The Zakharkovskaya floodplain of the Moscow River is located directly above the Moscow Ring Road. It is an example of a natural structure that is spontaneously restored after long-term economic use (hayfields, pastures, long-term plowing, summer cottege settlements, drainage and irrigation channels, silt sites, etc.) under conditions of cessation of intensive anthropogenic impact. The article deals with the history of the formation and development of the Zakharkovskaya floodplain in prehistoric times (late Holocene), in the early historical period (beginning-middle of the second millennium AD), and in the late historical period-XIX-XXI centuries. The regulation of water flow, which has occurred in recent decades, is accompanied by a relative stabilization of the Moscow riverbed, turning it into a canal, reducing the intensity of channel deformations, leveling the bottom relief with its general deepening. As in other floodplain plots, the territory of floodplain leaves the flood zone; depressions are filled in, lakes are degraded, and man-made terrain is formed. At the same time, the current restrictions on access to the territory of the Zakharkovskaya floodplain for 10-15 years have created conditions for the restoration of natural structures, in particular, forest and shrub tracts, and increased the landscape and ecological attractiveness of floodplain lands.

Floodplain of the Moskva River lower reaches is a typical man-made terrace, which was not flooded for almost 90 years, is intensively used in agriculture and gradually being built up by industrial and civil facilities. As a result of river flow regulation and long-term agricultural development the floodplain natural territorial complexes (NTC) underwent a profound transformation. Of 2,5 thousand urochisches only 179, i. e. 7,2%, or 6% of the territory, can be thought of as modal. About 13% (333 urochisches, 7% of the territory) have a slight degree of disturbance, 23,6% (587 urochisches, 54% of the territory) – medium degree and 546 urochisches (21,2%, 25% of the territory) strong degree of disturbance. More than one third (838 urochisches, i. e. 34,6%, or 9% of the territory) are technogenic, i. e. totally created by man not excepting the relief and lithological basement. In spite of the quantitative predominance technogenic complexes as linear objects occupy a small area. Due to high degree of landscape structure disturbance, the river floodplain requires increased attention, planning of economic activities, coordinated placement of engineering objects, agricultural areas and natural reserves, as well as strict compliance with land use standards and environmental legislation.

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 floodplainisland 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.

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 Rivers 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.

Тhis study aims to evaluate features of the formation and sources of the basin component of the sediment yield during flash floods. Measuring campaigns were conducted in the weakly disturbed section of the Tsanyk River basin, located in the Greater Sochi area in the foothill-lowland zone of the Caucasus Black Sea coast. We used a set of field and calculation methods, including sediment dating with application of 137Cs, pin method, Yang's method, erosion modeling and others techniques for determining the rate of denudation and deposition processes. We investigated the processes of local and long-distance sediment movement. It was established that the rate of creep is 2-2.2 cm/year, the intensity of scree processes varies depending on the rock types in the range 1-3.5 cm/year. The processes of sheet erosion and linear erosion contribute to the movement of part of the eroded material from the catchment area to the river channel. Four types of slopes and slope catchments are distinguished according to the features of a sediment delivery from the catchment area to the river channel. The average annual sedimentation rate in the gully fan is amounted to 2.3 cm/year since 1986. At the same time, on the basis of studying the accumulative deposits of the gully fan, including the content of the 137Cs isotope in the different layers, it was established that the main sources of sediments are material produced by gully erosion, scree processes and slopes settling. 5-6 episodes of catastrophic sediment removal occurred in this particular slope catchment for 30-year period. The ratio between a sediment removal from the slope catchments to the river channel and the measured sediment yield in the Tsanyk River during the rain floods of low repeatability makes it possible to state that the basin component of sediment yield is at least 75% of the total. Information about the ratio of slopes and slope catchments of various types within the small river basins of the subtropical belt of the Black Sea coast of the Caucasus should be taken into account when calculating engineering structures for protecting infrastructure facilities from the impact of flash floods or mudflows.

River channels characterized by the multi-thread patterns are most complex form points of view of morphology, structure and deformation regime. The paper presents an analysis of the largest river channel deformations at the adjoint braids with an example of the Lena River reach near its confluence with the Aldan River including the three consecutive braids – Haityallah, Omulagan and Arbyn. During the 20 th century and the first decade of the 21 st century the studied Lena River reach has experienced periodic shifts of the main arm, associated changes of discharge ratios between arms within braids and the resulting relocation of the navigable fairway track. Temporal patterns of discharge fluctuations in the Lena and Aldan Rivers do not coincide, causing alternations of the dominant influence of the main river flow onto its tributary or the opposite during the peak discharge periods. It is shown that the intermittent phase of temporal transformation of the adjoint braids channel pattern into the parallel arms channel pattern occurs between the longer stages of dominant development of left or right arms. Duration of that phase depends mainly upon the average water discharge relatively to its long-term fluctuations (increases during higher runoff periods and decreases during lower runoff periods), flow backing conditions caused by the inflowing tributary (the Aldan River) affecting the entire length of the studied Lena River reach and local channel deformation conditions. In general, such a transitional phase of the channel development (between the alternating stages of dominance of left or right arms within the adjoint braids chain) can last for significant period of 10-15 years or even more. Duration of the transitional phase is comparable to that of the alternating stages of dominance of left or right arms on large- or medium-sized rivers where parallel arms pattern of the multi-thread channel does not develop. In turn, channel deformations at the adjoint braids exert significant influence on development of main arms of the internal delta situated at the confluence of the Lena and Aldan Rivers, where the main control is associated with alternation of flow backing or no backing conditions related to different discharge ratios between the main river and its main tributary.

The paper presents results of the analysis of the Lena River channel deformations near the Yakutsk City over the period exceeding the past 100 years. The data presented enables to conclude that the main trend of the channel development over that period has been a transformation of the adjoint braids pattern into the parallel arms pattern accompanied with directed migration of the main flow line towards the right valley side along the entire studied reach. Such a tendency of channel evolution creates an unfavorable situation for operations of the Yakutsk water industry and transportation facilities. The paper also gives a predictive assessment of the future channel deformations and proposes a set of channel regulation measures aimed at improving the situation.