ИСТИНА

Studies aimed at quantifying sediment transfer in the mountains are essential from fundamental and practical perspectives. This is especially relevant now during global climate change and the adaptation of geomorphological systems to new conditions. However, quantitative assessments of sediment transport in proglacial areas are relatively rare worldwide, particularly in the Caucasus. This paper aimed to quantify 1) the total amount of mobilized sediments, 2) the portion of sediments that finally reaches the catchment outlet, and 3) the contribution of different processes to the sediment load in the high-mountain catchment of the Donguz-Orun Lake (northern slope of the Central Caucasus), composed of two tributary valleys. The annual volume of transported sediments was determined by geomorphological processes mapping and information on their rates obtained from monitoring work, as well as reviewing published materials in similar geological and geomorphological settings. To estimate the volume of material reaching the catchment outlet, we used the sediment delivery ratio calculation. This approach has an advantage in differentiating denudation by particular processes, but verification of results is required. The lake was formed by the damming of streams by a lateral moraine, which enabled us to quantify sedimentation rates. Additionally, sediment source fingerprinting allowed us to verify the contribution of sub-catchments. The total volume of mobilized material is 29300 mm yr-1 m3, corresponding to a denudation rate of 2.2 mm yr-1. With an average sediment delivery ratio of 58%, the sediment volume transported outside the catchment should be about 17000 m3, and the denudation rate (adjusted for accumulation) should be 1.3 mm yr-1. Gully erosion (67.5%), sheet wash (12.2%), rockfalls (10.9%), and glacial and fluvioglacial processes (8.6%) together contribute to 99% of the sediment load. On the other hand, channel erosion, rock creep, soil creep, and solifluction only contribute about 1% combined. Since the lake was created, 5×106 m3 of sediments have accumulated in its basin. This corresponds to sedimentation rates of 0.54 to 1.07 mm yr-1, depending on the age of the dam. Therefore, a denudation rate of 1.3 mm yr-1 is greater than the higher assessment of the sedimentation rate in the lake. However, with possible correction for removing a portion of suspended sediments, this is an adequate estimate of the denudation rate in the catchment area. Also, the source sediment fingerprinting results show that the sediment delivery ratio of the southern sub-catchment must be approximately 1.4 times less than calculated. Thus, only about 14000 m3 enters the lake basin annually from both valleys, which gives a denudation rate of 1.05 mm yr-1. This value fits into the estimated range of sediment volume (0.54-1.07 mm yr-1) in the lake basin. Our findings indicate that only 50-60% of the mobilized sediments reach the catchment outlet. The study was supported by Ministry of Science and Higher Education of Russian Federation under the Agreement 075-15-2024-614.