Variable fractal dimension: A major control for floc structure and flocculation kinematics of suspended cohesive sediment

Abstract

While the fractal dimension of suspended flocs of cohesive sediment is known to vary with the shear rate, electrochemical properties of the sediment and environment, geometrical restructuring, and presence of organic matter, experimental data presented in this work suggest changes in fractal dimension also during floc genesis at constant sedimentological and hydraulic conditions. A power law function is proposed to describe these changes in floc fractal dimension during floc growth and is used to analyze its impact on floc structural parameters, settling velocity, and kinematics of aggregation and breakup. An analysis of this model for the fractal. dimension highlights changes of approximately a factor of 2 or more in floc porosity and aggregation and breakup frequencies and of approximately 1 order of magnitude in floc excess density and settling velocity compared to values estimated with constant fractal dimension. The results from this model compare well with prior experimental data collected in situ (Khelifa and Hill, 2006; Manning and Dyer, 1999). Copyright 2007 by the American Geophysical Union.