Measured distributions of velocity and concentration for intense transport of bimodal lightweight sediment in tilting flume

The laboratory experiments on the intense transport of bimodal sediment were conducted in a tilted, glass-sided flume with a variable longitudinal slope. Two fractions of lightweight solids were used, primarily differing in particle size, and each had a distinct color. The observed solid-liquid flow exhibited characteristics of being steady, uniform, turbulent, and supercritical. The bimodal sediment was transported as a combined load, with the finer fraction primarily supported by carrier turbulence, and the coarser fraction supported by interparticle contacts in the transport layer above a plane surface of the bimodal stationary bed. Distributions of solids velocity and concentration were measured for each of the two fractions across the transport layer above the bed using optical methods employing high-speed cameras. Additionally, the distribution of carrier velocity was measured across the flow depth. The measurements revealed a non-uniform distribution of solids for both fractions, with the maximum concentrations at the top of the bed for the coarser fraction and within the transport layer for the finer fraction at the highest bed shear. The results of the measurements allowed for the identification of the degree of stratification in the high-concentration sediment-laden flow and facilitated the evaluation of the interaction between particles of different fractions in the transport layer at various elevations above the bed. Furthermore, they enabled the quantification of the proportion of particles of the two fractions in the total discharge of solids through the channel.