Sediment flocs: settling velocity, flocculation factor, and optical backscatter

Improved relationships for the flocculation factor and floc settling velocity are proposed. They differ from the existing formulas by accounting for the effect of floc porosity on the hydrodynamic drag and for the fractal properties of the floc projection on the plane. These relationships predict that the fractal dimension d influences the floc settling velocity W, only if d greater than or equal to 2. A flocculation effect on optical backscatter is also considered, and a fractal-based relationship for quantifying this effect is proposed. This relationship serves as a basis for a simple optical backscatter sensor (OBS) based technique for estimating some fractal-related parameters of sediment flocs involved in the proposed relationships for the settling velocity and flocculation factor. The technique is tested using data from three field sites. The potential effect of particle size on backscatter efficiency is highlighted, and an approach for accounting for this effect is suggested.