Hydromorphological identification of the classes of mountain and plain rivers

This paper provides a research-based solution of the complex problem of identification of mountain and plain classes of rivers and presents recommendations for solving the corresponding problems in the normative-legal regulation in Ukraine. As of now, there are no normative definitions of «mountain river» and «plain river». This creates certain problems in their management. Particularly, the notion «river» is genetically associated with the notion «flow-channel system» (FCS). The functioning of the latter is the foundation for the development of river landscapes. Adaptation of rivers to various geographic conditions first of all manifests in the formation of typical FCS features and parameters. In quantitative aspect, the first data to emerge were the coefficients of hydraulic roughness of channels of mountain and plain rivers. There are numerous tables, some notable examples presented in this paper. We demonstrated that they depict two classes of rivers: mountain and mountain-plain rivers and plain rivers. The corresponding adaptations and classes of river FCSs are also reflected in stream-morphology studies focused on changes in the kinetics of flows along the channel and the Froude numbers. Another aspect of studying the adaptations of river FCSs to the geographic conditions is the analysis of the capacities of their self-organization, free self-formation. The forms of channels are commonly divided into forced, or confined, and free; also, there is a classification of channels according to the parameters of their resilience. Furthermore, channels are designated based on where they develop: in rocky, poorly erodible materials or cohesive soils, and in alluvial environment (alluvial river channels). Three groups of river FCSs are proposed to be distinguished: structural, structural-alluvial, and alluvial. The alluvial group should be divided into three classes: coarse-alluvial, sandy, and loamy-sand. These classes and subclasses within large-alluvial FCSs have certain characteristics of friction losses and energy losses. This most naturally manifests in the conditions of active status of the FCS. In particular, this relates to typical values of hydraulic roughness coefficients. Changes (evolution) of the subclasses of coarse-alluvial FCSs along the currents of mountain rivers are a good indicator of gradual transition to the conditions of plains. In turn, this indicates that this transition is associated with the composition of channel-forming alluvium. This indicator is related to the hydraulic roughness coefficients, longitudinal stream gradients, and the Froude number. At the same time, it is objective and the most convenient for practical use. We recommend creating a data base of mountainous river regions, and also a definition of «mountain river». It refers to river areas (homogeneous components of a young river landscape) whose sequence along the current in natural conditions starts within a landscape (geographic) mountainous regions and proceeds to the boundaries of the mountainous river region.