Closure

Abstract

The physical process to be described in the simplest case is the transport of fine solid particles in a steady uniform turbulent flow. Matter becomes more complicated when flow conditions get non-uniform or unsteady as in natural river sections, reservoirs and under flood conditions. There are well known procedures to measure the size distribution for a sediment probe even for very tiny particles. All our rivers, however, have turbulent flow conditions and unfortunately the knowledge about the influence of turbulence on settling velocity is very scarce. The whole flow field in a river besides secondary currents in bends is strongly affected from the bed conditions. Every change of discharge may result in different bed conditions and flow parameters. Non-uniform flow conditions as mostly present in a natural rivers mean changing sedimentation respectively erosion rates. There is another severe lack in many suspended sediment transport models because of the integration of the diffusion equation a boundary value is missing.