| Summary: | Channel morphologies embody the physical reaction between channel substrate, bed material, and flow regime. This study examines reach-scale morphology variability in an ungauged tropical headwater stream. Field morphology classifications are validated through quantifying instream wood distribution and modeling the down-reach hydraulic variation of boundary shear stress and mean stream power. Bifurcated reaches display increased wood abundance and loading, as they provide a means of storage for unattached pieces. This corresponds with the transition from a stepped morphology to a widened, meandering reach that bifurcates around a mid-channel bar, followed by a transition back to a stepped morphology. Hydraulic modeling of two bifurcated reaches demonstrated significant variability in shear stress and stream power in one dimension through these transitions. These results substantiate the effectiveness of coupling field classification schemes with ultra-high resolution topographic surveys when investigating unmonitored streams and they indicate that transitional reaches can punctuate bedform regularity in high-energy drainages.
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