FORMATION OF BRANCHES AT RIVER MEANDERS

When studying channel morphodynamics, the processes and forms of meandering and branching are considered independently. However, the development of meanders on large rivers is complicated by the formation of islands on their limbs and in the neartop parts. The most striking manifestation of the process is the branched-winding channels, which develop as a result of the successive formation of islands, creating spurs of meanders if attached to the coastal floodplain. The relief of the floodplains of such rivers is hollow-island in contrast to the ridged relief of typical meandering rivers. Another form of such channels of large rivers is alternating unilateral ramifications, in which the meanders of the main (highwater) branch go around the groups of islands located in a checkerboard pattern, and the channel itself in the floodplain banks remains quasirectilinear while in a branched-winding channel it forms segmental meanders. The presence of branches at a meander of the channel disperses the runoff, and decreases the amount of water in the main branch, thus affecting the parameters of the meanders.Islands are also formed in the neartop parts of meanders, where its dynamic axis shifts towards the convex coast due to the violation of continuous flow around the banks, and erodes it. In the resulting local widening of the channel, a middle center appears and, when it is overgrown, an island is formed. A local widening of the channel is formed on rectilinear «inserts» between adjacent large meanders when the floodplain and channel flows intersect during the flood, and a middle or island is also formed in it. On the upper wings of steep bends, especially forced meanders, the formation of branches is associated with the flow backwater that occurs when it approaches the bedrock bank at the top of the meander at a high angle.The formation of branchings at the meanders of a channel should be taken into account during river development as a factor that can influence the conditions of navigation and influence the channel reshaping, which is particularly important at the places where linear structures, such as bridges and pipelines, cross the rivers.