UC Davis

ABSTRACT: Rivers exhibit self‐similarity, or spectral scaling, across a wide range of spatial scales, from clusters of individual sediment grains to periodic features such as ripples, dunes, and meanders, extending to entire river valleys and networks. Previous studies have identified relationships between reaches characterized by specific wavelet scales and distinct morphological units or valley controls. Drawing on available high‐resolution lidar‐based bathymetries of 35 channel reaches, this study investigates linkages between spectral analysis measures and established channel typologies and morphological attributes across diverse river settings. We use spectral analysis to demonstrate how sub‐reach‐scale topographic variability patterns vary by flow stage and channel type. Uniform channels had the mildest spectral slopes for bed elevation variability, while confined channels had the mildest spectral slopes for width variability. In contrast, braided channels had the steepest spectral slopes for both bed and width variability. Coherence analysis revealed that the harmonic components of bed and width are largely in‐phase (i.e., when the bed is high, the channel is wide) at bankfull and flood stage, but some out‐of‐phase relationships were found at baseflow within the low‐frequency range. Finally, the longitudinal bed elevation series exhibited steeper spectral slopes with increasing mean wetted width across channel types and flow stages. Our findings on spectral slope and coherence of bed and width undulations may help improve understanding and representation of the nested structure of a river's terrain and variability at different scales from sub‐reach to watershed.