ИСТИНА

Extreme and specific channel processes was classified with parameterization by their features. Hardly predictable abrupt occurrence, very high rates and duration of riverbed deformations which are exceeding typical values considered as signs of the process extremeness. Increased rates of riverbanks erosion, aimed sediment accumulation and downcutting, accelerated avulsions of braided streams and anomaly fast meander cutoffs considered as extreme manifestations. Factors of occurrence of extreme channel processes were allocated into groups. Main factor is underlying surface (of channel and valley), which is influencing the temporal variability of the vertical deformations, riverbed surface curve evolution and channel network formation. Banks resistance, their morphometry and grain-size features are influencing the rates of planar deformations and local formation of specific channel types. Influence of water regime most clearly shown during abrupt changes of stream power and may vary from temporary increasing of erosion-accumulative processes to complete stream rebuilding. Specific forms of channel processes can relate to: tidal effects in river mouths, logjams and timber drifting in forest regions, ice floating and jams, volcanic activity etc. Influences of catastrophic natural processes in channel regime are individual and depending on their direct or indirect impact. Most of that processes are accompanied with instant inflows of solid material and changes of local base levels, which involves changing of channel processes vectors from natural conditions. The author highlights 20 types of specific channel processes based on own surveys and scientific papers. Each type was identified by signs, kinds and factors of extremeness and distinctions from the typical features.