Processes of Initiation of Motion Leading to Bedload Transport in Gravel-bed Rivers

Abstract

[eng] Transport processes that lead to the initiation of bedload motion in gravel‐bed rivers have not yet been clarified. We report patch‐ and grain‐scale processes involved in the initiation of bedload motion in a natural gravel‐bed stream as observed through a series of video experiments. With increasing flow strength, the phases of initiation of motion that have been identified are (1) within‐patch grain instability (grain vibration, pivoting, and grain‐scale rolling), (2) within‐patch gyratory step‐and‐rest motion, and (3) general sediment motion involving downstream transport from an individual patch and the throughput of grains inherited from upstream.