Pokrovsko-Yakutsky reach of the Lena River: transformation of complex conjugated channel, recent deformations and management of channel changes

The article considers the conditions of conjugate branches’ system transformation into parallel-branched channel, which are the most complex morphologically (by the mode of deformations and management) on the example of the Pokrovsko-Yakutsky section of the middle Lena River basin in the 21st century. It may arise from the general increase in the Lena River’s water content and thawing frozen soils (composing shallow waters and near-shore shallows), as well as from the development of sleeves with unstable channel. At the same time, local conditions encouraged to the formation of a complex single (three-arm) branching at the beginning of the expansion of the valley bottom and the channel below city of Pokrovsk, the preservation of a straight unbranched channel upstream, the channel of the same type below the Tabaga Cape and alternating one-side branching at the end of the site. The modern riverbed reformation after the changes occurred consists in the transgressive displacement of floodplain-island massifs, intensive banks’ erosion, and the sediment accumulation zones’ formation. This has led to the significant complications in the river water usage (including water intake and port water areas’ sedimentation, creation an unfavorable environment in the port approaches area, berths and industrial infrastructure) and to creation of an emergency situation at the coastal infrastructure facilities. The revealed channel deformations’ regularities on the basis of long-term and modern researches and hydrodynamic modeling allowed to develop and justify the complex scheme of channel processes’ management, which implementation will allow to reduce or neutralize their adverse or dangerous manifestations.