Morphodynamic types of the Lower Irtysh

Despite its economic importance, the Lower Irtysh has not yet been sufficiently investigation. The first analysis of the channel formation conditions and its morphology is completed for the Lower Irtysh valley (from the confluence with the Tobol River to the mouth). The Lower Irtysh is characterized as a meandering channel. The valley is divided into three sections based on its geomorphological structure, bedrock, and changes in water discharge due to the confluence with tributaries. The upper reach of the valley includes a narrow floodplain, and a meander belt at the bottom, with meanders touching opposite sides of the valley. The second section of the valley becomes wider, and the channel siftes to its right side. The type of meanders changes to controlled and incised meanders in this section of the valley. The thirds section includes wide floodplain with channels, and meander belt located in the middle part of valley bottom. Flood discharges in the main stream decrease in the lower section of the valley due to diversion of the runoff to floodplain channels and dispersing of the flow to the floodplain during high water. Free meanders are branching at the head of bends and along the limbs forming the second-order streams. The morphological parameters of free bends and arms of branches decrease downstream, which is due to the expansion of the valley bottom, diversion of part of the water runoff to the floodplain channels. The Lower Irtysh has high rates of river banks erosion, increasing downstream and leading to a change in the morphological parameters of the channel shapes. The results are important for the water management and water transport development of the river.

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