VERTICAL CHANNEL DEFORMATIONS ON THE MIDDLE AND LOWER AMUR RIVER AND THEIR REFLECTION IN THE MORPHOLOGY OF THE CHANNEL AND FLOODPLAIN

Résumé fourni par la source

The article examines the features of the morphology of the middle and lower reaches of the Amur River channel. They are characterized by vertical channel deformations with different directions and intensities. The sediment accumulation is observed on most of the middle reach of the Amur (except for the section where the Maly Khingan ridge intersects, where the channel is incised, and floodplain don’t exist) and the entire lower reach of the Amur. A weak incision of the river is observed only below the confluence with the Zeya River. Increased sediment removal from the artificial channel is fixed in the lower reach of the Amur near the sandy Belaya Mountain (in the 20th century) after the construction of a hydroelectric complex on it. It led to a change from incision to accumulation in the first few tens of kilometers downstream, which has not yet manifested itself in the morphology of the river channel. Different directions of vertical deformations are recorded in the positions of the curves Q=f(H). This is reflected in changes in the type of the river channel and the relief of the valley bottom. With the directed accumulation of sediments, the Amur in its lower reaches is characterized by an excess of the low-water level above the floodplain surface, widespread floodplain multi-branching, the widespread formation of a complexly branched channel, and on the tributaries (except for the large rivers – Sungari and Ussuri) estuarine lakes-spills. The channel becomes incised according to the geomorphological type, but branched, downstream from the city of Komsomolsk-on-Amur, as the Amur river crosses the spurs of the Sikhote-Alin ridge. The alternation of wide-floodplain, adapted and incised sections of the riverbed also occurs against the background of the directed accumulation of sediments, which is manifested in channel branches, floodplain multi-branching and estuarine lakes on tributaries in the estuarine part of the Amur River. Thus, throughout almost the entire middle and lower reaches of the Amur River, systematic accumulation of sediments occurs. It is caused by negative tectonic movements and is interrupted in the middle reaches of the Amur River by incision when it intersects positive structures. Long-term (on a geological time scale) intensive accumulation of sediments determines the morphology and dynamics of the Amur riverbed even in those areas where its rates are reduced or it is replaced by weak incision.

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