Dispersal of Fine Sediment in the Coastal Ocean: Sensitivity to Aggregation and Stratification

Book excerpt: By improving numerical representations of coastal circulation, sediment properties, and waves, we seek to develop reliable estimates of sediment concentration, transport and deposition. Efforts to include sediment transport calculations within three-dimensional numerical hydrodynamic models can increase our ability to predict suspended sediment concentrations, water column turbidity, and seabed characteristics. Predicting the dispersal of fine grained material (silts and clays) is especially critical, because they often dominate fluvial input to the coastal ocean, and control light attenuation and backscatter there. Transport of fines is difficult to predict, however, because their hydrodynamic properties vary in response to bed consolidation and repackaging as particle aggregates. Calculations of sediment concentrations are extremely sensitive to the settling velocity of such particles, which can vary over an order of magnitude, depending on aggregate size and density. The vertical dispersal of particles also responds to stratification induced by concentration gradients of suspended sediments, which is usually neglected or poorly resolved in three-dimensional models.