资源环境科技发展态势分析平台

Bedload movement is fundamentally probabilistic. Our quantitative understanding of gravel transport is particularly limited when flow conditions just exceed thresholds of motion, in part because of difficulties in measuring transport statistics during natural floods. We used accelerometer‐embedded tracer clasts to precisely measure the timing of grain motions and rests during snowmelt floods in Halfmoon Creek, a gravel‐bed mountain stream in Colorado, USA. These new data let us explore how probabilities of tracer movement varied as functions of discharge and time. Bedload hysteresis occurred over both daily and seasonal timescales, and included clockwise, counter‐clockwise, and figure‐eight patterns. We empirically explain the hysteresis by modifying a bedload transport model to have an evolving threshold of motion parameter. We calculate how the thresholds of motion progressively evolved through time over 22 days during the 2015 snowmelt flood. Our results quantitatively show that thresholds of motion are functions of both (a) cumulative shear stress and (b) temporal changes in shear stress during floods.