Influence of Sediment Supply Timing on Bedload Transport and Bed Surface Texture During a Single Experimental Hydrograph in Gravel Bed Rivers

Channel stability and sediment transport in gravel bed streams depend on temporally and spatially variable fluid forces, bed surface structures, armoring, and sediment supply/storage. Of particular interest here is the influence of sediment supply timing on bedload transport rate and grain size distribution, bed surface composition and channel morphology. We conducted flume experiments in a sediment feed flume with poorly sorted sediment. A symmetrical, identical stepped hydrograph was used with five different sediment feeding schemes: no feed, constant feed, rising-limb only feed, falling-limb only feed, and variable feed. The same sediment mass of 800 kg was fed during each experiment. Sediment transport rates ranged over five orders of magnitude regardless of feeding scheme. Clockwise hysteresis was observed for bedload transport rate and bedload grain size, that is, the transport rate was larger and coarser during the rising limb. Counterclockwise hysteresis was observed for the grain size distribution of the bed surface, that is, the bed surface was finest during the rising limb. In all experiments sediment yield during the rising was higher than during the falling limb, indicating that the rising limb is more capable to transport the supplied sediment. Our study provides insight on how timing of sediment supply influences sediment transport and bed surface during a single hydrograph, essential information for artificial sediment supply projects to restore and habilitate gravel bed streams. Sediment yield during a single hydrograph is dominated by sediment supply in the rising limbClockwise hysteresis characterizes sediment transport despite the sediment feed timingCounterclockwise hysteresis was observed for bed surface grain size in most experiments

Automated summary

Channel stability and sediment transport in gravel bed streams are influenced by fluid forces, bed surface structures, armoring, and sediment supply/storage. This study focuses on the impact of sediment supply timing on bedload transport rate, grain size distribution, and channel morphology. Flume experiments were conducted with five different sediment feeding schemes. Results showed that sediment transport rates varied over five orders of magnitude regardless of the feeding scheme. Clockwise hysteresis was observed for bedload transport rate and grain size, indicating higher transport rate and coarser grain size during the rising limb. Counterclockwise hysteresis was observed for the grain size distribution of the bed surface, suggesting that the bed surface was finest during the rising limb. Sediment yield during the rising limb was higher than during the falling limb, indicating the importance of sediment supply timing in sediment transport. This study provides valuable insights for sediment supply projects in restoring gravel bed streams.