Hydrological and Geomorphological Features of the Mudflows Formation on Mountain Rivers of the Slyudyansky District of the Irkutsk Region

The article studies the hydrological and geomorphological conditions of mudflow formation on the rivers of the Slyudyanka district based on an integrated approach. For this purpose, the analysis of maximum rainfall water discharge series for the period 1966–2022 was performed on the mudflow- and flood-hazardous rivers of the Khamar-Daban. The characteristics of suspended sediments on the rivers according to the data of hydrological posts are given. The characteristics of the relief structure of the territory are given. The geomorphological factors of the development of catastrophic floods and mudflows are identified. According to Roshydromet data, empirical probability curves and various options for its analytical approximation were constructed for each series of maximum discharges. The calculated values of maximum annual expenses of standard provisions were obtained. The years with high floods with the probability of maximum discharges below than 10 % were determined. The analysis of suspended sediments was performed for these years. The subjects of the study to identify hydrological and geological hazards are fluvial systems, their dynamic properties, spatial and temporal patterns of their functioning. Particularly destructive mudflows occasionally flow along the Slyudyanka, Bezymyannaya, Utulik, and Khara-Murin rivers. The following geomorphological factors have a significant impact on the formation of the solid component of the runoff of the territory under consideration: slope steepness, the proportion of deeply dissected relief (i.e., its energy), and the thickness of loose sediments subject to denudation processes and participating in sediment transport (for the basins under consideration, these are groups of slope processes). This study examines morphometric characteristics. The influence of slope length and steepness was taken into account using a combined relief function, which is used to quantify the relief factor when calculating the soil loss modulus – the LS factor. Conclusions were obtained that during the passage of mudflow floods of rare probability, the increase of water discharges occurs primarily due to the increase in flow velocity, which increased 4–9 times. High flow velocities create prerequisites for mudflow manifestations. The most destructive mudflow was in July 1971, when the probability of maximum water discharge on the rivers was 0.001–1.9 %, and the values of suspended sediment flow rates were the highest according to observations. A multiple increase in suspended sediment flow rates and turbidity occurs during the passage of maximum water discharge with a probability of 10 % and lower. The Bezymyannaya, Slyudyanka, Khara-Murin, and Utulik rivers have the most favorable geomorphological conditions for the development of mudflows and catastrophic floods. The Snezhnaya and Pokhabikha river basins have minimal average values of the considered indicators, which is explained by their minimum and maximum areas, respectively.