Spatiotemporal Morphodynamics of the Malaya Belaya River in Its Lower Reaches

The morphological and morphodynamic features of the Malaya Belaya River in its lower reaches are considered. Various types of floodplain–channel complexes are identified, and some features of their functioning are characterized. The structure of the first terrace deposits in areas of different morphodynamic channel types are analyzed. Analysis shows a significant spatial differentiation of the deposits of the first terrace, associated with the heterogeneity of the morphostructural features of the Malaya Belaya River valley. It is found that the most stable part of the terrace, which has the most ancient age of the stabilization surface, is confined to the areas of development of a relatively rectilinear type of channel. The latter is apparently characteristic of the section of the valley considered and during the formation of the surface of the first terrace. In the meandering section upstream, the height of the terrace decreases slightly. Based on lithologic and facies analysis of sections of terrace and floodplain deposits, data on the rhythm of sedimentation within low morphological levels in the Malaya Belaya River valley are obtained. The main stages of the formation of floodplain generations have been identified. Stabilization of the surface of the first terrace in the areas of a straight channel begins at 10.8 ka. Fixing of the surface of the first terrace at the sites of meandering channel type occurs at 9.3‒89 ka. The formation of a high (up to 3 m) floodplain occurs around 3.5 ka. Low floodplain deposits with a height of up to 2 m begin to form after 2.6 ka. An analysis of the structure of the sediments of the floodplain–channel complexes and the first terrace of the Malaya Belaya River has made it possible to identify two stably developing floodplain–terrace complexes within a small section of the river channel.