Development of a spectrum-based scheme for flocculation processes in estuaries

Abstract

Flocculation processes of cohesive sediments in estuaries play a critical role on sediment transport and biogeochemical cycles in estuaries. Due to convergence of marine saltwater and freshwater runoff, coupled with periodic tidal cycles, cohesive sediment exhibits intricate flocculation processes that are challenging to simulate. It has been found that the size bin-based schemes are effective to simulate these processes, especially under highly variable conditions. However, the application of this kind of scheme is limited due to expensive computational cost. In the study, we develop a new spectrum scheme based on the spectral pattern of floc size distribution from a size bin-based scheme to expedite modeling execution. The newly-developed scheme is implemented into the Princeton Ocean Model (POM) and applied to simulate cohesive sediment transport in the Hudson River Estuary. The effectiveness of this spectrum scheme is evaluated by comparing simulation results with in-situ observations and results from a size bin-based scheme. The results indicate that the newly-developed scheme can well simulate the time evolution of floc concentrations. Compared to the original size bin-based scheme with 15 bin number, the average percentage error is about 1.86%, with an average acceleration of 4.60 times for cohesive sediment advection. Additionally, as the parallel core numbers and bin numbers increase, the acceleration effect of this bin-spectrum scheme gets better. In summary, the newly-developed spectrum scheme for flocculation processes provides significant acceleration benefits for size bin-based schemes, and has a potential to be widely used for simulating flocculation processes in estuaries.