Maxium Sediment Capacity of Saltating Sediment Size Mixtures
Watershed Physical Processes Research Unit
2012 Annual Report
1a.Objectives (from AD-416):
Improve predictive capability of the maximum transport capacity of sediment size mixtures in shallow flow
1b.Approach (from AD-416):
Experimental studies will be conducted in laboratory channels to determine the mode and rate of non-cohesive granular material in relation to differences in material characteristics and hydraulic flow regimes. Improved predictions of sediment transport capacities will be determined from experimental data sets, taking into account the effect of the boundary layer thickness in relation to particle size.
Studies concerning the movement of sediment mixtures in shallow overland flow were performed. Activities consisted of saltation experiments in which mixtures of two sand sizes, one with a medium diameter of 1.29 mm (coarse sand), and the other with a medium diameter of 0.78 mm, were seeded into several shallow flow regimes of 10, 15.7, 21.6, and 25 l/min, respectively. Three mixtures were studied which, by weight, consisted of 80% medium sand and 20% coarse sand, 50% medium sand and 50% coarse sand, and 20% medium sand and 80% coarse sand. The total weight of each mixture was the same. Velocities were measured with two closely spaced optical probes that were aligned in the direction of flow. Preliminary results indicate that the velocity of sand size mixtures are different from those of uniform size sand material at corresponding mass concentrations. Additional experiments and analytical considerations are planned to elucidate these findings.