On numerical modeling of flocculation and cohesive sediment transport in the bottom boundary layer

Cohesive sediment transport is crucial in aquatic systems since many processes (e.g., dissolved oxygen transfer, light extinction, fate of spilt oil, morphodynamics) can be altered via the flocculation, causing deterioration in ecosystems (Ye et al., 2020). Hence, many cohesive sediment transport models with flocculation capabilities have been developed using turbulence closures such as Reynolds-averaged models (Sherwood et al., 2018) or Large Eddy Simulation (LES) (Liu et al., 2019) to represent the physics of the aggregation/breakup process. These models use the computed turbulent shear rate () in the entire computation domain by calculating the turbulent dissipation rate () and the kinematic viscosity (). However, our general understanding on flocculation effect of cohesive sediment transport in bottom boundary layer is limited. This study focuses on developing a modelling framework for a statistically averaged turbulent flow in dilute conditions, which incorporates the Population Balance Equation (PBE) and predict the weight-averaged floc property profiles such as floc density, floc diameter and settling velocity. To obtain high-fidelity turbulence statistics in bottom boundary layer, we use Direct Numerical Simulation (DNS) data (Yue et al., 2020) to establish the initial conditions (i.e., turbulent shear rate and fine sediment profiles). The DNS model uses a constant particle settling velocity () and a flocculation effect on () is not included