Scale dependent spatial structuring of mountain river large bed elements maximizes flow resistance

Macro-roughness elements such as boulders and bedrock outcrops, collectively referred to large bed (LBEs), are key features influencing hydrodynamics morphodynamics in mountain rivers. Where LBEs abundant account for a substantial portion of total flow resistance, existing geomorphic theory, previous physical experiments, limited field observations support the theory that LBE configurations adjust maximize resistance. However, methods explicitly map individual along entire river segments lacking, thus limiting analysis spatial structure boulder-bedded In addressing these gaps, this study sought develop procedure mapping from 3D point-clouds, explore real river, test hypothesis were organized The applied ground classification algorithm produce roughness surface model, which extracted by marker controlled watershed algorithm. Implementing procedure, 42,176 mapped 13.2-km mountainous Yuba River (Northern California). Scale discharge-dependent concentration spacing metrics quantified multiple laterally and/or hierarchically nested domains classified differentiate three flow-resistance based hydrodynamic regimes: isolated roughness, wake interference, skimming flow. Of regimes, interference corresponds state maximum so testing involved determining if regime was dominant. Results confirmed 25 28 segment- reach-scale concentrations regime. 24 same Concentration metrics, quantify density given area, differ represent proximity one another. While comparison segment classifications each metric concluded superior purposes, disparities leave open questions about extremal model adjustment. Lastly, lateral variability across corridor had implications