In‐channel surficial fine‐grained sediment laminae. Part I: Physical characteristics and formational processes

Abstract An in‐channel surficial depositional feature (surficial fine‐grained laminae) composed of loosely bound fine sediment deposited during low flow conditions has often been observed in river systems in south‐western Ontario. The physical characteristics of this feature have been determined by a direct observation image analysis system. This sediment consists primarily of flocculated fine‐grained material. The size distributions of surficial fine‐grained laminae and suspended sediment were not significantly different. Each distribution is bimodal in nature and shows a characteristic grain size deficiency in the 4‐5 μm size range. This observation suggests that flocculation and not low discharge or low competence is the dominant mechanism for the formation of surficial fine‐grained laminae under conditions of low flow in fluvial systems of south‐western Ontario. A quantitative assessment of this feature shows its potential importance as a source of fine‐grained sediment and associated contaminants for downstream transport.