The effect of shear-dependent flocculation on the multimodality of effective particle size distributions in a gravel-bed river during high flows

Abstract Purpose Multimodal effective particle size distributions (EPSDs) develop as flocculation and breakage occur dynamically in a fluid shear such have been previously reported coastal estuarine waters to understand processes. Here, we use time varying multimodal EPSDs hydraulic parameters (discharge bed stress) assess freshwater gravel-bed river southern Alberta, Canada. Methods Instantaneous discharge, volume concentration (VC), EPSD of suspended solids were measured during three high discharge events at four study sites 10 km reach the Crowsnest River. The VC (< 500 µm) centroid flow with LISST-200x. Bed stress for was obtained using model, MOBED. Results consisted primary particles, flocculi, microflocs, macroflocs. Shear dependent consistently observed all events, due low flocculation, breakage, mobilization tributary sub-catchment derived particles. Higher limited smaller floc sizes, while lower conditions created higher volumes Conclusion Flocculation processes based on relationships between properties presented herein implications advancing fine sediment transport models by variable cohesion factor function class.