The Effect of Floc Strength in a Size Class-Based Flocculation Model
Abstract
Flocculation controls the settling velocity of cohesive sediments while the porous aggregates can contain organic carbon, nutrients, pollutants, biologically secreted substances, and even sand grains. Due to the complexity of flocculation, the effects of flocculation on sediment and substance transport are parameterized with simple empirical formulas or simply used as tuning parameters in existing models. A more quantitative description of flocculation may be accomplished by examining the floc dynamic for a range of size classes. We investigate a size-class-based floc population balance model (Verney et al., 2011, Cont. Shelf Res.) for its capability to predict flocculation timescale and floc size distribution in order to constrain several highly uncertain empirical parameters during aggregation and breakup processes. The model results were compared with measured time series data of floc size for and reported by Keyvani and Strom (2014, Marine Geo.) in homogeneous turbulence. Our preliminary investigation indicates that there is no unique set of model coefficient values that can reproduce the measured data. We hypothesize that the description of floc strength may be too simple to successfully describe the flocculation timescale and floc size distribution simultaneously. Most existing models assume that floc strength is a given empirical constant and independent of the floc size. Consequently, researchers have proposed to specify the floc strength as an empirical constant (Maggi et al., 2007, J. Hydro.) and it is often incorporated into another coefficient called fragmentation rate. We adopt the experimental results of Jarvis et al., (2005, Water Res.), which indicate that floc strength is a variable. Preliminary results for the improved model capability due to variable floc yield strength will be presented in the conference. Our ongoing work focuses on a comprehensive investigation on flocculation using particle-scale simulation (Vowinckel et al. 2019, Zhao et al. 2020, J. Fluid Mech.) and laboratory experiment (Ye et al., this meeting). Improved flocculation model and parameterization for settling velocity will be incorporated in a Eulerian turbulence-resolving model (Yue et al. 2020, J. Geophys. Res.) for more realistic simulation of fine sediment processes in the benthic zone.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMEP0010020P
- Keywords:
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- 1861 Sedimentation;
- HYDROLOGY;
- 3022 Marine sediments: processes and transport;
- MARINE GEOLOGY AND GEOPHYSICS;
- 4863 Sedimentation;
- OCEANOGRAPHY: BIOLOGICAL;
- 4558 Sediment transport;
- OCEANOGRAPHY: PHYSICAL