Particle-Resolving Simulations of Cohesive Sediment Dynamics: Towards a Better Understanding of Sedimentation, Stability, and Erosion

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The dynamics of cohesive sediment is governed by the interplay of gravitational, electrostatic and hydrodynamic forces. Earth-based laboratories do not allow for the investigation of cohesive and adhesive forces in isolation, as these are usually obscured by the effects of gravity and gravitational settling. Consequently, existing models for the dynamics of cohesive sediment have severe shortcomings, and reliable scaling laws for the magnitude of the inter-particle forces and the resulting flocculation rates and erodibility as functions of such parameters as grain size, surface size, grain material, and water salinity are not available. This represents a serious impediment for predictive modeling efforts of a range of environmental systems, in which cohesive sediment plays a central role, among them rivers, lakes, estuaries, the coastal ocean, fisheries and benthic habitats. By quantifying the dynamics of cohesive sediment using a sophisticated computational approach of particle-resolving Direct Numerical Simulations, the proposed research will create and analyze a unique type of dataset to provide scaling laws for flocculation and erosion processes. This will be accomplished by enhancing state-of-the-art numerical models for cohesive forces that will be validated using microgravity experiments carried out at the International Space Station (ISS). The obtained data can then serve as a benchmark for the scaling of cohesive forces to account for the complex interaction of cohesive sediment and its ambient fluid within the framework of particle-resolving Direct Numerical Simulations. Questions to be asked are (a) Can effects of varying salinity and porous aggregates be incorporated into the existing framework of phase-resolved simulations? (b) How accurate is such a model with respect to experimental benchmark data? (c) How do settling speeds of cohesive sediment vary as a function of sediment and salt concentration? (d) How does the formation of agglomerates impact on the depositional behavior of fine sediment and contaminants/nutrients? (e) How is cohesive sediment eroded and transported as it alters flow conditions under the influence of external shear? (f) Can the numerical data be used to reproduce critical thresholds for erosion and sediment transport rates from experimental data? The proposed research will result in advanced predictive models in hydraulic engineering, water resources management, and geophysical sciences.