Flume investigations into the influence of shear stress history on a graded sediment bed

A series of flume‐based experiments was undertaken to investigate the effect of below‐threshold antecedent flow conditions on the stability of a graded sediment bed (D16 = 1.8 mm, D50 = 4.8 mm, D84 = 7.8 mm, and σg = 2.08). The experiments revealed that stability is dependent not only on the applied shear stress of the antecedent flow (1.46, 2.08, 2.19, 2.41, and 2.63 N m−2) but also on its duration (0, 15, 30, 60, 1440 and 5760 min). A new stability diagram has been developed to illustrate stress history effects for the graded substrates and hydraulic conditions used in the investigation. The diagram has implications for flume‐based experimental practice, the prediction of sediment transport rates, and sediment management in river restoration.