Graded bed load transport in sediment supply limited channels under unsteady flow hydrographs

Natural river channels that are sediment supply limited due to upstream water management practices and/or flow regulation often subject in-channel bed degradation and surface restructuring during natural flood hydrographs or controlled releases from dams. The heterogeneity of sizes present in these means different size classes transported more actively parts the hydrograph. A series laboratory experiments is conducted investigate response a graded range design when no supplied at boundary. results show varying temporal lag load transport hysteresis for fractions, defined by fine, medium coarse mixture. class typically exhibits clockwise hysteresis, indicating active rising hydrograph limb, whereas fine demonstrates either no/mixed counterclockwise as it becomes falling limb. On this separate limb basis, predictions fractional rates improved calculating unique reference threshold shear stresses each initiation cessation grain motions on limbs, respectively. Corresponding variations median vary depending total work unsteadiness, with peak values generally attained overall fining observed Analysis three also indicates medium-coarse fractions larger relative proportions smaller magnitude, flashy flatter hydrographs, resulting armouring post-hydrograph layer most significant end channel decreases exponentially downstream direction. Two empirical models, based combined descriptors, shown predict reasonably well yields generated under satisfactory collapse current experimental data previous datasets both uniform sediments. These provide an describe extent after passage individual hydrographs.