ABSTRACT
In this study, bed load transport of non-uniform sediment was studied in a laboratory flume. The sediment feeding system was not used in the flume directly, but bed material erosion in the primary parts of the flume was considered as a source to feed bed topography changes. The water discharges were 20,30 and 40 lit/s in a 10 m long and 0.9 m wide flume with longitudinal bed slopes of 0.002,0.004 and 0.006. The experiments were done with four sediment particle size distributions with different sediment sorting coefficient of 6,8,10 and 12 . The time for each experimental run was 4 hours. The observations showed that by increasing the sediment sorting coefficient the dune forms in the channel bed and got a stable condition faster. By increasing dune height, the bed surface became flatter and the dune moves slower. A major part of fine sediments has been trapped with coarser sediments, most of the sediment that trapped at the end of the flume were fine sediment. Dimensionless analysis showed that by increasing the ratio of equivalent mean diameter of the bed material to mean flow depth (De/h), Froude number increased generally, the particle Reynolds number decreased and dimensionless shear stress decreased specially for sediments with higher standard deviations and by increasing the standard deviation of sediments, the De/h ratio decreased. In addition, milder bed slopes have less Froude numbers, less particle Reynolds numbers and less dimensionless shear stress and there are lower ratios of average flow velocity to shear flow velocity https://www.w3.org/1998/Math/MathML"> u / u * https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429069246/b59e18fc-9e1d-4389-b000-a1069c1cd27e/content/eq4976.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> for steeper slopes.
