Another comparison, using the theory of minimum variance for meander formation, confirms that hierarchical reference lines improve meander characterization.