ЭКСТРЕМАЛЬНЫЕ И СПЕЦИФИЧЕСКИЕ ПРОЯВЛЕНИЯ РУСЛОВЫХ ПРОЦЕССОВ: ОСНОВНЫЕ ПОНЯТИЯ, КЛАССИФИКАЦИИ, КРИТЕРИИ ОЦЕНКИ

This paper represents definitions of extreme and specific manifestations of channel processes and reviews relationships between themselves and connections with extreme or extraordinary hydrological situations. The main sign for referring channel processes as extreme is the anomaly of their manifestation, which is reflected in extremely high rates and duration of development (significantly exceeding the mean maximum values), unexpectedness of occurrence and difficulties or impossibility of forecasting. Specific channel processes occur in conditions of channel formation, which differ from typical for a river or rivers in the region and have limited distribution. Criteria provided to characterize the extremality or specificity of the manifestations of channel processes, their qualitative and quantitative assessments, as well as the analysis of hydrological, geological, geomorphological and anthropogenic factors of their origin and development are given. The spatial scale of manifestations, their frequency, negative social and economic consequences and the possibility of prevention are considered. An approach to the classification of extreme and specific channel processes and the evaluation of their risk to economic activity is proposed. Typical examples of extreme and specific manifestations of channel processes in various temporal and spatial scales and natural zones are shown.