Suspended Load from Error-Function Models

Models for the vertical distributions of flow velocity and sediment concentration based on the assumption of an error-function distribution of turbulent diffusivity are used in calculating the suspended-load discharges for two sets of flume data. The flow and sediment variables required for the calculation procedure are the mean flow velocity, flow depth, shear velocity, and fall velocity and diameter of the sediment particles. For coarse sand (D=0.54 mm), the effective bed concentration serves as a convenient reference concentration for the suspension calculations, but for the fine sand (D=0.1 mm) for which statistical bed-form data are not available, a measured reference concentration is required to facilitate agreement between measured and calculated discharges of suspended sediment. For the 0.54 mm sand, the effective bed concentration is obtained from the probability density function of the bed surface, which can be approximated by a gamma function.