Modeling the growth of cohesive sediment flocs in three-dimensional space

Abstract

This paper presents a model to simulate the growth of cohesive sediment flocs in 3-D space, which takes into account: Brownian motion contribution, gravity contribution, flow contribution, flow shear stress, floc breakage, and non-uniform initial sediment size distribution. Results of validation tests indicate the model is feasible to simulate the growth of cohesive sediment floc under different contributions. Floc structure in different water depths and the influence of initial sediment size distribution were tested using the new model, taking fractal dimension as an index. The simulated results show that, the sediment floc at the lower region possesses a larger fractal dimension than that of the upper region. It is mainly due to the reproduction of new stronger, denser flocs from the breakage and reform under the higher flow shear stress in the lower region. Additionally, on the assumption condition that the initial sediment size distribution follows normal distribution, an increase in the standard deviation results in the fractal dimension presents a trend from increasing to decreasing.