COMPARATIVE HYDRO-MORPHOLOGICAL ANALYSIS OF THE ISLANDS OF DIFFERENTLY BRANCHED UPPER OB AND MIDDLE LENA RIVER CHANNELS

This article is devoted to the formation conditions and morphometric features of the river islands. Also it considers the rate of branching of the Upper Ob and Middle Lena river channels. They are the largest rivers, but the Middle Lena River is bigger than the Upper Ob River by 6.15 times of total runoff and 2.5 times of width. However, both of them have unstable or weakly stable channels, characterized by parallel-sleeve, alternating, one-sided and single branchings, formed by numerous islands. Their comparison makes it possible to establish the dependence of the conditions of islands formation, their parameters (length - L , width - B , shape - L / B ), types and number on the indicators of stability, total runoff, branching types and location in the channel (active or peripheral part). These correlations based on hydro-morphological analysis show that the shape of islands L / B and the branching rate of the channel - n / x depend on the degree of stability. It is a common feature of all branching types and stages of island evolution (elementary, small, large islands and island massifs). Uniform dependencies of island parameters on river bed stability for both rivers, despite their large-scale distortions, were obtained by taking into account the connection of channel width ( b ) with its runoff ( Q ) by introducing a correction factor of 2.5 for the river size. Also the formation conditions of elongated islands ( L / B > 5), were determined. Their shape does not correspond to the optimal ratio L / B = 3...4. The revealed patterns give an opportunity to clarify the previously proposed classification of the islands.