Abstract
The flocculation of cohesive sediments represents a critical process in coastal sediment transport, with its appropriate representation in numerical models crucial for the prediction of contaminant transport, coastal morphodynamics and engineering problems. In this study, a flocculation model considering the effects of multiple fractal dimensions is incorporated into a two-phase numerical modelling framework and used to investigate the effects of spatio-temporal variations in sediment concentrations on the temporal evolution of local floc sizes. Initially, the model is applied to simulate the aggregation of clay suspensions in a vertical grid-stirred settling column, with results confirming the importance of multiple fractal dimensions when predicting the time evolution of floc sizes. The adoption of multiple fractal dimensions, in particular, allows the two-phase numerical model to better match the measured settling column data with improved overall correlation. This is especially the case when predicting initial floc size growth during the early period of settling when the flocs tend to adjust more rapidly to their equilibrium sizes. The two-phase model is then applied to simulate field measurements of mud resuspension process in a tidally driven channel. Again, by considering multiple fractal dimensions within the flocculation model, better agreement is obtained between observed and modelled suspended sediment concentrations, while predicted floc sizes are also in general accord with previous field measurements made within the same estuary.
Highlights
Understanding the flocculation of cohesive sediments is very important for the accurate prediction of suspended sediment and contaminant transport in coastal environments, and associated impacts initiated by coastal engineering works (Mayerle et al, 2015; Guo et al, 2017; Watson et al, 2018)
The corresponding 1DV two-phase flocculation model results indicate that Model B provides far closer agreement with the measured time evolution of rms floc sizes, both in terms of the initial rapid flocculation and equilibrium floc size attained, while Model With Constant Fractal Dimension (Model A) significantly underpredicts the initial flocculation rate before reaching the same equilibrium floc size at a later elapsed time
A new two-phase model that accounts for detailed cohesive sediment flocculation processes was applied to simulate the time evolution of floc sizes measured in an idealized, grid-stirred settling column
Summary
Understanding the flocculation of cohesive sediments is very important for the accurate prediction of suspended sediment and contaminant transport in coastal environments, and associated impacts initiated by coastal engineering works (Mayerle et al, 2015; Guo et al, 2017; Watson et al, 2018). The effective density and yield strengths of the flocs, determined by the solids content, the size and density of primary particles, and the irregular shape and porous structure of the flocs, can vary during sedimentation, affecting deposition, consolidation, and erosion processes within cohesive sediment beds (He et al, 2016; Xu, 2019; Yang et al, 2019). This spatio-temporal variability suggests that mere reliance on information associated with equilibrium floc sizes or SSC may be insufficient to fully characterize flocculation processes in highly dynamic coastal waters. In order to accurately predict the transport and fate of cohesive sediments within such aquatic environments, the transient nature of the physical floc properties throughout their life cycle needs to be better accounted for in predictive numerical models
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
