On the genetic classification of natural river systems: stream–channel

The importance of applying a genetic approach to the classification and typology of river channels and fluvial processes is emphasized. The concept of the “flow–channel system” encompasses both hydrodynamic and geomorphological aspects of its essence. It is noted that the development of classifications and typologies is an important component in advancing the theory of fluvial processes. A critical review of the main approaches to the genetic classification of river channels is carried out. It covers works by both domestic and foreign researchers from the mid-twentieth century to the present, including review studies. It is shown that the most well-known and developed classifications provide explanations of the main types of river channel morphology and morphodynamics in combination with analyses of controlling factors and specific geographical conditions. At the same time, a significant number of classifications rely on the use of formalized features or classification criteria and are structured hierarchically. An implementation of the principle of the dual nature of fluvial processes, as well as the essence of the concept of a “channel,” is proposed based on the concept of identifying and analyzing a specific type of morphogenesis of jet-like flows within the geographical envelope. To reflect the adaptation of such flows to terrestrial conditions and the development conditions of flow–channel systems, the factor of erosion resistance of the underlying bedrock is placed at the highest level of classification. It is proposed to distinguish groups of structural, structural-alluvial, and alluvial river channels. The second level consists of classes of river channels. The group of structural channels includes classes of bedrock, conglomerate, and clay channels. The group of alluvial channels includes classes of coarse alluvial, sandy, and sandy-loam channels. Classes within the structural-alluvial group arise as possible combinations of the structural and alluvial channel classes. The two upper ranks (levels) of the genetic classification of river channels correspond to the physics of self-formation processes, as well as to the processes of hydraulic resistance and sediment transport. These represent the main conditions for the adaptation of jet-like flow–channel systems to interaction with a solid underlying surface. However, they do not fully reflect the complete picture of river channel morphology and hydromorphology. The subsequent ranks reflect the influence of local hydromorphological conditions. These include: conditions of vertical deformation and their constraints; conditions of horizontal deformation and their constraints and variations; the hierarchical system of morphodynamic levels of flow–channel systems; specific geographical conditions; as well as the absolute size and order of the river reach. Keywords: fluvial process; genetic classifications and typologies of natural river channels; jet stream–channel systems; river landscapes; regional features of the fluvial process; geospatial objects at different levels; riverbed science; river hydraulics.