Erosion and accumulative processes in river valleys of the Upper Angara region (as exemplified by the catastrophic floods in 2019 on the rivers of Irkutsk Oblast)

Abstract

The article considers development features of erosion-accumulative processes during catastrophic floods in 2019 on the rivers of Irkutsk oblast, in the Angara river basin (as exemplified by the Bol’shaya Belaya river). Considering the combination of morphodynamic channel types we preliminary determined main types, interaction degree of flood waters and floodplain-channel complexes in different areas. We revealed that the most intensive transformations of the floodplain-channel relief are associated with engineering and construction structures that hinder the natural exchange of floodplain and channel flows. The rates of coastal recession during the flood period were revealed; on average, they amounted to 2 m. The processes of coastal erosion-tearing away of bank are typical of sandy loam deposits composing the upper part of floodplain surfaces. The most dynamic areas of bank destruction correspond to the concave parts of the channel bends. Note is taken that the presence of linear infrastructure objects (roads) within the floodplain massifs often caused the flow rates increase and an increase in the volume of transported material, as well as formation of accumulative landforms, which can hinder water exchange between channel and floodplain streams in the future, and also serve as an additional development factor of processes that are negative for a person and can lead to total destruction of infrastructures, or cause significant damage to them.