| I examine the behavior of fine particles transported in turbulent flows using complimentary laboratory and field studies. Previous experimental studies of fine-particles comprise a useful dataset directly applicable in some cases to silt-sized particle behavior. However, no clear consensus has emerged among earlier workers on the behavior of silt-particles in environmental or artificially-generated open-channel flows---nor has a unifying or phenomenological understanding been articulated. In order to resolve these outstanding questions, I systematically perturb or alter well-characterized experimental environments to identify and characterize processes controlling deposition, entrainment, and infiltration of fine particles. The resulting experimental data indicate that silt-sized particle deposition slows with increasing flow intensity regardless of bed state, while particle entrainment is bed state dependent and effectively eliminated for immobile, porous beds. Entrainment processes do not size-selectively erode or transport fine, silt-sized particles to a discernable or consistent degree. These findings are consistent with and support the hypothesis that viscous-shear lift on particles is induced at the sediment-water interface and in the water column by channel-flow turbulence anisotropy. Conversely, mass flux and extent of fine-particle infiltration into permeable sediments increase with mean and turbulent measures of flow in a fashion generally consistent with that of passively-transported mass but with apparent asymptotic limits. Results reported here highlight relationships between particle transport, bed conditions, and turbulent environmental flows---and are directly relevant to: (1) transport and fate of contaminants, (2) behavior of particulate organic matter and, (3) use of silt grain-size as a proxy for past flow intensity. |
