Conditions responsible for the formation and morphodynamics features of the middle Irtysh branched channel

The results of channel analysis of the Middle Irtysh River (from the state border to the city of Omsk) are for the first time presented. Despite its water management and transport importance, until recently it remained a practically unstudied river in relation to channel processes. The Irtysh River channel doesn’t comply with generally accepted ideas about the meandering of medium and small rivers and the predominant branching of large and largest rivers. It was revealed that the meandering channel within Kazakhstan is replaced by a branched one to the city of Omsk and downstream, and then, becoming a largest river, it meanders, only being complicated by islands that appear on the wings and in the top parts of the bends. It has been determined that the changing geomorphologic type of the channel along the length of the Middle Irtysh River (state border – Omsk) leads to the morphological complication of branches. Parallel-arm branches are widespread there, characterized by the elongation of large islands (L_o/B_o >> 3–4) and the straightness of the arms. The location of the channel along the right leading bedrock bank leads to the formation of branches below its ledges and irregularities that deflect the flow to the opposite floodplain bank. High anthropogenic load on the river (regulation of flow and interception of sediment by reservoirs, quarrying, and construction of dams) led to the incision of the riverbed, transformation of branches, as well as to the regression and shallowing of low-water branches, and, in other cases, to the emergence of branches and dispersal of runoff. The resulting changes in the Irtysh River bed lead to deterioration and complication of the waterway operation and water management of the river.

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