Finesediment

Finesediment refers to the fine-grained portion of sediment, typically comprising clay and silt particles that are smaller than sand. In sedimentology, fines are distinguished from coarser grains by particle size and transport dynamics. Clay particles are generally less than 2 micrometers in diameter, while silt ranges from about 2 to 63 micrometers; some classification schemes also include very fine sand within the broader category of fines depending on context.

Formation and sources of finesediment arise from chemical and mechanical weathering of rocks, as well as biological and biochemical processes. They are commonly produced and maintained by erosion and weathering processes, and are transported as suspended load by rivers, wind, and ocean currents. In calm water bodies such as lakes, floodplains, marshes, deltas, and deep-sea environments, fines tend to settle out and accumulate as cohesive layers.

Physical properties of fine sediments include a high specific surface area and, in the case of clays, notable cohesive strength due to electrochemical interactions. They often exhibit low permeability despite relatively high porosity. Because of slow settling velocities, fines are readily transported and can form stratified deposits in low-energy environments; their behavior is influenced by concentration, salinity, and water chemistry.

Environmental and engineering considerations surrounding finesediment include their potential to carry pollutants and nutrients, affect light penetration and habitat quality through turbidity, and influence reservoir and coastal dynamics. In engineering practice, management concerns focus on dredging, sedimentation control, resuspension, and the impact of fine sediments on foundations, waterways, and water treatment.