HYPERCONCENTRATED SAND-WATER MIXTURE FLOWS OVER FLAT BED

Field surveys and experiments in two tilting flumes on hyperconcentrated sand-water-mixture (swm) flows were conducted. This paper is limited to supercritical flows over a flat bed. It is shown that an equilibrium slope can be defined at which sedimentation and erosion are in balance. For laminar flow conditions this slope is only dependent on the average sand concentration, whereas for turbulent conditions the flow rale per unit width is the main parameter. The sand concentration near the bed measured about 35% by volume for most test conditions. The vertical gradient in sand concentration decreased with increasing mean sand concentration, indicating a decrease in the damping of turbulence. The velocity distribution behaved fairly logarithmically, showing a variation in slope with varying sand concentration. A minimum value of the effective von Karman constant was found at concentrations of about 20%. Finally, it appears plausible that at high concentrations a considerable growth of the viscous sublayer occurs, resulting in an increase in bed shear stress. © ASCE.