Particle Attachment and Entrainment in Marine Substrates Using Numerical Modeling and Laboratory Experiments

Abstract

This thesis investigates the interaction of sediment particles with flow, and marine and riverine substrates, focusing on particle attachment to emergent vegetation stems and fine sand winnowing from immobile rough substrates. Using a CFD-DEM (Computational Fluid Dynamics–Discrete Element Method) approach, it explores particle capture mechanisms within a patch of emergent vegetation, represented by cylindrical collectors, and assesses flow dynamics and fine sand movement threshold entrapped in large immobile roughness elements such as gravel beds, or Oyster beds. Particle attachment to a single vegetation stem was investigated in CFD-DEM model framework with varying adhesive forces on the vegetation stems formed by biofilms, and the effect of this surface energy was explored in attachment efficiency of the stem or collector (Chapter 2). The CFD-DEM model was also applied to study the suspended particle attachment to group of stems resembling a saltmarsh vegetation patch in regular and random arrangements, and the effect of density of vegetation patch (solid volume fraction of stems) on particle capture efficiency was explored (Chapter 3). Findings reveal that patch-averaged capture efficiency increases with vegetation density with part of the suspended load deposited at the rear of the collectors or stems. In chapter 4, sand entrainment from the interstices of immobile rough substrates was observed through laboratory experiments, relevant to applications like oyster bed restoration and gravel bed flushing in rivers. This work identifies hydrodynamic conditions for entrainment of fine sand, aiding in designing flow rates for habitat restoration by removing excess fine sediment. The results of this research offer insights into designing wetlands and bioretention zones for sediment capture and maintaining habitat health in marine in riverine environments.